Sleep-disordered breathing and respiratory failure in acid maltase deficiency

Sleep-disordered breathing (SDB) and respiratory failure (RF) are complications of acid maltase deficiency (AMD), a rare hereditary myopathy.

To define the relationship between lung and respiratory muscle function, to establish incidence and patterns of SDB, and to determine daytime predictors of SDB.

Sitting and supine lung and respiratory muscle function tests were obtained in 27 subjects with juvenile and adult AMD (aged 39 +/- 19 years) and compared with outcomes of polysomnography.

Ventilatory restriction was present in 17/27 subjects. Inspiratory vital capacity (IVC) correlated (p < 0.005) with peak inspiratory muscle pressure (PIP, R = 0.61), respiratory muscle strain (P(0.1)/P(0.1max), R = -0.68), and gas exchange by day (PaO(2): R = 0.71; PaCO(2): R = -0.64) and night (SaO(2): R = 0.73; P(tc)CO(2): R = -0.75). Diaphragm weakness (DW) was present in 13 subjects, 10 of whom had hypercapnic RF (PaCO(2) 65 +/- 7 mm Hg), and was associated with longer disease course. SDB was found in 13 subjects, 12 with DW. It was characterized by REM-sleep hypopneas that, as ventilatory restriction worsened, were complemented by hypoventilation (P(tc)CO(2) > 50 mm Hg) first in REM sleep, then in non-REM sleep (p < 0.005). SDB was predicted by DW (sensitivity 80%, specificity 86%) and nocturnal hypoventilation by IVC < 40% (sensitivity 80%, specificity 93%). Noninvasive ventilation, instituted for daytime respiratory failure or nocturnal hypoventilation, normalized daytime and nocturnal gas exchange (p < 0.005).

Vital capacity correlates with respiratory muscle function in AMD. Diaphragm weakness is the major cause of SDB and RF. SDB and nocturnal hypoventilation are predictable from daytime function tests.