Plasiticity in Normoxic Ventilation and Apnea Frequency in Neonatal Rats Exposed to Chronic Hyperoxia

Abstract

Rats chronically exposed to hyperoxia exhibit hypopnea and lower metabolic rates when returned to room air (e.g., Bavis et al. Respir Physiol Neurobiol 198: 1–12, 2014), but we have not previously measured ventilation and metabolism simultaneously in the same individuals. In this study, we assessed these characteristics in 4–5 and 13–14 day old rats (i.e., P4–5 and P13–14) that were reared in 21% O2 (Control) or 60% O2 (Hyperoxia) from birth; ventilation and O2 consumption rates were measured via head‐body plethysmography paired with continuous monitoring of expired gas concentrations. The ventilation‐to‐O2 consumption ratio was lower in Hyperoxia rats at P4–5 (37.6±1.9 vs. 48.9±3.3 in Control; mean±SEM, P<0.01) and at P13–14 (24.3±1.3 vs. 31.7±2.9 in Control; P=0.04), consistent with hypoventilation. We also quantified the frequency and duration of apneas during the 30 minute recording period. When apnea was defined as a respiratory pause twice the average breath duration (TTot), apnea duration tended to be longer in Hyperoxia rats at P4–5 (1.87±0.15 s vs. 1.48±0.08 s in Control; P=0.03); apnea durations were not different between groups at P13–14. However, this analysis may be confounded by a significantly lower breathing frequency (and thus longer TTot) in Hyperoxia rats. Indeed, apnea durations were no longer different between groups when adjusted for TTot (ANCOVA, P=0.47). To confirm this result, we reanalyzed apneas at P4–5 using the average TTot for all Control rats (rather than for each individual) to identify apneas. This analysis yielded no significant difference in apnea duration between groups (P=0.20), but there was a greater apnea frequency in P4–5 Hyperoxia rats (0.8±0.2 apneas min−1 vs. 0.4±0.1 apneas min−1; P=0.04). We conclude that chronic hyperoxia causes a persistent hypoventilation in neonatal rats that may be accompanied by a modest increase in apnea frequency, but these effects generally diminish with age.Support or Funding InformationSupported by NIH grant P20 GM‐103423 (Maine INBRE).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.