Respiratory exchange ratio sensor

摘要

A device for directly measuring a person's respiratory exchange ratio (RER) utilizes a Zn-air battery cell and a constant current load circuit as an O₂ pump capable of drawing oxygen from expired air. A thermistor located in the flow path forms a leg of a bridge circuit whose output is proportional to oxygen concentration in the expired air and, therefore, to oxygen uptake. The thermistor flowmeter circuit utilizes the thermal conductivity differences between O₂ and CO₂ to provide a measure at the relative ratio of the two gases present.