[Sleep-disordered breathing in neuromuscular diseases]

Sleep-disordered breathing is common in neuromuscular diseases but remains poorly defined in its relationship to daytime respiratory function.

We prospectively compared supine lung and respiratory muscle function with results of polysomnography/capnometry in 35 patients with progressive myopathies (age 32.5 +/- 15 years).

32/35 patients had restrictive ventilatory defect, 9/32 had hypercapnic respiratory failure by day (PaCO(2) 66.0 +/- 15.7 mm Hg). Supine inspiratory vital capacity (IVC(S)) correlated with maximal inspiratory muscle pressure (R = 0.75), respiratory muscle strain (P0.1/PImax, R = - 0.68), and daytime blood gases (p < 0.005 for all). SDB in the way of REM-sleep hypopneas, circumscribed hypoventilation episodes and sleep-stage independent continuous hypoventilation (PtcCO(2) > 50 mmHg > 50% of sleep time) was common at IVC(S)< 60% pred, and preceded daytime hypercapnia. IVC(S) correlated with nocturnal SaO(2) (R = 0.64), PtcCO(2) (R = - 0.87), percent light sleep (R = 0.67) and deep sleep (R = - 0.76). IVC(S) correlated only marginally with respiratory disturbance index (total sleep, R = - 0.45; REM-sleep, R = - 0.44). IVC(S) < 60% was 96% sensitive, 78% specific for presence of SDB. IVC(S) < 20 % was 89% sensitive, 96% specific for daytime hypercapnia.

IVC(S) correlates with respiratory muscle function, daytime and nocturnal blood gases, and is highly predictive of SDB and daytime hypercapnia.