Slow vital capacity : differences between expiratory and inspiratory vital capacities

Introduction: Vital capacity (VC) can be determined through expiratory (EVC) or inspiratory maneuvers (IVC). It is fundamental for determination of lung volumes and its incomplete mobilization has repercussions on the detection of air trapping or pulmonary hyperinflation. VC is also essential for detection of airway obstruction through the FEV1/VC ratio. Aims: To determine the differences between EVC and IVC (EVC-IVC) according to ventilatory pattern; to characterize the FEV1/EVC and FEV1/IVC ratios; to study the effects of EVC or IVC on the detection of air trapping or pulmonary hyperinflation. Methods: The sample included 388 subjects of both genders. In half of the sample the VC was determined first by the EVC and then by the IVC and in the other half in the reverse order. The sample was divided into 3 groups: without ventilatory changes (normal), airway obstruction and pulmonary restriction. Results: The EVC-IVC parameter was greater than 200 mL in 34.8% of the normal group, 28.4% of the airway obstruction group and 22.4% of the pulmonary restriction group. The ratio FEV1/EVC Conclusions: The EVC and IVC maneuvers shouldn’t be considered interchangeable due to differences in the volume obtained for each of them. These differences consequently influence the interpretation of lung function results.