Method and apparatus for determining airway resistance and lung compliance
First Claim
1. A method of establishing the airway resistance and lung compliance of a subject using a non-linear circuit model, the subject inspiring and expiring breathing gases through an airway, said method comprising the steps of:
- sensing breathing gas flow rate through the airway;
sensing breathing gas pressure in the airway;
calculating a gas volume moved through the airway from the sensed breathing gas flow rate;
determining an invariant exponential based on physical characteristics of the airway; and
calculating airway resistance and lung compliance based on the gas flow rate, the gas pressure, the gas volume, and the invariant exponential.
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Accused Products
Abstract
A method and apparatus is disclosed for determining airway resistance and lung compliance using an electrical circuit model wherein at least one component parameter is non-linear. The system non-intrusively obtains pressure and flow data signals from a pressure transducer and a laminar flow element without interrupting or interfering with normal breathing and gas supply to a patient. An invariant exponential is determined empirically based on physical characteristics of the airway. The non-linear airway resistance and lung compliance can then be calculated based on the sensed flow rate, gas pressure, a calculated gas volume, and the invariant exponential using linear techniques. The resulting airway resistance can be normalized to a standard reporting flow rate value. The system is particularly useful in anesthesia applications, but is also useful in any breathing system where fresh gas is supplied constantly from a gas source other than a ventilator.
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Citations
19 Claims
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1. A method of establishing the airway resistance and lung compliance of a subject using a non-linear circuit model, the subject inspiring and expiring breathing gases through an airway, said method comprising the steps of:
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sensing breathing gas flow rate through the airway; sensing breathing gas pressure in the airway; calculating a gas volume moved through the airway from the sensed breathing gas flow rate; determining an invariant exponential based on physical characteristics of the airway; and calculating airway resistance and lung compliance based on the gas flow rate, the gas pressure, the gas volume, and the invariant exponential. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An apparatus to determine the airway resistance and lung compliance of a subject using a non-linear circuit model, the subject inspiring and expiring breathing gases through an airway, said apparatus comprising:
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a breathing gas flow rate sensor attachable to the airway to sense a gas flow therethrough and produce a flow rate signal therefrom; a breathing gas pressure sensor locatable in the airway to sense a gas pressure therein and produce a pressure signal therefrom; and a processor connected to the gas flow and pressure sensors to receive the flow and pressure signals, the processor calculating a gas volume moved through the airway and employing an invariant exponential based on the physical characteristics of the airway to calculate airway resistance and lung compliance using the gas flow rate, the gas pressure, the gas volume, and the invariant exponential. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification