Control of the administration of continuous positive airway pressure treatment

[0002] This invention relates to control of the provision of Continuous Positive Airway Pressure (CPAP) treatment.

[0003] Early forms of CPAP treatment provided pressurised air or breathable gas to the entrance of a patient's airways continuously at a pressure elevated above atmospheric pressure, typically in the range 4-20 cmH₂O. 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 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.

[0004] 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 “I-E” and “EI” 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.

[0005] 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. 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.

[0006] It is an objective of the present invention to overcome or at least ameliorate one or more of the problems in the prior art.

[0007] 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.

[0008] Therefore, invention discloses a CPAP flow generator comprising:

[0009] a blower for providing a supply of pressurised air or breathable gas; and

[0010] 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 flow threshold being crossed and selectively triggering generation of a pressure intermediate of the expiratory phase and the inspiratory phase pressures for a period of time as a transitional state upon the second flow threshold being crossed.

[0011] The invention further discloses CPAP treatment apparatus, comprising:

[0012] 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;

[0013] a blower for providing a supply of pressurised air or breathable gas; and

[0014] 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 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 flow threshold being crossed and selectively triggering generation of a pressure intermediate of the expiratory phase and the inspiratory phase pressures for a period of time as a transitional state upon the second flow threshold being crossed.

[0015] The invention further discloses a method for the administration of CPAP treatment, comprising the steps of:

[0016] providing a source of pressured air or breathable gas to a patient;

[0017] controlling the pressure of gas between an inspiratory phase level and a lower expiratory phase level;

[0018] setting a first patient respiratory flow threshold;

[0019] setting a second patient respiratory flow threshold; and

[0020] selectively generating an intermediate pressure for a period of time as a transitional state upon the first flow threshold patient respiratory threshold being crossed; and selectively generating another intermediate pressure for a period of time as a transitional state upon the second patient respiratory flow threshold being crossed.

[0021] Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[0022] FIGS. 1aand 1bshow a prior art bi-level arrangement;

[0023] FIG. 2 shows a schematic block diagram of CPAP treatment apparatus;

[0024] FIGS. 3aand 3bshow traces of pressure and flow in one embodiment;

[0025] FIGS. 4 and 5 are flow diagrams relating to FIGS. 3aand 3b;

[0026] FIGS. 6aand 6bshow traces of pressure and flow in another embodiment;

[0027] FIGS. 7 and 8 are flow diagrams relating to FIGS. 6aand 6b;

[0028] FIGS. 9aand 9bshow traces of pressure and flow in yet a further embodiment; and

[0029] FIGS. 10 and 11 are flow diagrams relating to FIGS. 9aand 9b.

[0030] FIGS. 1aand 1bshow a snapshot of slightly more than a single respiratory event, including the bi-level treatment pressures and patient respiration (flow) for the respective inspiratory (I) and expiratory (E) phases. The apparatus implementing the conventional CPAP treatment has a flow threshold, f₁, that is ascribed as the triggering point between inspiratory and expiratory transitions. Therefore, at time=t₁it is determined that the patient has commenced inspiration and the flow generator steps the treatment pressure from the lower expiratory value P_Eto the high inspiratory value P_I. The P_Ilevel continues until time=t₂when the patient flow reduces to below the threshold value f₁and the lower treatment pressure P_Eis applied. This pressure continues until subsequent detection of the flow at time=t₃increasing above the threshold f₁, at which time the cycle repeats.

[0031] 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 (i.e. the hatched region shown in FIG. 1a), when the lower treatment pressure P_Emay not be adequate to prevent occlusions of the airway, and thus unintended apneas can occur.

[0032] 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, 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 20 in turn receives controlling signals from a microprocessor-based controller 22.

[0033] 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 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 of the blower inlet is choked. The invention may be embodied in devices incorporating all of these methods.

[0034] 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 30.

[0035] 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.

[0036] All of the components described above are known and practised in the present applicant's Sullivan™ VPAP II machine.

[0037] In the embodiment of FIGS. 3aand 3ba second flow threshold value, f₃, having a negative value, is provided. For ease of description, it is easiest to firstly consider the E-I transition. FIGS. 3aand 3bshould 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. “(50)”. In the period time=t₂to t₈, the normal expiratory pressure P_Eis applied (50). At time=t₈the threshold f₃is crossed (52) and the flow generator is caused to supply an intermediate pressure P_Y(54) until time=t₃(58) when the full inspiratory pressure P_Iis applied (60). The intermediate pressure P_Yis greater than P_E, 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 f₃at time=t₇, the controller 22 is programmed to ignore this transition and maintain the lower expiratory pressure P_E.

[0038] It will be appreciated that the flow curve shown in FIG. 3brepresents the case of no leak (e.g. no mask leak). If leak were present, then the flow curve is shifted upwards, and thus the flow thresholds f₁and f₃would reed to have an equivalent offset adjustment applied.

[0039] FIG. 4 has a modification over FIG. 5, in that a reversion is allowable (56) to the previous state, i.e. back to P_E.

[0040] FIGS. 6aand 6b, and related flow diagrams FIGS. 7 and 8, show a further embodiment that differs from that of FIGS. 3aand 3bin that at time=t₂(76) the intermediate treatment P_Xis applied (78) until time=t₇(80,82) when the EPAP pressure P_Eis applied (70). This stratagem is intended to reduce the uncomfortable effect of the full pressure change between P_Iand P_Ein the low flow region between f₁and f₃. In this embodiment, the controller 22 is programmed to ignore the flow threshold f₃at time=t₈, waiting until the positive flow threshold f₁is passed at time=t₃before changing the treatment pressure from P_Eto P_I.

[0041] The flow diagram of FIG. 7 differs from FIG. 8 in that a reversion is allowable (80), i.e. back to P_I.

[0042] FIGS. 9aand 9b, in conjunction with FIG. 10, show a yet further embodiment that combines the intermediate pressure transitions occurring at time=t₂and =t₈of the previous embodiments. This embodiment thereby includes all of the benefits of the 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.

[0043] In further embodiments, the pressures P_Xand P_Ymay or may not be equal.

[0044] The microcontroller 22 is appropriately programmed to give effect to the methodologies described in the preceding embodiments.

[0045] As will be apparent, numerous other arrangements are possible to derive the 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.

[0046] 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.