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Abstract

A method for analyzing the concentration of selected constituent gases in the expiratory gas streams from a patient. The method includes the steps of: (a) measuring the flow rate of the expiratory gas stream to provide a flow rate signal; (b) generating a tidal volume signal in response to the flow rate signal; (c) generating a sample control signal in response to the tidal volume signal and the flow rate signal to mark an interval within the end tidal periods of several successive expiratory gas streams; (d) extracting a sample of each of the several successive expiratory gas streams during the marked interval in response to the sample control signal; (e) accumulating each extracted sample in a variable volume reservoir; (f) transferring the accumulated gas samples within the variable volume reservoir into a sample cell in response to the variable volume reaching a predetermined limit; and (g) measuring the concentration of the selected constituent gas in the volume of gas contained in the cell. The method optionally includes the further steps of (h) measuring the concentration of oxygen in an inspiratory gas stream conducted to the patient; and (i) calculating the patient's oxygen consumption by comparing the measured concentration of oxygen in the gas contained in the sample cell with the measured concentration of oxygen in the inspiratory gas stream.

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