Central chemoreflex ventilatory responses in humans following passive heat acclimation.

Since there is temperature dependence of pulmonary ventilation (V˙(E)) in response to the normal modulators (i.e. [Formula: see text] , [Formula: see text] ), it was asked in this study if passive heat acclimation (HA) modifies the human central chemoreflex ventilatory response to CO(2). Nine males performed normothermic- and hyperthermic modified Read re-breathing tests before and after HA. Heat acclimation consisted of 2hday(-1) exposures to 50°C and 20% RH for 10 consecutive days and each exposure elevated rectal temperature to between 38.5 and 39.0°C. Ventilatory recruitment thresholds (VRTs) and central chemosensitivity were assessed before and after HA during normothermia with an oesophageal temperature (T(es)) of ∼37°C and in hyperthermia when T(es) was 38.5-39.0°C. Results showed VRT and central chemosensitivities were unaltered by HA (p≥0.375) and hyperthermia increased pre- (p=0.010) but not post-acclimation (p=0.332) central chemosensitivity. Additionally, during hyperthermia V˙(E) became progressively greater (p=0.027) relative to corresponding normothermic values in the re-breathing tests. In conclusion, the ventilatory response to hyperoxic CO(2) was unaltered by heat Acclimation State.