DE3854255T2 - METHOD AND DEVICE FOR CHANGING PRESSURE IN A PATIENT SUPPORT SYSTEM WITH LITTLE AIR LOSS. - Google Patents

Abstract

Method and apparatus for preventing bed sores in a bedridden patient. A low air loss bed (10) is provided including a frame (12), a first set of substantially rectangular air bags (58) for supporting a patient thereon mounted transversely on the frame, and a second set of substantially rectangular air bags (58) for supporting a patient thereon mounted transversely on the frame, and all of the air bags are connected to a gas source. The configuration of the air bags (58) is such that when the first set of air bags (58) is inflated, the patient supported thereon is moved toward the first side of the frame (12) of the low air loss bed (10) and when the second set of air bags (58) is inflated while the first set of air bags (58) is deflated, the patient is moved toward the second side of the low air loss bed (10). The configuration of the air bags (58) also retains the patient on the top surface of the air bags when the patient is rolled in one direction or the other. The operator of the low air loss bed defines the pressures in individual air bags (58) corresponding to each of three positions to which the patient is rotated. The pressures are maintained by a feed back control system which actuates valves connecting the gas source to separate sets of air bags. The three positions to be sequentially attained thereby causing controlled oscillation of the patient from one side of the bed frame to the other. Because each rotation position corresponds to operator defined pressures, the oscillation is customized for individuals of different body weights.

Description

The present invention relates to a method and apparatus for alternately varying the air pressure of a patient support system with low air loss. More particularly, the invention relates to a bed comprising a frame having two sets of air bags attached thereto, a gas source, means provided on each air bag for moving a patient lying thereon toward one side of the frame and then back to the other side of the frame as gas is introduced into the first set of air bags and then into the second set of air bags, and means provided on the air bags for retaining the patient to the air bags as the patient is moved toward the respective sides of the frame.

Such a bed can be used advantageously to prevent bedsores and fluid accumulation in the lungs of bedridden patients. Devices for this purpose are known, but they suffer from various difficulties. In particular, US Patent No. 3,822,425 describes an air mattress consisting of a number of cells or bags, each having a patient support surface made of a material that is permeable to gases but impermeable to liquids and solids. There are also described an air supply for inflating the cells to the required pressure and outlets or exhaust openings for allowing air to escape. The purpose of these outlets is stated to be to remove condensed vapor from the cells or bags. The outlets on the mattress may be provided with valves to regulate the air pressure in the cells, as opposed to regulating the air pressure in the cells by controlling the amount of air flowing into the cells. However, the bed described in this patent and currently marketed under this patent suffers from certain disadvantages and limitations.

For example, the bed has a single air inlet coupling device located directly and centrally under the air mattress for connection to the air source. Access to this connection is difficult because it can only be reached while lying on your back. The location of the connection places a limitation on the frame construction because the air hose has to pass through the bed frame elements. In the case of the air source, with to which the air hose is connected is a blower or air pump located in a remote housing mounted on casters to provide the necessary mobility. In practice, it is common for the housing to have to be moved to allow other equipment, such as IV stands, to be moved around the housing or to provide access to the patient. However, if the blower unit is to be removed to a significant extent, it is necessary to disconnect the air hose from the frame (which is impractical due to its location below the frame) or from the hanging line to prevent the air hose from wrapping around the bed frame members. Of course, disconnecting the air hose will result in a loss of air pressure in the air mattress, which is even less desirable.

Furthermore, the bed described in this patent is limited in that only a limited amount of air can be forced or pumped into the air mattress. By completely eliminating the outlets described in this patent, the air pressure in the bags can be maintained at least at the level corresponding to the maximum output of the gas source. If it is necessary to further increase the pressure in the air bags in the bed described in this patent, and if the outlets are used for the stated purpose, the only way to do this is to install a higher capacity blower in the housing. High air pressures may be required, for example, to support corpulent patients. A higher capacity blower generally consumes more power and requires a higher power circuit which may not be readily available. Furthermore, the larger the blower, the greater the noise, which is undesirable.

Another limitation of this bed is the need for constant adjustment of the air pressure in the air bags on which the patients lie. Although low air loss beds are generally used for bedridden patients, not all bedridden patients are immobile. Any movement of these patients, even movements of just one arm, or any act of adjusting an immobilized patient by the nursing staff causes changes in the area of the patient's weight supported by the sets of air bags attached to the respective head, back, buttocks and leg sections of the bed frame. To achieve a To avoid a local increase in the pressure exerted against the patient's skin due to such movements, the air pressure in that section must be readjusted. Adjusting the air supply to one set of air sacs will almost invariably affect the pressure in one or more adjacent sets of air sacs, so it is often necessary to change the air supply to each set of air sacs at the bedside.

Furthermore, low air loss beds of the type described in the '425 patent are provided with means for adjusting the position of the patient on the bed. For example, the head of the bed can be raised to sit the patient up, or the angle of the entire bed frame can be changed with respect to the horizontal plane when, for therapeutic reasons, the patient is placed in the Trendelenburg position or in the reverse Trendelenburg position. Such changes require readjustment of the air supply in each set of air bags, usually to a greater extent than is required by the movement of the patient.

The limitations and disadvantages that characterise other previous attempts to solve the problem of preventing pressure ulcers in bedridden patients are described in GB Patent 1 474 018 and US Patent 4 425 676.

European Patent Specification 0168213 relates to an air mattress with air cells that can be selectively inflated and deflated to temporarily change areas of the mattress that serve to support a person's body, information regarding the selection of the air cells to be inflated or deflated based on the patient's body weight and weight distribution being fed to a control unit.

The prior art also describes a number of devices which serve to weigh a patient backwards and forwards using air pressure. For example, US Patents 3,477,071 and 3,775,781 describe hospital beds with an inflatable device for displacing or turning a patient lying on the bed by alternately inflating and deflating one or more inflatable cushions. GB Patent Application 2,026,315 describes a cushion, pillow or mattress of similar construction. US Patent 3,485,240 describes a patient support system in which two longitudinally extending bags, each of which has a triangular cross-section, are arranged one above the other beneath a patient. The bags are alternately fully inflated and fully deflated to roll the patient from side to side on the bags. US Patent 4,797,962 describes a patient support system having a set of inflatable air bags maintained at a predetermined inflation level by a control system including a feedback device. DE-PS 2 816 642 describes an air mattress for a bedridden person or hospital patient consisting of three inflatable longitudinal cells attached to supports, the amount of air injected into each cell being varied so as to rock the patient alternately from one side of the mattress to the other. However, none of these mattresses or devices is designed for use in a low air loss patient support system. Furthermore, the GB and DE patents and US patents 3 477 071 and 3 775 781 describe devices consisting of parallel air compartments extending longitudinally along the bed which are alternately inflated and deflated. Such constructions do not allow the device to be used on a bed with foldable sections in correspondence with the part of the body of the patient lying on the bed so that the inclination and angle of the various sections of the bed can be adjusted to ensure comfort for the patient.

US Patent 3,678,520 describes an air cell for use in a pressure cushion provided with a plurality of tubes projecting from a manifold head so that the air cell in the inflated state assumes a comb-like shape when viewed from above. Two such air cells are enclosed in the pressure cushion with the projecting tubes interlocking with one another. Air is alternately supplied to and discharged from one cell and then the other. This device is not suitable for use on a bed with foldable sections corresponding to the body parts of the patient lying on the bed so that the angle of inclination of the various parts of the bed can be adjusted to ensure patient comfort. Furthermore, the function of the bed in the manner described above is not guaranteed when it is used for a low air loss design.

A number of patents, both US patents and patents from other countries, describe air mattresses or cushions consisting of sets of cells which are alternately inflated and deflated, with a patient lying first on one group of air cells and then on the other group. These patents include the following US patents: 1,772,310, 2,245,909, 2,998,817, 3,390,674, 3,467,081, 3,587,568, 3,653,083, 4,068,334, 4,175,297, 4,193,149, 4,197,837, 4,225,989, 4,347,633, 4,391,009 and 4,472,847; and the following patents from other countries: GB- 959 103, AU-401 767, DE-24 46 935, DE-29 19 438 and DE-28 07 038. None of the devices described in these patents cause a rocking motion or an alternate movement of the patient lying thereon to distribute the patient's body weight over additional air cushions or cells or to alternately relieve pressure under areas of the patient's body.

There are also a number of patents that describe an inflatable device other than an air mattress or air cushion, but which also involve alternating air supply to one set of cells and then to another set of cells. These patents include US patents 1,147,560, 3,595,223 and 3,867,732 and UK patent 1,405,333. Of these patents, only the UK patent describes the movement of the body with changes in air pressure in the cells of the device. None of these documents describe a device suitable for use in a low air loss patient support system.

GB Patent 946,831 describes an air mattress having inflatable elongated bags placed side by side and in fluid communication with each other. A valve is provided in the conduit connecting the interior of the two bags. Air is supplied to both bags in a quantity sufficient to support the patient, thereby lifting the patient from the bed or other surface on which the air mattress rests. Any imbalance in the weight distribution of the patient will cause the air to be forced from one bag to the other, allowing the patient to turn towards the now deflated bag. An automatic change-over valve, of which no details are given, is then intended to inflate the deflated bag whilst the bag which was originally inflated is deflated, with the patient rocking in the other direction. This device is limited in its suitability for preventing pressure ulcers since as the patient rocks towards the deflated bag the quantity of air is not sufficient to support the patient. in a position raised from the bed or other surface on which the air mattress rests, is sufficient to cause pressure to be exerted on the patient's skin which is substantially as great a pressure as would be exerted by the bed or other surface without the air mattress. Even if a sufficient amount of air remained in the deflated bag to support the patient, if the air mattress were of a low-deflation design, the air remaining in the bag would slowly escape from the bag until the patient came to lie directly on the bed or other surface, which would produce the same result. Finally, this device is not suitable for use on a bed having foldable sections corresponding to the parts of the body of the patient lying on the bed, where the angle of inclination of the various sections of the bed can be adjusted for the comfort of the patient.

The present invention provides an improved device over the prior art. It is characterized by a number of advantages which increase its value over conventional devices, including flexibility of use, ability to maintain a relatively constant air pressure in the air bags despite patient movement or changes in the position of the bed frame, the ability to quickly and easily replace one or more air bags while the device is in use, and the ease of adjusting the air pressure in the air bags.

It is therefore an object of the invention to provide a bed with low air loss, comprising: a frame, a first set of substantially rectangular, gas-permeable air bags for supporting a patient, which are attached transversely to the frame, a second set of substantially rectangular, gas-permeable air bags for supporting a patient, which are attached transversely to the frame, means for connecting the individual air bags to a gas source, means integral with the individual air bags of the first set of air bags for moving the patient lying thereon towards a first side of the frame when the individual air bags of the first set of air bags are inflated in the first region, means integral with the individual air bags of the second set of air bags for moving the patient lying thereon towards a second side of the frame when the air bags in the first set of air bags are deflated and the air bags in the second set of air bags are inflated, integral means on each of the air bags for supporting the patient lying alternately on the first or second set of air bags as he is moved toward the first or second side of the frame, and means for selecting the pressure in the air bags at any given time.

Another object of the present invention is to provide an air bed whose air pressure can be quickly and conveniently adjusted to support a patient of known body weight by simply selecting a target pressure to be maintained in the air bags, resulting in adjustment of the valves which regulate the amount of air flowing from the air source accordingly.

Another object of the present invention is to provide a low air loss bed with an integral gas source that can be raised, lowered or tilted, allowing a portion of the bed to be raised or lowered while maintaining a selected pressure or range of pressures in the air bags at any given time.

Another object of the present invention is to provide a low air loss bed capable of rolling a patient backwards and forwards on the bed while securely restraining the patient on the bed.

Another object of the present invention is to provide a bed with low air loss suitable for alternately moving a patient in one direction and then in a second direction, the bed being divided into at least three sections roughly corresponding to the body parts of the patient lying thereon, the sections being hinged together and being provided with means for raising and lowering the sections according to the patient's body to ensure an increase in comfort and therapeutic value for the patient while the patient is alternately moved on the bed in the first and second directions.

Another object of the present invention is to provide a low air loss bed capable of alternately rolling a portion of a patient in one direction and then in a second direction while maintaining another portion of the patient in a relatively fixed position.

Further objects and advantages of the invention will become apparent to those skilled in the art from the following description.

The invention provides a method of operating a feedback controlled patient support system of the type having a patient support with a plurality of inflatable air bags, the patient support comprising at least a first and a second separately inflatable air bag for supporting a patient and connected in controllable fluid communication to an air supply means, the first air bag being adapted to roll a patient in a first direction in response to the inflation control and the second air bag being adapted to roll a patient in a second, opposite direction in response to the inflation control, the air supply means being connected in controllable fluid communication to the air bags to separately and alternately inflate the air bags, characterized in that the method comprises measuring the air pressure in at least a portion of the first and second air bags; and includes controlling the air supply means in the form of feedback by using means connected to the air pressure measuring means to roll the patient first in the first direction and then in the second direction, ensuring that during the process of controlling the air supply to raise or lower the air pressure in the bags, the level of air pressure in the bags cannot fall below a specified minimum value.

According to the invention there is further provided a feedback controlled patient support system of the type having a support for a patient including a plurality of inflatable air bags connected in the form of a controllable fluid connection to an air supply means comprising:

a patient support including at least first and second separately inflatable air bag chambers for supporting a patient, the first chamber being adapted to rotate a patient in a first direction in response to the inflation control, and the second chamber being adapted to rotate the patient in a second opposite direction in response to the inflation control;

an air supply means connected in the form of a controllable fluid connection to the air bags for selectively inflating the air bag chambers, characterized by:

a means for measuring the air pressure in the first and second chambers; and

means connected to the air pressure measuring means for controlling the air supply means in the form of a feedback to roll the patient in the first and then in the second direction by monitoring and controlling the air pressure in the first and second chambers, whereby it is ensured that during the operation of the air supply control means the level of air pressure in the chambers cannot fall below a certain minimum level.

In an example of a system according to the invention, a plurality of sets of gas permeable air bags mounted on the frame are provided, each set of air bags corresponding to an area of a patient lying in an inclined position on the bed. Each one of a plurality of separate gas manifolds is in communication with the gas source and one of the sets of air bags. Means is also provided for separately varying the amount of gas supplied from a gas source to each of the gas manifolds, thereby varying the amount of support provided to each area of the patient.

There is also provided a low air loss bed comprising a bed frame having a gas source and a plurality of sets of water vapor permeable air bags mounted thereon. Separate gas manifolds communicate with the interior of the air bags at one of the sets of air bags and the gas source. An air control box is mounted to the bed frame and interposed in the flow of air from the gas source to the gas manifolds. This box is provided with individually adjustable valves for varying the amount of gas supplied to each gas manifold. The air control box is also provided with a means for selectively opening all of the valves to atmosphere to vent gas from each of the sets of air bags, thereby collapsing the air bags, causing the patient to rest on the frame rather than the air bags.

Further provided is a low air loss bed comprising a bed frame and a plurality of sets of air bags attached thereto, with a plurality of gas manifolds separately communicating with the gas source and the interior of the air bags. An air control box is attached to the bed frame in fluid communication with the gas source and the gas manifolds and is provided with valves which are individually are adjustable to vary the amount of flow from the gas source through the air control box to the individual gas manifolds. The air control box is also provided with a means which can be operated to simultaneously fully open the valves to completely deflate the air bags.

There is also provided a low air loss bed comprising a frame and a plurality of sets of air bags attached thereto, a plurality of gas manifolds separately communicating with the gas source and the interior of the air bags. An air control box is also attached to the frame, the interior of the air control box communicating with the gas manifolds and the gas source and having means for separately varying the amount of gas supplied from the gas source to each gas manifold. The air control box is also provided with means for heating the gas flowing through the air control box and means for turning the heating means on and off in response to the temperature in the air control box. Further, means including a sensor is provided in one of the gas manifolds operable to selectively control the heating means, the means being operable to turn the heating means on and off in response to the temperature in the air control box at a predetermined temperature.

There is also provided a low air loss bed comprising: a frame, a first set of air bags for supporting a patient transversely attached to the frame, a second set of air bags for supporting a patient transversely attached to the frame, means for connecting the individual air bags to a gas source, the individual air bags of the first set of air bags including means integral therewith for moving the patient lying thereon toward a first side of the frame when the air bags in the first set of air bags are inflated, the individual air bags of the second set of air bags including means integral therewith for moving the patient lying thereon toward the second side of the frame when the air bags in the second set of air bags are inflated and the air bags in the first set of air bags are deflated, and means on the air bags for restraining the patient lying thereon when the patient moves toward the respective first and second sides of the frame. becomes.

Means are also provided for controlling the pressures in the air bags corresponding to the three different rotational positions. These pressures are adjustable by the operator and serve to define the respective rotational position according to the size and weight of a particular patient. Means are provided for causing the individual rotational positions to be reached one after the other and maintained at a rate determined by the operator.

Short description of the drawing

Figure 1 is a perspective view of a presently preferred embodiment of the low air loss bed of the present invention.

Fig. 2 is a cross-sectional view of the bed of Fig. 1 taken along line 2-2 of Fig. 1 and showing an air bag with a second air bag disposed behind it, the second air bag being shown in dashed lines for clarity.

Fig. 3 is a schematic representation of the air duct installation of the low air loss bed of Fig. 1.

Fig. 4 is a perspective view of one of the base plates of the low air loss bed of Fig. 1.

Fig. 5 is an enlarged, exploded perspective view of the underside of the base plate of Fig. 4, with the base plate partially removed to show the details of the attachment of the low air loss air bags.

Fig. 6 is an end view of the low air loss bed of Fig. 1 with the head section raised to show the construction of the frame and attached components.

Fig. 7 is an end view of the low air loss bed of Fig. 1 with the foot area raised to show the construction of the frame and attached components.

Fig. 8 is a sectional view of the air box of the bed of Fig. 1 with low air loss taken along line 8-8 of Fig. 9A.

Figs. 9A and 9B are cross-sectional views taken along lines 9A-9A and 9B-9B, respectively, through the manifold assembly of the air box shown in Fig. 8.

Figs. 10A-10D are end views of a patient lying on the head surface of the air bags of the low air loss bed of the present invention, with the patient (10D) being rocked toward one side of the frame of the low air loss bed (10A), then rocked towards the other side (10C) or resting on the air bags when all air bags are fully inflated (Fig. 10B).

Fig. 11 is a composite longitudinal cross-section taken along line 11-11 of Fig. 1 of a portion of the foot base of a low air loss bed according to the teachings of the present invention, showing the various alternative methods for attaching the air bags to the bed frame.

Fig. 12 is a schematic electrical diagram of the low air loss bed of Fig. 1.

Fig. 13 is a perspective view of a portion of the bed frame of the bed of Fig. 1 showing that a potentiometer is mounted on a frame section pivotally connected to an adjacent frame section.

Figure 14 is a schematic of the electrical wiring and controls that open and close the valves for supplying air to the air bags of the low air loss bed of Figure 1.

Figure 15 is a flow diagram of the presently preferred embodiment of the program for controlling the low air loss operation of the bed of Figure 1 from the control panel shown in Figure 12.

Fig. 16 is a flow chart of the general timer subroutine for controlling the operation of the low air loss bed of Fig. 1.

Fig. 17 is a flow diagram of the switching subroutine for controlling the operation of the low air loss bed of Fig. 1.

Fig. 18 is a flow chart of the rotation subroutine for controlling the low air loss operation of the bed of Fig. 1.

Fig. 19 is a flow chart of the valve motor subroutine for controlling the low air loss operation of the bed of Fig. 1.

Fig. 20 is a flow chart of the power failure interrupt subroutine for controlling the operation of the low air loss bed of Fig. 1.

Figure 21 is an end view of an alternative embodiment of an air bag for use in the bed of Figure 1 with low air loss.

Fig. 22 is an end view of one of the air bags for use in the low air loss bed of Fig. 1.

Fig. 23 is an end view of another air bag for use in the bed of Fig. 1 with low air loss.

Fig. 24 is a general schematic representation of the control software for controlling the operation of the low air loss bed of Fig. 1.

Detailed Description of the Preferred Embodiments

In Fig. 1, a bed 10 is shown with a frame 12. The frame 12 consists of a plurality of sections 14', 14", 14"' and 14"", which are hinged at the points 44', 44" and 44"', and end elements 16. For additional stiffening, cross elements 18 (Figs. 6 and 7) and braces 19 (Fig. 7) are provided. The frame 12 is provided with a head plate 20 at one end and a foot plate 21 at the other end. The head plate 20 and the foot plate 21 are actually constructed from two plates 20' and 20" and 21' and 21" respectively, which are arranged head to head one above the other by means of the vertical rods 25 to which the plates 20', 20", 21' and 21" are attached.

A separate sub-frame, generally indicated by reference numeral 27 in Figures 6 and 7, is secured to a base 22 consisting of longitudinal beams 24, transverse beams 26 and cross members 28 by means of a vertical height adjustment mechanism described below. The base 22 is secured at its corners to rollers 30. A foot pedal 42 is provided for braking and controlling the rollers 30.

The sub-frame 27 consists of cross beams 29, a bracket brace 35 and longitudinal beams 31 (see Figs. 6 and 7). The sub-frame 27 is provided with posts 33 at the corners to which are attached fastening devices 33' for fastening IV bottles and other devices. A means in the form of a conventional vertical height adjustment mechanism is provided for raising and lowering the sub-frame 27 relative to the base 22, not all details of which are shown. The height is adjusted by rotating an axle with a drive screw which is hidden in Fig. 7 by the control channel beam 37, the drive screw being driven by a motor which is also not visible. The power is transmitted from the drive screw to the axle by means of eccentric levers, the axle of which is secured in the control channel beam 37 by a pin and is hidden in the illustration by this beam. The subframe 27 is raised by levers which are pivotally attached to the crossbeams of the base 22.

The levers and the elements to which they are attached are hidden by the crossbar 29 in Figs. 6 and 7.

Section 14" of frame 12 is attached to longitudinal beams 31 of sub-frame 27 by means of support members 41 (see Fig. 6). Section 14" of frame 12 with head base plate 52 thereon and section 14"" of frame 12 with foot base plate 46 thereon are pivoted upwards from the horizontal at pivots 44" and 44"" respectively. The purpose of this pivoting movement is to provide for the adjustment of the angle of inclination of the various parts of the patient's body. The details of this pivoting movement are known in the art and are not shown for clarity, but the motors are located within the boxes designated by reference numeral 45. The motors are controlled by switches 233, 235, 236, 237, 238 and 239 on the Control panel 346 or by redundant controls on the bed hand control 368 (see Fig. 14). The circuitry for these functions is contained in box 43 (Fig. 7), which is shown schematically with the reference numeral 367 (see Fig. 14), and is explained in more detail below.

Supports 17 are provided on the cross member 18 beneath the head base plate 52 and rest on the longitudinal beams 31 of the sub-frame 27 when the head base plate 52 is horizontal. When the foot base plate 46 is raised (Fig. 7), the crossbar 47 moves upwardly with it by means of the pivotal connection created by the crossbar 47 and the notches 49 in the brace 19 (the crossbar 47 is separated from the braces 19 for clarity in Fig. 7). The adjustments of the notches 49 provide means for adjusting the height to which the crossbar 47 can be raised, the foot base plate 46 being pivoted upwardly on support arms 51 pivotally attached to the longitudinal beams 31 of the sub-frame 27. The tips 53 of the crossbar 47 rest on a longitudinal beam 31 when the foot base plate 46 is lowered into the horizontal position.

Side bars 81 are attached to support arms 83 (see Fig. 6) which are pivotally attached to mounting arms 85 arranged on the underside of the head base plate 52. Side bars 87 are attached to support arms 89 (Fig. 7) and support arms 89 are pivotally attached to the mounting arms 91. The mounting arms 91 are attached to the braces 19 on the underside of the foot base plate 46.

The frame 12 is provided with a foot base 46, a leg base 48, a seat base 50 and a head base 52 (shown in dashed lines in Fig. 3) which are each secured to the respective sections 14', 14", 14'" and 14"" of the frame 12 by rivets 54 (see Fig. 11). Means are provided for releasably securing the air bags 58 to the bed 10 with little air loss. A presently preferred embodiment of this releasable securing means is shown in Figs. 2, 4 and 5. In Figs. 4 and 5, a portion of the foot base plate 46 is shown provided with through holes 64 extending alternately and oppositely along the length of the foot base plate 46, as well as the leg base plate 48, the buttock base plate 50 and the head base plate 52. Every other hole 64 is provided with a keyway 11 for receiving the post 32 with a retainer 34 attached thereto, the post protruding through the bottom surface 79 of the air bag 58 and the flange 71 of which is retained between the patch 69 sewn onto the bottom surface 79 of the air bag 58 and the bottom surface 72. The air bag 58 is shown in cut-away and dashed lines in Fig. 5 for clarity. The air bag 58 is further provided with a nipple 23 of elastic polymeric plastic material with an attachment piece 15 integrally connected thereto. To releasably secure the air bag 58 to the foot base plate 46 or to one of the other base plates 48, 50 or 52, the post 32 is inserted through the hole 64 until the retaining device 34 protrudes from the bottom. The post 32 is then brought into engagement with the keyway 11, whereby the retaining device 34 comes into engagement with the bottom side of the foot plate 46 around the edge of the hole 64, thereby holding the air bag 58 to the foot base plate 46. The nipple 23 is then inserted into the hole 64 opposite the hole 64 with the keyway 11 and rotated until the extension 15 engages the bottom of the head of the flat head screw 13 to assist in securing the nipple 23.

According to an alternative embodiment, the base plates 46, 48, 50 and 52 are provided with means for releasably securing the air bags 58 to the bed 10 with low air loss in the form of plunger snaps 56 (Fig. 11) along their edges. The air bags 58 are provided with beads 60 each provided with ring snaps 62 which fit into the plunger snaps 56. The beads 60 are alternatively provided with a strip of VELCRO tape 55 and the edges of the base plates 46, 48, 50 and 52 are provided with complementary strips of VELCRO hooks 57 to secure the individual air bags 58 in place. Alternatively, the bead 60 and the base plates 46, 48, 50 and 52 are provided with both VELCRO and snap fasteners.

The air bags 58 are generally rectangular in shape and are made of coated fabric or a similar material that is permeable to water vapor but impermeable to water and other liquids. The fabric sold under the trade name "GORE-TEX" is one such suitable material. The air bags 58 may have one or more outlets for the air used to inflate them or they may be constructed as "low air loss" bags.

Referring to Figures 1 and 2, the air bags are shown in different configurations according to their position on the frame 12 of the bed 10. For example, the air bags attached to the foot base plate 48 and to the buttocks base plate 50 are designated by the reference numeral 322. The air bags 321, 322, 325 and 328 are made in the form of a generally rectangular envelope, at least the upper surface 323 of which is made of the water vapor permeable material described above. The air bags 321, 322, 325 or 328 are provided with a means for connecting the inside of the envelope to a gas source, such as a blower 108, for inflating the envelope with gas in the form of the nipple 23 (see Figure 2) which extends through the base plate 50 into the buttocks gas manifold 80 attached thereto. The air bag 321, 322, 325 or 328 is further provided with a means for releasably securing the envelope to the bed 10 with low pressure loss in the form of the post 32 and the retaining device 34 described above. Means are provided for moving a patient lying on the air bags 322, 325 or 328 toward one side of the frame 12 when the air bags 322, 325 or 328 are inflated and for retaining the patient 348 to the upper surface 323 of the air bags 322, 325 or 328 when the patient 348 is rolled or rocked toward one side of the frame 12 or the other side (see Figs. 10A-10D). The means for moving the patient lying on the air bags 322, 325 or 328 toward one side of the frame 12 when the air bags 322, 325 or 328 are inflated comprises a cutout 324 in the top 323 the substantially rectangular shape of the individual air bags 322, 325 or 328.

The individual air bags 322, 325 or 328 are further provided with a means for retaining a patient 348 on the upper surface 323 of the air bag 322, 325 or 328 when the patient 348 is rolled towards the side of the frame 12 by inflation of the air bags 322, 325 or 328. This means is in the form of a column 326 which is integral with the individual air bags 322, 325 or 328 and which, when inflated, projects upwardly to form the end and corner of the substantially rectangular envelope of the air bag 322, 325 or 328. The means for restraining the patient 348 on the top 323 of the air bags 322, 325 or 328 may also be in the form of a large foam cushion (not shown) attached to the side bars 81 and 87 on either side of the bed frame 12. This cushion may be removably attached to the side bars 81 and 87 or it may be split so that part is attached to the side bar 81 and part is attached to the side bar 87. The air pressure in the air bags 322, 325 or 328 is then adjusted in the manner explained below until the patient 348 is gently rocked against this foam cushion on one side of the bed frame 12 and then back to the other side of the bed frame 12.

As shown in Fig. 1, a plurality of air bags 58, 321, 322, 325 and/or 328 are transversely secured to the frame 12 of the bed 10. The air bags 322, 325 or 328 are divided into a first set in which the column 326 and the cutout 324 are located closer to one side of the bed frame 12 than the other side, and a second set of air bags 322, 325 or 328 in which the column 326 and the cutout 324 are located closer to the second side of the bed frame 12. The air bags 322, 325 or 328 of the first set and the air bags 322, 325 or 328 of the second set alternate with one another along the length of the base plates 46, 48, 50 and 52. As explained below, the first set of air bags 322, 325 or 328 is inflated with air from the blower 108, causing the patient 348 (not shown in Fig. 1; see Figs. 10A-10D) lying on the air bags 322 to be rolled toward the first side of the bed frame 12. The air is then deflated while the second set of air bags 322, 325 or 328 is inflated, moving the patient 348 toward the other side of the bed frame 12.

The air bags 321, which are attached to the head base 52, are provided with a flat upper surface 323 so that the head of the patient 348 is held in a relatively constant position while the body of the patient 348 is alternately rolled to one side of the bed frame 12 and then back to the other side of the bed frame 12. Referring to Fig. 23, an air bag 321 is shown for use under the head of a patient 348. The air bag 321 is generally rectangular in shape but is provided with a beveled upper surface 323 in the region 331 adjacent the corners 448. The height of the air bag 321 is less than the height of the air bags 58, 322, 325 and 328 because when the patient 348 lies on the air bags 58, 322, 325 and/or 328 the heavier areas, i.e. the body parts other than the head, sink into the air bags 58, 322, 325 and/or 328 as shown in Fig. 10D. When the patient 348 sinks into the air bags 58, 322, 325 and/or 328, the head rests at the same height on the air bags 321 because the head does not sink into the air bags 321 as much as the other body parts.

The air bags 328 attached to the foot base 46 and the air bags 328 attached to a portion of the leg base 48 are also provided with a cutout 324 and a column 326 as described for the air bags 322. In addition, the air bags 328 are provided with a hump 330 so that the legs of the patient 348 are relatively prevented from moving during the alternate backward and forward movement of the patient 348, which helps to hold the patient 348 to the upper surface 323 of the air bags 58, 321, 322, 325 and 328 and also helps to distribute the pressure exerted against the skin of the patient 348 over an increased area.

In Fig. 22, there is shown a side view (by the term "side view" is meant the air bag itself; if the air bag 328 (or 321 or 322) were attached to the bed 10, it would be an end view of the bed) of an air bag 328 having a hump 330 formed on the upper surface 323 thereof. As can be seen, when the air bag 328 is inflated, the hump 330 and the post 326 project upwardly to help prevent the patient 348 from rolling too far toward one side of the bed frame 12 or the other. An alternative construction of the air bag 322 is shown at 325 in Fig. 21. The airbag 325 is provided with a cutout 324 of approximately the same depth as the cutout 324 of the airbags 322 and 328, but the inclination of the upper surface 323 in region 327 is less than the slope of the upper surface 323 in region 329 of the air bags 322 and 328. The air bag 325 can be used in conjunction with adjusting the air pressure in the air bags 58, 321, 322 and/or 328 under various areas of the body of the patient 348 to increase or decrease the extent and speed at which the patient 348 is rolled from one side of the bed frame 12 to the other. For example, the air bag 325 is particularly well suited for use under the shoulders of a patient 348.

As previously mentioned, each of the air bags 58, 321, 322, 325 and 328 is generally rectangular in shape, measuring approximately 18 inches by 39 inches. Each air bag is provided with a baffle 460 secured to the side walls 61 to prevent arcuate deformation of the side walls 61 when the air bag 58, 321, 322, 325 or 328 is inflated. Each corner 448 has a radius of curvature of approximately 3 inches. The depth of the cutout 324 is approximately 10 inches. The dimension of the column 326 of the air bags 325 and 328 in the direction shown by line 450 is approximately 7 inches, as is the dimension of the cutout 324 in the direction shown by line 452. The dimension of the column 326 of the air bag 322 in the direction shown by line 451 is approximately 12 inches. The dimension of the upper surface 323 of the air bag 325 along line 453 is approximately 20 inches. This upper surface 323 slopes into the cutout 324 with a curve 455 having a radius of approximately 6 inches. Referring to Figure 2, the dimension of the upper surface 323 along line 458 is approximately 19 inches. The dimension of the hump 330 on the air bag 328 in the direction shown by line 454 is approximately 5 inches. The dimension in the direction shown by line 456 is approximately 2 inches. The dimension of the surface 333 along line 458 is approximately 14 inches.

According to an alternative construction for securing the air bags 58, 322 and 328 to the bed 10 (shown in Fig. 11), each air bag 58 (it should be noted that throughout this specification, a reference to an air bag 58 may also refer to an air bag 321, 322, 325 or 328) is provided with a flanged nipple 70, the flange 71 being retained between a patch 74 and the bottom 72 of the air bag 58. As described below, each air bag 58 is separately secured to the base plates 46, 48, 50 and 52 by snapping the ring snaps 62 into the beads 60 of the individual air bags 58 to the plunger snaps 56 on the edges of the base plates 46, 48, 50 and 52 or with the VELCRO tape 55 and the VELCRO hooks 57 or both. Once so positioned, the flanged nipple 70 on the inside bottom 72 of the air bag 58 projects through the holes 64 and 64' in the base plates 46, 48, 50 or 52 over which the air bags 58 are positioned. An O-ring 68 is provided in a groove (not referenced) around each flanged nipple 70 to ensure a relatively gas-tight fit between the flanged nipple 70 and the corresponding base plate 46, 48, 50 or 52 through which the flanged nipples 70 project.

The use of individual air bags 58, 321, 322, 325 or 328 instead of a single air cushion allows for the replacement of individual bags should this become necessary due to leakage, cleaning or other maintenance. If it is desired to remove an individual air bag 58, 321, 322, 325 or 328 from the respective base plate 46, 48, 50 or 52, the post 32 is slid out of the keyway 11 and the retainer 34 and post 32 are removed from the hole 64. The nipple 23 is then unscrewed from engagement with the screw 13 until the extension is unscrewed and removed from the hole 64 by pulling firmly. In the case of the air bag 58, the ring snaps 62 at each end of the air bag 58 are released from the stamp snaps 56 (or the VELCRO strips are released from each other) at the edges of the base plates 46, 48, 50 or 52. The air bag 58 is removed by twisting up the flanged nipple 70 and removing it from the hole 64 in the base plate 46, 48, 50 or 52. Removal can also be done while the patient is lying on the inflated air bags 58, 321, 322, 325 or 328.

For additional security in retaining the air bags 58 to the base plates 46, 48, 50 and 52 and to help ensure a gas-tight fit between the flanged nipple 70 and the respective base plates 46, 48, 50 or 52 through which the nipple projects, a spring clip 73 (see Fig. 11) is inserted through the nipple 70 of the air bag 58. To insert the nipple 70 into the hole 64, the bracket portion 75 of the spring clip 73 is compressed (by the fabric of the air bag 58), causing the flanges 77 at the ends of the shaft portion 101 of the spring clip 73 to move toward each other so that they can enter the hole 64. After insertion through the hole 64, the flanges 77 spring apart and no longer allow the removal of the nipple 70 from the hole 64 without the bracket area 75 of the spring clip 73 being compressed again.

An end view of a bed constructed in accordance with the present invention is shown in Fig. 6. The brace 102 is attached to the crossbeam 29 of the sub-frame 27 by bolts 104. Fans 108 are attached to the brace 102 by bolts 110 passing through mounting plates 112 integral with the fan housing 116. A gasket, a piece of plywood or particle board (not shown) or other sound and vibration dampening material is placed between the mounting plates 112 and the brace 102. A strip of such material (not shown) may also be placed between the brace 102 and the crossbeam 29. The blowers 108 include integrated permanently isolating capacitor electric motors 114. When the motors 114 are actuated, the blowers 108 push air out of the blower housings 116, through the blower funnels 118 and up into the blower hoses 120 to the air box funnels 122 and further into the air box 124 (see Figs. 3 and 6).

The fans 108 take in air from the filter box 96 through hoses 98 (see Fig. 3). The filter box 96 is held in a frame 100 for easy removal (see Fig. 6). The frame 100 is attached to the frame 27 and is largely hidden in Fig. 6 by the crossbar 26 of the base 22 and the crossbar 29 of the frame 27. The second fan 108 is provided to increase the volume delivered to the air bags 58, thereby increasing the air pressure within the air bags 58. A cover (not shown) lined with a sound absorbing material may also be provided to cover the fans 108 and thus reduce noise.

The air control box 124 is an airtight box which is secured to the underside of the head base plate 52 by brackets 125, details of which are shown in Figs. 8, 9A and 9B. The front of the air box 124 is provided with a manifold assembly 126. The manifold assembly 126 is provided with a manifold plate 145 with holes (not numbered) for connection to a means for varying the amount of air supplied to the air bags mounted on the base plates 46, 48, 50 and 52 in the area of the feet, legs, buttocks, back and head, respectively. A seal 115 prevents the leakage of air between the air box 124 and the manifold plate 145. In a presently preferred embodiment, the means for varying the amount of air supplied to the air bags 58 takes the form of a plurality of valves generally designated by the reference numerals 128, 130a and 130b, 132a and 132b and 134a and 134b (see also Fig. 3). The individual valves 128, 130a and 130b, 132a and 132b and 134a and 134b are provided with a motor 138 which has a threaded nylon shaft 139 (see Figs. 8, 9A and 9B) which is attached to the drive shaft (not shown) of the individual motors 138 and is held on the neck 148 by a set screw 149. A piston 140 rotatably moves inward and outward along the threaded shaft 139 when the limit pin 141 of the piston 140 engages one of the two supports 142 located immediately adjacent to the special piston 140 and which hold the motor mounting bracket 143 on the back of the full inflation plate 144.

The full inflation plate 144 with openings 202 which form part of the valves 128, 130a and 130b, 132a and 132b and 134a and 134b is attached to the back of the manifold plate 145 by hinges 146 (see also Figs. 9A and 9B). A seal 147 is provided to prevent the escape of air between the full inflation plate 144 and the manifold plate 145. The motors 138 are not provided with limit switches, but the movement of the ram 140 in the backward and forward directions along the threaded shaft 139 of each motor 138 is limited by engagement of the ram 140 with the opening 202 when the ram 140 moves in the forward direction and by engagement of the rear of the ram 140 with the neck 148 when the ram 140 moves in the backward direction on the threaded shaft 139. An O-ring 204 is provided on the ram 140 which is compressed between the ram 140 and the opening 202 when the ram 140 moves in the forward direction into the opening 202. The compression continues until the load on the motor 138 is sufficient to cause it to stop and rest. The O-ring 206, provided on the neck 148, operates in a similar manner, when it is engaged by the back of the punch 140.

The stopping of the motor 138 by loading the O-rings 204 and 206 facilitates the reversal of the motors 138 and the direction of movement of the plunger 140 along the threaded shaft 139, since the threaded shaft 139 is not stopped. The threaded shaft 139 is free to move in the opposite direction and reverse so that the force generated by the compression of the O-rings 204 or 206 is released by rotating the threaded shaft 139. The ram 140 then rotates on the threaded shaft 139 until the stop pin 141 comes into contact with the support 142, thereby stopping the rotation of the ram 140 and causing it to move along the shaft 139 while continuing to rotate.

A tilt plate 150 is attached to the outside of the manifold plate 145 by means of hinges 151 (see Figs. 9A and 9B). A seal 106 is provided to prevent the escape of air from the space between the manifold plate 145 and the tilt plate 150. The tilt plate 150 is provided with couplings 153, the inner portions of which are continuous with the holes in the manifold plate 145 when the tilt plate 150 is in the position shown in Figs. 8, 9A and 9B, for connecting the respective bed frame gas supply hoses 174, 176a and 176b, 178a and 178b and 182a and 182b, as will be explained below.

A block 154 is secured to the tilt plate 150 by screws 155 and serves as a location to which the cable 156 can be anchored by means of a groove 157 so that a conduit 158 can slide back and forth within the cable 156 to selectively pivot the tilt plate 150 away from the manifold plate 145 at the hinge 151. The conduit 158 is secured to the manifold plate 145 by the threaded cable end and a lock nut 159. The conduit 158 is secured at its other end to the support arm 183 attached to the tube 190 (see Fig. 7). The bed frame 12 is provided with quick-tilt levers 165 on both sides, the quick-tilt levers 165 being connected by the tube 190 so that both levers 165 ensure remote control of the tilt plate 150 causing movement of the line 158 by the cable 156. When one of the quick-tilt levers 165 is moved from the position shown in Fig. 7, an eccentric lever arm 181 presses on the line 158, the cable 156 being anchored to the support arm 183 so that the line 158 moves by the cable 156. The details of the anchoring of the cable 156 and the movement of the line 158 by the cable under the influence of the lever arm 181 are the same as for the anchoring of the cable 160 and the movement of the line 162 by the cable under the influence of the lever arm 185 (see below). Movement of the conduit 158 causes the pivot plate 150 to move away from the manifold plate 145, thereby discharging the air in the air bags 58 through the manifolds 76, 78, 80, 82 and 84 and bed frame gas supply hoses 174, 176a, 178a, 180a, 176b, 178b and 180b to escape to the atmosphere through the openings thereby created between manifold plate 145 and tilt plate 150 so that air bags 58 are rapidly deflated. A coil spring 201' closes off conduit 158 within the holes (not numbered) in tilt plate 150 and manifold plate 145 to urge tilt plate 150 and manifold plate 145 apart.

As best seen in Figures 8 and 9B, a separate cable 160 passes through the manifold plate 145 in the threaded fitting 161 so that the conduit 162 can slide back and forth therein. The conduit 162 is anchored to the full inflation plate 144 by means of a groove 163 which allows the full inflation plate 144 to pivot away from the manifold plate 145 at the hinge 146. The pivotal movement of the full inflation plate 144 away from the manifold plate 145 thus removes the full inflation plate 144, the motor mounting bracket 143 and all other parts attached thereto from the air stream and allows unimpeded access of air in the air box 124 to the couplings 153 of the valves 128, 130a and 130b, 132a and 132b and 134a and 134b and to the bed frame gas supply hoses 174, 176a and 176b, 178a and 178b and 182a and 182b, resulting in rapid and complete inflation of the air bags 58 while elevating the patient 348 to the position shown in Fig. 10B, thereby facilitating patient movement or other necessary operations. A coil spring 201 encloses the conduit 162 in a bore (not numbered) in the manifold plate 145 and the full inflation plate 144, thereby urging the manifold plate 145 and the full inflation plate 144 apart.

The line 162 is anchored at its other end to the lever arm 185 (Fig. 7) which in turn is attached to the rod 195 on which a full inflation button 193 is attached. The bed frame 12 is provided with full inflation buttons 193 on both sides. The full inflation buttons 193 are connected to a rod 195 so that both control the movement of the line 162 through the cable 160. The cable 160 is attached to the support arm 187 by means of the threaded cable end 199 which is attached to a DELRIN bearing 209 which is integral with the support member 210 and receives the rod 195 so that rotation of the full inflation knobs 193 causes the conduit 162 to slide therein pivoting the full inflation plate 144 at the hinge 146. The weight of the motors 138, the supports 142 and the motor mounting arm 143 bias the full inflation plate 144 toward the position where the full inflation plate 144, the motor mounting arm 143 and the parts attached thereto are removed from the gas stream into the couplings 153 of the valves 128, 130a and 130b, 132a and 132b and 134a and 134b. This bias allows the knobs 193 to act as a release means so that one of the knobs 193 need only be rotated sufficiently to move the connection between the line 162 and the lever arm 185 from its over-center position, whereupon gravity causes the plate 144 to open. Referring to Fig. 10B, a patient 348 is shown in a supine position lying on the air bags 322 (and/or 58, 321, 325 or 328), whereupon the plate 144 is opened for full inflation. When the knobs 193 are returned to their original position, the lever arm 185 returns to the position where the connection between the line 162 and the lever arm 185 is rotated 180º from where the line 162 reaches the rod 195, i.e., over-center. As previously mentioned, a microprocessor 240 includes an audible alarm (not shown). Switches (not shown) may also be provided to activate the alarm when one of the buttons 193 or the lever 165 is used to inflate or deflate the air bags 58, 321, 322, 325 and/or 328.

Air enters the air box 124 through the air box hoppers 122 in the base plate 121 (Fig. 3). The air box hopper 122 is provided with a one-way impact valve, shown schematically at 117, so that air cannot escape from the air box 124 when only one fan 108 is operated. The air box 124 is provided with a heating strip, shown schematically at 172. The heating strip 172 is attached to a partition wall 133 in the air box 124 which effectively divides the air box 124 into two compartments. Since air enters the air box 124 in one compartment (i.e., behind the heating element 172) and exits the air box 124 from the other compartment, an air stream must pass through the space 135 between the partition wall 133 to which the heating element 172 is attached, whereby a mixing and heating process takes place.

As shown in Fig. 3, when the blowers 108 are turned on, air (or other gases) coming from the filter box 96 is forced or pumped through the hoses 98 to the blower hoses 120, through the one-way valves 117 and into the air box 124. A valve 109 is provided to provide increased control of the air pressure in the air bags 58, 321, 322, 325 and 328 and to close off one end of the blowers 108 so that the bed 10 can be operated at either of the blowers 108 or at the blower 432 (see Fig. 7). The valve 109 is used to restrict the air flow from one of the fans 108 when both fans 108 are operating, which allows additional adjustability of the air pressure.

The air escapes from the air box 124 through the valves 128, 130a and 130b, 132a and 132b and 134a and 134b into the respective bed frame gas supply hoses 174, 176a and 176b, 178a and 178b and 182a and 182b. Bed frame gas supply hoses 174, 176a and 176b, 178a and 178b, and 182a and 182b direct air to manifolds 76 and 76', 78 and 78', 80 and 80', 82 and 82', and 84. Bed frame gas supply hoses 178a and 178b are connected to buttock gas manifolds 78 and 78a, which are connected to leg gas manifolds 78 and 78' by bed frame gas supply hoses 180a and 180b. Bed frame gas supply hoses 182a and 182b direct air to back gas manifolds 82 and 82', respectively. The bed frame gas supply hose 174 supplies air to the head gas manifold 84. The individual gas manifolds 76 and 76', 78 and 78', 80 and 80', 82 and 82' and 84 are attached to the underside of the base plates 46, 48, 50 and 52, with the gas manifolds 76 and 76' attached to the foot base plate 48, the gas manifolds 78 and 78' attached to the leg base plate and the gas manifolds 80 and 80' attached to the buttocks base plate 50. The head base plate 52 and its corresponding section 14"" of the frame 12 is provided with two back gas manifolds 82 and 82' and the head gas manifold 84.

Since the foot base plate 46 extends beyond the end member 16 of the frame 12 at the foot of the bed, T-sections 86 and 86' are provided on the foot gas manifolds 76 and 76', respectively, to direct the foot extension hoses 88 and 88' to the holes 64 and 64' at the extreme ends of the foot base plate 46 (see Figs. 3, 7 and 11). Clamps 65 are provided to hold the foot extension hoses 88 and 88' to the nipples 23 in the holes 64 and 64' and to the T-sections 86 and 86'. The head base plate 52 similarly extends beyond the end member 16 of the frame 12 at the head end of the bed (Figs. 3 and 6). A T-section 92 is provided on the head gas manifold 84 to direct air to the hole 64 at the outermost end of the head base plate 52 by means of the head extension hose 94. A clamp 65 is provided to hold the head extension hose 94 to the T-section 92 and the seat 66 in the hole 64.

Air enters the gas manifolds 76 and 76', 78 and 78', 80 and 80', 82 and 82' and 84 from the respective bed frame gas supply tubes 174, 176a and 176b, 178a and 178b 180a and 180b or 182a and then flows through the length of the individual gas manifolds 76 and 76', 78 and 78', 80 and 80', 82 and 82' and 84. Air exits the gas manifolds 76 and 76', 78 and 78', 80 and 80', 82 and 82' or 84 into the air bags 58 through the holes 64 and 64' in the base plates 46, 48, 50 and 52 and inflates the air bags 58.

The holes 64 and 64' through the base plates 46, 48, 50 and 52 and into the respective air bags 322, 325 and 328 are staggered along the length of the frame 12 of the bed 10. In other words, every other hole 64 or 64' is provided with a keyway 11 (see Fig. 4). Air bags 322, 325 and 328 are provided with a single nipple 70 or 23 respectively and with a post 32 with a retainer 34 attached thereto for engaging the keyway 11 in the hole 64 or 64' at the other end thereof. The air bags 322, 325 and 328 alternate in their orientation on the base plates 46, 48, 50 and 52, resulting in approximately half of the air bags 322, 325 and 328 having the nipple 70 or 23 oriented closer to one side of the bed frame 12 than the nipple 70 or 23 of the other half of the air bags 322, 325 or 328 mounted thereon.

Since each of the bed frame gas supply hoses 174, 176a and 176b, 178a and 178b, 180a and 180b, and 182a and 182b continues into a corresponding gas manifold 76 and 76', 78 and 78', 80 and 80', 82 and 82', or 84, the amount of air supplied to each of the gas manifolds 76 and 76', 78 and 78', 80 and 80', 82 and 82', or 84 can be varied using the valves 128, 130a and 130b, 132a and 132b, and 134a and 134b on the air box 124. Since the individual valves 128, 130a and 130b, 132a and 132b and 134a and 134b control the amount of air supplied to one of the manifolds 76 and 76', 78 and 78', 80 and 80', 82 and 82' or 84, the individual valves 128, 130a and 130b, 132a and 132b, 134a and 134b control the amount of air supplied to the set of air bags 322, 325 or 328 through the individual gas manifolds 76 and 76', 78 and 78', 80 and 80', 82 and 82' or 84.

Also shown in Figures 3 and 7 is a portable power unit or transport device, generally designated 426. The portable power unit 426 consists of a housing 428 which includes batteries 430, a blower 432 and a battery charger 434, and a hose 436. The hose 436 is connected to a releasable coupling 438 which fits into the coupling 440 of the hose 442 which is attached to the sub-frame 27 and connects to the air box 124 through the funnel 444. Clamps 446 are attached to the sub-frame 27 for releasably connecting the housing 428 to the portable power unit 426. The portable power unit 426 provides air pressure to provide support for a patient when an electrical outlet is not available, for example during patient transport.

As explained below, means are provided for alternately first inflating the air bags 322 and 328 connected to the back, seat, leg and foot gas manifolds 76, 78, 80 and 82 and then deflating those air bags while inflating the air bags 322 and 328 connected to the back, seat, leg and foot gas manifolds 76', 78', 80' and 82'. The alternate inflation and deflation of the first set of air bags 322 and 328 and the second set of air bags 322 and 328 causes the patient 348 lying thereon to be rocked alternately in one direction and then in the other direction (see Figs. 10A-10D), which is due to the alternating arrangement of the cutouts 324 on the air bags 322 and 328.

To effect rocking of the patient 348, the respective air bags are alternately inflated and deflated under microprocessor control. Referring to Fig. 3, valves 130a, 132a and 134a supply air to manifolds 82, 80, 78 and 76. These manifolds supply air to a first set of air bags 322, 325 and 328 whose columns 326 and cutouts 324 are located closer to a first side of the bed frame 12. Similarly, valves 130b, 132b and 134b supply air to manifolds 82', 80', 78' and 76', which in turn supply air to a second set of air bags 322, 325 and 328 whose columns 326 and cutouts 324 are located closer to the second side of bed frame 12. Valve 128 supplies air to manifold 84, which supplies air to air bags 321 that support patient's head 348. The Pressure in the individual manifolds can be controlled by a microprocessor 240 by adjusting the individual valves supplying air to the individual manifolds. The software is programmed to move the patient sequentially to each of three positions according to pressures set by the operator. Figs. 10A, 10C and 10D show three such positions which are sequentially stepped through by the software.

The hump 330 in the air bags 328 provides a longitudinal barrier along the upper surface of the air bags 328 such that one of the legs of the patient 348 is retained on either side of the longitudinal barrier formed by the humps 330 even during the alternate inflation and deflation of the bags 328. In this way, the hump 330 prevents the patient 348 from rolling too far to one side of the bed frame 12 or the other side. Furthermore, sliding and/or rubbing of the legs of the patient 348 does not occur when the patient 348 is alternately rolled from one side of the bed frame 12 to the other. It will be apparent to those skilled in the art that the air sacs 328 with the bumps 330 can be replaced by air sacs 321, 322 or 325 depending on the type of therapy and the amount of movement desired for a particular patient.

The software operates on an internal interrupt basis. This means that the software remains idle until a certain number of clock pulses have been received, at which time an interrupt signal is generated internally by the microprocessor 240. When the software detects this internal interrupt, the various functional software modules shown in Figure 24 are executed sequentially. Since the microprocessor 240 is configured to generate the internal interrupt every 50 milliseconds, the functional software modules of Figure 24 are executed every 50 milliseconds.

Figure 24 shows a block diagram of the functional software modules used to achieve the control functions of the invention. The software also includes the initialization and shutdown routines described below, but these have been omitted from this diagram for ease of illustration. Furthermore, the various service interrupt routines have been omitted. Figure 24 shows only the application software which is executed every 50 milliseconds by the microprocessor 240.

Below, some of the functional modules or routines of Figure 24 are described in more detail. The following is an overview of how these routines are integrated to achieve the objectives of the invention.

The RAM data table 903 is a block of memory used to store the various variables required to control the software. These variables include software timers, status flags, switch inputs, analog data inputs, target pressure values, and a target temperature value. The software timers are simply memory contents that are initialized to a specified value and then decremented every 50 milliseconds by the general timer routine 252. The switch inputs are digital inputs received from the control panel or from various switches described elsewhere. The status of these switches is stored in the RAM data table 903 so that false switch bounce conditions can be detected, as described in more detail below. The status flags are memory expressions used by the software to communicate a specific status to the software modules that indicate how to operate a software module. For example, a status flag is used to indicate whether to rotate the bed left, right, or center. The status flags can be changed by external inputs or by timing certain software timers. Analog data corresponding to the values received from the pressure and temperature transducers is also stored in the RAM data table 903. Also stored in the RAM data table 903 are the target pressures and target temperature that the software attempts to maintain and which are adjustable by operator input.

Upon receipt of the aforementioned internal interrupt, the first module to be executed by the microprocessor 240 is the general timer routine 252. This routine decrements the various software timers and sets certain status flags that affect the operation of the remaining modules when a timeout condition occurs. Next, the switch processing routine 254, which samples all digital inputs, is executed. When a change in a digital input is detected, the corresponding switch function routine 284 is executed. As described below, these Switch processing routines update the data in the RAM data table 903 according to the type of switch input change detected.

After all digital inputs have been sampled, the rotation control routine 292 is executed. The rotation control 292 determines whether the valves 128, 130a and 130b, 132a and 132b, or 134a and 134b must be opened, closed, or held in their current state. To make this decision, the rotation control routine 292 relies on analog data from the pressure transducers, target pressure values, and status flags that tell the routine which target pressure values to use. The rotation control routine 292 sets status flags that are then read by the motor valve routine 316. The motor valve routine 316 controls the valve motors 138 according to the decisions made by the rotation control routine 292. These decisions are communicated to the engine valve routine 316 through status flags.

The heater control routine 905 retrieves the current and target temperature values from the RAM data table 903, compares them, and turns the heater strip 172 either on or off with a digital output. The last module executed as part of the internal interrupt control loop is the display write routine 901. This routine retrieves the data from the RAM data table 903 to be output to the control panel. The display write routine 901 then controls the bar graph display 356 of the control panel 346 according to the retrieved data. The analog input routine 904 operates continuously in response to external interrupts generated by an analog to digital converter. This converter is shown schematically at 800, but is located within the control box 198 and is therefore not otherwise shown. The analog input routine 904 accepts the data from the analog-to-digital converter 800 and updates the corresponding location in the RAM data table 903.

Referring now to Figures 15-20, the programming of the microprocessor 240 is discussed. As shown in Figure 15, initialization of the program occurs at 242. The variable memory or RAM is cleared in step 244. Before internal or external interrupts are allowed, all RAM variables are zeroed and those requiring special data, such as the data stored in the electrically variable ROM described below, are initialized in step 246. The data and direction registers for the four 8 Bit outputs of microprocessor 240 are then initialized in stage 248.

The control software then remains idle in loop 250 until it receives a 50 millisecond interrupt signal from the hardware interrupt timer located within microprocessor 240. Microprocessor 240 then sequentially executes subroutines 252, 254, 292 and 316, which are schematically illustrated in Figures 16-19. The general timer subroutine 252 (see Figure 16) decrements most of the software controlled timers in RAM, including the electrically alterable ROM power "ON" delay timer before erase, the cardiopulmonary switched "OFF" to the audible alarm "ON" delay timer, the audible beep silence timer, and the spin timer. The general timer subroutine 252 of Fig. 15 begins at terminal 253. The first step 254 is to check whether the power ON/OFF pushbutton 851 (see Fig. 14) is switched to the "OFF" position or whether the pause setting buttons 728, 730 or 732 have been operated, a step which is necessary because the loop 250 runs at 50 msec intervals each time the main power cable 218 (see Fig. 12) is plugged into a power source (not shown). If any of these buttons 851 or 728, 730 or 732 have been operated, the subroutine 252 continues to step 259A; if not, the status of the rotary timer is checked in step 256. If the target value (zero) is not reached, the timer is decremented in step 257. If the target value has been reached, the spin mode continues to the next sequential spin phase and the timer is reinitialized in step 258 with the appropriate time delay valve input by the operator using one of switches 728, 730 or 732 on control panel 346.

As described below, the temperature switch 152 is used in conjunction with the display 168 on the control panel 346 (see Fig. 14) to set the target temperature in the air bags 321, 322, 325 and 328 by pressing and holding either switch 152A or 152B to increment or decrement the counter which increases the target temperature by one increment each time a selected number of 50 msec pulses have elapsed (or decrements by the same increment). When the switch 152A or 152B has been actuated by the operator, a test is performed in step 259B to determine which switch has been operated. If the decrease/decrement switch 152B is operated, the counter is checked to see if the count at step 259C is at the minimum count. If so, the subroutine proceeds to step 259; if not, the counter is decremented in step 259D and subroutine 252 continues to step 259. If the status display in step 259B indicates that the temperature increase increment switch 152 has been operated, the counter is checked to see if the count at step 259E is at a maximum value. If so, subroutine 252 continues to step 259; if not, the count is decremented in step 259F and subroutine 252 then continues to step 259.

If the power ON delay timer is not zero at step 259, this timer is decremented at 260 until zero is reached. The subroutine then proceeds to the cardiopulmonary "OFF" audible alarm "ON" delay timer for similar processing at step 261. This timer is decremented at step 262 if the timer is not zero and checked again at step 263. If the timer is still not cleared, the alarm (not shown) in microprocessor 240 is activated at 264. If the timer has expired, the routine proceeds to the audible beep silence timer at 265. If this timer has not expired, it is decremented at 266 and checked again at 267. If it has still not expired, the alarm will continue to be activated at 268. The general timer subroutine 252 will then exit when the last timer has expired and then return to the control software at 270 (see Fig. 15).

The switch processing subroutine 254 is shown schematically in Fig. 17. It monitors the status of the switches on the control panel 346, the switches 226 and 228 in the air box 124, the status of the switches (not shown) on the hand control 361 (see Fig. 14) and the pressure sensor pad switches 231a and 231b. The switch processing subroutine 254 enters from Fig. 15 at terminal 272, assigns a number to each input in stage 274 and processes each numbered input in a loop. Each input is tested for status in stage 276 at 50 millisecond intervals, although it will be apparent to one skilled in the art having knowledge of the present description that other time intervals may be suitable for testing the status of the inputs. The switch status is determined by comparing the current switch status with the Switch status from the last interrupt is compared at step 278. If a change is detected, a switch bounce condition is assumed and the switch count is incremented at step 280 to process the next switch input. If no change is detected from the previous switch status, a switch position change test is performed at step 282 and the switch function is executed at step 284 if a switch change is detected. If the switch status matches over three consecutive tests, no switch position change is indicated and the switch count is incremented at step 280 in the manner described above. The switch count is compared to a limit number at step 286. If the value is less than the limit number, the switch count is incremented at 285 and the above processing in loop 288 is repeated for the incremented switch count. Provision is made to initialize the switch status at power up by testing at step 287 to determine if the first pass through the switches is made. If so, the power off memory is read at 289. The switches for which data is stored in the electrically alterable ROM are initialized at 283 to reflect the switch status at the time of the previous power off operation. The switch processing subroutine 254 is exited when the last number of switches has been processed. The program then returns to the control software at 290.

There are separate switch functions 284 for each functional setting of the operator inputs on the control panel 346. In Fig. 14, the control panel 346 shows air adjustment switches 349, 350, 351, 352, 353, 354 and 355. Each of the air adjustment switches 349, 350, 351, 352, 353, 354 and 355 is a pair of buttons or a toggle switch that increases or decreases the target pressure to be achieved in the air bags 58, 321, 322, 325 and 328 through the valves 128, 130a and 130b, 132a and 132b and 134a and 134b. These target pressures are stored in memory locations by the microprocessor 240. In the rotation subroutine described below, the target pressures are used as settings that the software attempts to achieve and/or maintain by opening and closing valves 128, 130a and 130b, 132a and 132b, and 134a and 134b. There are seven target pressures corresponding to the following parts of the patient's body: head, right leg, right trunk, right shoulder, left leg, left trunk, and left shoulder. The Air adjustment switches 349, 350, 351, 352, 353, 354 and 355 correspond to each of the patient's 348 body parts. There are also three rotational positions designated center, right and left (see Figs. 10A, 10C and 10D) for which corresponding switches 628, 340 and 632 are located on the control panel 346, so that there are a total of 21 target pressures. The microprocessor 240 issues valve control commands which cause the air bags 58, 321, 322, 325 and 328 to inflate and deflate in sequence and repeatedly to achieve each of the three rotational positions. Each rotational position is defined by seven target pressures corresponding to that position. Under normal conditions, the target pressures are indicated by the bar graph display 356 above the corresponding air adjustment switch. To change a target pressure, one of the rotary position switches 628, 630 or 632 is depressed and the operator presses either the upper or lower air adjustment switch corresponding to the patient body part for which the target pressure is to be changed. A switch function routine 284 then increments or decrements the memory location in RAM corresponding to the target pressure. At this time, the changing target pressure is output on the bar graph 356 corresponding to the particular air adjustment switch. In this manner, each of the seven target pressures for each of the three rotary positions is set by the operator.

Another switch function routine 284 similar to the routine described above allows the operator to set the pause time, i.e., the amount of time the patient 348 remains in each of the positions shown in Figures 10A, 10C and/or 10D, for each rotational position. The pause time is stored in a timer location which is decremented by the timer routine after each interval interruption. The pause times for the center, right and left positions are set by pressing the pause setting buttons 728, 730 and 732, respectively.

Another switch function routine 284 is executed when the switch processing routine 254 detects operator input from the height adjustment switches 233, 235, 236, 237, 238 and 239. The switches 233 and 237 raise and lower the frame section 14' of the bed 10, while the switches 236 and 239 raise or lower the frame section 14"". The switches 235 and 238 raise or lower the entire frame 12 of the bed 10. The switch function routine that is executed when any of these switches is depressed causes the above-described described drive screws to make the appropriate height adjustment.

Similarly, another switch function routine 284 allows the operator to set the temperature to be maintained when supplying air to the air bags 321, 322, 325, or/and 328. The target temperature is used as a set point for the microprocessor 240 to control the heater strip 172. The target temperature is set using switches 152A and 152B, and a digital display 168 of the target temperature is controlled by the software.

The rotation subroutine 292 is shown in Figure 18. This routine begins at port 294 after the general timer subroutine 252 has set the appropriate software timers to determine the rotational position to which the bed is to be steered or held. The subroutine 292 is executed for the individual valves 128, 130a and 130b, 132a and 132b, and 134a and 134b to alternately inflate or deflate the two sets of air bags 322, 325, and 328 supplied by the manifolds 76, 78, 80, and 82, and 76', 78', 80', and 82' to roll the patient 348 from one side of the bed frame 12 to the other. The specific valve number is read in step 296. The target pressure for the specific valve setting described above is then read in step 300. In step 308, the individual valve 128, 130a and 130b, 132a and 132b, or 134a and 134b, if applicable, can be adjusted in accordance with the output signal of a potentiometer 468, which is also read in step 300. The potentiometer 468 inputs a voltage value to the analog-to-digital converter 474, which converts the voltage into a digital value corresponding to the angular displacement of the section 14', 14", 14'" or 14"" of the bed frame 12 with respect to the adjacent section 14', 14", 14'" or 14"". For example, when section 14' of frame 12 is pivoted relative to section 14", the weight distribution of the patient's body 348 resting on air bags 321, 322, 325 and/or 328 changes as discussed below. Accordingly, microprocessor 240 adjusts target pressures to compensate for the change in weight distribution.

In Fig. 13, two adjacent frame sections 14' and 14" are shown connected by the joint 44'. The support arm 462 is attached to the frame section 14" by the bolt 464 and the nut 466. The potentiometer 468 is attached to the support arm 462 so that its shaft 467 can rotate freely over its entire operating range. The shaft 467 of the potentiometer 468 and the joint 44' are arranged so that their axes of rotation are aligned with each other. The shaft 467 of the potentiometer 468 is journalled in the frame section 14'. When the frame section 14" is pivoted with respect to the section 14', the link 470 is also rotated accordingly, causing the shaft 467 of the potentiometer 468 to rotate, resulting in a change in the output voltage of the potentiometer 468 which is proportional to the angular displacement between the sections 14' and 14". This change in the output results in a signal which is transmitted through the wire 472 to the microprocessor 240 (Fig. 12). The output signal of potentiometer 468 is adjusted so that for each increment of elevation of frame section 14" from the horizontal by approximately 15º, the pressure in the sets of air bags attached to base plates 48 and 50 is increased by approximately 20% above the base pressure until a maximum angle of 45º from the horizontal is reached.

The threaded shafts 139 of the motors 138 which close the valves 128, 130a and 130b, 132a and 132b, and 134a and 134b rotate very slowly so that the amount of time a motor 138 has run is used in a linear proportional type algorithm as a timer increment to calculate the theoretical pressure in the clutch 153 of each of the valves 128, 130a and 130b, 132a and 132b, or 134a and 134b in step 302. The actual pressure is then read from the air chuck 212 (see Figs. 8, 9A and 9B) according to the special valve 128, 130a and 130b, 132a and 132b or 134a and 134b in step 304. The pressure from the air chucks 212 is transmitted through air pressure lines 213 to pressure transducers (not shown) mounted in the control box 198. The pressure transducers are of a type suitable for reading pressures in the range of approximately 0-1 psig (available from Microswitch Corp. (Freeport, Illinois) and Sensym Corp. (Sunnyvale, California). The pressure transducers provide a voltage proportional to the specific pressure as an input to an analog-to-digital converter in the control box 198, which then inputs it to the microprocessor 240. The actual pressure is then compared to the target pressure in step 306. A decision is then made to leave the valve open, close it, or open it. The appropriate operation is performed in steps 308a, 308b, or 308c, which causes the valve motor subroutine 316 to perform the appropriate action as specified below.

After execution of step 308, a display of the air pressure in the couplings 153 of the valves 128, 130a and 130b, 132a and 132b and 134a and 134b is provided on the bar graphs 356. The operator makes a selection in step 310 whether actual or target pressures are displayed depending on whether the switches 628, 630 or 632 (see Fig. 14) have been operated. The actual display data is calculated in step 312 and output on the bar graphs 356 in step 314. If one of the switches 628, 630 or 632 has been operated, the target display data is calculated in step 315 and output in step 314 as above. The rotation subroutine 292 is then exited at the transition point 298.

Referring to Figures 1 and 14, an auxiliary control panel 850 is mounted on the foot plate 21 with push button switches 851, 357, 358, 852 and 853 mounted thereon. Push button 851 is the main switch for turning the power on and off. By pressing push button 358, the bed 10 is placed in the low pressure loss swinging patient therapy mode, with the microprocessor 240 sequentially moving through the three previously programmed rotation positions. By pressing push button 358, the bed 10 is placed in the air floating therapy mode, i.e. the rotation of the patient 348 is stopped in any position between the two extreme positions shown in Figures 10A and 10C. Pressing either push button 852 or 853 causes microprocessor 240 to hold the bed in the previously programmed left or right rotation position.

The valve motor subroutine 316, shown schematically in Fig. 19, converts the valve motor movement commands generated by the switch processing and rotation subroutines 254 and 292, respectively, into valve motor actions, i.e., starting, braking, idling and reversing of the individual motors 138 used to open and/or close the valves 128, 130a and 130b, 132a and 132b, and 134a and 134b. The valve motor subroutine 316 begins at transition point 318. Each motor 138 is assigned a number in step 320 and tested for its required status, i.e., running or stopped, and for its direction relative to the current status in step 370. Whenever a running motor 138 is to be stopped, the status of that motor is tested in step 372. After or during stopping, the brake timer is Step 374 is tested to determine if the brake timer is set to zero. If the brake timer is not set to zero, it is decremented in step 376 and tested again in step 378 to determine if it is now set to zero. If so, the brake is released in step 380 and the number assigned to that motor 138 is compared to the limit number in step 382 to determine if that motor 138 is the last motor. If it is determined in step 372 that motor 138 is in the running condition, motor 138 is stopped and the brake is applied in step 388. The timer is then initialized in step 390. If motor 138 is not the last motor, the motor timer is decremented in step 386 and the above process is repeated.

Referring again to step 370, if the required status of the motor 138 under test indicates that the motor 138 should be running, the current motor status is tested in 392. If the status of the motor 138 under test indicates that it is stopped or is being stopped, the required status and the current status of the motor are compared to determine if they are the same in step 394. If the required status and the current status are not the same, the brake timer is tested in step 396 to determine if the brake timer is at zero. If the brake timer is not at zero, it is decremented in step 398 and the number associated with that motor 138 is tested in step 382 to determine if that motor 138 is the last motor. If motor 138 is not the last motor, the motor timer is decremented in step 386 and the above process is repeated. If the brake timer is set to zero in step 396, the direction of rotation of motor 138 is reversed in step 400, motor 138 is turned on in step 402, the motor run timer is initialized in step 404 and the number associated with this motor 138 is tested in step 382 to determine if this motor 138 is the last motor. If motor 138 is not the last motor, the motor timer is decremented in step 386 and the above process is repeated. If the required status and the current status in step 394 are the same, then the motor 138 is turned on in step 402, the motor run timer is initialized in step 404, and the number associated with that motor 138 is tested to determine if that motor 138 is the last motor. If the motor 138 is not the last motor, then the motor timer is decremented in step 386 and the above process is repeated.

If the current status of the motor 138 in step 392 indicates that the motor 138 is running, the required status and the current status are compared in step 406 to determine if they are identical. If the required status and the current status are not identical, the motor 138 is turned off, the brake is applied in step 388, and the brake timer is initialized in step 390. The process then continues in the manner described above. If the required status and the current status of the motor 138 are identical, the motor run timer is tested in step 408 to determine if the run timer is set to zero. If the run timer is not set to zero, the motor run timer is decremented in step 410 and tested again in step 412 to determine if the run timer is set to zero. If so, the motor 138 is stopped in step 414, the number assigned to the motor 138 is compared to the limit number in step 382 to determine if the motor 138 is the last motor, and then the process continues as described above. If the run timer is set to zero in step 408 or 412, the number assigned to the motor 138 is compared to the limit number in step 382 to determine if the motor 138 is the last motor, and then the process continues as described above.

A power failure interrupt subroutine 416, shown schematically in Fig. 20, writes certain control configuration parameters, such as the fan and spin mode status, to the electrically alterable ROM in the event that power is lost or the low air loss bed 10 is unplugged. The power failure interrupt subroutine 416 begins upon receipt of an interrupt from an external hardware interrupt (not shown). If the electrically alterable ROM power on delay before clearing (EEROM) timer tested in step 418 is set to zero, that is, if the low air loss bed 10 has been powered on for more than a few seconds so that the electrically alterable ROM is available for writing, the aforementioned parameters are stored in memory in step 420 and the EEROM timer is initiated in step 422 prior to returning to the pre-interrupt characteristics in step 424. If the EEROM timer in step 418 is not reset to zero, the bed 10 has probably just been powered up with a small air leak, so the memory is not available for writing. If the control software (see Fig. 15) experiences a power interruption that causes the power failure interrupt and causes the memory to be written, but does not actually remove power from the control software, the power failure interrupt subroutine 416 initializes the EEROM timer and is available for re-writing to memory after the EEROM timer is triggered again.

As previously mentioned, the frame 12 is hinged at 44', 44" and 44'" whereby the base plates 46 and 52 can be raised from the horizontal and the angle of inclination can be changed for the comfort of the patient 348 or for therapeutic purposes. However, when the head base 52 in particular is raised, the deviation from the horizontal places a disproportionate amount of the patient's weight 348 on the air bags 322 via the leg base 48 and the buttocks base 50. In a presently preferred embodiment of the invention, only three air bags 322 are attached to the respective bases 48 and 50, so that a large portion of the patient's weight, which is distributed among more than 20 of the air bags 58, 322, and 328 when the sections 14', 14", 14'" and 14"" are all in the same horizontal plane, is concentrated on only six of the air bags 322. Pressure sensing pad switches 231a and 231b (see Fig. 14) are mounted flat on the leg base 48 and the buttocks base 50 so that in the event that any part of the patient's weight comes into contact with either of these switches 231a or 231b, the buzzer described above is actuated by the microprocessor 240. It can be silenced by the operator by actuating the switch 347. The air pressure in the air bags 322 attached to the buttocks base 50 can be increased by the operator.

Fig. 12 shows a schematic circuit diagram of a low air loss bed constructed in accordance with the teachings of the invention. Alternating current enters the circuit in electrical cable 218 which is connected to a power distribution panel 219. The power distribution panel 219 includes a power supply module 220 for supplying power to the microprocessor 240 via cable 211 and solid state relays for controlling the fans 108 and the heater strip 172. The power distribution panel 219 supplies power to the motors (not shown) within the boxes 45 for raising, lowering and positioning the frame 12 of the low air loss bed 10 by means of a line 223 which connects to the junction box 224 of the bed circuit 43. The power distribution panel 219 also supplies power to the electric motors 114 of the fans 108. with power. Each of the fans 108 is provided with a capacitor 236. A switch 192 is provided on the control panel 346 to deactivate one of the fans 108 by connection by cable 243 to switch 241 on the fans 108.

Referring to Fig. 14, a temperature sensor, shown schematically at 194, is located in the buttock manifold 80. When the target temperature set by the operator using switches 152A or 152B and display 168 is less than the temperature of the air in the buttock manifold 80, the heater strip 172 is turned on by the microprocessor 240. The heater strip 172 is powered by wires 167i and 167o from the main power module 220 (see Fig. 12). The switch 191 on the control panel 346 is used to turn the heater strip 172 on or off.

Limit switches 226 and 228 are provided in the manifold plate 145 and on the full inflation plate 144, respectively (see Figs. 4, 8, 9A and 14). The limit switch 226 is closed when the push button 230 is actuated by the tilt plate. When the push button 230 is released by movement of the tilt plate 150 away from the manifold plate 145 under the influence of the levers 165, the circuit is opened and the fans 108 are turned off. The limit switch 228 is attached to the full inflation plate 144 by screws 232. The circuit is open when the lever arm 234 engages the manifold plate 145. When the full inflation plate 144 is opened under the influence of the full inflation buttons 193, the limit switch 228 is closed, activating the fans 108, if they are not already running, and the buzzer incorporated in the microprocessor 240. A switch 347 is provided on the control panel 346 to silence this buzzer.

The control panel 346 is connected to the control unit 198 via ribbon connections 200. The control unit 198 includes the microprocessor 240 and the other necessary circuitry. The control unit 198 is provided with plug-like receptacles 205 for receiving the plugs 207 of the cables 208, 211, 225, 227 and 229.

Cable 208 connects the control unit 198 to a temperature sensor 194 and the pressure sensor pad switches 231. Cable 211 provides a direct connection to the power distribution panel 219 and supplies power to the control unit 198 while sending control signals to the power distribution panel 219 to control the functions of the fans 108 and the heater strip 172. Cables 170a and 170b are connected to separate Wires 184i and 184o for each motor 138, directing low voltage DC current to each motor 138. Cable 170a is also provided with separate wires 226i and 226o and 228i and 228o which separately connect to limit switches 226 and 228, respectively.

The cable 227 is provided with connectors 359 at the end opposite the connector 207 for connection to a complementary connector 360 on a separate hand control 361 which duplicates the function of the switches 349-358 on the control panel 346. The hand controls 361 are shown schematically in Fig. 14 as they merely duplicate the functions of the keypad 346. The connectors 359 are provided on both sides of the bed frame 12 (not shown in Fig. 14) to allow easier access to the hand control 361 by hospital personnel.

The cable 229 is provided with connectors 362 and 363 at the end opposite the connector 207 for connection to complementary connectors 364 and 366, respectively. The connector 364 is located in the circuit of the bed frame 12 in the control box 43 (see Fig. 7), which is shown schematically as box 367. The connector 366 is located on a hand control, shown schematically at 368, which duplicates the function of the switches 233 and 235-239 on the control panel 346. When the hand control 368 is used to adjust the angle of inclination of the head and foot base plates 54 and 46, respectively, signals generated by activating the switches (not shown) on the hand control 368 are transmitted directly to the circuit 367 of the bed frame 12.

Although the present invention has been described with reference to the foregoing preferred embodiments, the description is for illustrative purposes only and is not intended to be limiting in any way the invention, the scope of which is limited only by the following claims.

Claims (16)

1. A method of operating a feedback controlled patient support system of the type having a patient support (10) with a plurality of inflatable air bags, said patient support comprising at least a first and a second separately inflatable air bag (322) for supporting a patient (348) and connected in a controllable fluid connection to an air supply means (108), said first air bag (322) being adapted to roll a patient in a first direction in response to the inflation control and said second air bag (322) being adapted to roll a patient in a second, opposite, direction in response to the inflation control, said air supply means (108) being connected in a controllable fluid connection to said air bags (322) for separately and alternately inflating said air bags; characterized in that the method includes measuring the air pressure in at least a portion of the first and second air bags; and controlling the air supply means (108) in a feedback manner through the use of means (240) connected to the air pressure measuring means to roll the patient first in the first direction and then in the second direction, ensuring that during the process of controlling the air supply to raise or lower the air pressure in the bags, the level of air pressure in the bags cannot fall below a predetermined minimum value. 2. A method according to claim 1, characterized in that a gauge pressure is selected in the first and second air bags by selection means (628 and 349), first and second target pressures to which at least a portion of the first and second air bags are to be inflated are selected by the selection means; and the air pressure in the air bags (322) is compared by a control means (240) connected to the measuring means with the target pressure selected for each of the first and second air bags and then alternately inflating the first air bag to the selected first target pressure when the air pressure in the first air bag is lower than the first target pressure so as to roll the patient in the first direction when the first air bag is inflated and the second air bag is inflated to the selected second target pressure when the air pressure in the second air bag is lower than the second target pressure so as to roll the patient in the second direction. 3. A method according to claim 2, characterized in that timer means (252) are provided for controlling the intervals during which the air bags are maintained at the first and second target pressures and for controlling when the air bags are inflated and deflated. 4. A method according to claim 1, characterized in that the air pressure measuring means includes a probe in the air supply to the air bags (322). 5. Method according to claim 1, characterized in that a microprocessor (240) is provided to control the air pressures in the air bags. 6. A method according to claim 1, characterized in that the air supply means (124) is arranged to selectively inflate the air bags to support a patient thereon and to keep the interface backs low to roll a patient thereon and to measure the air pressure in the air bags and to maintain a controlled, adjustable level of air pressure in the air bags during inflation and deflation of the air bags to uniformly roll a patient lying on the air bags, the air bags and the air bags of each of the first and second sets of air bags being arranged transversely relative to the support of the patient. 7. Method according to claim 6, characterized in that the measuring line air pressures in the air bags (322) are determined by the control means. 8. Method according to one of claims 6 and 7, characterized in that the target air pressures in the air bags (322) are determined by the control means. 9. A method according to claim 8, characterized in that the control means is provided with a timer means for determining the intervals between the pressures and to determine the times when the air bags are inflated and deflated. 10. Method according to claim 1, characterized in that in addition to the determination of a certain minimum level for the air pressure in the air bags, a certain upper or target level is also determined which is greater than the minimum level. 11. The method of claim 10, characterized by the step of inflating and deflating at least a portion of adjacent air bags between the target pressure and the minimum pressure. 12. A feedback controlled patient support system of the type having a support for a patient including a plurality of inflatable air bags connected in the form of a controllable fluid connection to an air supply means comprising: a patient support (10) including at least first and second separately inflatable air bag chambers (322) for supporting a patient (348), the first chamber being adapted to rotate a patient in a first direction in response to the inflation control and the second chamber being adapted to rotate the patient in a second, opposite direction in response to the inflation control; an air supply means (108) connected in the form of a controllable fluid connection to the air bags (322) for inflating the air bag chambers, characterized by: a means for measuring the air pressure in the first and second chambers (322); and means connected to the air pressure measuring means for controlling the air supply means (108) in the form of a feedback to roll the patient in the first and then in the second direction by monitoring and controlling the air pressure in the first and second chambers (322), ensuring that during operation of the air supply control means the level of air pressure in the chambers cannot fall below a certain minimum level. 13. System according to claim 12, characterized in that the control and measuring means maintains at least a predetermined minimum air pressure in the air bags during rolling. 14. A system according to claim 12, characterized in that the plurality of air bags are mounted on an articulated frame having control means (240) for controlling, in response to pressures measured in the air bags, the supply of a pressurized gas to a plurality of air bags (322) for inflation thereof, a first set of the air bags being mounted on a first section (14") of a frame (12); the control means including means for increasing the pressure in the first set of air bags in response to pivotal movement of a second section (14') of the frame relative to the first section of the frame. 15. A system according to claim 14, characterized in that the frame (12) is articulated to change the position of a patient lying on the support system, the frame including an articulated first section (14") and the plurality of elongated inflatable air bags (322 and 328) are arranged on top of the frame; gas supply means (124) in communication with each of the air bags for supplying gas thereto, the control means (240) associated with the gas supply means and the air bags for controlling the supply of gas to each of the air bags according to certain values of the target pressure and according to a plurality of predetermined groups of air bags, each of the groups defining a separate support zone; that there are also provided: means (468) associated with the frame (12) for measuring one of a plurality of degrees of articulation of the first section of the frame; Control means (240) operatively connected to the articulation position measuring means for varying the gas pressure in the air bags according to the degree of elevation of the first section of the frame determined by the articulation position measuring means; and pressure measuring means in fluid communication with the air bags for measuring the pressures in the air bags; the control means being operatively associated with the pressure measuring means for controlling the gas pressure in the air bags (322) in response to the pressures measured by the air pressure measuring means. 16. A system according to claim 15, characterized in that the control means is further provided with a valve control circuit and a multiple outlet variable flow gas valve means having at least one motor (138) for varying the flow through one of the outlets of the gas valve means: the valve control circuit being provided with a power supply for driving the motor(s) (138) of the valve means, the power supply being connected to the motor for driving the motor and regulating the flow through the at least one outlet; the control means (240) further comprising: pressure adjustment means for the articulation; pressure measuring means in fluid communication with the air bags (322) for measuring the pressures in the air bags; and wherein the control means (240) is operatively connected to the pressure measuring means for controlling the gas pressure in the air bags (322) in response to the pressures measured by the pressure measuring means.