Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
1998-03-31
2001-05-29
Ruhl, Dennis (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204180, C128S204210, C128S204240
Reexamination Certificate
active
06237593
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and apparatus for the determination of volumetric respiratory flow during assisted respiration, including continuous positive airway pressure (CPAP) treatment.
BACKGROUND OF THE INVENTION
The administration of CPAP is common in the treatment of Obstructive Sleep Apnea (OSA) syndrome and Upper Airway Resistance syndrome. CPAP treatment may be considered as one form of assisted ventilation generally. The fundamental disclosure of CPAP is made in the specification of PCT/AU82/00063, published under WO 82/03548. CPAP treatment effectively acts as a pneumatic splint of a patient's upper airway by the provision of a positive air pressure a approximately 10 cm H
2
O, although pressures in the range of approximately 2-20 cm H
2
O are encountered. More sophisticated forms of CPAP, such as bi-level CPAP and autosectting CPAP, are described in U.S. Pat. No. 5,245,995. Common to all forms of CPAP is a nose, mouth or face mask fitted to a patient having connection via a flexible air delivery tube to an air flow generator.
In more advanced forms of CPAP treatment, the measurement of airflow in the air delivery tube is used to detect the average volume breathed by the patient and to determine whether that person is inhaling (inspiring) or exhaling (expiring). Currently this is done using an in-line sensor to measure flow directly, or by measuring the pressure drop across a restriction in the air delivery tube (or alternatively, the pressure drop along the air delivery tube). These methods require the use of additional transducers and, in some cases, additional wiring or tubing to connect the transducer to the appropriate point in the circuit. A determination of respiratory flow determined in this way can lead to the determination of patient volumetric flow, which is a clinically useful metric.
In this specification any reference to a “mask” is to be understood as embracing a nose, mouth or combination nose and mouth (face) mask suitable for the administration of CPAP treatment. Furthermore, a “mask” can include nasal prongs (cannulae) that are inserted into the nares at the entrance to the airway.
Finally, CPAP treatment may occur at a single pressure or multiple pressures, such as in bilevel or autosetting treatments.
SUMMARY OF THE INVENTION
It is a preferred object of the present invention to offer an improvement over existing methods at least by removing the need for additional transducers, wires or tubing to measure airflow and, in turn, volumetric respiratory airflow.
Therefore the invention discloses a method for determination volumetric respiratory flow during the administration of continuous positive airway pressure (CPAP) treatment by CPAP apparatus, said method comprising the steps of:
providing a flow generator for supplying breathable gas to a mask via a gas delivery tube;
measuring an electrical parameter indicative of power consumed by said flow generator to derive a power signal;
filtering said power signal to remove non-respiratory components; and
linearising said filtered signal with respect to a predetermined characteristic of said gas delivery tube and said mask relating flow to consumed power to provide a volumetric measure of respiratory flow.
The invention further discloses an apparatus for the detection of respiration during the administration of CPAP treatment by a CPAP system, said apparatus comprising:
a flow generator for supplying breathable gas to a mask via a gas delivery tube;
means for measuring an electrical parameter indicative of power consumed by said flow generator and deriving a power signal thereof;
means for filtering said power signal to remove non-respiratory components; and
means for linearising said filtered signal with respect to a signal of a predetermined characteristic of said gas delivery tube relating flow to consumed power to provide a measure of respiratory flow.
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Derwent: Flowmeter for fluids-has turbine transducer and volumetric sensor for simultaneous calibration.
Mark Kantrowitz, Erik Horskotte and Cliff Joslyn, “Answers to Frequently Asked Questions About Fuzzy Logic and Fuzz Expert System”, Version 1.24, last modified Feb. 20, 1996.
Pillsbury & Winthrop LLP
ResMed Limited
Ruhl Dennis
Srivastava V.
LandOfFree
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