Skeletal Muscle Morphology and Aerobic Capacity in Patients with Obstructive Sleep Apnoea Syndrome

BACKGROUND: Despite the fact that patients with obstructive sleep apnoea syndrome (OSAS) often have symptoms at the level of skeletal muscle such as fatigue, the question of whether the structural, cellular and functional properties of limb skeletal muscles are affected has not been fully examined. OBJECTIVE: The aim was to examine physiological and muscular parameters in patients with OSAS and to assess the relationship between these parameters and the clinical symptoms. METHOD: Eighteen patients with OSAS and 16 controls participated. Aerobic capacity was assessed using a submaximal test. Fibre type distribution and fibre area were analyzed on muscle biopsies taken from the tibialis anterior. The microvascularization was assessed using the following parameters: (1) the number of capillaries per fibre (CAF), (2) CAF per fibre area (CAFA), (3) capillary to fibre perimeter exchange (CFPE) index, which represents the interface between muscle fibre and capillaries, and (4) length of capillary/perimeter of the fibre (LC/PF) index or capillary tortuosity, which represents the percent of muscle fibre perimeter in contact with the wall of the microvessel. RESULTS: The OSAS group had significantly lower predicted relative maximal oxygen uptake (p = 0.0047) which was inversely correlated to the apnoea/hypopnoea index (AHI; r = -0.6, p = 0.017). There was a significantly higher CFPE index for slow type I fibres (p = 0.007) and fast type II fibres (p = 0.0126) and a significantly higher LC/PF index for type I fibres (p = 0.0003) and type II fibres (p = 0.0285) in OSAS patients compared to controls. CONCLUSION: OSAS patients have a higher muscle microvascularization and a lower aerobic capacity than controls. Furthermore the aerobic capacity was inversely correlated to AHI.