Neuromuscular Dysfunction and Cortical Impairment in Sleep Apnea Syndrome

PURPOSELower 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. METHODSTwelve OSA patients and 11 healthy controls performed intermittent knee extensions until task failure before and after 8 weeks of CPAP treatment or control period. Maximal voluntary contraction (MVC), voluntary activation (VA) and corticospinal excitability and inhibition assessed by single- and paired-pulse transcranial magnetic stimulation (TMS) were measured before and during the fatiguing task. RESULTSTime to exhaustion was lower in OSA (before CPAP treatment1008 ± 549 s; after CPAP treatment975 ± 378 s) compared to controls (before control period1476 ± 633 s; after control period1274 ± 506 s; p = 0.017). OSA patients had reduced MVC and VATMS compared to controls throughout the fatiguing task as well as increased intracortical inhibition (all p < 0.05). CPAP treatment did not induce any changes in neuromuscular function (p > 0.05 for all parameters). CONCLUSIONThis 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 following 8 weeks of CPAP treatment.