Drs. Kang and Bach1raise several interesting methodologic issues regarding use of the mechanical in-exsufflator (MI-E) in patients with neuromuscular disease. As noted, the use of air stacking has been shown to preserve inspiratory capacity in adults with neuromuscular weakness. The degree to which such a maneuver affects lung or chest wall mechanics in young children with neuromuscular disease, however, is not known. Unlike adults with neuromuscular weakness who have abnormally stiff chest walls,2–3 children with neuromuscular weakness studied up to 4 years of age demonstrate abnormally high chest wall compliance.4 Those authors speculated that relative immobility and reduced exposure to normal mechanical stress during growth and development of chest wall structures contributes to the abnormally high compliance. The effects of passive deep lung inflation, therefore, could have important effects on both maturation and function of the chest wall and lung in children with neuromuscular weakness, and should be carefully studied. We sought to demonstrate that the use of the MI-E was safe, well tolerated, and effective in preventing pulmonary complications in pediatric patients with neuromuscular disease. We did not assess changes in lung or chest wall mechanics resulting from MI-E use in this group of patients as part of our study, but agree that similar studies would be useful. Additionally, 86% of our patients were receiving assisted positive pressure ventilation during the observation period of our report. Thus, any effect of air stacking with the MI-E would have been difficult to distinguish from the respiratory system stretch that patients received all or part of the day from their mechanical ventilatory support.