Neuromuscular Dysfunction and Cortical Impairment in Sleep Apnea Syndrome

Purpose Lower muscle strength and endurance have been reported in severe obstructive sleep apnea (OSA). Increased intracortical inhibition previously reported at rest in OSA suggests central neuromuscular impairments in these patients. We hypothesized that (i) OSA patients demonstrate reduced knee extensor strength and endurance due to central impairments and (ii) continuous positive airway pressure (CPAP) treatment improves neuromuscular function in these patients. Methods Twelve OSA patients and 11 healthy controls performed intermittent knee extensions until task failure before and after 8 wk of CPAP treatment or control period. Maximal voluntary contraction, voluntary activation and corticospinal excitability and inhibition assessed by single- and paired-pulse transcranial magnetic stimulation were measured before and during the fatiguing task. Results Time to exhaustion was lower in OSA (before CPAP treatment: 1008 549 s; after CPAP treatment: 975 +/- 378 s) compared with controls (before control period: 1476 +/- 633 s; after control period: 1274 +/- 506 s; P = 0.017). Obstructive sleep apnea patients had reduced maximal voluntary contraction and VA(TMS) compared with controls throughout the fatiguing task as well as increased intracortical inhibition (all P < 0.05). Continuous positive airway pressure treatment did not induce any changes in neuromuscular function (P > 0.05 for all parameters). Conclusions This study demonstrates that severe OSA patients have cortical impairments which are likely contributing to their reduced knee extensors strength and endurance. Both cortical impairments and neuromuscular function are not improved after 8 wk of CPAP treatment.