MAXIMUM VOLUNTARY VENTILATION - SPIROMETRIC DETERMINANTS IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASE PATIENTS AND NORMAL SUBJECTS

The 12-s maximum voluntary ventilation (MVV) provides an estimate of the ventilatory reserves available to meet the physiologic demands of exercise. Earlier studies established a general relationship between MVV and FEV,. We hypothesized that the resting maximum inspiratory flow rate (MIFR) also serves as a clinically useful predictor of the MVV. A total of 105 subjects, 45 women and 60 men (age 57 +/- 5 yr, mean +/- SD), with expiratory impairment categories of severe (n = 26), moderate (n = 22), mild (n = 18), and normal (n = 39) based on FEV1 (percentage of predicted), comprised the study samples. The ratio MVV/FEV1 averaged 41 +/- 7 overall. The FEV1 correlated with MVV in normal subjects (p < 0.05, r2 = 0.642) and patients (p < 0.05, r2 = 0.787) better than MIFR (p < 0.05, r2 greater-than-or-equal-to 0.480). MIFR joined with FEV1 in multiple linear regression to significantly improve the description of MVV: MVV L/min = 30.77FEV1 (L) + 5.94MIFR (L/s) - 4.77 (n = 105; p < 0.05, r2 = 0.849). The 95% confidence limits for MVV varied from 90 to 110% of predicted from the equation for this sample. The factors sex and impairment category did not reduce the unexplained variability in MVV after inclusion of FEV1 and MIFR as covariates in ANOVA (p > 0.05). Addition of MIFR to the model with FEV1 produced greater improvement in r2 than Pi(max). We conclude that MIFR, although secondary in importance to FEV1, is a significant determinant of MVV in patients with COPD and normal subjects. Estimation of MVV from FEV1 alone is less accurate than either direct measurement of MVV or estimation by inclusion of MIFR.