Human ventilatory response to acute hyperoxia during and after 8 h of both isocapnic and poikilocapnic hypoxia

Tansley, J. G., C. Clar, M. E. F. Pedersen, and P. A. Robbins. Human ventilatory response to acute hyperoxia during and after 8 h of both isocapnic and poikilocapnic hypoxia. J. Appl. Physiol. 82(2): 513–519, 1997.—During 8 h of either isocapnic or poikilocapnic hypoxia, there may be a rise in ventilation (V˙e) that cannot be rapidly reversed with a return to higher[Formula: see text] (L. S. G. E. Howard and P. A. Robbins. J. Appl. Physiol. 78: 1098–1107, 1995). To investigate this further, three protocols were compared: 1) 8-h isocapnic hypoxia [end-tidal[Formula: see text]([Formula: see text] ) held at prestudy value, end-tidal [Formula: see text]([Formula: see text]) = 55 Torr], followed by 8-h isocapnic euoxia[Formula: see text] = 100 Torr); 2) 8-h poikilocapnic hypoxia followed by 8-h poikilocapnic euoxia; and 3) 16-h air-breathing control. Before and at intervals throughout each protocol, theV˙e response to eucapnic hyperoxia [Formula: see text] held 1–2 Torr above prestudy value,[Formula: see text] = 300 Torr) was determined. There was a significant rise in hyperoxicV˙e over 8 h during both forms of hypoxia ( P < 0.05, analysis of variance) that persisted during the subsequent 8-h euoxic period ( P < 0.05, analysis of variance). These results support the notion that an 8-h period of hypoxia increases subsequent hyperoxic V˙e, even if acid-base changes have been minimized through maintenance of isocapnia during the hypoxic period.