Effects of Air Stacking on Dyspnea and Lung Function in Neuromuscular Diseases

Objective: To investigate whether the decrease in dyspnea in neuromuscular diseases after air stacking (AS) occurs mostly in patients with decreased inspiratory muscle force and ensuing chest wall restriction or heterogeneous ventilation across the lungs. Design: Interventional, before-after study. Setting: A neurorehabilitation inpatient and outpatient center. Participants: Fifteen consecutive adult patients affected by neuromuscular diseases (N=15). Interventions: AS treatment. Main Outcome Measures: Patients had vital capacity (VC) and sniff nasal inspiratory pressure (SNIP) measured. We measured Borg score, oxygen saturation, and ventilation heterogeneity across the lung as estimated from the difference between respiratory resistance at 5 and 19 Hz (R_5-19) with the forced oscillation technique before and 5, 30, 60, and 120 minutes after applying AS. Results: Before AS, Borg score was significantly related to R_5-19 (r² 0.46, P<.05) but not to VC % predicted, SNIP % predicted, and time since symptom onset. After AS, average Borg score gradually decreased (P=.005), whereas inspiratory flow resistance at 5 Hz, R_5-19, and inspiratory reactance at 5 Hz tended to improve, despite not reaching statistical significance. The decrease in dyspnea at 60 and 120 minutes after AS significantly correlated with baseline R_5-19 (r² 0.49, P<.01 and r² 0.29, P<.05, respectively), but not with VC % predicted, SNIP % predicted, time since symptom onset, and clinical severity score for patients affected by amyotrophic lateral sclerosis. Conclusions: These findings suggest that dyspnea in neuromuscular diseases is related to heterogeneous ventilation rather than inspiratory muscle force and/or lung volumes decrease. Restoring ventilation distribution across the lungs with AS appears to improve dyspnea.