Bronchodilatation and the inspiratory flow volume curve.

The inspiratory flow volume curve is included in the spirometric tracing provided by most pulmonary function laboratories and is useful in assessing upper airway abnormalities. We analyzed the changes in peak inspiratory flow (PIF), forced inspiratory flow at 50% (FIF50), and forced inspiratory vital capacity (FIVC) that occur with bronchodilator challenge testing (3 puffs of a beta-agonist by metered-dose inhaler without a spacer device) in 145 consecutive patients. Fifty-five patients responded to bronchodilators with either a 12% or 200-mL change in FEV1 or FVC. All of these subjects produced forced expiratory maneuvers that fulfilled American Thoracic Society criteria or acceptability. The FIVC was the only inspiratory parameter that consistently showed a similar correlation to the bronchodilator responsiveness demonstrated by the FEV1 or FVC. With the reduction in air trapping, a 12% or 200-mL change in the FIVC is additional confirmatory evidence of bronchodilator responsiveness.