Measurement system for respiratory water vapor and temperature dynamics

An instrumentation system has been developed to simultaneously measure water vapor and temperature at the same point within respiratory airways during breathing. A mass spectrometer was used to analyze gas continuously sampled through a modified inlet catheter. At the tip of the catheter, gas temperature is sensed by a microbead thermistor. Adequate water vapor dynamics is achieved by a two-step procedure. First, the tip of the sampling catheter is constricted to reduce the catheter's internal pressure and thereby prevent condensation and evaporation. Second, the water vapor signal from the mass spectrometer is compensated electronically to improve its transient response. As part of the evaluation of the system, water vapor and gas temperature were measured in the oropharynx of human subjects.