Sleep-disordered breathing and respiratory failure in acid maltase deficiency

Background: Sleep-disordered breathing (SDB) and respiratory failure (RF) a re complications of acid maltase deficiency (AMD), a rare hereditary myopat hy. Objective: To define the relationship between lung and respiratory musc le function, to establish incidence and patterns of SDB, and to determine d aytime predictors of SDB. Methods: 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. R esults: Ventilatory restriction was present in 17/27 subjects. Inspiratory vital capacity (IVC) correlated (p < 0.005) with peak inspiratory muscle pr essure (PIP, R = 0.61), respiratory muscle strain (P-0.1/P-0.1max, R = -0.6 8), and gas exchange by day (PaO2: R = 0.71; PaCO2: R = -0.64) and night (S aO(2): R = 0.73; PtcCO2: R = -0.75). Diaphragm weakness (DW) was present in 13 subjects, 10 of whom had hypercapnic RF (PaCO2 65 +/- 7 min Hg), and wa s associated with longer disease course. SDB was found in 13 subjects, 12 w ith DW. It was characterized by REM-sleep hypopneas that, as ventilatory re striction worsened, were complemented by hypoventilation (PtcCO2 > 50 min H g) 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, inst ituted for daytime respiratory failure or nocturnal hypoventilation, normal ized daytime and nocturnal gas exchange (p < 0.005). Conclusion: Vital capa city correlates with respiratory muscle function in AMD. Diaphragm weakness is the major cause of SDB and RF. SDB and nocturnal hypoventilation are pr edictable from daytime function tests.