Do changes in cardiac output affect the inspiratory to end-trial oxygen difference?

Abstract

The paramagnetic technique has made it possible to monitor the end-tidal oxygen concentration and P(1-ET)O2, i.e. inspiratory to end-tidal oxygen difference, breath-by-breath. Little is known about the implications of a changing P(1-ET)O2, but so far studies have shown it to be a quick and sensitive variable to detect hypoventilation. This study was designed to observe the circulatory effects on P(1-ET)O2 in an experimental setting but monitored as in a clinical situation. We assessed the oxygen difference during changes in cardiac output induced by intravenous ephedrine-hydrochloride in 12 healthy male volunteers. P(1-ET)O2 was measured with a fast-response paramagnetic differential oxygen sensor. Cardiac output was measured with non-invasive transthoracic electrical bioimpedance. As simultaneous changes in metabolism and ventilation will also influence P(1-ET)O2 oxygen uptake and expired minute volume were monitored. After a rest period, the subjects had an intravenous injection of ephedrine-hydrochloride 0.1 mg.kg-1 followed by a 30-min observation period. Cardiac output increased significantly as did the oxygen uptake and the ventilation. We found no biological significant correlation between cardiac output and P(1-ET)O2. The P(1-ET)O2 was influenced by ventilation and metabolism.