AU727265B2 - Control of the administration of continuous positive airway pressure treatment - Google Patents

Description

S F Ref: 456280

AUSTRALIA

PATENTS ACT 1990 COMPLIETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: ASSOCIATED PROVISIONAL 1311 Application No(s) PP3701 ResMed Limited 97 Waterloo Road North Ryde New South Wales 2113

AUSTRALIA

Shane Darren Finn Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Control of the Administration of Continuous Positive Airway Pressure Treatment APPLICATION DETAILS [331 Country

AU

[321 Application Date 25 May 1998 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5815 -1- CONTROL OF THE ADMINISTRATION OF CONTINUOUS POSITIVE AIRWAY PRESSURE TREATMENT Field of the Invention This invention relates to control of the provision of Continuous Positive Airway Pressure (CPAP) treatment.

Background of the Invention Early forms of CPAP treatment provided pressurised air or breathable gas to 10 the entrance of a patient's airways continuously at a pressure elevated above atmospheric pressure, typically in the range 4-20 cmH20. CPAP treatment is a common ameliorative treatment for breathing disorders, including Obstructive Sleep Apnea (OSA) syndrome. In its simplest form, CPAP treatment provides a single pressure level to the patient throughout the inspiratory and expiratory phases of 15 respiration. It is also known for the level to vary over the course of many breaths in accordance with patient need, that form being known as automatically adjusting CPAP treatment.

Another form of CPAP treatment is 'bi-level', in which a higher pressure of gas is provided to the patient during the inspiratory phase of respiration and a relatively lower pressure during the expiratory phase. Bi-level CPAP treatment requires a determination of the onset of a transition between the inspiratory and expiratory phases (the and transitions). The detection of these transitions is vital in controlling operation of a flow generator to provide pressurised air or breathable gas to the patient to maintain the therapeutic effect of treatment. Bi-level CPAP is used to treat respiratory insufficiency and acute respiratory failure, for example.

Many known bi-level CPAP devices rely on the detection of a change in patient respiratory flow as a trigger for a transition between treatment pressures.

In:\libkl01256:JLS -2- Delays in sensing patient breathing patterns is known to cause an increase in the work of breathing and discomfort for the patient due to pneumatic asynchrony. Such delays can also result in the unintended occurrence of apneas when treatment should be effective.

It is an objective of the present invention to overcome or at least ameliorate one or more of the problems in the prior art.

Summary of the Invention 10 Accordingly, the gist of the invention is to provide an intermediate treatment :pressure for a period of time as a transitional state between selected changes from the inspiratory and expiratory phase pressures of CPAP treatment.

Therefore, invention discloses a CPAP flow generator comprising: 15 a blower for providing a supply of pressurised air or breathable gas; and a controller having control over the blower to supply an inspiratory phase pressure and an expiratory phase pressure, and operable to set a first flow threshold and a second flow threshold, the controller further sensing flow due to a patient respiration and selectively triggering generation of a pressure intermediate of the inspiratory phase go and expiratory phase pressures for a period of time as a transitional state upon the first flow threshold and/or the second flow threshold being crossed.

The invention further discloses CPAP treatment apparatus, comprising: a patient mask coupled to an air delivery conduit, in turn coupled to a blower operable to provide a positive pressure of air or breathable gas to said conduit; and a controller comprising: a blower for providing a supply of pressurised air or breathable gas; and a controller having control over the blower to supply an inspiratory phase pressure and an expiratory phase pressure, and operable to set a first flow threshold [n:\libkOl 256:JLS marking transitions between the inspiratory phase pressure and the expiratory phase pressure, and to set a second flow threshold, the controller further sensing flow due to a patient respiration and selectively triggering genreation of a pressure intermediate of the inspiratory phase and expiratory phase pressures for a period of time as a transitional state upon the first flow threshold and/or the second flow threshold being crossed.

The invention further discloses a method for the administration of CPAP treatment, comprising the steps of: providing a source of pressured air or breathable gas to a patient; controlling the pressure of gas between an inspiratory phase level and a lower expiratory phase level; setting a first patient respiratory flow threshold; setting a second flow threshold; and 15 selectively generating an intermediate pressure for a period of time as a transitional state upon the first flow threshold and the second flow threshold being crossed.

Brief Description of the Drawings Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figs. la and lb show a prior art bi-level arrangement; Fig. 2 shows a schematic block diagram of CPAP treatment apparatus; Figs 3a and 3b show traces of pressure and flow in one embodiment; Figs. 4 and 5 are flow diagrams relating to Figs. 3a and 3b; Figs. 6a and 6b show traces of pressure and flow in another embodiment; Figs. 7 and 8 are flow diagrams relating to Figs. 6a and 6b; [n:\libk]Ol 256:JLS Figs. 9a and 9b show traces of pressure and flow in yet a further embodiment; and Figs. 10 and 11 are flow diagrams relating to Figs. 9a and 9b.

Description of Preferred Embodiments and Best Mode Figs. la and lb show a snapshot of slightly more than a single respiratory event, including the bi-level treatment pressures and patient respiration (flow) for the respective inspiratory and expiratory phases. The apparatus implementing the conventional CPAP treatment has a flow threshold, fl, that is ascribed as the triggering 10 point between inspiratory and expiratory transitions. Therefore, at time t 1 it is determined that the patient has commenced inspiration and the flow generator steps the treatment pressure from the lower expiratory value PE to the high inspiratory value PI.

The PI level continues until time t 2 when the patient flow reduces to below the threshold value fl and the lower treatment pressure PE is applied. This pressure continues until subsequent detection of the flow at time t 3 increasing above the threshold fl, at which time the cycle repeats.

As can be noted from the flow characteristic, high flows usually only occur during the initial portion of the respiratory phase, with the flow significantly reducing thereafter. At these low flow levels, the relatively large change in treatment pressure at the end of the inspiratory phase can cause discomfort to a patient who has, in effect, finished the work of active breathing. A further concern arises at the end of the expiratory phase the hatched region shown in Fig. la), when the lower treatment pressure PE may not be adequate to prevent occlusions of the airway, and thus unintended apneas can occur.

Fig. 2 shows a simplified schematic block diagram of a CPAP machine 10 in which embodiments of the invention can be implemented. An impeller 12 provides air or breathable gas at a pressure elevated at above atmospheric to a flexible conduit 14, [n:\libkl0 256:JLS in turn coupled with a patient mask 16. The mask can be of any convenient type, and provides the air or breathable gas to the entrance of a patient's airways at the desired treatment pressure. The impeller 12 is powered by an electric motor 18, together termed a blower, under the control of a servo unit 20, to achieve the desired turbine rotational speed and thus delivery pressure applied to the conduit 14. The servo unit in turn receives controlling signals from a microprocessor-based controller 22.

There are several known methods of altering the pressure delivered to the patient. In the present method, the motor speed is varied. In another method, a 10 variable fraction of the blower outlet is diverted to atmosphere instead of being directed to the patient. In a further method, also using a single speed motor, a variable fraction o• of the blower inlet is choked. The invention may be embodied in devices incorporating all of these methods.

15 The controller 22 receives a number of input signals, including a signal representative of flow provided by a flow transducer 24 and a signal representative of delivery pressure from a pressure transducer 26. In practice one or more of these transducers may be incorporated within the controller 22, however they are shown as discrete inputs thereto for the purposes of explanation. The controller 22 also receives a signal indicative of motor speed from the motor speed sensor The controller 22 also has inputs and outputs directed to various controls and displays 34 typically located on the casing of the CPAP machine. The inputs can include pushbuttons for effecting operation of the machine in a timed or spontaneous mode. The output displays can include treatment pressure indicators and 'power on' indicators.

All of the components described above are known and practised in the present applicant's Sullivan "M VPAP II machine.

In:\libkIO1256:JLS In the embodiment of Figs. 3a and 3b a second flow threshold value, f 3 having a negative value, is provided. For ease of description, it is easiest to firstly consider the E-I transition. Figs. 3a and 3b should be considered in conjunction with Figs. 4 and 5, where the steps of the flow diagram are indicated by numerals placed in parentheses, i.e. In the period time t 2 to t 8 the normal expiratory pressure PE is applied At time t 8 the threshold f 3 is crossed (52) and the flow generator is caused to supply an intermediate pressure Py (54) until time t 3 (58) when the full inspiratory pressure PI is applied The intermediate pressure Py is greater than 10 PE, and, by occurring in the period between the tail end of expiration and the early stages of inspiration, the airway tends to remain splinted open, and the possibility of an apnea is reduced in the presence of time misalignment in triggering. As will be noted, whilst the flow signal passes through the threshold f 3 at time t 7 the controller 22 is programmed to ignore this transition and maintain the lower expiratory pressure PE.

It will be appreciated that the flow curve shown in Fig. 3b represents the case of no leak no mask leak). If leak were present, then the flow curve is shifted upwards, and thus the flow thresholds f, and f 3 would need to have an equivalent offset 2 adjustment applied.

Fig. 4 has a modification over Fig. 5, in that a reversion is allowable (56) to the previous state, i.e. back to PE.

Figs. 6a and 6b, and related flow diagrams Figs. 7 and 8, show a further embodiment that differs from that of Figs. 3a and 3b in that at time t 2 (76) the intermediate treatment Px is applied (78) until time t 7 (80,82) when the EPAP pressure PE is applied This stratagem is intended to reduce the uncomfortable effect of the full pressure change between PI and PE in the low flow region between fl and f 3 In this embodiment, the controller 22 is programmed to ignore the flow [n:\libk01256:JLS threshold f 3 at time t 8 waiting until the positive flow threshold fl is passed at time t 3 before changing the treatment pressure from PE to PI.

The flow diagram of Fig. 7 differs from Fig. 8 in that a reversion is allowable i.e. back to PI.

Figs. 9a and 9b, in conjunction with Fig. 10, show a yet further embodiment that combines the intermediate pressure transitions occurring at time t 2 and t 8 of the previous embodiments. This embodiment thereby includes all of the benefits of the 10 earlier embodiments. The flow diagrams of Figs. 10 and 11 are respectively equivalent to Figs. 4 and 5 and Figs. 7 and 8 in combination.

In further embodiments, the pressures Px and Py may or may not be equal.

15 The microcontroller 22 is appropriately programmed to give effect to the methodologies described in the preceding embodiments.

o.

As will be apparent, numerous other arrangements are possible to derive the 2 treatment pressure and patient respiratory flow signals that then can be that processed in the manner described above. These can include all other known forms of detection of transition between inspiration and expiration in substitution for flow per se.

Although the invention has been described with reference to preferred embodiments, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

[n:\libklOl 256:JLS

Claims (21)

1. A CPAP flow generator comprising: a blower for providing a supply of pressurised air or breathable gas; and a controller having control over the blower to supply an inspiratory phase pressure and an expiratory phase pressure, and operable to set a first flow threshold and a second flow threshold, the controller further sensing flow due to a patient respiration and selectively triggering generation of a pressure intermediate of the inspiratory phase and expiratory phase pressures for a period of time as a transitional state upon the first 10 flow threshold and/or the second flow threshold being crossed. .i2. Apparatus as claimed in claim 1, wherein said intermediate pressure is selectively generated on the second flow threshold being crossed only during transitions from the expiratory phase pressure to the inspiratory phase pressure. 15

2. Apparatus as claimed in claim 1, wherein said intermediate pressure is selectively generated on the frsecond flow threshold being crossed only during transitions from the inexpiratory phase pressure to the insexpiratory phase pressure. 15

3. Apparatus as claimed in claim 1, wherein said intermediate pressure is ~selectively generated on the firstecond flow threshold being crossed only during transitions **from the insexpiratory phase pressure to the inexpiratory phase pressure and on the first 20

4. Apparatus as claimed in claim 1, wherein said intermediate pressure is selectively generated on the second flow threshold being crossed during transitions from the expiratory phase pressure to the inspiratory phase pressure and on the first flow threshold being crossed during transitions from the inspiratory phase pressure to the expiratory phase pressure. Apparatus as claimed in claim 4, wherein the intermediate pressure is set to be at a different level depending upon whether the transition is from the inspiration phase pressure or from the expiration phase pressure.

In:\libk01256:JLS -9-

6. Apparatus as claimed in any one of the preceding claims, wherein the controller sets the intermediate pressure to be generated for a period of time falling between crossing of one of said thresholds and crossing of the next-occurring other of said thresholds.

7. Apparatus as claimed in any one of the preceding claims, wherein the first flow threshold is greater than any leak flow, and the second flow threshold is less than any leak flow. 10

8. CPAP treatment apparatus, comprising: o o. a patient mask coupled to an air delivery conduit, in turn coupled to a blower o° operable to provide a positive pressure of air or breathable gas to said conduit; and a controller comprising: a blower for providing a supply of pressurised air or breathable gas; and 15 a controller having control over the blower to supply an inspiratory phase pressure and an expiratory phase pressure, and operable to set a first flow threshold marking transitions between the inspiratory phase pressure and the expiratory phase pressure, and to set a second flow threshold, the controller further sensing flow due to a patient respiration and selectively triggering genreation of a pressure intermediate of 20 the inspiratory phase and expiratory phase pressures for a period of time as a transitional state upon the first flow threshold and/or the second flow threshold being crossed.

9. CPAP apparatus as claimed in claim 8, wherein said intermediate pressure is selectively generated on the second flow threshold being crossed only during transitions from the expiratory phase pressure to the inspiratory phase pressure.

In:\Iibkl0256:JLS CPAP apparatus as claimed in claim 8, wherein said intermediate pressure is selectively generated on the first flow threshold being crossed only during transitions from the inspiratory phase pressure to the expiratory phase pressure.

11. CPAP apparatus as claimed in claim 8, wherein said intermediate pressure is selectively generated on the second flow threshold being crossed during transitions from the expiratory phase pressure to the inspiratory phase pressure and on the first flow threshold being crossed during transitions from the inspiratory phase pressure to the expiratory phase pressure.

12. CPAP apparatus as claimed in claim 11, wherein the intermediate pressure is set to be at a different level depending upon whether the transition is from the inspiration phase pressure or from the expiration phase pressure. 15

13. CPAP apparatus as claimed in any one of claims 8 to 12, wherein the controller sets the intermediate pressure to be generated for a period of time falling between crossing of one of said thresholds and crossing of the next-occurring other of said thresholds. S .I o 1 20

14. Apparatus as claimed in any one of claims 8 to 13, wherein the first flow threshold is greater than any leak flow, and the second flow threshold is less than any leak flow.

A method for the administration of CPAP treatment, comprising the steps of: providing a source of pressured air or breathable gas to a patient; controlling the pressure of gas between an inspiratory phase level and a lower expiratory phase level; setting a first patient respiratory flow threshold; In:\libkl0256:JLS -11- setting a second flow threshold; and selectively generating an intermediate pressure for a period of time as a transitional state upon the first flow threshold and the second flow threshold being crossed.

16. A method as claimed in claim 15, whereby said intermediate pressure is selectively generated on the second flow threshold being crossed only during transitions from the expiratory phase pressure to the inspiratory phase pressure. 10

17. A method as claimed in claim 15, whereby said intermediate pressure S.is selectively generated on the first flow threshold being crossed only during transitions o• 9. 9 9o from the inspiratory phase pressure to the expiratory phase pressure. o

18. A method as claimed in claim 15, whereby said intermediate pressure is selectively generated on the second flow threshold being crossed during transitions from the expiratory phase pressure to the inspiratory phase pressure and on the first flow threshold being crossed during transitions from the inspiratory phase pressure to the expiratory phase pressure. 20

19. A method as claimed in claim 18, whereby the intermediate pressure is set to be at a different level depending upon whether the transition is from the inspiration phase pressure or from the expiration phase pressure. A method as claimed in any one of claims 15 to 19, whereby the step of controlling sets the intermediate pressure to be generated for a period of time falling between crossing of one of said thresholds and crossing of the next-occurring other of said thresholds.

In:\libklOl 256:JLS 12-

21. A method as claimed in any one of claims 15 to 20, whereby the first flow threshold is greater than any leak flow, and the second flow threshold is less than any leak flow. DATED this Twenty-fifth Day of May, 1999 ResMed Limited Patent Attorneys for the Applicant SPRUSON FERGUSON goes so* '00:00 6* S 900 S [n:\IibkI0l 256:JLS