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 muscles 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 15 consecutive adult patients affected by neuromuscular diseases. INTERVENTION AS treatment. MAIN OUTCOME MEASURES subjects had vital capacity (VC) and sniff nasal inspiratory pressure (SNIP) measured. Borg score, oxygen saturation and ventilation heterogeneity across the lung as estimated from the difference between respiratory resistance at 5 and 19 Hz (R5-19) with the forced oscillation technique were measured before and 5, 30, 60, and 120 min after applying AS. RESULTS Before AS, Borg score was significantly related to R5-19 (r2 0.46, p< 0.05), but not to VC % pred, SNIP % pred, and time since symptom onset. After AS, average Borg score gradually decreased (p=0.005), whereas R5, R5-19, and X5 tended to improve, despite not reaching statistical significance. The decrease in dyspnea at 60 and 120 min after AS significantly correlated with baseline R5-19 (r2 0.49, p< 0.01 and r2 0.29, p< 0.05, respectively), but not with VC % pred, SNIP % pred, time since symptom onset, and clinical severity score for patients affected by amyotrophic lateral sclerosis. CONCLUSION 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.