Daily hyperbaric oxygen therapy increases diaphragm electromyographic activity and alters diaphragm gene expression after cervical spinal cord injury.

Hyperbaric oxygen (HBO) therapy can enhance motor recovery when initiated shortly after spinal cord injury (SCI). HBO can also induce a biphasic ventilatory response that includes hypo- and hyperventilation, but this has not been evaluated after SCI. We studied adult Sprague-Dawley rats with cervical SCI to determine how an acute bout of HBO impacts diaphragm activation and to test the hypothesis that daily HBO treatment can accelerate recovery of diaphragm activation. Indwelling electromyogram (EMG) electrodes were placed in the mid-costal diaphragm prior to lateral mid-cervical contusion injury. Rats were treated with HBO (10 days, 1 h/day, 100% O2, 3 atm, n = 9) or normobaric normoxia (NORM, n = 9) beginning the day of SCI. EMG was recorded daily in freely behaving rats before and during HBO. The diaphragm EMG inspiratory burst rate and peak amplitude (ipsi- and contralateral to SCI) decreased during HBO (p < 0.05) on days 3-10. Daily HBO increased baseline (recorded prior to HBO on days 3-10) ipsilateral "minute EMG" output (area under curve x rate; p = 0.038). RNAseq evaluation of ipsilateral hemidiaphragm tissues harvested, from a separate cohort (n=4 per group) at day 11 revealed SCI-induced changes in gene expression related to muscle structure and function, some of which were normalized by HBO treatment. We conclude that acute exposure to HBO reduces diaphragm activity after cervical SCI, and daily bouts of HBO may increase the rate of diaphragm recovery.