Ventilatory control in infant rats after daily episodes of anoxia.

We asked whether the ventilatory control of the newborn rat was modified by preceding daily episodes of anoxia. At thermoneutrality (ambient temperature, 32 degrees C) during anoxia, respiratory efforts lasted, on average, 28, 20, and 11 min at 1, 3, and 7 d, respectively. Therefore, we chose 10 min as the duration of a daily exposure to anoxia (100% N2 breathing) from d 1 to d 6 (experimental group). During the 7 d of the study, body growth was not different between the two groups. On d 7, respiratory measurements were performed and compared with those of rats never exposed to anoxia (controls). In normoxia, oxygen consumption (VO2, measured with an open-flow system) and ventilation (VE, measured by flow-plethysmography) were similar between control and experimental groups. Acute exposure to hypoxia (10 min of 10% O2) resulted in a similar drop in VO2 and increase in VE in both groups. During the last exposure to anoxia on d 7, heart rate and breathing rate rapidly dropped; the attained degree of acidosis (blood pH and PCO2) was also similar to that of control rats. The results of the present experimental approach suggest that, in the newborn rat, daily episodes of anoxia during the 1st postnatal wk have no appreciable impact on body growth, ventilatory control, and the response to additional hypoxia.