Bronchodilator response in residual volume in irreversible airway obstruction

BACKGROUND: Although airway obstruction, as defined by improvement of forced expiratory volume in one second (FEV1) and/or forced vital capacity (FVC), is irreversible in patients with COPD, they clearly seem to benefit from treatment with inhaled bronchodilators. AIMS: To assess the response pattern of residual volume (RV) compared to FEV1 after bronchodilation in patients with reversible and irreversible airway obstruction. METHODS: Changes in static lung volumes were compared with improvement in dynamic lung volumes in 396 consecutive patients undergoing reversibility testing with repeat bodyplethysmography. Reversibility was defined as improvement of FEV1 <200 ml and <12% after inhalation of fenoterol hydrobromide. RESULTS: Irreversibility was found in 297 out of 396 patients with airway obstruction. Except for total lung capacity (TLC), all parameters (residual volume [RV], vital capacity [VC], forced inspiratory vital capacity [IVC], forced vital capacity [FVC], forced expiratory volume in one second [FEV1] and the FEV1/VC ratio) showed statistically significant changes after bronchodilation in 396 patients. The multiple linear regression model adjusted for age, sex and BMI showed a non-linear relationship between DeltaFEV1 or DeltaVC compared to DeltaRV after bronchodilation. If the increase in DeltaFEV1 is lower than 0.1 L, DeltaRV remains constant. However, if the increase in DeltaFEV1 is more than 0.1 L, DeltaRV decreases too. The same is found at an increase in VC of 0.3 L. CONCLUSION: In summary, in patients with irreversible airway obstruction DeltaRV cannot be predicted by DeltaFEV1 or DeltaVC after bronchodilation. Therefore, spirometric assessment should be complemented by bodyplethysmography.