Vital capacity and inspiratory capacity as additional parameters to evaluate bronchodilator response in asthmatic patients: a cross sectional study

BACKGROUND Bronchodilator response in patients with asthma is evaluated based on post-bronchodilator increase in forced expiratory volume in one second (FEV1) and forced vital capacity (FVC). However, the need for additional parameters, mainly among patients with severe asthma, has already been demonstrated. METHODS The aim of this study was to evaluate the usefulness of vital capacity (VC) and inspiratory capacity (IC) to evaluate bronchodilator response in asthma patients with persistent airflow obstruction. The 43 asthma patients enrolled in the study were stratified into moderate or severe airflow obstruction groups based on baseline FEV1. All patients performed a 6-minute walk test before and after the bronchodilator (BD). A bipolar visual analogue scale post-BD was performed to assess clinical effect. The correlation between VC and IC and clinical response, determined by visual analogue scale (VAS) and 6-minute walk test (6MWT), was investigated. RESULTS Patients in the severe group presented: 1) greater bronchodilator response in VC (48% vs 15%, p = 0.02), 2) a significant correlation between VC variation and the reduction in air trapping (Rs = 0.70; p < 0.01), 3) a significant agreement between VC and VAS score (kappa = 0.57; p < 0.01). There was no correlation between IC and the reduction in air trapping or clinical data. CONCLUSIONS VC may be a useful additional parameter to evaluate bronchodilator response in asthma patients with severe airflow obstruction.