The influence of airway obstruction and respiratory muscle strength on maximal voluntary ventilation in lung disease

To assess the effects of airway conductance (Gaw) and respiratory muscle strength (RMS) on maximal voluntary ventilation (MVV), we studied 8 normal subjects (N), 8 patients with interstitial lung disease (ILD), and 16 with chronic airflow limitation (CAL). In the patients with ILD, RMS explains 83% of the variance in MVV (p < 0.005), but Gaw explains none. In the patients with CAL, Gaw and RMS explain, respectively, 65 and 34% of the variance in MVV (p < 0.02). Considering Gaw and RMS together increases the explained variance to 77% (p < 0.005). In groups CAL and N combined, Gaw and RMS explain 86% of the variance in MVV, with 71% explained by Gaw and 34% by RMS, which the other variable alone failed to explain (p < 0.005). When the data are normalized for age, sex, height, and lung volume, the influence of %RMS on %MVV is halved, but remains significant (p < 0.05). We conclude that RMS is a primary determinant of MVV in patients with ILD, and an important determinant in patients with CAL.