Comparison of Responses to Methacholine and Cold Air in Patients Suspected of Having Asthma: Positive responses
Of previous studies comparing cold-air and methacholine challenges, three noted age and sex distributions. In two, 40 to 50 percent of the patients were female, as in our study; in the other, 11/13 were female. Our patients were, on average, older than those examined by other workers because we studied a substantial number of middle-aged and elderly patients. Because our lower age limit was 17 years, the large SD of Tables 1 and 2 reflect the inclusion of older patients. Although our methacholine-positive patients were significantly younger than those with PC20 ^8 mg/L, we doubt that this played a major role in our results. There were no significant cold response-related age differences in either group (Table 2), and many older patients had positive responses. Indeed, our oldest patient, a woman of 83, had positive results on both challenges. More info
Because we examined patients suspected of having asthma, as opposed to those with established asthma, our patients were in general less sensitive to methacholine than those of other comparative studies, which was the case when only patients with positive responses were considered. In all previous studies more than 50 percent of responsive subjects had PC20 <1.0 mg/ml, and less than a quarter had PC20 of 4 to 8 mg/ ml. In our series 17 of 63 methacholine responders had PC20 <1.0 mg/ml and 24 had PC20 —4 mg/ml. Our distribution of methacholine response was similar to that of Adelroth et al,2 who also studied patients with suspected as opposed to established asthma. The relative insensitivity of our subjects to methacholine did not account for the relatively poor correlation with cold-air challenge, however, since the scatter in the data did not vary with the level of PC). Although the mean response to cold air increased as PC20 decreased, the variance was wide at all levels (Fig 1).