Fatemian, Marzieh, and Peter A. Robbins. Human ventilatory response to CO 2 after 8 h of isocapnic or poikilocapnic hypoxia. J. Appl. Physiol. 85(5): 1922-1928, 1998.-During ventilatory acclimatization to hypoxia (VAH), the relationship between ventilation (V E) and end-tidal PCO 2 (PET CO 2 ) changes. This study was designed to determine 1) whether these changes can be seen early in VAH and 2) if these changes are present, whether the responses differ between isocapnic and poikilocapnic

more »

... es. Ten healthy volunteers were studied by using three 8-h exposures: 1) isocapnic hypoxia (IH), end-tidal PO 2 (PET O 2 ) ϭ 55 Torr and PET CO 2 held at the subject's normal prehypoxic value; 2) poikilocapnic hypoxia (PH), PET O 2 ϭ 55 Torr; and 3) control (C), air breathing. The V E-PET CO 2 relationship was determined in hyperoxia (PET O 2 ϭ 200 Torr) before and after the exposures. We found a significant increase in the slopes of V E-PET CO 2 relationship after both hypoxic exposures compared with control (IH vs. C, P Ͻ 0.01; PH vs. C, P Ͻ 0.001; analysis of covariance with pairwise comparisons). This increase was not significantly different between protocols IH and PH. No significant changes in the intercept were detected. We conclude that 8 h of hypoxia, whether isocapnic or poikilocapnic, increases the sensitivity of the hyperoxic chemoreflex response to CO 2 .