Inspiratory muscle dysfunction in patients with severe obstructive sleep apnoea.

Repetitive inspiratory effort against an obstructed airway and intermittent hypoxia may be deleterious to the inspiratory muscles in patients with obstructive sleep apnoea (OSA). We investigated muscular dysfunction by comparing the strength, endurance and fatigability of inspiratory muscles and knee extensors in patients with newly diagnosed severe OSA compared with matched controls. The measurements included strength and endurance tests of both muscles, and a fatigue trial with simultaneous surface electromyography of the diaphragm and the vastus lateralis during voluntary contractions and in response to magnetic stimulation. To our knowledge, this is the first investigation to assess peripheral muscle performance in severe OSA patients versus controls. Patients in the OSA group exhibited significantly lower strength and endurance in both muscles than the control group. The fatigue index decreased significantly exclusively in the inspiratory muscles of OSA patients. Magnetic stimulation-evoked compound muscle action potential latencies increased and the amplitudes decreased significantly in the diaphragm, but not in the vastus lateralis after a fatigue test in the OSA group. In conclusion, a significantly lower functional performance was shown for both inspiratory muscles and knee extensors in the OSA group. However, higher fatigability was only seen in the inspiratory muscles of patients with severe OSA.