Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
1997-12-12
2001-04-10
Weiss, John G. (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204180, C128S204210, C128S204260
Reexamination Certificate
active
06213119
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the selection and/or automatic control of IPAP duration during CPAP or assisted respiration treatment. In preferred non-exclusive forms, it relates to the selection of a variable maximum IPAP duration, a variable minimum IPAP duration and the automatic adjustment of a variable IPAP duration, or combinations of these.
In this specification references to “transitions between inspiration and expiration” are to be understood as transitions both from inspiration to expiration and from expiration to inspiration.
BACKGROUND OF THE INVENTION
The administration of non-invasive CPAP (Continuous Positive Airway Pressure) is an effective way of treating patients who suffer from OSA (Obstructive Sleep Apnea) and upper airway resistance syndrome. CPAP treatment effectively acts as a pneumatic splint of the patient's upper airway. Common to all forms of non-invasive CPAP apparatus is a nose, mouth or face mask which is fitted to a patient and connected to a flow generator via a flexible air delivery tube/conduit. The flow generator includes an electric motor driving a turbine to supply air or breathable gas for the administration of CPAP treatment to the patient during sleep. The positive air pressures supplied at the entrance to the patient's airway typically is in the range 2-20 cm H
2
O.
In bilevel CPAP, the pressure of the delivered air or breathable gas is ideally switched between two levels coinciding (in synchronism) with patient breathing. The pressure required to maintain adequate airway patency is typically substantially higher in inspiration than in expiration. Further, the pressure level required during inspiration is approximately equal to the single fixed pressure level used in CPAP therapy. This observation permits the administration of a lower pressure (referred to as EPAP) in expiration, and a higher pressure (referred to as IPAP) during inspiration. Therefore, the mean pressure delivered to the patient is reduced compared with CPAP therapy, leading to increased comfort and potential compliance. In some instances bilevel CPAP may also be used to provide respiratory assistance or ventilation. Much of the practical difficulty in designing CPAP apparatus is the accurate detection of the transition between inspiration to expiration so that synchronism with respiration is maintained.
When bilevel CPAP treatment is employed using only a nose mask, for some patients the higher IPAP pressure can introduce a mouth leak by which air entering the nose escapes via the mouth. The presence of a mouth leak during IPAP makes it difficult for the CPAP apparatus to accurately detect when the patient exhales. The IPAP pressure therefore may erroneously be maintained during expiration, thereby increasing the work of breathing, possibly leading to an arousal from sleep.
One method of circumventing the problem of mouth-leak is to use a full face mask or a combined nose/mouth mask; however this may lead to discomfort for some patients and effectively sealing the mask is difficult.
An alternate manner of minimising the effect of mouth-leak is to limit the maximum time for which the CPAP apparatus can remain in the IPAP state. With an appropriate limit on the duration of the IPAP time, the machine eventually ‘times-out’ and reverts to EPAP treatment pressure if it is unable to detect, as a result of a leak, that the patient has exhaled. When the patient next inhales, the CPAP apparatus detects this occurrence and reverts to the IPAP treatment pressure.
In all known bilevel CPAP apparatus the IPAP time-out is of a fixed duration, typically three seconds, which is longer than the usual maximum inspiratory time. From clinical trials conducted by the present inventors, it has become apparent that problems still arise, as it is possible for a patient to take a number of breaths before the time-out occurs. The patient must therefore still breath against the IPAP pressure, so the work of breathing is increased. The benefits of the delivered therapy are therefore diminished and, in some cases, the device may act to the patient's detriment.
The present invention is directed to overcoming or at least ameliorating one or more of the above-mentioned disadvantages.
DISCLOSURE OF THE INVENTION
In one broad form, the invention discloses a controller for a flow generator to supply breathable gas cyclically at an inspiration pressure and at a lower expiration pressure substantially in synchronism with the patient's respiration, the controller comprising:
data processing means for receiving an input respiratory flow signal and for detecting transitions between inspiration and expiration from said flow signal to discriminate between patient inspiration and expiration, and for outputting a control signal to the flow generator to set the inspiratory pressure and the expiratory pressure, and
timer means operable to select a time duration commencing from the last transition to inspiration whereby if said first time inspiratory duration elapses before the data processing means detects a transition to expiration by the patient, the output signal from the data processing means causes the flow generator to supply said expiration pressure.
The time duration can be user adjustable. In another form, there is provided a second time duration commencing from the last transition to inspiration corresponding to the data processing means forcing said flow generator to supply said inspiration pressure until said second time duration elapses even if during said second time duration there is a transition to expiration by the patient. Furthermore, data processing means can periodically update said first time duration based on one or more subsequent respiratory transitions to expiration and whether the first time duration elapses before one or more of said subsequent transitions occur, to converge the elapse of said first time duration with said subsequent transitions to expiration.
The invention further discloses CPAP or assisted respiration apparatus comprising a controller as described above, a flow generator coupled to the controller for supplying breathable gas to a gas delivery system providing the breathable gas to the patient's airway, and a flow sensor located in said gas delivery system.
The invention further discloses a method for controlling the supply of breathable gas to a patient cyclically at an inspiration pressure and at a lower expiration pressure substantially in synchronism with the patient's respiration, the method comprising the steps of:
(a) measuring patient respiratory flow;
(b) detecting transitions between inspiration and expiration from said respiratory flow to discriminate between patient inspiration and expiration;
(c) controlling the pressure of gas to be at the inspiration pressure during patient inspiration and at the expiratory pressure during patient expiration; and
(d) prescribing a first time duration commencing from the last transition to inspiration by the patient, and if a said duration elapses before patient transition to expiration, causing the pressure of gas to be at the expiratory pressure.
Preferably, the method comprises the further step of:
(e) prescribing a second time duration commencing from the last transition to inspiration, and causing the pressure of gas to be at the inspiratory pressure until the elapse of said second time duration even if there is a transition to expiration by the patient during the second time duration.
Yet further, there can be the further step of:
(f) updating said first time duration based on one or more previous respiratory transitions to expiration and whether the first time duration elapses before one or more of said previous transitions occur to converge the elapse of said first time duration with said previous transitions to expiration.
The provision of a variable maximum inspiratory treatment pressure duration is advantageous in maintaining synchronism between CPAP apparatus and a patient's breathing, thereby maintaining efficacy of the treatment and ensuring that the work
Brydon John William Ernest
Willson Grant
Pillsbury Madison & Sutro LLP
ResMed Limited
Weiss John G.
Weiss, Jr. Joseph F.
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