BRONCHIAL REACTIVITY TO ISOCAPNIC HYPERVENTILATION - RESULTS IN AN UNSELECTED POPULATION OF OUTPATIENTS WITH KNOWN OR SUSPECTED ASTHMA

Isocapnic hyperventilation with dry air is nearly as effective as with dry cold air, and appears to be a valuable screening test for bronchi al hyperresponsiveness. However some incidental factors such as precha llenge bronchoconstriction, level of hyperventilation, age and smoking habits have barely been examined or were investigated in small sample s of either normals or well-characterised asthmatics. In an inhomogene ous population of 186 outpatients with known asthma, 286 with suspecte d asthma and 32 normals, a single isocapnic hyperventilation challenge of 6-min duration was performed. There was a weak, but significant co rrelation between the degree of prechallenge airway function and the b ronchial response, assessed by the change in forced expiratory volume in 1 s (r = 0.27, p = 0.000) in known asthmatics, but not in patients with suspected asthma and in normals. No significant relation was foun d between the level of hyperventilation and the bronchial response whe n comparing the bronchial response to the single-dose hyperventilation test between the subjects (NS). Increasing age appears to be associat ed with an attenuation of the response in known asthmatics (r = 0.21, p = 0.004), but not in patients with suspected asthma. Smoking habits did not affect the bronchial response in this study. In conclusion, th e main finding is that there is a weak correlation between baseline ai rway obstruction and the subsequent response to isocapnic hyperventila tion, a slow decline in response with age and no increase in responsiv eness in smokers. Hence, isocapnic hyperventilation is a relatively ro bust test for assessing bronchial reactivity in an inhomogeneous popul ation of outpatients like ours.