Metabolic gas exchange and noninvasive cardiac output monitor

摘要

A respiratory gas analyzer for measuring the metabolic activity and the cardiac output of a subject includes a bi-directional flow meter and a capnometer sensor interconnected by conduits and valving between a mouthpiece and a source of respiratory gasses which may be a controlled source or the atmosphere. A pass-through carbon dioxide scrubber may be plugged into the conduits and the valving controlled so that upon inhalation by the subject gasses are passed through the flow meter to the mouthpiece and upon exhalation the exhaled gasses are passed first through the scrubber and then through the flow meter in a direction opposite to the inhaled gasses. A computer connected to receive the signals from the flow meter and the capnometer can then calculate the subject's metabolic activity. When the valving is shifted a portion of the exhaled gasses are stored in the conduit so that upon inhalation the subject inhales a substantial portion of rebreathed gasses. The computer can then calculate the patient's cardiac output as a function of the changes in total carbon dioxide content of the exhaled gas before and after the valve is shifted from a direct input to a rebreathed position and the difference in end-tidal carbon dioxide between these two positions. The carbon dioxide scrubber may be removed from the circuitry during calculation of cardiac output to conserve the scrubber life.