Changes in ventilatory response to hypoxia in the rat during growth and aging.

The influence of aging on the ventilatory response to hypoxia was studied in the halothane-anesthetized male Wistar rats of various ages (1.5-20 months). The magnitude of increase in ventilation (normalized for body weight) during hypoxia in isocapnic conditions was attenuated in parallel with advancing age. However, ventilation in hyperoxia, normoxia or mild hypoxia did not differ among various age groups when the ventilatory volume was normalized for O2 consumption. Furthermore, threshold end-tidal PO2 for ventilatory depression in deeper hypoxia became progressively lower with advancing age. The results suggest that the age change in ventilatory response to hypoxia depends largely upon the progressive reduction in basal O2 requirement (consumption) with age.