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 FEV₁. 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 ≥ 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.