Use of isovolume flow curves in the detection of exercise-induced bronchospasm

A simple 9-min progressive cycle ergometer test revealed exercise-induced bronchospasm in 23 of 29 asthmatic subjects (80%) in terms of a 15% decrement in the isovolume forced expiratory flow rate at 50% of the baseline vital capacity (Vmax iso 50%VC). A similar percentage was detected by the Vmax iso 60% TLC (78%), but that found with the FVC (35%) and FEV1.0 (48%) was somewhat lower The maximum change of Vmax iso 50%VC following exercise in normal subjects was -5.2 +/- 2.1%. The Vmax iso 50%VC thus combines sensitivity with specificity, and seems a very suitable procedure for routine clinical use. Asthmatics showing a positive reaction to this test were distinguished by poor pre-exercise lung function.