Rapidly and slowly progressive neuromuscular disease: differences in pulmonary function, respiratory tract infections and response to lung volume recruitment therapy (LVR)

INTRODUCTION: Reduced lung volumes are a hallmark of respiratory muscle weakness in neuromuscular disease (NMD). Low respiratory system compliance (C(rs)) may contribute to restriction and be amenable to lung volume recruitment (LVR) therapy. This study evaluated respiratory function and the immediate impact of LVR in rapidly progressive compared to slowly progressive NMD. METHODS: We compared vital capacity (VC), static lung volumes, maximal inspiratory and expiratory pressures (MIP, MEP), C(rs) and peak cough flow (PCF) in 80 adult participants with motor neuron disease (‘MND’=27) and more slowly progressive NMDs (‘other NMD’=53), pre and post a single session of LVR. Relationships between respiratory markers and a history of respiratory tract infections (RTI) were examined. RESULTS: Participants with other NMD had lower lung volumes and C(rs) but similar reduction in respiratory muscle strength compared with participants with MND (VC=1.30±0.77 vs 2.12±0.75 L, p<0.001; C(rs)=0.0331±0.0245 vs 0.0473±0.0241 L/cmH(2)O, p=0.024; MIP=39.8±21.3 vs 37.8±19.5 cmH(2)O). More participants with other NMD reported an RTI in the previous year (53% vs 22%, p=0.01). The likelihood of having a prior RTI was associated with baseline VC (%predicted) (OR=1.03 (95% CI 1.00 to 1.06), p=0.029). Published thresholds (VC<1.1 L or PCF<270 L/min) were, however, not associated with prior RTI. A single session of LVR improved C(rs) (mean (95% CI) increase = 0.0038 (0.0001 to 0.0075) L/cmH(2)O, p=0.047) but not VC. CONCLUSION: These findings corroborate the hypothesis that ventilatory restriction in NMD is related to weakness initially with respiratory system stiffness potentiating lung volume loss in slowly progressive disease. A single session of LVR can improve C(rs). A randomised controlled trial of regular LVR is needed to assess longer-term effects.