A continuous method for measuring acetylene in expired gas using glow discharge and its application to assessment of pulmonary blood flow

In order to measure a rapid change in pulmonary blood flow the suitability of a glow discharge gas analyser for the continuous analysis of C2H2 was examined. The analyser was originally designed for continuous analyses of O2 and CO2 in expired air. However, we found that it responded specifically to C2H2, when a gas mixture containing 5% O2, 40% CO2 with a balance of N2 was used as a carrier gas and a negative voltage of 20 V was applied to the proximal collector electrode against the distal. Under these conditions the C2H2 current was reproducible within 0.1 mmHg, the base line drift was smaller than 1 mmHg/hr and the 90% response time was about 0.6 sec. This method was applied to analysis of C2H2 in expired air in combination with a constant rate expiration technique. When a C2H2 gas mixture was inhaled and expired at a constant rate, the observed C2H2 curves agreed with the theoretical ones calculated at the pulmonary blood flow rates obtained separately with the conventional breath-holding method. The decay rate of the C2H2 curve showed a rapid change within 1.5 sec when exercise and a Valsalva-like maneuver were made during continuous expiration, suggesting a quick alternation in pulmonary blood flow.