AN APPARATUS AND METHOD FOR SUPPLYING ON-DEMAND ADDITIONAL BREATHABLE GAS

Abstract: An apparatus (10) for supplying on-demand additional breathable gas to a patient receiving a primary flow of gas from a primary breathable gas supply (10). The apparatus includes a controllable gas source (118) in selective fluid communication with the patient (12) and a control means (122) adapted to activate the controllable gas source (118) in response to receiving an input signal indicative of the primary gas supply (10) being unable to meet patient inspiratory requirements. The method includes monitoring the breathable gas supply (10) and activating the controllable gas source (118) when the monitoring indicates the primary gas supply (10) is unable to meet patient inspiratory requirements.

Description: AN APPARATUS AND METHOD FOR SUPPLYING ON-DEMAND ADDITIONAL BREATHABLE GAS FIELD OF THE INVENTION The present invention relates to an apparatus and method for supplying on- demand additional breathable gas to a patient receiving a primary flow of breathable gas from a primary breathable gas supply. The invention has been developed primarily to adapt gas supply apparatus designed for Continuous Positive Airway Pressure (CPAP) treatment of, for example, Obstructive Sleep Apnea (OS A), for suitability in treating other syndromes and diseases including, for example, Chronic Obstructive Pulmonary Disease (COPD), cystic fibrosis, emphysema and various other neurologic or other disorders of the respiratory system that require higher gas flow rates than typically provided by CPAP gas supply apparatus. BACKGROUND OF THE INVENTION Treatment of OS A by CPAP gas supply apparatus involves the continuous delivery of air (or other breathable gas) pressurised above atmospheric pressure to a patient's airways, generally via a conduit and a nose and/or mouth mask. The pressure of the gas delivered to the patient can be constant level, bi-level (in synchronism with patient inspiration and expiration) or auto setting in level. Fig. 1 schematically shows a prior art apparatus 10 for supplying breathable gas to a patient 12 via a conduit 14 and a nose mask 16 used in, for example, CPAP treatment. The apparatus 10 includes a flow generator 18 in the form of a motor and fan assembly whose power is provided by a drive means 20 which commonly consist of a brushless motor control circuit which drives power transistors connected to the motor windings. The drive means 20 are controlled by an electronic or computerised control means 22. The control means 22 causes the speed of the motor to be varied to control the pressure of the delivered gas. Alternatively, the control means 22 can regulate a solenoid driver to regulate the gas pressure by spilling off excess gas via a solenoid controlled vent. The control means 22 can be programmed by the clinician to deliver a single or preset pattern of sequential pressures, such as those mentioned above, in response to the patient's breathing pattern and desired treatment. Such prior art apparatus may be unsuitable for treating patients with, for example, COPD as flow generators designed for CPAP treatment produce a maximum flow, without a significant drop in treatment pressure, of 100 1/min or less which may not completely satisfy the respiratory requirements of the impulsive inspirations of, for example, a COPD patient. Further, COPD sufferers have a significantly faster inspiration time compared to "normal" breathing and this short inspiration is often accompanied by a considerable increase in maximum inspiratory flow. Conventional CPAP flow generators cannot meet this sudden increase in flow demand and as a consequence the pressure in the air delivery system falls when the patient requires gas at a higher pressure. Manufacturing flow generators with sufficient continuous flow capacity to meet the breathing requirements of COPD patients is generally uneconomic given the small market size compared to that of OS A sufferers. It is an object of the present invention to substantially overcome or at least ameliorate these prior art deficiencies. SUMMARY OF THE INVENTION Accordingly, in a first aspect, the present invention discloses an apparatus for supplying on-demand additional breathable gas to a patient receiving a primary flow of gas from a primary breathable gas supply, the apparatus including: a controllable secondary breathable gas source in selective fluid communication with the patient; and a control means adapted to activate said controllable secondary breathable gas source in response to receiving an input signal indicative of the primary gas supply being unable to meet patient inspiratory requirements. In a second aspect, the present invention discloses an apparatus for supplying breathable gas to a patient, the apparatus including a primary breathable gas source in fluid communication with a patient's airways; a controllable secondary breathable gas source in selective fluid communication with a patient's airways; and a control means adapted to activate said controllable secondary gas source in response to receiving an input signal indicative of said primary gas source being unable to meet patient inspiratory requirements. The breathable gas is desirably air. The primary breathable gas source preferably includes a flow generator in the form of a fan driven by an electric motor. The controllable secondary gas source preferably includes a flow generator in the form of one of a fan driven by an electric motor, a pressurised gas storage chamber, a connection to a constant pressurised gas source, a positive displacement device or combinations thereof. The positive displacement device is desirably a diaphragm substantially sealing a chamber in fluid communication with the patient, the diaphragm moving through said chamber in response to an electromagnetic actuator to supply the gas in the chamber to the patient. In an embodiment, the control means input signal is a signal indicative of the primary flow generator reaching maximum output. In another embodiment, the control means input signal is a signal indicative of the pressure of the gas supplied to the patient falling below a predetermined minimum level. In this embodiment, the controllable or secondary gas source does not receive control signals from the primary gas source but from, for example, a pressure transducer or other device that measures the pressure in the patient gas supply conduit or mask. In yet another embodiment, the control means input signal is a signal indicative of patient inspiration commencing, such as is indicated by a sudden rise in the flow of air supplied to the patient. In a third aspect, the present invention discloses a plurality of breathable gas supply apparatus in fluid communication with a common patient. The gas supply apparatus are preferably connected in parallel. In a fourth aspect, the present invention discloses a method for supplying on- demand additional breathable gas to a patient receiving a primary flow of breathable gas, the method including the steps of: monitoring the primary flow of breathable gas supplied to the patient; and activating a controllable secondary breathable gas source in selective fluid communication with the patient when the monitoring indicates that the primary gas supply is unable to meet patient inspiratory requirements. In a fifth aspect, the present invention discloses a method for supplying breathable gas to a patient, the method including the steps of: supplying a primary flow of breathable gas to the patient; monitoring the primary flow of gas supplied to the patient; activating a controllable secondary breathable gas source in selective fluid communication with the patient when the monitoring indicates that the primary gas supply is unable to meet patient inspiratory requirements. In one embodiment, the secondary breathable gas source is activated when the monitoring step indicates the primary breathable gas supply is at maximum output. In another embodiment, the secondary breathable gas source is activated when the monitoring step indicates the pressure of the primary breathable gas supply is below a predetermined minimum level. In this embodiment, the pressure of the primary gas supply is preferably measured at a mask worn by the patient or a gas supply conduit connecting the mask to the primary breathable gas supply. In a further embodiment, the secondary breathable gas source is activated when the monitoring step indicates the commencement of patient inspiration. BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will now be described, by way of examples only, with reference to the accompanying drawings in which: Fig. 1 is a schematic diagram of a prior art CPAP breathable gas supply apparatus; Fig. 2 is a schematic diagram of a first embodiment of an apparatus for supplying on-demand additional breathable gas; Fig. 3 is a schematic side diagram of a second embodiment of an apparatus for supplying on-demand additional breathable gas; Fig. 4 is a schematic diagram of a third embodiment of an apparatus for supplying on-demand additional breathable gas; Fig. 5 is a schematic diagram of a fourth embodiment of an apparatus for supplying on-demand additional breathable gas; Fig. 6 is a schematic diagram of a fifth embodiment of an apparatus for supplying on-demand additional breathable gas; and Figs. 7a to 7e are approximate plots of patient air flow rate, breath detection, primary flow generator output pressure, secondary flow generator output pressure and combined flow generator output pressure respectively between the time of inspiration and expiration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 2, there is shown a first embodiment of an apparatus for supplying on-demand additional breathable gas in the form of a second breathable gas supply system 110 used in conjunction with a first conventional breathable gas supply apparatus 10, similar to that shown in Fig. 1. The second breathable gas supply apparatus 110 is comprised of a flow generator 118 powered by a drive means 120 under control of a control means 122 incorporated into the gas supply apparatus 10. The output of the second flow generator 118 is introduced into the patient gas supply conduit 14 through conduit branch 114. When the control means 122 senses that the flow generator 18 cannot meet patient inspiratory requirements, for example, by sensing a pressure drop of the supplied gas when expecting the gas pressure to rise, a signal is sent to the drive means 120 causing the flow generator 118 to be energised and thereby provide an almost instantaneous additional flow of gas to the patient 12 (not shown). Similarly, when control means 122 senses that additional gas is no longer required it de-energises the flow generator 118. This embodiment allows treatment of patients whose inspiratory requirements exceed those of a conventional CPAP flow generator to be met by the addition a simple low cost motor, fan and driver assembly to a conventional apparatus. In another embodiment (not shown), a one-way valve is incorporated into the conduit branch 114 to stop gas from the first flow generator 18 being forced into the second flow generator 118 (rather than the patient) when the second flow generator 118 is not supplying gas. Fig. 3 shows a second embodiment in which a second gas supply apparatus 210 includes a flow generator 218 constantly energised by a drive means 220. In its simplest form, fluid communication between the flow generator 218 and conduit branch 214 is selectively blocked by a valve 226 which is controlled by a control means 222. As with the first embodiment, when the control means 222 senses that the patient's inspiratory requirements are not being met, it opens valve 226 to allow additional gas to be supplied through branch conduit 214 into the main conduit 14 and so to the patient. Similarly, when the control means 222 senses that the patient's inspiratory needs have been met it closes the valve 226. In another form of this embodiment, a pneumatic reservoir 228 is interposed between the flow generator 218 and the valve 226, as shown. The reservoir 228 is continually pressurised by the flow generator 218 and when the control means 222 opens the valve 226 a bolus of high pressure gas is able to be delivered to meet the instantaneous inspiratory demand of the patient. In a further variation (not shown), the flow generator 218 and drive means 220 are replaced with a high pressure oxygen or compressed air feed, for example from an external source such as a compressed gas storage tank or the internal gas supply of a hospital ward, and directly connected to the valve 226 or the reservoir 228, as the case may be. Fig. 4 shows a third embodiment essentially comprised of a primary breathable gas supply apparatus, for example in the form of a conventional CPAP gas supply apparatus 10 shown in Fig. 1, and a second CPAP gas supply apparatus 310 connected to the patient's gas supply conduit 14 by a branch conduit 314. In this embodiment, control means 322b of the second apparatus 310 receives control signals from the control means 322a of the primary apparatus 10. As with the earlier embodiments, when the patient's inspiratory demands are sensed as not being met, the control means 322a provides a signal to the control means 322b causing the second drive means 320 to energise the second flow generator 318 and thereby causing additional gas flow through the branch conduit 314 into the primary conduit 14 and so to the patient 12. In this third embodiment, the secondary gas supply apparatus acts automatically as a slave unit due to the connection of the second control means 322b to the first control means 322a. Fig. 5 shows a fourth embodiment in which a second gas supply apparatus 410 receives control signals from a control means 422 incorporating a differential pressure transducer. The transducer receives an indication of pressure from either side of a flow restrictor 430 via pressure tubing 432. When the transducer senses that the pressure in the patient's gas supply conduit 14 has fallen below a predetermined minimum level, the control means 422 causes drive means 420 to energise flow generator 418 thereby providing additional gas supply. The control means 422 is programmed to provide additional gas flow when the pressure drop across the flow restrictor 430 is less than about, for example, 0.5 cm H2O. As before, the flow generator 418 is deactivated when the pressure transducer of the control system 422 indicates the pressure in the patient supply conduit 14 is above this level or, alternatively, after a predetermined time has elapsed. In a variation of the fourth embodiment (not shown), the pressure in the patient's mask 16 is measured via a pressure line connected thereto. This variation obviates the need for any flow measuring devices in the patient gas supply conduit 14. Fig. 6 shows a fifth embodiment with a second gas supply apparatus 510 comprising a chamber 540, a diaphragm 542 and an electromagnetic actuator 544. The apparatus 510 is similar to a loudspeaker mounted within an enclosure. The chamber 540 is in fluid communication with the patient's gas supply conduit 14 through branch 5 conduit 514. This embodiment also has a control means 522 which utilises a differential pressure transducer 520 connected either side of restrictor 530 by tubing 532. When the transducer 520 senses a sudden fall in patient gas supply pressure, the control means 522 energises the electromagnetic actuator 544 to drive the ι o diaphragm 542 across the chamber 540 thereby forcing the volume of shaded air 546 into the patient's gas supply conduit 14 to supplement the primary gas supply from the primary flow generator 10. In this embodiment, a flow restrictor 548 is provided to stop the additional gas from being forced into the primary flow generator 10 instead of the patient. A one-way 15 valve can also be used for this purpose. The effect of the additional gas is best described with reference to Figs. 7a to 7e which respectively show plots of patient air flow rate 600, breath detection 610, primary flow generator output pressure 620, secondary flow generator output pressure 630 and combined output pressure 640 between the time of inspiration (Ti) and the time 20 expiration (Te). Line 600 shows the patient flow rate (F) changing from negative to positive at the beginning of inspiration Ti and vice-versa at the start of expiration Te. Line 610 shows the pressure transducer output becoming high at Ti indicating inspiration and becoming low at Te indicating expiration. 25 Line 620 shows the pressure (P) of the primary gas supply apparatus 10 increase to full flow as the fan undergoes finite acceleration between no flow at 621 and full flow at 622. Line 630 shows the pressure of the second gas supply apparatus after energisation at Ti and de-energisation at Te. Line 640 shows the sum of 620 and 630 and demonstrates how the fifth embodiment more quickly achieves full pressure to satisfy patient inspiration demand compared to that of the fan alone indicated by line 620 of Fig. 7c. The opposite occurs at expiration Te and thereby quickly reduces the output pressure as the diaphragm is withdrawn to allow easier patient expiration. An advantage of the above-described embodiments of the invention, is that the first or primary gas supply apparatus requires minimal modification to work in conjunction with the additional gas supply apparatus, especially in relation to the fifth embodiment which is operatively connected to the patient gas supply conduit or mask and not the primary gas supply apparatus. The primary gas supply apparatus can also be of largely conventional CPAP design thereby reducing inventory. Further, the additional flow generator(s) can be adapted to function with CPAP flow generators produced by various different manufacturers, not just those produced by the same manufacturer of the primary flow generator. Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. As examples, it will be understood that the invention is not limited to only a first and a second gas supply apparatus and that multiple gas supply apparatus may be connected in accordance with the invention with either a control system activating all the other flow generators when the flow provided by the first is insufficient or, for example, successively energising additional flow generators upon sensing the flow generator, or flow generators, already energised is/are providing insufficient flow.

Claims: CLAIMS 1. An apparatus for supplying on-demand additional breathable gas to a patient receiving a primary flow of gas from a primary breathable gas supply, the apparatus including: a controllable secondary breathable gas source in selective fluid communication with the patient; and a control means adapted to activate said controllable secondary breathable gas source in response to receiving an input signal indicative of the primary gas supply being unable to meet patient inspiratory requirements. 2. An apparatus for supplying breathable gas to a patient, the apparatus including a primary breathable gas source in fluid communication with a patient's airways; a controllable secondary breathable gas source in selective fluid communication with a patient's airways; and a control means adapted to activate said controllable secondary breathable gas source in response to receiving an input signal indicative of said primary gas source being unable to meet patient inspiratory requirements. 3. An apparatus as claimed in claim 1 or 2, wherein the breathable gas is air. 4 An apparatus as claimed in claim 1, 2 or 3, wherein the primary breathable gas supply or source includes a flow generator in the form of a fan driven by an electric motor. 5. An apparatus as claimed in any one of the preceding claims, wherein the controllable secondary gas supply source includes a flow generator in the form of one of a fan driven by an electric motor, a pressurised gas storage chamber, a connection to a constant pressurised gas source, a positive displacement device or combinations thereof. 6. An apparatus as claimed in claim 5, wherein the positive displacement device is a diaphragm substantially sealing a chamber in fluid communication with the patient, the diaphragm moving through said chamber in response to an electromagnetic actuator to supply the gas in the chamber to the patient. 7. An apparatus as claimed in claim 5 further including a controllable valve downstream of the pressurised gas storage chamber, said valve adapted to be opened in response to said control means receiving said input signal. 8. An apparatus as claimed in any one of the preceding claims, wherein the control means input signal is a signal indicative of the primary flow generator reaching maximum output. 9. An apparatus as claimed in any one of the preceding claims 1 to 8, wherein the control means input signal is a signal indicative of the pressure of the gas supplied to the patient falling below a predetermined minimum level. 10. An apparatus as claimed in claim 9, wherein the controllable secondary gas source receives control signals from a pressure transducer or other device that measures the pressure in the patient gas supply conduit or mask. of 11. An apparatus as claimed in any one 'claims 1 to 8, wherein the control means input signal is a signal indicative of patient inspiration commencing. 12. An apparatus as claimed in claim 11, wherein the commencement of inspiration is indicated by a sudden rise in the flow rate of air supplied to the patient. 13. An apparatus as claimed in any one of the preceding claims further including a one-way valve in a flow path between the controllable secondary breathable gas source and the patient. 14. A plurality of breathable gas supply apparatus in fluid communication with a common patient. 15. A plurality of breathable gas supply apparatus as claimed in claim 14, wherein the gas supply apparatus' are connected in parallel. 16. A plurality of breathable gas supply apparatus as claimed in claim 14 or 15, wherein the gas supply apparatus' are under common control. 17. A method for supplying on-demand additional breathable gas to a patient receiving a primary flow of breathable gas, the method including the steps of: monitoring the primary flow of breathable gas supplied to the patient; and activating a controllable secondary breathable gas source in selective fluid communication with the patient when the monitoring indicates that the primary gas supply is unable to meet patient inspiratory requirements. 18. A method for supplying breathable gas to a patient, the method including the steps of: supplying a primary flow of breathable gas to the patient; monitoring the primary flow of gas supplied to the patient; activating a controllable secondary breathable gas source in selective fluid communication with the patient when the monitoring indicates that the primary gas supply is unable to meet patient inspiratory requirements. 19. A method as claimed in claim 17 or 18, wherein the secondary breathable gas source is activated when the monitoring step indicates the primary breathable gas supply is at maximum output. 20. A method as claimed in claim 17 or 18, wherein the secondary breathable gas source is activated when the monitoring step indicates the pressure of the primary breathable gas supply is below a predetermined minimum level. 21. A method as claimed in claim 20, wherein the pressure of the primary gas supply is measured at a mask worn by the patient or a gas supply conduit connecting the mask to the primary breathable gas supply. 22. A method as claimed in claim 17 or 18, wherein the secondary breathable gas source is activated when the monitoring step indicates the commencement of patient inspiration.

Inventors: BRYDON JOHN WILLIAM ERNEST, WICKHAM PETER JOHN DEACON, BRYDON, JOHN, WILLIAM, ERNEST, WICKHAM, PETER, JOHN, DEACON
Applicants: BRYDON JOHN WILLIAM ERNEST, RESMED LTD, WICKHAM PETER JOHN DEACON, BRYDON, JOHN, WILLIAM, ERNEST, RESMED LIMITED, WICKHAM, PETER, JOHN, DEACON
Application year: 1998
Main classification: A61M16
IPC codes: A61M16