Slow Vital Capacity: Differences Between the Expiratory Vital Capacity and the Inspiratory Vital Capacity

ABSTRACT

ABSTRACT Introduction: The vital capacity (VC) can be determined by means of the expiratory vital capacity (EVC) or the inspiratory vital capacity (IVC). Obtaining the highest VC volume is essential for the correct interpretation of lung function tests. Objectives: To determine the differences between the EVC and the IVC (EVC-IVC) according to the ventilatory pattern; to characterize the FEV1/EVC and FEV1/IVC ratios when an obstruction of the airways is detected; to study the effects of the EVC or IVC on the detec tion of air trapping or lung hyperinflation. Materials and Methods: Cross-sectional study. The sample included 388 individuals divided in 3 groups healthy, airway obstruc tion, and restrictive lung disease. In order to detect the airway obstruction, we studied the FEV1/EVC and FEV1/IVC ratios. The presence of air trapping or lung hyperinflation was determined by means of a lung volume test. The differences between the EVC and the IVC (EVC-IVC) according to the ventilatory pattern were grouped into classes. Results: In the normal group, there was an EVC-IVC difference of ≥ 200 ml in 34.8% of the individuals; in the airway obstruction group, 28.4%, and in the restrictive lung disease group, 22.4%. The FEV1/EVC ratio detected airway obstruction in 44.8% of the individuals, and the FEV1/IVC ratio in 39.4%. In patients with airway obstruction, the EVC maneuver determined the presence of air trapping in 21.6% of subjects and lung hyperinflation in 9.5%. The IVC maneuver showed 18.2% and 10.8%, respectively. Conclusions: The EVC and IVC should not be used as interchangeable maneuvers, considering the volume differences obtained with each one of them. Their results influenced the interpretation of lung function.