Bronchial response to hyperventilation of dry air at room temperature in normals and asthmatics

Abstract

The bronchial effects of three levels (25, 40 and 60 1 X min-1) of voluntary isocapnic hyperventilation of dry air at room temperature (20-22 degrees C) have been studied in 18 normal, non-atopic subjects and in 25 nonperennial asthmatics who were asymptomatic and whose airway obstruction at the time of the study was mild, with a peak expiratory flow rate of 6.1 +/- 1.5 (SD) 1 X s-1 vs a predicted 8.4 +/- 1.3 1 X s-1. The bronchial response was assessed by use of maximal expiratory flow-volume curves obtained before and 1, 5, 10 and 15 min after the 5 min hyperventilation challenge. In normal subjects, there was a minimal though significant (p less than 0.001; two-way analysis of variance) fall in maximal expiratory flows which did not increase with the level of hyperventilation and was not accompanied by a fall in forced vital capacity. The bronchial response of asthmatics differed from that in normal: the fall in maximal expiratory flows was significantly greater, associated with a significant fall in forced vital capacity and increased with the level of hyperventilation. Results in 10 asthmatics studied on two different study days were highly reproducible. Sensitivity and specificity are excellent (approximately equal to 1) for the 40 1 X min-1 hyperventilation challenge. Our results suggest that isocapnic voluntary hyperventilation of dry air at room temperature (20-22 degrees C) is a highly satisfactory screening test to detect bronchial hyperreactivity.