Hypoxic ventilatory responses in rats after hypercapnic hyperoxia and intermittent hyperoxia

Long-term effects of the perinatal environment on respiratory control

“…In that study, hyperoxia-treated rats increased ventilation only onethird as much as the untreated control group at similar arterial PO 2 . Similar observations have now been made for adult rats previously exposed to only 1-2 wk of 30 or 60% O 2 (7,10) or to 2 wk of intermittent exposure to 60% O 2 (21 or 60% O 2 at 1-h intervals; 10) in the early postnatal period; this plasticity does not differ between sexes (10, 33). The HCVR of adult rats is not altered by perinatal hyperoxia (56), indicating that this plasticity is specific to the hypoxic chemoreflex vs. a more general impairment of the respiratory system.…”

“…Thus there are no apparent differences between the transient blunting of the HCVR following neonatal hypercapnia and the ventilatory acclimation to chronic hypercapnia in adult rats and other mammals (23). Intermittent hypercapnia (0 or 7.5% CO 2 at 1-h intervals) for the first 2 postnatal wk has no effect on the HCVR at either 2 or 7 wk of age in rats (K. E. R. Russell, J.C. Simons, and R. W. Bavis, unpublished observations); the adult HVR is also unchanged following this intermittent hypercapnia protocol (10).…”

“…Furthermore, these effects of hyperoxia are unique to development because exposure to similar levels and durations of hyperoxia have no lasting effect on respiratory control if presented after the second postnatal week (6,56,57). The effects of developmental hyperoxia on normoxic ventilation are not consistent across studies, with different groups of rats showing either mild hyperventilation (10,56) or no persistent changes as adults (7,10).…”

“…If hyperoxia alters development of the carotid body by silencing its normal activity, it should be possible to rescue the HVR by experimentally increasing carotid body activity during the hyperoxic exposure. Indeed, rats given intermittent hypercapnia (0 or 7.5% CO 2 at 1-h intervals) throughout their exposure to perinatal hyperoxia achieved a greater adult HVR than rats exposed to hyperoxia alone (10). Because intermittent hypercapnia had no effect on the HVR in normoxia-reared rats, it is likely that hypercapnia increased carotid body activity and permitted normal, activity-dependent development.…”

Postnatal development of eupneic ventilation and metabolism in rats chronically exposed to moderate hyperoxia

“…Several studies have examined the normoxic ventilation of adult rats that had been reared in hyperoxia (60% O 2 ) for the first 1-4 postnatal weeks and subsequently maintained in room air (i.e., after 1-4 months of normoxic recovery). Normoxic ventilation was similar to that of age-matched control rats in some groups of rats (Wenninger et al, 2006; Bavis et al, 2007, 2011a), while the rats in other studies exhibited a mild hyperpnea and/or hyperventilation (generally <15% increase relative to controls; Ling et al, 1996; Bavis et al, 2007, 2008). Normoxic minute ventilation also tends to be normal in adult mice reared in hyperoxia (Dauger et al, 2003; Bavis et al, 2011a), but the respiratory pattern was altered in the mice in one study (i.e., slower, deeper breathing pattern following postnatal exposure to 65% O 2 ; Dauger et al, 2003).…”