An on-demand system of delivering pre-mixed inspiratory gas for use during physical activity.

This study analysed the effectiveness of an on-demand system of supplying pre-mixed inspiratory gases to subjects under working conditions. A supply of pre-mixed inspiratory gas is often required in order to study the effects of acute hypoxia/hyperoxia on numerous physiological variables whilst normobaric pressure is maintained. The principle aim of this investigation was to determine if the introduction of the on-demand system resulted in any changes in minute ventilation (VE), oxygen consumption (VO2), respiratory rate (RR), tidal volume (VT) or endurance performance during incremental cycle ergometry to exhaustion. Trained male subjects participated in the study (n = 9). The subjects completed two incremental trials on a Monark cycle ergometer. The trials commenced at a power output of 60W implementing a 30 W.4 min-1 work increment. In one trial the subjects inspired ambient room air as per normal VO2max testing, whilst in the other trial the subjects inspired compressed air supplied from high pressure cylinders using a demand valve. Trial order was randomised. Raw data (time, heart rate, VI[ATPS], respiratory rate, tidal volume, FEO2 and FECO2) were recorded on line every 15 seconds. No differences in gas exchange variables were apparent at rest (VO2 VE RR, VT) nor during submaximal work between normal and on-demand trials. VO2max, VEmax and physical performance were also not significantly different between trials. On the basis of these findings, it was suggested that the on-demand system of supplying inspiratory gas resulted in minimal changes in gas exchange variables and performance during incremental work. Using this system of gas supply researchers can effectively supply subjects with premixed gas for little financial expense.