PULSE MODULE FOR BREATHING ASSISTANCE APPARATUS
BACKGROUND OF THE INVENTION Field of Invention The present invention relates to apparatus and method for adding pulses or perturbations to the gases supplied to a patient who is receiving gases from a ventilation or respiration system, the device located so that expiratory gases from the patient pass through the device. Description of the Prior Art
The use of ventilators to facilitate breathing is well known. Generally, patients are provided air via an inspiratory line running between a patient interface and the ventilation or respiration system. Typically, this ventilation takes the form of CPAP, PEEP or BiPAP therapy, as appropriate. It is well-known that providing air to a patient at a pressure above atmospheric can have a plurality of benefits, especially for neonatal patients or patients with impaired lung function, who may have difficulty breathing unassisted. When ventilating a patient in this manner, it is usual to add other auxiliary devices between the respirator and the patient interface. One of the most commonly used auxiliary devices is a humidifier, which is used to add moisture to the air inhaled by the patient.
The inspiratory/expiratory cycle of an average patient will typically be a curved waveform, for example roughly sinusoidal over time as a patient inhales and exhales. A typical patient breathing cycle is shown in Figure 1. The cycle will repeat once every few seconds as the patient inhales and exhales. Ventilators used for CPAP therapy provide a continuous and constant pressure to the airway of a patient. This added pressure will increase the pressure through the inspiratory and expiratory branches of the breathing cycle, but will not substantially affect the generally sinusoidal shape of the breathing cycle. It is further known that adding a high-frequency perturbation to the overall cycle, overlaid onto the inhale/exhale cycle of the patient, similar to that shown in Figure 2, can have beneficial effects. The frequency of the pulses is usually at least one order of magnitude greater than the patients breathing cycle, which will repeat e.g. every few seconds. The overlaid pulse frequency can be anything up to, and beyond, 50 Hz. The beneficial effects of adding these pulses can include opening up the bronchioles of the lungs to allow gas to penetrate deeper into the lung structure (with a corresponding increase in lung function), and aiding in the loosening of mucus and other undesirable secretions from inside the lungs. A number of devices have been described which utilise different methods or equipment to overlay a high-frequency perturbation onto the gases supplied to a patient.
US 2,918,917 discusses a device employing a reciprocating diaphragm to vibrate a column of gas supplied to a subject. The pulses from the reciprocating diaphragm are overlaid onto the gases on a gases inlet conduit.
Similarly, US 4,821,709 discloses a device which provides high frequency oscillations in the gases supplied to a patient using a flexible diaphragm. The pulses from the diaphragm are overlaid onto the inspiratory gases flow.
US 4,646,733 discloses an apparatus where gases supplied to a patient are pulsed by means of a rotating valve, located at the end of a inspiratory line on an endotracheal tube. The body of the valve rotates to alternately open and close the exit opening at the end of an inspiratory line.
US 6,708,690 discloses a device that uses a rotating valve on the inspiratory line to overlay perturbations on top of the patients normal breathing cycle. The valve rotates within the conduit and blocks the inspiratory line across a portion of the 360 degree rotation cycle. The speed of rotation of the valve can be adjusted to suit individual patients. Variations of the equipment are discussed, including a partial block of the inspiratory line, with the partial block allegedly still producing the necessary perturbations in the inspiratory/expiratory wave. Another variation that is discussed is the use of a one-way valve, that would allow perturbations to be added only to the inspiratory or expiratory part of the breathing cycle.
In the disclosures of the prior art documents above, the pulses or perturbations are added to the inspiratory air flow, and the devices sit on the inspiratory breathing limb.
As noted above, when ventilating patients, it is common for other auxiliary equipment to be added to the line from the respirator or ventilator to the patient. If these auxiliary additions are required for treatment of a patient, it can be difficult to configure the system to include such devices, and also add pulses or perturbations to the inspiratory air. For example, if a patient is supplied with humidified gases, a humidifier will usually be added between the respirator outlet and the patient interface. Adding perturbation equipment such as a valve or diaphragm along the inspiratory limb downstream of the humidifier can be impractical, and it can be difficult to successfully achieve the desired pulsing effect. That is, it may be difficult to achieve a balance of correctly heated and humidified gases and correct pulses, given the constraints of space and weight, and the added volume of gases contained in the humidifier.
Furthermore, it is usual to keep the inspiratory conduits from the humidifier as short as possible, bearing in mind patient comfort and other practical concerns such as the relative locations of the patient and respirator. This is to keep 'rain-out' or condensation in the conduits to a minimum. It is common to heat the respiratory conduits by means of heating elements
wrapped within the length of the conduit to minimise rain-out. This can add to the difficulty of correctly configuring a system to both provide humidified gases, and which also provides an overlaid perturbation or pulse pattern, as adding auxiliary pulse equipment to the line can, for example, have a detrimental effect on conduit heating. Furthermore, it is usual to keep the inspiratory conduits as light as possible, in order to avoid adding extra weight that a patient will have to 'carry' via the interface. The addition of extra weight to the inspiratory line, for example a motorised valve or an additional limb for adding pulses to the main air stream, can increase the weight on the inspiratory limb, and this extra weight will increase patient discomfort. It may also be impractical to locate the equipment for creating a pulse or perturbation pattern upstream of the humidifier, in order to avoid adding it to the inspiratory line, as the humidifier or its contents can act to absorb or distort the pulses, and at least partially negate their effectiveness.
In short, adding the additional equipment required to create the pulse pattern to a humidified gases stream, or adding a humidifier to a pulsed gases stream, will create a system with too many variables to accurately adjust the required parameters, such as pulse frequency or amplitude, or humidification parameters.
For these reasons, there is a need for a method that can add pulses to a patient breathing cycle, but which will not interfere with the operation of any auxiliary equipment that may also be being used. There is also the need for a device that has the capability to overlay high- frequency pulses onto the breathing cycle of a patient, without interfering with the operation of other auxiliary equipment that may also be required.
There is also the need for a device where the overall pressure of the system can be easily controlled, at the same time as pulses of known and highly controllable amplitude and frequency are overlaid onto a breathing cycle.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved device, or system, or method for adding perturbations to the gases provided to a patient, or one which will at least provide the healthcare industry with a useful choice.
Accordingly in one aspect of the present invention consists in a device for introducing pulses to a patient breathing cycle which is at least partially assisted by a respiratory support system, said device comprising: a body, said body having an inlet and an outlet,
a passage through said body between said inlet and said outlet, a valve located in said passage, said valve cycling between a first position where said passage is substantially open, and a second position where said passage is at least partially closed, said cycling having a frequency greater than the frequency of said patient breathing cycle, a motor cycling said valve between said first position and said second position, said device connected in use to said patient respiratory support system in such a manner that at least a portion of the expiratory gases from said patient pass into said inlet and through said passage. In a second aspect of the present invention consists in a method for introducing pulses to a patient breathing cycle which is at least partially assisted by a respiratory support system, said respiratory support system including a patient interface, said interface having an outlet aperture to vent an expiratory gases stream from said patient, wherein said method comprises: connecting a pulse device to said respiratory support system such that pulses produced by said device will travel along the expiratory gases stream from said device to said patient, said pulses being produced at a higher frequency than said patient breathing cycle.
In a third aspect the present invention consists in respiratory support system that includes a device introducing pulses to a patient breathing cycle which is at least partially assisted by a respiratory support system, said respiratory support system including an expiratory line to carry an expired gases stream away from said patient, said device located in use on said expiratory line, said device comprising: a passage, a piston, said piston in use linearly reciprocating within said passage.
In a fourth aspect of the present invention consists a device for introducing pulses to a patient breathing cycle which is at least partially assisted by a respiratory support system, said respiratory support system including an expiratory line to carry an expired gases stream away from said patient, said device located in use on said expiratory line, said device comprising: a passage, a piston, said piston in use linearly reciprocating within said passage. This invention may also be said to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.
The invention consists in the foregoing and also envisages constructions of which the following gives examples only. BRIEF DESCRIPTION OF THE DRAWINGS
One preferred form of the present invention will now be described with reference to the accompanying drawings in which;
Figure 1 is a graph showing the shape of a typical inspiratory/expiratory breathing cycle, with pressure shown on the vertical axis against time horizontally.
Figure 2 a is a graph of the breathing cycle of Figure 1, with overlaid high-frequency pulses or perturbations. Figure 2b is a graph of the perturbations and breathing cycle of Figure 2a, shown combined.
Figure 3 shows part of a breathing assistance apparatus that forms part of one embodiment of the present invention.
Figure 4 is a view of a first embodiment of the device of the present invention. Figure 5 is a cross sectional view of the embodiment shown in Figure 4.
Figure 6 is a view of a second embodiment of the device of the present invention. Figure 7 is a cross-sectional view of the embodiment shown in Figure 6.
DETAILED DESCRIPTION While the invention is susceptible to embodiment in different forms, a specific embodiment is shown in the drawings, and described in detail. The present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein.
The device of the current invention can be used with any known system for providing ventilation to a patient, such as CPAP, BiPAP, PEEP or similar. It should be appreciated that the device can be used with respiratory support system for a patient who is self-respiring, and also a patient who is undergoing forced respiration. For simplicity, what is described below is a device and a method of using that device for a normal inhale/exhale breathing cycle, such as that shown in Figure 1. Part of a system for delivering gases including pulses or perturbations is shown in
Figure 3. Air, oxygen or similar gases under pressure enter a humidifier chamber 1 through an air inlet line 2. This humidified air exits the humidifier chamber 1 through an inspiratory limb 3, travelling along the inspiratory limb 3 to a patient interface 4, such as the nasal cannula shown in Figure 3. It will be appreciated that any suitable patient interface, such as a mask,
could be used in this system. The patient inhales the gases provided via the patient interface 4. When the patient exhales, the gases pass out of the patient through the patient interface 4, down the expiratory line 5, through an exit module 7, and then out of the respiration system, to atmosphere. As can be seen in Figure 3, the system shown also includes a feedback line 6, which can be connected to a temperature sensor or similar in the inspiratory line, in order to provide information about the state of the humidified gases to a ventilator or respirator control system (not shown). This is an optional addition to the system , and is not necessary for the correct working of the current invention. As discussed above, one typical inspiratory/expiratory cycle for a patient will have a varying amplitude that forms a generally sinusoidal wave, such as is shown in Figure 1. It has been found that high-frequency pulses or perturbations can be added to a waveform, to achieve the benefits described in the prior art section and other benefits, by including a valve or oscillatory device in either the expiratory line, to send pulses up the gases stream in the expiratory line and then to the lungs of a patient, or by including the pulse device on or close to the patient interface, separate from the inspiratory line.
This device can be used, for example, to add pulses to produce a waveform substantially similar to that shown in Figure 2b. Adding the pulses to the air flow in this manner has the advantage that other auxiliary equipment such as a humidifier 2 can also be simultaneously used with a breathing circuit.
In the preferred form of the device of the current invention, as shown in Figure 3, a device is included at the end of the expiratory limb 5. This device is shown generally as exit module 7. The device adds pulses to the inspiratory/expiratory wave form and these travel up the gases stream in the expiratory tube or limb 5 to the lungs of a patient. Two exemplary forms of exit module 7, suitable for adding perturbations in this manner, are described in detail below, although these are intended to exemplify the invention, and not to restrict the most generic aspect of the invention to the devices as described.
As shown in Figure 3, and as described above, the patient is provided humidified gases via an inspiratory breathing line 3 running between the outlet of a humidifier 1, and a patient interface 4. On the expiratory phase of the inspiratory/expiratory cycle, the exhaled gases from a patient pass from the patient down an expiratory line 5. The body of exit module 7 is located connected to the end of the expiratory line 5.
A first embodiment of exit module 7 is shown in greater detail in Figures 4 and 5. The exit module 7 has an inlet 8, suitable for attachment to the end of the expiratory line 5. The exit module 7 includes an outlet or exit port 9 and a motor 10. Exit port 9 vents to atmosphere.
The method by which the exit module 7 adds pulses or perturbations to the inspiratory/expiratory flow shall now be described in more detail, with reference to Figure 3.
Expired air from the patient exits the expiratory line 5 and simultaneously enters the inlet 8 of the exit module 7. The path between the inlet 8 and the outlet 9 is blocked by an insert
11, except for an insert passage 12 which passes through insert 11. The passage 12 allows expiratory gases from the patient to pass from the inlet 8, through the insert 11, to the exit port 9, and then to atmosphere.
Insert 11 also includes a valve passage 13, aligned substantially perpendicular to insert passage 12 and passing across insert passage 12.
The motor 10 is located attached to the body of the exit module 7, with one end inserted into a side branch 14 on the body of exit module 7, as shown in Figure 3. Valve passage 13 is filled in use by a shaft 15, which is connected to, and rotated by, motor 10. Shaft 15 is cross- drilled with a passage 16 passing through it. As the shaft 15 rotates, the passage 16 aligns twice for every full revolution with the insert passage 12, allowing expiratory air to pass through insert passage 12 and passage 16, through the outlet 9 to atmosphere. For the remainder of the rotation of the shaft 15, passage 12 is blocked. Effectively, the shaft 15 acts as a valve, cycling open and closed as it rotates.
The effect of this periodic blockage is to cause pressure to periodically increase in the expiratory line 5, until the insert passage 12 and the passage 16 align, allowing a release of pressure in the expiratory line 5. As the shaft 15 is rotating rapidly (that is, with a frequency at least an order of magnitude faster than the breathing cycle of a patient), the overall effect of the periodic high-frequency blocking and pressure release is to send pressure waves (that is, pulses or perturbations) back up the gases in the expiratory line 5, to the patient.
The frequency of rotation of the shaft 15 in the preferred embodiment should be variable between approximately 20 and 50 Hz, with the device preferably including a controller, or working in association with a controller 24, to control the speed of the motor 10 to achieve this. It would be a simple matter for a person skilled in the art to produce a device outside these arbitrary frequency limits.
Variations in the basic design outlined above are envisaged, with, for example, a safety blow-off valve included in the exit module 7 between the end of the expiratory conduit and the
insert 11, so that if the passage 16 becomes blocked or occluded for some reason, the safety valve opens and the patient can still exhale comfortably.
It is also recognised that individual patients will have different breathing cycles and respiratory needs. Also, each user will respond in a different manner to variations in the pulse frequency, or pulse strength, or both. Therefore, the speed of the motor 10 can be adjusted by a user, in order that the pulse frequency can be altered. This speed is adjusted either by means of a control connected directly to the motor, or via the control system of the respirator itself, which may in turn be controlled via a remotely located computer or similar. It is envisaged that other data could also be fed into the control system or the computer, such as data related to lung mechanics, to enable an automatic adjustment of the pulse frequency to suit the patient. This would be particularly useful as the lung mechanics, and therefore the required respiration system outputs, will change with changes in the state of a patient (e.g. sleep/waking), or the position of a patient. Also, the condition of the lungs, e.g. the lung compliance, will change with time as a patient receives therapy, and feedback of these conditions will allow automatic adjustment.
The size of the insert passage 12 and the size of the passage 16 can also be changed, for example by changing the insert 11 for an insert with a different size of passage 12, and also changing the shaft 15 for one containing a larger passage 16. Variations are also possible where for example the passage 16 is not aligned perpendicular with the passage 12, so that as the shaft rotates, the passage may only be partially blocked. It is also possible to align the rotation of the shaft 15 so that this is angled, rather than perpendicular, to the passage 12, with the same effect as has just been described. The same effect could also be achieved by other shapes of the passage 16.
One problem that is commonly found with rotating electric motors such as the motor 10 is that of 'speed creep'. This occurs when an electric motor is set to run or rotate at a desired speed. Over time, if not adjusted, the speed of the motor may have a tendency to change, or 'creep', either gradually accelerating or decelerating away from the desired rotation speed.
It is therefore desirable, especially where critical patient care is required, that once a motor is set to run at a certain speed, that it remain running at that speed. In order that this can be achieved with the device of the current invention, a feedback mechanism can be used with the motor 10 of the exit module 7 to manage the speed of the motorlO. In the preferred embodiment, this feedback mechanism includes a sensor in the form of a pair of holes 17 in the side passage 14. These align with a hole 18 in the shaft 15 twice for every revolution of the shaft 15. An LED (not shown) is inserted into one of the holes 17, and a light sensitive diode
(not shown) into the other of the holes 17. The LED is constantly lit when the module 7 is in use with the motor 10 rotating the valve shaft 15. The shaft and holes 15 will cyclically occlude the path between the LED and the diode, so that the overall effect will be that the light sensitive diode will 'see' flashes from the LED as the shaft 15 rotates. The frequency of these flashes can be fed back to the motor controller 24 via cable 25, and the electrical current to the motor adjusted accordingly via cable 26 in order ensure the motor is running at the required speed, and not 'creeping'. It is preferred that the feedback will be via a motor controller or computer, however, 'motor' as read in this text should be taken to mean the motor 10 and the controller
25. A variation of this feedback mechanism can also be used, with shaft 15 having a pair of cross-drilled holes 18 at right angles, which will increase the frequency of the flashes 'seen' by the light sensor.
A second embodiment of the device of the present invention will now be described, with reference to figures 6 and 7. This embodiment is particularly useful for CPAP respiration. An exit module 7a is connected to the expiratory line of a respiratory system in a similar manner to that already described. Gases from a patient pass into the inlet 8a.
The module 7a includes an outlet 9a through which at least a portion of the gases vented to atmosphere will pass. In a similar fashion to the apparatus described above, the path between the inlet 8a and the outlet 9a is substantially blocked by an insert 11a, except for passage 12a. Passage 12a passes through the insert between inlet 8a and outlet 9a. As can been seen in Figure
7, in this embodiment the passage 12a has a perpendicular side branch to allow flow of gases to the outlet vent 9a, which is located on a side branch of the module 7a.
As in the first embodiment, the passage 12a is substantially blocked by a shaft 15a, which rotates within the passage 12a, powered by a motor 10a. In the preferred embodiment, motor 10a is attached to insert 11a, with motor 10a partially enclosed by insert 1 Ia. In the form of this embodiment described and shown in Figure 5, insert 11a extends out of the main body of module 7a.
Shaft 15a includes a passage 16a, which in this embodiment is dog-legged. That is, the inlet of the passage is end-on to the flow from the inlet 8a, and the outlet is angled at 90 degrees to this, so that for part of the rotation of the shaft 15a, the passage 16a will align with the passage 12a, to allow expiratory gases to vent to atmosphere. For the remainder of the rotation cycle, the passage 12a will be fully blocked.
As in the first embodiment, the motor 10a causes the shaft 16a to rotate at the selected frequency of rotation, usually between approximately 20-50Hz.
In a similar fashion to what has been described for the first embodiment, a feedback mechanism can be used with the motor 10a. This feedback mechanism takes the form of a pair of holes 17a in the shaft 15a, located on the insert 11a. These align with a hole 18a in the shaft 15 twice for every revolution of the shaft 15. An LED (not shown) and a light sensitive diode (not shown) are inserted one each into the holes 17a, and the 'flashes' from the LED are detected by the light sensitive diode, with the frequency of these flashes fed back to the control mechanism in order to keep the speed at the required frequency.
Another advantageous variation of this embodiment will now be described with reference to Figure 7. The exit module 7a includes an adjustable pressure valve. In the preferred embodiment, this takes the form of a second side branch passage 19, upstream of the insert 11a. The passage 19 connects with the interior space of 7a via a hole 21 passing from the outside to the inside of the module 7a. Exhalatory gases are prevented from exiting through the hole 21 by an externally located valve 20, which blocks the passage 21. The valve 20 is held closed in a first position against the external aperture of the passage 21 by a spring 22. The valve 20 and the spring 22 are contained within the body of the passage 19. The tension in the spring is adjusted by a user-adjustable screw cap 23 which screws over the end of the passage 19. Tightening or loosening the screw cap 22 onto the end of the passage lowers or raises the cap onto or off the spring and valve, and in this manner the tension in the spring 22 can be increased or decreased. As the pressure of the exhalatory gases builds up within the body of the module 7a, the valve 20 will open to a second position against the tension of the spring 22, and allow at least a portion of the gases inside to vent to atmosphere. Increasing or decreasing the tension in the spring 22 will increase or decrease the internal pressure necessary to open the valve 20. In this manner, the CPAP pressure of the system can be easily adjusted by adjusting the tension of the spring 22, and if necessary balancing this with the other exit port 9a.
It has been found that that adjusting the fixed end resistance in this manner adds to the controllability of the system, and that the pressure of the system (e.g. the CPAP pressure), can be altered in a simple manner by adjusting the tension of the spring 22, without any need to adjust e.g. the controls of a ventilator. It can further be seen that the pressure of the system can be altered by adjusting the tension of the spring 22, and that this pressure adjustment is independent of any adjustment to the air flow in the system.
It can also be seen that it is not necessary to use the exit module of the current invention with an expiratory line. An exit module similar to those described above could be added close
to, or on, the patient interface. Gases enter the lungs of a patient via an inspiratory line to the patient interface. A module located on or close to the interface opens and closes an exit aperture that vents to atmosphere, to add perturbations to the gases in the interface, and consequently to the lungs of the patient, in a similar manner to that described above. As the patient exhales, the gases from their lungs would vent to atmosphere around the edges of an interface, or via a separate one-way exit valve located on the body of the patient interface, located separately from the module.
Further embodiments of the system described above are possible without departing from the inventive principles described so far. For example, the motor 10a of the second embodiment could drive a linear plunger backwards and forwards along the passage 12a. If required, the plunger can be aligned and sized so that it partially or completely blocks venting of gases through exit aperture 9a at the furthest point of travel. The travel distance and reciprocating frequency of the plunger can be easily adjusted in order to cause only a partial blocking of the exit aperture 9a. This will alter the frequency and amplitude of the pulses or perturbations.
In a variation of this embodiment, it would not be necessary for the plunger to block an exit aperture in order to cause the pulses. If the plunger device as described above is used with a sprung valve 20 as described above, the valve 20 allows gases to vent to atmosphere, and the plunger causes the pulses in the gases in the exhalatory line. Alternatively, exhaled gases from the patient could vent to atmosphere around the edges of a mask, or via any other suitable route. It can be seen that using a device that includes a vibrating diaphragm on the expiratory line will also produce similar pulses and effects to those already described.