Temperature compensation of a respiratory gas sensor
First Claim
1. A system for measuring an amount of a gas component within a gas flow, comprising:
- a gas sensor configured to measure an amount of a component of gas within a flow of gas, wherein the gas sensor has a sensing element configured to contact the flow of gas, and wherein an output of the sensing element is sensitive to temperature fluctuations of the sensing element;
a pressure sensor configured to measure a pressure of the flow of gas;
a flow sensor configured to measure the flow of gas; and
a processor configured to receive first signals as a function of the amount of the component of gas measured by the gas sensor and second signals as a function of the pressure measured by the pressure sensor and the flow measured by the flow sensor, wherein the processor is further configured to adjust the measurement of the amount of the component of gas measured by the gas sensor based upon the measured pressure measured by the pressure sensor and the measured flow measured by the flow sensor,wherein the gas sensor comprises an oxygen sensor, and wherein the processor adjusts the amount of oxygen measured by the oxygen sensor according to the equation;
% oxygen—
flow—
compensated[n]=% oxygen—
pressure—
compensated[n]*(1.0+KX*flowfiltered[n]),where “
% oxygen—
flow—
compensated[n]”
is a flow compensated percent oxygen for a current (nth) sample, KX=KI during inspiration, KX=KE during expiration, “
KI”
is a compensation factor applied for inspiratory flow, “
KE”
is a compensation factor applied for expiratory flow, and “
flowfiltered[n]”
is a flow signal delayed and low-pass filtered to match a time response of the oxygen signal, andwhere % oxygen—
pressure—
compensate [n]=% oxygen—
raw[n](total airway pressure[n]/barometric pressure) and % oxygen—
raw[n] is a non-pressure compensated oxygen signal measured by the oxygen sensor for the current (nth) sample.
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Accused Products
Abstract
A mainstream gas monitoring system and method that includes a mainstream airway adapter, and a gas sensing assembly associated with the mainstream airway adapter to measure an analyte of a gas flow through the adapter. A gas sensing portion outputs a signal indicative of the analyte in a gas flow in the mainstream airway adapter. A processing portion receives the signal from the gas sensing portion and determines an amount of the analyte in the gas flow based on the signal from the gas sensing portion. The gas sensing portion is subject to temperature variations associated with variations in flow rate and direction of respiratory gases. Methods are described that utilize the measurement of instantaneous respiratory flow rate combined with estimates of gas temperature and composition to estimate the sensor cooling effects from which a flow based time varying compensation factor is derived.
19 Citations
30 Claims
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1. A system for measuring an amount of a gas component within a gas flow, comprising:
-
a gas sensor configured to measure an amount of a component of gas within a flow of gas, wherein the gas sensor has a sensing element configured to contact the flow of gas, and wherein an output of the sensing element is sensitive to temperature fluctuations of the sensing element; a pressure sensor configured to measure a pressure of the flow of gas; a flow sensor configured to measure the flow of gas; and a processor configured to receive first signals as a function of the amount of the component of gas measured by the gas sensor and second signals as a function of the pressure measured by the pressure sensor and the flow measured by the flow sensor, wherein the processor is further configured to adjust the measurement of the amount of the component of gas measured by the gas sensor based upon the measured pressure measured by the pressure sensor and the measured flow measured by the flow sensor, wherein the gas sensor comprises an oxygen sensor, and wherein the processor adjusts the amount of oxygen measured by the oxygen sensor according to the equation;
% oxygen—
flow—
compensated[n]=% oxygen—
pressure—
compensated[n]*(1.0+KX*flowfiltered[n]),where “
% oxygen—
flow—
compensated[n]”
is a flow compensated percent oxygen for a current (nth) sample, KX=KI during inspiration, KX=KE during expiration, “
KI”
is a compensation factor applied for inspiratory flow, “
KE”
is a compensation factor applied for expiratory flow, and “
flowfiltered[n]”
is a flow signal delayed and low-pass filtered to match a time response of the oxygen signal, andwhere % oxygen—
pressure—
compensate [n]=% oxygen—
raw[n](total airway pressure[n]/barometric pressure) and % oxygen—
raw[n] is a non-pressure compensated oxygen signal measured by the oxygen sensor for the current (nth) sample. - View Dependent Claims (2, 3, 4, 5, 6, 7, 26)
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8. A system for measuring an amount of oxygen in a gas flow, comprising:
-
a conduit through which a gas flow passes; an oxygen sensor having a sensing element exposed to the gas flow within the conduit, the oxygen sensor sensing an amount of oxygen in the gas flow; a pressure sensor constructed and arranged to measure a pressure of the gas flow in the conduit; a flow sensor configured to measure a flow rate of the gas flow; and a processor that receives a first signal based on the amount of oxygen sensed by the oxygen sensor and that receives a second signal based on the pressure measured by the pressure sensor and the flow rate measured by the flow sensor, the processor adjusting the amount of oxygen sensed by the oxygen sensor based on the measured pressure and the measured flow rate, wherein the processor adjusts the amount of oxygen measured by the oxygen sensor according to the equation;
% oxygen—
flow—
compensated[n]=% oxygen—
pressure—
compensated[n]*(1.0+KX*flowfiltered[n]),where “
% oxygen—
flow—
compensated[n]”
is a flow compensated percent oxygen for a current (nth) sample, KX=KI during inspiration, KX=KE during expiration, “
KI”
is a compensation factor applied for inspiratory flow, “
KE”
is a compensation factor applied for expiratory flow, and “
flowfiltered[n]”
is a flow signal delayed and low-pass filtered to match a time response of the oxygen signal, andwhere % oxygen—
pressure—
compensated [n]=% oxygen—
raw[n](total airway pressure[n]/barometric pressure) and % oxygen—
raw[n] is a non-pressure compensated oxygen signal measured by the oxygen sensor for the current (nth) sample. - View Dependent Claims (9, 10, 11, 12, 27)
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13. A method of measuring an amount of oxygen in a flow of gas, comprising the acts of:
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measuring an amount of oxygen in a gas flow; measuring a characteristic associated with the gas flow; and adjusting by a processor the measurement of the amount of oxygen in the gas flow based upon the measured characteristic associated with the gas flow and according to the equation;
% oxygen—
flow—
compensated[n]=% oxygen—
pressure—
compensated[n]*(1.0+KX*flowfiltered[n]),where “
% oxygen—
flow—
compensated[n]”
is a flow compensated percent oxygen for a current (nth) sample, KX=KI during inspiration, KX=KE during expiration, “
KI”
is a compensation factor applied for inspiratory flow, “
KE”
is a compensation factor applied for expiratory flow, and “
flowfiltered[n]”
is a flow signal delayed and low-pass filtered to match a time response of the oxygen signal, andwhere % oxygen—
pressure—
compensated [n]=% oxygen—
raw[n](total airway pressure[n]/barometric pressure) and % oxygen—
raw[n] is a non-pressure compensated oxygen signal measured by the oxygen sensor for the current (nth) sample. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 28, 29)
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21. A system for measuring an amount of a gas component within a gas flow, comprising:
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means for measuring an amount of a component of gas within a gas flow; means for measuring a characteristic associated with the gas flow, wherein the measured characteristic includes a pressure of the gas flow and a flow rate of the gas flow; and means for adjusting the measured amount of the component of gas based upon the measured characteristic associated with the gas flow, wherein the gas comprises oxygen, and wherein the means for adjusting adjusts the amount of oxygen measured by the means for measuring according to the equation;
% oxygen—
flow—
compensated[n]=% oxygen—
pressure—
compensated[n]*(1.0+KX*flowfiltered[n]),where “
% oxygen—
flow—
compensated[n]”
is a flow compensated percent oxygen for a current (nth) sample, KX=KI during inspiration, KX=KE during expiration, “
KI”
is a compensation factor applied for inspiratory flow, “
KE”
is a compensation factor applied for expiratory flow, and “
flowfiltered[n]”
is a flow signal delayed and low-pass filtered to match a time response of the oxygen signal, andwhere % oxygen—
pressure—
compensated [n]=% oxygen—
raw[n](total airway pressure[n]/barometric pressure) and % oxygen—
raw[n] is a non-pressure compensated oxygen signal measured by the oxygen sensor for the current (nth) sample. - View Dependent Claims (22, 23, 24, 25, 30)
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Specification