Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
1999-09-07
2001-11-20
Weiss, John G. (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204180
Reexamination Certificate
active
06318365
ABSTRACT:
The invention relates to a method of switching or changing from the inhalation phase to the exhalation phase or vice versa in the CPAP (continuous positive airways pressure) therapy, in which a positive air pressure is continuously exerted onto the airways (CPAP therapy).
The CPAP therapy serves for pneumatically supporting the larynx by continuously supplying a positive air pressure onto the airways. The pressure level is individually adjusted to the patient. The invention is used in a varied CPAP method wherein the exhalation takes place at a lower pressure level than the inhalation. This has the advantage that the patient does not have to exhale against the high pressure level. It is of great importance for the patient's safety that the adjustment of the different pressure levels during the transition from the inhalation phase to the exhalation phase and vice versa takes place with high precision.
In the state of the art, usually the respiratory gas flow from and to the patient is measured and differentiated with respect to time (first derivative) for obtaining a more distinct transition between the inhalation and exhalation phases. The differential functions of the flanks of the gas flow curve are compared with threshold values indicating a transition to the respective other breathing phase. However, the patient's respiratory gas flow may comprise deviations; furthermore, influences of the patient's pulse may have an effect on the gas flow. This may result in an overshooting of the first differential function, wherein the threshold value for changing to the other breathing phase is achieved prior to the required time so that it is changed to the other pressure level and the patient's safety may be jeopardized.
A method of changing to the inhalation phase or exhalation phase in the CPAP therapy is known from EP-A
2-0 656 216
. In this method, the motor speed and current consumption of a generator for supplying a patient with air is controlled and an operation signal is derived for the purpose of determining the inhalation and exhalation phases. A signal representative of the gas flow to the patient is derived from the operation signal. The flow signal d“flow”/dt differentiated with respect to time is compared with a first and a second threshold value and the change in the breathing phase is derived therefrom.
The invention is based on the problem of providing an improved method for changing to the inhalation or exhalation phase in the CPAP therapy, wherein the transition to the inhalation or exhalation phase is recognized with high precision and the patient's safety is increased.
The problem is solved with the features of the claims.
According to the invention, the solution is based on the following principal concepts.
The first derivative of a respiratory gas flow curve from and to the patient is compared with two subsequent threshold values for the variation of the first derivative. The first threshold value is higher and therefore more insensitive. Deviations, which often occur at the beginning of a breathing phase, cannot reach said high threshold value and thus trigger any erroneous change of a pressure level in the CPAP therapy. Subsequent to the high threshold value, a low threshold value, which therefore is more sensitive, is set for the purpose of determining the transition to the next breathing phase with high precision. The change to the other breathing phase takes place when the first derivative has reached the second threshold value.
In the case of forced breathing, the high threshold may also be exceeded, which is the reason why spontaneous breathing is possible at any time.
In a specific embodiment of the invention, the time history of the gas flow in the exhalation phase is sampled in at least one sequence of three sampling values in addition to the comparison with the second, low value. If in such a sequence the condition is fulfilled that the second and the third sampling values exceed the respective preceding sampling values by a predetermined amount &Dgr;, the change to the inhalation phase occurs at the third sampling value; if this change-over does not occur, the change to the inhalation phase is triggered by said comparison of the first derivative with the low threshold value.
If none of the two aforementioned changing operations to the inhalation phase is triggered, the change-over occurs on account of a limiting time switching operation, e.g. at the latest after 3 to 4 s for the exhalation phase.
The advantages of the invention reside both in a low susceptibility to trouble and in a high precision during changing to the inhalation or exhalation phase in the CPAP therapy.
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Griebel Jutta
Madaus Stefan
Vögele Harald
MAP Medizintechnik fur Arzt und Patient GmbH
Mitchell Teena
Ohlandt Greeley Ruggiero & Perle LLP
Rauchfuss, Jr. George W.
Weiss John G.
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