Hypoxic ventilatory response of adult rats and mice after developmental hyperoxia.

Chronic postnatal hyperoxia attenuates the hypoxic ventilatory response (HVR) of rats. To determine whether the ability to detect deficits in the HVR depends on the degree of hypoxia, we assessed the HVR at several levels of hypoxia in adult rats reared in 60% O(2) for the first two postnatal weeks. Hyperoxia-treated rats exhibited smaller increases in ventilation than control rats at 12% O(2) (30±8 vs. 53±4% baseline, mean±SEM; P=0.02) but not at 10% O(2) (83±11 vs. 96±14% baseline; P=0.47). Interestingly, 10% O(2) was used as the test gas in the only study to assess HVR in mice exposed to developmental hyperoxia, and that study reported normal HVR (Dauger et al., Chest 123 (2003), 530-538). Therefore, we assessed the HVR at 12.5% O(2) in adult mice reared in 60% O(2) for the first two postnatal weeks. Hyperoxia-treated mice exhibited smaller increases in ventilation (28±7 vs. 58±8% baseline; P<0.01) and smaller carotid bodies than control mice. We conclude that hyperoxia impairs the HVR in both rats and mice, but this effect is most evident at moderate levels of hypoxia.