Impaired hypoxic ventilatory response following neonatal sustained and subsequent chronic intermittent hypoxia in rats

- Neonatal sustained hypoxia prior to CIH attenuated the acute HVR.
- Neither sustained or CIH alone affected the HVR.
- Sustained periods of reduced O2 saturation should be avoided in neonates vulnerable to apnea and CIH.

Neonatal chronic intermittent hypoxia (CIH) enhances the ventilatory sensitivity to acute hypoxia (acute hypoxic ventilatory response, HVR), whereas sustained hypoxia (SH) can have the opposite effect. Therefore, we investigated whether neonatal rats pre-treated with SH prior to CIH exhibit a modified HVR. Rat pups were exposed to CIH (5% O2/5 min, 8 h/day) between 6 and 15 days of postnatal age (P6-15) after pre-treatment with either normoxia or SH (11% O2; P1-5). Using whole-body plethysmography, the acute (5 min, 10% O2) HVR at P16 (1 day post-CIH) was unchanged following CIH (67.9 ± 6.7% above baseline) and also SH (58.8 ± 10.5%) compared to age-matched normoxic rats (54.7 ± 6.3%). In contrast, the HVR was attenuated (16.5 ± 6.0%) in CIH exposed rats pre-treated with SH. These data suggest that while neonatal SH and CIH alone have little effect on the magnitude of the acute HVR, their combined effects impose a synergistic disturbance to postnatal development of the HVR. These data could provide important insight into the consequences of not maintaining adequate levels of oxygen saturation during the early neonatal period, especially in vulnerable preterm infants susceptible to frequent bouts of hypoxemic events (CIH) that are commonly associated with apnea of prematurity.