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 (Delta SVC-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: Delta SVC-FVC >= 200 mL and Delta SVC-FVC < 200 mL. The intergroup correlations were analyzed, and binomial logistic regression analysis was performed. Results: The sample comprised 187 individuals. In the sample as a whole, the mean Delta SVC-FVC was 0.17 +/- 0.14 L, and 61 individuals (32.62%) had a Delta SVC-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/m(2)), OLD and findings of air trapping (high functional residual capacity and a low inspiratory capacity/TLC ratio) were predictors of a Delta SVC-FVC >= 200 mL. The chance of a bronchodilator response was found to be greater in the Delta SVC-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 Delta SVC-FVC >= 200 mL, which is probably the result of OLD and air trapping, are apparently more likely to respond to bronchodilator administration.