The Institutes of Medical Sciences

Stanley E Elliott

Jack H Shore

A pneumotachograph having an improved air flow to pressure differential transducer is disclosed for producing a pressure differential during inspiration and expiration of respirative air to and from a hospital patient. Typically, the air flow to pressure differential transducer is attached to endotracheal tubing between the patient's trachea and the respirator valve. Specifically, the transducer provides the endotracheal tube with an enlarged and typically cylindrical volume having offset air passages communicating to the endotracheal tube. The unit area of the measuring chamber is greater than the unit area of the communicated endotracheal tubing and is typically cylindrical with respect to such tubing. Likewise, the area of the communicated endotracheal tube is preferably less than one quarter the cross-sectional area of the chamber. The endotracheal tubings are preferably offset so that their respective air flows are not in line and the generated air flow interior of the volume is turbulent but not circuitous. Both the communicated endotracheal tubings are provided with manometer taps substantially normal to the path of fluid flow therein so that pressure differential and not velocity head of the fluid flow is measured. The manometer taps are communicated to a differential pressure transducer. The output of this transducer passes to a linearization circuit to produce a measure of intake and outflow during the patient's respective inspiration and expiration to provide a quantitative measure of patient respiration.

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San Bruno, CA, United States of America

Stanley E Elliott