Phrenic motor output following acute hyperbaric oxygen exposure

We studied adult male rats to determine if phrenic motor output is altered following acute hyperbaric oxygen (HBO) pretreatment. Rats were treated with 1-h of 100 % O₂ at 2 atmospheres (HBO, n = 12) or 21 % O₂ at 1 atmosphere (normoxia, n = 12) and then anesthetized and ventilated to enable phrenic nerve recordings. Baseline phrenic output and blood pressure were similar between groups. Sixty minutes after exposure to acute intermittent hypoxia (AIH), inspiratory phrenic burst amplitude was +66 ± 47 (HBO) and +43 ± 13 % baseline (normoxia). Thus, both groups expressed phrenic long-term facilitation, pLTF (time effect, P = 0.008). The pLTF magnitude had a larger coefficient of variation after HBO (71 %) vs. normoxia (30 %). This resulted from a bimodal data distribution, with 4 of 12 HBO rats showing pLTF > +70 % baseline (vs. 0 of 12 normoxia). We conclude that acute HBO does not impact baseline phrenic output in this preparation, but further study of HBO and phrenic neuroplasticity is warranted.