Respiratory muscle training in neuromuscular disease: long-term effects on strength and load perception

Purpose: Deterioration of respiratory muscle function in patients with neuromuscular disorders is primarily responsible for the high morbidity and mortality associated with these diseases. Methods: The potential benefit of respiratory muscle training (RMT) on preservation of respiratory muscle strength and respiratory load perception (RLP) was examined in 21 children (mean age: 12.2 +/- 1.8 yr [SD], 16 male) with Duchenne's muscular dystrophy or spinal muscular atrophy type III, and in 20 age-, weight-, and sex-matched controls. Subjects were randomly allocated to undergo incremental RMT with resistive inspiratory and expiratory loads for a period of 6 months (trained group, TR) or to perform similar exercises with no load (NT). Maximal static inspiratory (Pi(max)) and expiratory (Pe(max)) pressures and RLP (modified Borg visual analog scale 0-10) were assessed on two separate occasions before beginning of the training protocol, monthly throughout RMT duration, and every 3-6 months upon cessation of RMT for 1 yr. Results: In controls, no significant changes in maximal static pressures or load perception occurred during RMT or thereafter. Training in neuromuscular disorder (NMD) patients was associated with improvements in Pi(max) (mean Delta max: +19.8 +/- 3.8 cmH(2)O in TR vs +4.2 +/- 3.6 cmH(2)O in NT; P < 0.02) and in Pe(max) (mean Delta max: +27.1 +/- 4.9 cmH(2)O in TR vs -1.8 +/- 3.4 cmH(2)O in NT; P < 0.004). Similarly, RLP significantly decreased during the RMT period in TR (mean Delta: 1.9 +/- 0.3; P < 0.01) but did not change in NT (-0.2 +/- 0.2). In addition, with cessation of RMT, static pressures returned to pretraining values in TR within similar to 3 months. However, RLP was still improved after 12 months. Conclusions: We conclude that in children with NMD, although RMT-induced increases in expiratory muscle strength are rapidly reversible, long-lasting improvements in RLP occur and could be associated with decreased respiratory symptoms.