Comparison of Responses to Methacholine and Cold Air in Patients Suspected of Having Asthma: Discussion
The patients we studied were referred to our laboratory to help establish the diagnosis of asthma. Nearly all were referred by the eight pulmonary specialists in our university group for symptoms such as cough and dyspnea, but there was no prospective agreement as to specific indications for inhalation challenge, nor were clinical data such as symptoms and signs collected in a systematic way. Therefore, the fact that 65 patients, about 46 percent of these tested, had negative results on both provocation tests cannot be interpreted beyond stating that there is a relatively high level of suspicion of airways hyperreactivity among physicians in our clinic.
It should be noted, however, that our results were very similar to those of Adelroth, et al2 in that both studies found that 45 percent of patients referred because of suspected asthma had positive results on methacholine challenge. This agreement suggests similar levels of suspicion regarding the diagnosis of asthma in the two clinics. Because we did not collect clinical data in a systematic way, we cannot compare these data with the results of bronchoprovocation tests. Our aim was to compare results of the different provocation tests. read more
Previous studies have compared responses to cold-air hyperventilation and methacholine challenge in asthma, and most found a distinctly better correlation than we did. Our study differed in several ways. First, it was larger. Second, it examined patients suspected of having asthma as opposed to established asthmatic and normal subjects. Third, our test protocol differed from those employed by most others; we did both tests on the same day in most patients, and we employed only one level of ventilation in our cold-air testing, not constructing dose-response curves by having our subjects breathe cold air at successively increasing levels of ventilation. We will consider these discrepancies, with particular emphasis on whether differences in patient selection and test protocol contributed to the scatter of results.