Cold air as a bronchial provocation technique. Reproducibility and comparison with histamine and methacholine inhalation.
Bronchial provocation testing with cold air was carried out on 36 asthmatic and 13 normal subjects in order to assess the reproducibility and clinical relevance of the technique as a test of airways reactivity. Sixteen subjects underwent repeat testing after an interval of two to three weeks. Using a least squares linear regression analysis, the technique was highly reproducible, with a correlation of r = 0.93 (p less than 0.001). The 21 asthmatic subjects who had exercise-provoked symptoms required a significantly lower level of ventilation of cold air to produce a 35 percent drop in specific airways conductance (PD35) than did those who had no exercise-induced asthma (33.9 L min-1 vs 45.8 L min-1; p less than 0.02). Subjects requiring no regular treatment for their asthma had a geometric mean PD35 of 62.6 L min-1, significantly higher than those requiring inhaled therapy (44.9 L min-1; p less than 0.005). Subjects requiring oral in addition to inhaled treatment had the lowest PD35 (23.6 L min-1; p less than 0.02). Atopic status did not appear to influence the response. There was a strong correlation between the PD35 to cold air and to histamine (r = 0.92; p less than 0.001) and between the PD35 to cold air and to methacholine (r = 0.86; p less than 0.001). The three techniques of assessing bronchial reactivity were equally successful in separating the normal and asthmatic groups. The results indicate that cold air provocation may be reliably and reproducibly used to assess bronchial reactivity. The use of a naturally-occurring stimulus of asthma in all subjects has great potential as an investigational technique.