Exhaled Breath Temperature in Asthmatics and Controls after Eucapnic Voluntary Hyperventilation and a Methacholine Challenge Test

Abstract

Background: It has been suggested that exhaled breath temperature (EBT) is increased in asthmatic subjects. Objectives: Our aim was to investigate EBT in asthmatics compared to healthy controls before and after eucapnic voluntary hyperventilation (EVH) and a methacholine challenge test (MCT). Methods: A total of 26 asthmatics and 29 healthy controls were included. Forced expiratory volume in 1 s (FEV₁), EBT and oral, axillary and auricular temperatures were measured before and after EVH and MCT. Results: FEV₁ % predicted (%p) was significantly lower in asthmatic subjects compared to healthy controls at all time points. EBT was significantly increased in all subjects 15-30 min after EVH and 5-45 min after MCT. Oral temperature displayed a similar pattern of increase, in contrast to axillary and auricular temperature, and correlated with EBT before and after both of the challenge tests. EBT after 5 min correlated with the largest drop in FEV₁%p after EVH in asthmatic subjects. No significant differences or changes in EBT were found when comparing asthmatics to healthy controls before or after any of the tests. Conclusions: EBT is increased after both EVH and MCT, possibly reflecting a vascular response. This is related to both the fall in FEV₁ and to oral temperature, suggesting an effect on the whole respiratory tract including the oral cavity. No differences in EBT are seen between asthmatics and healthy controls, indicating that the increase in EBT is mainly physiological rather than pathophysiological.