Clinical and functional correlations of the difference between slow vital capacity and FVC

OBJECTIVE: To evaluate the relationship that the difference between slow vital capacity (SVC) and FVC (DeltaSVC-FVC) has with demographic, clinical, and pulmonary function data. METHODS: This was an analytical cross-sectional study in which participants completed a respiratory health questionnaire, as well as undergoing spirometry and plethysmography. The sample was divided into two groups: DeltaSVC-FVC >/= 200 mL and DeltaSVC-FVC /= 200 mL. The use of an SVC maneuver reduced the prevalence of nonspecific lung disease and of normal spirometry results by revealing obstructive lung disease (OLD). In the final logistic regression model (adjusted for weight and body mass index > 30 kg/m2), OLD and findings of air trapping (high functional residual capacity and a low inspiratory capacity/TLC ratio) were predictors of a DeltaSVC-FVC >/= 200 mL. The chance of a bronchodilator response was found to be greater in the DeltaSVC-FVC >/= 200 mL group: for FEV1 (OR = 4.38; 95% CI: 1.45-13.26); and for FVC (OR = 3.83; 95% CI: 1.26-11.71). CONCLUSIONS: The use of an SVC maneuver appears to decrease the prevalence of nonspecific lung disease and of normal spirometry results. Individuals with a DeltaSVC-FVC >/= 200 mL, which is probably the result of OLD and air trapping, are apparently more likely to respond to bronchodilator administration.