Lung insufflation capacity in neuromuscular disease

Objective: To compare maximal passive lung insufflation capacity (LIC) with lung inflation by air stacking (to maximum insufflation capacity [MIC]) and with vital capacity (VC); to explore relationships between these variables that correlate with glottic function and cough peak flows (CPF); to demonstrate the effect of routine inflation therapy on LIC and MIC; and to determine the relative importance of lung inflation therapy as a function of disease severity. Design: Case series of 282 consecutive neuromuscular disease (NMD) clinic patients 7 yrs and older with VC < 70% of the predicted normal value. All cooperative patients meeting these criteria were prescribed thrice-daily air stacking and/or maximal passive lung insufflation to pressures of 40-80 cm H2O, and they underwent measurements of VC, MIC, LIC, and unassisted and assisted CPF on every visit. Results: Means +/- standard deviations for VC, MIC, and LIC were 1131 +/- 744, 1712 +/- 926, and 2069 +/- 867 ml, respectively, and, for unassisted and assisted CPF, they were 2.5 +/- 2.0 and 4.3 +/- 2.2 liters/sec, respectively, with all differences statistically significant (P < 0.001). MIC minus VC correlated inversely with LIC minus MIC (P = 0.01) and, therefore, with glottic function. Both MIC and LIC increased with practice (P < 0.001). Increases in LIC but not MIC over VC were greatest for patients with the lowest VC (P < 0.05). There were no complications of lung mobilization therapy. Conclusions: Passive lung insufflation can distend the lungs of patients with NMD significantly greater than air stacking, particularly when glottic and bulbar-innervated muscle dysfunction is severe. LIC, MIC, and VC measurements permit quantifiable assessment of glottic integrity and, therefore, bulbar-innervated muscle function for patients with NMD. The patients who benefit the most from insufflation therapy are those who have the lowest VC.