Abstract: | Tansley, John G., Michala E. F. Pedersen, Christine Clar,and Peter A. Robbins. Human ventilatory response to 8 h of euoxic hypercapnia. J. Appl.Physiol. 84(2): 431-434, 1998. Ventilation ( E) risesthroughout 40 min of constant elevated end-tidalPCO2 without reaching steady state(S. Khamnei and P. A. Robbins. Respir. Physiol. 81: 117-134, 1990). The present studyinvestigates 8 h of euoxic hypercapnia to determine whether E reachessteady state within this time. Two protocols were employed:1) 8-h euoxic hypercapnia (end-tidalPCO2 = 6.5 Torr above prestudy value,end-tidal PO2 = 100 Torr) followed by 8-h poikilocapnic euoxia; and2) control, where the inspired gaswas air. Ewas measured over a 5-min period before the experiment and then hourly over a 16-h period. In the hypercapnia protocol, E had notreached a steady state by the first hour(P < 0.001, analysis of variance), but there were no further significant differences in Eover hours 2-8 (analysis ofvariance). Efell promptly on return to eucapnic conditions. We conclude that,whereas there is a component of the E responseto hypercapnia that is slow, there is no progressive rise in E throughoutthe 8-h period. |