HK1069306B - External counterpulsation cardiac assist device - Google Patents

Description

External counterpulsation cardiac assist device

Technical Field

The present invention relates to an external counterpulsation cardiac assist device which functions by applying positive and negative relative pressure to the limb, and more particularly to a relatively rigid, sealed shield for applying positive and negative relative (to atmosphere) pressure to the limb counterpulsating with cardiac function, the shield being adapted for field assembly to provide a specific fit and requiring only reduced pump capacity.

Background

Us patent 5,222,478 discloses a device and method for applying pressure to the human body. The respirator, artificial respirator, sheath or shield provides a close fitting shell adapted to be placed adjacent a portion of the human body to form a thin portion between the shell and the body portion, and a minimal space pressure receiving cavity to receive a pressure different from ambient pressure.

A method is known for assisting circulation without invading the vascular system by applying intermittent pressure to the body from the outside. Studies have shown that a pulse applying positive relative pressure to the lower extremities during diastole can raise the diastolic pressure by 40% to 50%, while applying negative relative pressure (vacuum) during systole can lower the systolic pressure by about 30%. Hereinafter, "relative" pressure refers to pressure relative to atmosphere (gauge).

This externally applied positive and negative relative pressure increases venous return to the heart due to the unidirectional valve in the peripheral venous bed. In cardiogenic shock accompanied by myocardial ischemia, increased coronary flow can improve cardiac function and thus indirectly affect the hemodynamic response to this procedure. Second, it is believed to promote the growth of parallel passage vascular delivery heart tissue and reduce the symptoms of angina.

The therapeutic effect of this method is widely reported in the literature. However, as a practical matter, the devices for externally applying positive and negative relative pressure to the limb are also very inefficient, and thus the procedure has not been widely accepted.

Early devices for this purpose included a prefabricated, pivoting, conical metal or housing shroud. Within the shield, a hollow cylindrical expandable rubber balloon-like tube is positioned, enclosing the limb segment. The balloon-like rubber tube is filled with water, which is pressurized to expand the tube, thereby filling the interior of the shell and applying pressure to the surface area of the limb segment.

To apply a negative relative pressure, water is first pumped out of the rubber tube, leaving an air gap between the rubber tube and the limb. An impermeable rubber-like coated fabric is placed around the outside of the shield and sealed around the limb to trap air between the limb and the rubber tube. By pumping out the air trapped in the sealed fabric, the fabric first collapses around the shield and then a negative pressure begins to develop in the gap between the limb and the rubber tube.

This system has many operational difficulties. Due to the high resistance to flow, it is almost impossible to pressurize the rubber tube and pump water out of the rubber tube fast enough to match the heart beat. As a result, even the process of applying positive relative pressure is very difficult. This process is even more difficult because a pre-fabricated cover may not fit closely to each patient, leaving a considerable gap between the rubber tube and the limb filled with the inflated rubber tube. The amount of air that has to be pumped out of the space enclosed by the rubber-coated fabric surrounding the shield and between the limb and the rubber tube is considerable, thereby requiring a large air pumping action. Furthermore, due to the softness of the rubber-coated fabric, the fabric tends to deform and enter the space between the limb and the rubber tube, whereby it is difficult to obtain the desired level of negative pressure (vacuum) around the limb.

Current applicators utilize a preformed and relatively inextensible fabric in which a balloon-like member is positioned. The balloon-like member and its surrounding cover or cuff surround the limb and are secured by a strip provided with hook tape (trade name VELCRO). Such applicators are currently available from Vassmedical, Inc. of Westbury, New York.

During its operation, the balloon is pressurized with air, thereby applying pressure to the surface of the surrounding limb. Due to the expansion and deformation of the cuff when the bladder is pressurized, a relatively large volume of air is required to achieve the desired limb surface pressure. This is the case even if the sleeve material is relatively inextensible and the sleeve is applied snugly over the limb segment. As a result, a large capacity pump is required to drive the device since a large volume of air must be rapidly admitted into and in most cases discharged from the bladder to alternately expand and collapse the bladder to apply the desired pressure to the limb. This applicator design, and all its variations, which utilize a bladder to apply pressure, cannot be used to apply a relative negative pressure to the limb. Another disadvantage of the current applicators is that due to the large air volume required, the system becomes non-portable and therefore cannot be used outside of a fixed treatment room, nor in emergency situations.

Recent attempts have been made to develop a balloon having a rigid or semi-rigid outer shell surrounding an expandable balloon-type interior. This type of pressure applicator is illustrated in U.S. patent No.5,554,103 to 10 th grant et al 1996 and U.S. patent No.5,997,540 to 7 th grant et al 1999, both owned by vasomedia corporation of Westbury, new york. These compression devices are described in the patent as being wrapped around the limb and held in place with some mechanism, such as VELCRO strips. However, such prefabricated applicator designs do not closely fit the limb and therefore still require a large amount of air to provide the desired level of limb surface pressure. This is the case because such pre-fabricated applicators cannot be made to fit exactly one limb segment, leaving a considerable dead space between the balloon-like tube and the limb.

The above patent proposes filling the dead space with spacers to reduce the amount of air required to operate the pressure applicator. These spacers must be cut to different shapes and thicknesses, and are therefore very cumbersome and impractical.

These outer shells and applicators may be custom made to fit the limb segment. Many applicators of different sizes and shapes can also be manufactured to approximately accommodate the contours of the limbs of different patients. Custom made applicators are obviously impractical. It is also impractical to manufacture and stock in a hospital a large number of applicators of different sizes and shapes suitable for a wide variety of patients of different sizes.

Furthermore, because such applicators operate by pressurizing balloon-like tubes around a limb segment, they cannot be used to apply negative relative pressure to a limb segment.

The present invention overcomes these disadvantages by using a uniquely designed applicator shield with an internal air distribution system. The applicator is custom made to fit the limb and therefore requires a much smaller volume of operating air than prior art applicators. Because much less air volume is required to operate the shroud, much less capacity, lighter weight and cheaper air pumps are required. Because the applicator shield is assembled in situ from components that can be deformed and rigidified as it is secured to the patient, and thus can be customized for each patient, there is no need to stock a large number of prefabricated shield components, while at the same time greatly improving the accuracy of the fit for each individual patient.

Because the gap between the shell and the limb surface can be made very small, the amount of air volume required is reduced, thereby minimizing the total space that must be pressurized. A major limitation in using a small gap between the shell and the limb surface is the resistance to airflow into and out of the shell. However, the air flow can be easily enhanced by the internal air distribution system of the housing and by utilizing multiple air inlets to the housing.

Second, by minimizing the volume of air required, substantially equal volumes of air can be rapidly pumped in and out of the shroud to create positive and negative relative pressures in a system that is fairly closed together. This provides a means of effectively controlling the air pressure while allowing close control of the air temperature. Controlling the air temperature is important because warmer air promotes vasodilation, resulting in greater blood flow, and thus more efficient operation of the device.

Furthermore, the expandable balloon-like interior of the prior art systems is eliminated by the use of a relatively rigid housing with an internal air distribution system. This allows the applicator limb of the present invention to apply both negative and positive relative blood pressure. The vasodialal pressure device (for example) cannot apply negative relative pressure.

Disclosure of Invention

It is therefore a primary object of the present invention to provide an external counterpulsation cardiac assist device with an applicator capable of providing both positive and negative relative pressure to the limb.

It is another object of the present invention to provide a counterpulsation cardiac assist device with a pressurizing means that requires a relatively small volume of operating air, thus reducing pump capacity.

It is another object of the present invention to provide an external counterpulsation cardiac assist device that does not use an expandable balloon-like tube.

It is another object of the present invention to provide an external counterpulsation cardiac assist device including a positive and negative relative pressure applicator that can be assembled in situ, thereby custom fitting precisely to each patient's limb.

It is another object of the present invention to provide an external counterpulsation cardiac assist device that is significantly lighter than prior systems, thereby allowing for a portable device that can be carried to a patient without requiring the patient to go to a specially equipped treatment facility.

It is another object of the present invention to provide an external counterpulsation cardiac assist device that is preferentially used wherein the air temperature can be easily controlled to induce vasodilation.

It is another object of the present invention to provide an external counterpulsation cardiac assist device having an applicator with a relatively rigid shell that can be easily secured to a limb segment while sealing the applicator's internal chamber around the limb segment.

It is another object of the present invention to provide an external counterpulsation cardiac assist device that is preferably used with an air permeable inner layer covering a limb segment to which a relatively rigid shell is secured and sealed.

It is another object of the present invention to provide an external counterpulsation cardiac assist device including a positive or negative relative pressure applicator with a rigid or substantially rigid housing, an internal air distribution system within the sealed outer housing, the system being separated from the limb surface by radial and/or longitudinal elements forming a tubular chamber adapted to be connected to a pumping system for moving air into and out of the chamber in synchronism with the action of the heart.

The applicator of the present invention provides positive and negative relative pressure (vacuum) pressure to the limb by pressurizing and creating a vacuum in the sealed interior of the housing. The shell defining the interior of the shield is sufficiently rigid and non-expandable, once secured around the limb, to contain positive pressure and to be sufficiently non-collapsible to allow a significant vacuum to be generated.

In one embodiment of the invention, the inner housing wall is separated from the outer housing wall by a meridional and/or longitudinal element, thereby forming a tubular chamber. The chamber is adapted to be connected to a pump for delivering air into and out of the chamber in synchronism with the action of the heart.

The shell is preferably initially deformable so that the shell can be shaped and dimensioned to closely conform to the limb. Once in place, the interior of the housing is sealed. Once the housing is secured, the housing becomes relatively rigid.

An inner layer is preferably disposed within the shell adjacent the limb. The layer is preferably made of a highly air permeable material such as a fabric, felt or sponge material which is flexible but relatively resistant to pressure, i.e. not easily compressible under pressure.

The shell members are preferably initially spaced from the permeable inner layer. The tubular space between the inner and outer walls of the housing forms an internal air distribution system that allows air to flow freely between the pump and the permeable inner layer within the interior of the housing. The permeable inner layer is designed to provide minimal resistance to air flow.

The positive and negative relative pressure cycles and their time profiles are preferably controlled by a microprocessor-based computer system that receives input signals from an electrocardiogram or other cardiac function monitoring device. The positive relative pressure may be provided by an air compressor, a pressurized air tank, and/or an air pump. The negative relative pressure can be provided by a vacuum pump. However, as described below, it is preferred to use a spring-loaded pump mechanism that provides both positive and negative relative pressures.

In accordance with one aspect of the present invention, an external counterpulsation cardiac assist device is described for providing positive and negative relative pressure to a segment of the body in synchronization with the motion of the heart. The device includes a shield. The shield includes a relatively rigid tubular shell surrounding the body segment and an air permeable flexible inner layer located inside the shell adjacent the body segment. A mechanism is provided for sealing the interior of the housing. The housing has an internal air distribution system operatively connecting an air supply source and the interior of the housing.

The housing is preferably formed by spaced apart inner and outer walls. The spacing means is disposed between the inner and outer walls of the housing to define an air chamber therebetween. The interior wall of the housing has a plurality of apertures for facilitating the free flow of air between the chamber and the interior of the housing.

One or more holes are provided in the outer wall of the housing. The apertures operatively connect the chamber and an air supply.

The spacing mechanism divides the internal air chamber of the housing into sections. Air passages are provided to connect the compartments of the chamber through spacing means. The spacing section may have radially or longitudinally extending partition walls. Other shapes such as honeycomb, etc. may also be used depending on the configuration.

The inner wall of the housing and the spacing means are preferably combined to form a single assembly. The housing outer wall is seated on the fitting. Means are provided for securing the outer wall of the housing to the fitting to increase the rigidity of the housing.

The inner wall of the housing is preferably made of a relatively rigid material such as a plastic plate or hard rubber or a plurality of movably connected plastic sections or the like or metal sections.

The inner layer is preferably made of a fabric, felt or sponge-like material. The layer is hard enough to resist the pressure of the inner wall of the shell during assembly of the applicator, but soft enough not to create significant resistance to the expanding limb during application of negative relative pressure. The material is again flexible enough to bend significantly, easily forming the shape of the limb during fitting.

The outer walls of the housing are impermeable to air and are preferably formed from a flexible yet inextensible sheet material such as various sealed fabrics or plastics.

The inner wall of the housing and the spacing means are preferably integral. Alternatively, the inner and outer walls of the housing and the spacing means may be integral.

The means for sealing the housing to the inner layer preferably comprises a sealing strip. The means for securing the outer wall of the housing comprises a relatively inextensible strip or band.

The outer wall may be held in place relative to the top end of the spacer with snap band segments or simply by friction of an enhanced roughened surface. In this case, the top end surface of the spacer wall may be enlarged to enhance the fixing action.

In another preferred embodiment of the invention, the housing consists of only one outer wall. The inner wall is not used. An air permeable, flexible inner layer is placed over the body segment. The inner air permeable layer is separated from the outer wall of the shell by a separation mechanism to form an inner air chamber. The spacing mechanism divides the internal air chamber of the housing into zones. Air passages are provided through the spacing means to connect the compartments of the chamber. The spacer means may have radially or longitudinally extending spacer walls. Other shapes such as honeycomb, etc. may also be used.

As in the above-described embodiments of the present invention, a mechanism for sealing the inside of the housing is provided. An interior air distribution system of the housing operatively connects the air source and the housing interior. One or more apertures are provided in the outer wall of the housing to operatively connect the housing interior chamber and the air source.

The spacing means and the housing outer wall may be integral. Alternatively, the spacing means and the outer wall of the housing may be separate, in which case the spacing means is cut to fit around the air permeable flexible inner layer. The outer wall is then placed over the fitting. Means are provided for securing the outer wall of the housing to the fitting to enhance the rigidity of the housing.

The inner layer described in the above embodiments may or may not be used in this preferred embodiment. If the inner layer is not used, the spacing means is placed in the vicinity of the body segment.

Throughout this specification, the invention is described as being pneumatically driven for illustrative purposes. While air is the preferred fluid for many reasons, including low viscosity, non-toxicity, non-flammability, availability, etc., it should be understood that other gases or liquids may be used.

Drawings

To these and other objects that may hereinafter occur, the present invention is directed to an external counterpulsation cardiac assist device, described in detail in the following specification and illustrated in the accompanying drawings in which like reference numerals indicate like parts, and wherein:

FIG. 1 is an exploded isometric view of a typical section of a first preferred embodiment of the shield of the device;

FIG. 2 is a cross-sectional view of the shield of FIG. 1 as it would appear mounted on a patient's limb;

FIG. 3 is an isometric cross-sectional view taken along line 2-2 of FIG. 2;

FIG. 4 is a sectional view showing a portion of adjacent sections of the inner wall of the housing joined by a "living pivot";

FIG. 5 is a view similar to FIG. 4 but showing a portion of adjacent sections pivotally connected;

FIG. 6 is an isometric view of a typical section of a housing of a second preferred embodiment of the present invention;

FIG. 7 is a cross-sectional view of a typical section of the housing of the third preferred embodiment of the present invention;

FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 7;

FIG. 9 is a sectional view showing a typical section of a housing of a fourth preferred embodiment of the present invention;

FIG. 10 is a side elevational view of a fifth preferred embodiment of the invention;

FIG. 11 is a sectional view showing a typical section of a housing of a sixth preferred embodiment of the present invention;

FIG. 12 is a cross-sectional view of a seventh preferred embodiment of the present invention;

FIG. 13 is an elevational view of the embodiment illustrated in FIG. 11; and

fig. 14 is an isometric view of a fifth preferred embodiment of the invention.

Detailed Description

As shown in fig. 1, 2 and 3, the first preferred embodiment of the present invention comprises a tubular shield, a typical pre-cut section of which is shown. The shield is adapted to be assembled on site and custom fitted to a limb such as an arm or leg or the entire lower body part including the thigh and buttocks. The shield consists of a soft air permeable inner layer 10, the inner layer 10 being made of fibrous cardboard, felt or sponge-like material. The inner layer 10 is placed around the limb 12 and trimmed to the desired size with scissors or blades.

A hollow shell 14 is tightly fitted around the inner layer 10, the shell 14 being initially deformable enough to closely conform to the contour of the limb. After the shell 14 is sealed and secured in position around the limb as described above, it will become quite rigid.

The housing 14 is comprised of an inner wall 16 and an outer wall 18. The walls 16 and 18 are separated by a plurality of upstanding spacer elements 20 to form an internal air distribution system defined by an air flow chamber 22 between the housing inner and outer walls.

The housing inner wall 16 has a plurality of holes 24 that allow air to flow freely between the chamber 22 and the housing interior. The apertures 24 are arranged in a pattern determined by the configuration of the spacing elements. The wall 16 is relatively rigid, particularly in the transverse and longitudinal directions. It can be made of a single, previously deformable, hard rubber or plastic plate 16 as shown in figures 1, 2 and 3, or of hard rubber or plastic sections 16a, 16b connected by "living pivots" 17 as shown in figure 4, or of metal sections 16c, 16d connected by mechanical pivots 23 as shown in figure 5. In the case of rubber or plastic, the sections of the wall 16 can be provided in a flat plane and then deformed as required to fit snugly around the inner layer 10.

The spacing elements maintain the separation between the inner and outer walls to ensure free flow of air through the housing 14. These elements may take various configurations, such as spaced, radially extending rectangular elements 20 as exemplified in FIGS. 1-6, honeycomb elements 21 as exemplified in FIGS. 7, 8, 14, or spacers 25 having a bellows-type configuration as exemplified in FIGS. 9 and 11. The spacer elements are preferably made of the same material as the wall 16. Regardless of the form of spacer elements utilized, a plurality of air passages 26 are provided through each spacer element such that air will flow freely between the sections of the chamber 22 defined by the spacer elements.

These spacing elements are preferably formed integrally with the housing inner wall 16, as shown in FIGS. 1-6. However, when the elements are connected to each other so that they stand alone as a unit (e.g., the honeycomb elements 21 of fig. 7, 8, 14 or the corrugated spacers 25 of fig. 9, 11), the spacers may be supplied in the form of rolls or sheets that are separate from the wall 16. In that case, if the wall 16 is not present, the spacer is suitably trimmed and mounted on the inner layer 10, as shown in fig. 14, or on the wall 16 when the wall 16 is already around the inner layer 10. As shown in fig. 11, hook strip 27 can be used at the corners of the spacer 25, in combination with hook strips 31 on the walls 16 and 18, to provide a more slip-resistant fit relative to the housing walls.

The shield is completed by mounting a relatively flexible (curved) but inextensible outer wall 18, the outer wall 18 being secured to hold the structure tightly together around the limb and sealed to provide an airtight seal isolating the interior of the shield. The wall 18 is made of a flexible material such as plastic, reinforced plastic, fabric, etc. or an elastomeric sheet of sufficient thickness (reinforced) to withstand the pressure variations exerted on the shroud, deform as little as possible during the process and maintain a tight fit of the shroud.

The wall 18 may be provided in rolls or in sheet form and trimmed as required. And then tightly fitted over the inner wall and spacer fitting. The edges of the walls 18 are superimposed and sealed to each other to form an airtight joint by means of a hook and loop tape or adhesive sealing tape 19 or the like. The ends of the shield are also sealed to the limb with adhesive sealing tape or other conventional means such as clips or straps to prevent air from escaping.

The shroud is simultaneously wrapped with straps or bands 28 at various locations along its length and tightened to maintain the secure fit of the shroud. This makes the housing sufficiently rigid to withstand rapid pressure changes. The strap or strip 28 is bendable but relatively inextensible and may have a buckle or other securing mechanism 29. Hook and loop tape may be used to secure the outer wall or to make the inner wall slip resistant.

Fig. 6 illustrates a preferred embodiment of the housing 14 'in which the walls 16, 18 and the spacer element 20 are fully integrated such that the housing 14' is of one unitary construction. In this case, the housing 14' is initially deformable and may be provided in roll form or in sheet form. The shell 14' is then cut and trimmed as appropriate, wrapped around the inner layer 10, sealed and secured.

Instead of providing the shell as a roll or in sheet material, the shell may be provided in sections, each several inches wide, individually mounted around the limb and surrounding the inner layer side by side adjacent to each other transversely to the axis of the limb. The sections are sealed together with sealing tape and secured as required by tape or strip 28. This transverse segment embodiment is illustrated in fig. 10, which fig. 10 shows a plurality of successive shell segments 14a, 14b, 14c, 14d extending transversely to the limb axis. The use of transverse shell segments in this manner enables greater conformity to the shape of the limb and greater flexibility with respect to the length of the shield.

Fig. 12 and 13 illustrate another preferred embodiment of the invention, wherein the shell is divided into longitudinal sections 42a, 42b, 42c. The sections are preferably pivotally connected together by a "living pivot". As in other embodiments, the sections 42a, 42b, 42c. The inner wall 16 of each section 42 is provided with a plurality of air holes 24. Each segment 42 includes a spacer element 20, thereby forming an inner air chamber 22. Sections 42a, 42b, 42c are connected together with a hose 44 to allow air to pass freely therebetween. A plurality of connectors 34 are provided for connection to an air source.

The sections 42a, 42b, 42c are surrounded by a band or strap 28 to secure and make fairly rigid the shell surrounding the limb. These fastening mechanisms may be formed from hook and loop tape or other non-extensible fabric.

Fig. 14 illustrates a preferred embodiment of the housing 14 "without the inner layer 10 and inner wall 16. The spacing means 21 is shown as being of honeycomb configuration.

Air enters and exits the housing interior chamber 22 through one or more apertures 32 in the outer wall 18. Each aperture 32 is provided with a connector 34 of conventional design allowing a hose or conduit to be connected between the aperture and the air source.

As mentioned above, the fluid used is preferably air, but other gases and even liquids (e.g., water) may be used. However, since the fluid must rapidly enter and exit the shield, a fluid having a low viscosity is preferred.

For some applications, the positive relative pressure can be applied using compressed air from the tank 50, while the inner air chamber can simply be vented to relieve the pressure. However, if a negative relative pressure is required, a vacuum generating device 52 is required. The canister 50 and vacuum apparatus 52 can be connected to the shield by suitable valves 54.

Figure 2 schematically illustrates a pump 36 that may be used to move air into and out of the shroud. The pump 36 includes an air tight bellows 37 that contracts to push air into the inner air flow chamber of the housing to pressurize the shroud and expands to draw the indoor air out to create a relative vacuum inside the housing.

Expansion and contraction of the bellows is controlled by an off-center cam 38 that rotates on a shaft 40. The shaft 40 is driven by a motor (also not shown) through a commonly used deceleration and controlled clutch system (also not shown) to operate the pump in accordance with signals sensed by an electrocardiograph or other cardiac function monitoring device (also not shown). The pump 36 is spring loaded towards the expanded state of the bellows 37 so that a negative relative pressure (vacuum) is provided during each cycle. Suitable valves (not shown) are provided between the pump and the shroud holes to deliver air to the holes.

In fig. 2, the mechanism that affects expansion and contraction of the bellows is represented for simplicity by an off-center cam driven by an electric motor. However, any mechanism that uses electricity to generate linear motion may be used, such as a push screw mechanism or a linear electric motor with appropriate motion transmission and control. Furthermore, because the periods of positive relative pressure and relative vacuum generation are only a fraction of the overall period of system operation, the motor driving the pump can be used to store mechanical energy in the form of potential energy in the pump springs and in a flywheel mounted on the motor. This would greatly reduce the size of the motor required to operate the pump.

The pump 36 shown in fig. 2 is uniquely suited for use with the shield of the present invention because together they form a closed system in which the same air moves back and forth between the pump and the shield as the bellows 37 expands and contracts. This allows the use of a smaller capacity pump and greater control over the temperature of the air in the shroud. The smaller volume pump allows the device to be portable, making it easier to bring to the patient in an emergency. Of course, the capacity of the pump depends on the size of the shroud with which it is used.

Preferably, as shown in fig. 6, a heating element 45 and a temperature sensor 46 are utilized to maintain the temperature of the air introduced into the shroud at a high level. The heat causes the blood vessel to dilate and thus increase blood flow, resulting in increased effectiveness of the device.

Other possible air sources may include a "double acting" pump, without the need for an internal spring. Such a pump has the advantage of more precise control of the pressure level and profile. Piston pumps and rotary pumps may also be used.

More than one air source may also be used. Multiple pumps operating in synchronization can provide a more uniform applied pressure. More than one pump may be installed to allow the system to operate at many cycles per second than a single pump. If used alternately, one pump or group of pumps may compress air as the other pumps force compressed air into the shroud, and vice versa.

Regardless of the type of air supply device used, it is important to keep the volume inside the housing and the continuous conduit as small as possible, while the shield fits the contour of the limb as closely as possible. This reduces the volume of the space to be pressurized, the amount of air and vacuum required and thus the capacity of the air supply pump.

It will be apparent that the present invention relates to an external counterpulsation cardiac assist device including a sealed housing adapted to be assembled to custom fit and fit around the limb to provide alternating positive and negative relative pressures in synchrony with cardiac function.

The shield includes an air permeable fabric-like inner layer surrounded by a relatively rigid but previously deformable shell. The shell includes an inner air flow distribution system defined between an initially deformable inner wall capable of snugly conforming to the limb and a flexible outer wall spaced from the inner wall by spacer elements to define an air flow chamber to facilitate the passage of air into and out of the interior of the shell. The shell is sealed around the limb with an adhesive sealing tape or the like and is tightly secured to the limb with a strap, strip or the like.

Although only a limited number of preferred embodiments of the invention have been disclosed for purposes of illustration, it will be apparent that numerous variations and modifications may be made thereto. It is intended that all such variations and modifications be included within the scope of the present invention.

Claims (44)

1. An external counterpulsation cardiac assist device for applying pressure to a body segment in synchrony with cardiac function, the device including air supply means and a shield adapted to surround the body segment, said shield comprising: a substantially rigid tubular shell and an air permeable inner layer located inside said shell adjacent to the body segment; means for sealing said shell to the body segment; the housing includes an internal air distribution system operatively connecting the air supply mechanism and the interior of the housing, wherein the housing includes an inner wall and an outer wall and a spacing mechanism between the walls of the inner housing and the walls of the housing.

2. The apparatus of claim 1 wherein said spacing means defines an air flow chamber between said inner and outer walls.

3. The apparatus of claim 2, wherein said spacing means defines a chamber and said inner housing wall includes a plurality of openings to facilitate air flow between said chamber and said housing interior.

4. The apparatus of claim 3, further comprising an orifice in said outer wall of the housing communicating with said chamber, said air supply being connected to said orifice.

5. The apparatus of claim 3, wherein said spacing means divides said chamber into several compartments.

6. The apparatus of claim 1, further comprising an air flow path through said spacing means.

7. The apparatus of claim 1 wherein said housing inner wall and said spacing means are joined to form a fitting.

8. The apparatus of claim 7 wherein said housing outer wall is located on said fitting.

9. The apparatus of claim 7, further comprising means for securing said housing outer wall to said fitting.

10. The apparatus of claim 1 wherein said housing inner wall is integral with said spacing means.

11. The apparatus of claim 1 wherein said housing interior wall is formed of rubber.

12. The apparatus of claim 1 wherein said housing interior wall is formed of plastic.

13. The device of claim 1 wherein said inner layer is formed from a fabric.

14. The apparatus of claim 1, wherein said inner layer is made of felt.

15. The device of claim 1, wherein said inner layer is formed of a sponge-like material.

16. The apparatus of claim 1 wherein said housing interior wall is comprised of removably attached segments.

17. The device of claim 16, wherein said zone extends longitudinally relative to the body segment.

18. The apparatus of claim 1 wherein said housing inner wall includes first and second relatively movable regions.

19. The apparatus of claim 16, wherein said intervals are actively connected.

20. The device of claim 1, wherein said outer wall is comprised of a zone extending transversely relative to the body segment.

21. The device of claim 1, wherein said outer wall is comprised of a segment extending longitudinally relative to the body segment.

22. The apparatus of claim 1 wherein said housing outer wall is formed of a relatively inextensible plastic material having a relatively high degree of flexibility in bending.

23. The apparatus of claim 1, wherein the inner wall, outer wall and spacer element are integral.

24. The apparatus of claim 1 wherein said means for sealing said housing comprises an adhesive sealing tape.

25. The device of claim 1, further comprising means for securing said housing to said inner layer.

26. The apparatus of claim 1, further comprising means for controlling the temperature of air in said air distribution system.

27. The apparatus of claim 1, wherein said air supply mechanism comprises a pump.

28. The apparatus of claim 27, wherein said pump and said shield comprise a closed system.

29. The apparatus of claim 27, wherein said pump comprises a bellows.

30. The apparatus of claim 29, wherein said pump includes a rotating cam cooperating with said bellows for expanding and contracting said bellows as said cam rotates.

31. The apparatus of claim 30, further comprising a mechanism for rotating said cam.

32. The apparatus of claim 30, further comprising means for spring loading said bellows in a direction of expansion of the bellows.

33. The apparatus of claim 1, wherein said air supply mechanism comprises a vacuum device.

34. The apparatus of claim 1, wherein said air supply means comprises a compressor and a vacuum pump.

35. An external counterpulsation cardiac assist device for applying positive and negative relative pressure to a body segment in synchrony with cardiac function, said device including a shield adapted to surround the segment of the body, said shield comprising: a relatively rigid housing; an air permeable inner layer located inside said shell adjacent to the section of the body; means for sealing the housing around the segment; said housing including inner and outer walls and spacing means between said inner and outer walls to define an air flow chamber therebetween, said housing inner wall including a plurality of apertures connecting said chamber with said housing interior; an orifice in the outer wall of the housing communicating with the chamber; an air supply and a relative vacuum mechanism coupled to the port to provide pressurized air and relative vacuum to the port in accordance with cardiac function.

36. The apparatus of claim 35, wherein said spacing means divides said chamber into compartments.

37. The apparatus of claim 35, further comprising a flow path through said spacing means.

38. The apparatus of claim 35 wherein the walls of the housing are formed with removably attachable sections.

39. The apparatus of claim 38, wherein said intervals are actively connected.

40. The apparatus of claim 39, further comprising means for controlling the temperature of the air in said chamber.

41. A shield comprising a relatively rigid tubular shell adapted to be externally adjacent a section of a body; means for sealing an end of said housing to the section of the body; said housing including inner and outer walls and spacing means between said inner and outer walls defining an air flow chamber therebetween, said housing inner wall including a plurality of apertures facing said body segment, an aperture in said housing outer wall communicating with said chamber and air supply means connecting said aperture.

42. The shroud of claim 41, further comprising an air permeable layer disposed between said body segment and said housing.

43. The shroud of claim 41, wherein said inner wall of said housing is formed of a relatively rigid material.

44. The shroud of claim 41, wherein said housing outer wall is formed of a flexible material.