Comparison of Responses to Methacholine and Cold Air in Patients Suspected of Having Asthma: Results
Of the patients with negative methacholine responses, 12 responded to cold-air hyperventilation with decreases in FEVX that exceeded 10 percent, and in four patients the decrease was greater than 20 percent. These 12 patients did not differ significantly from the others in terms of age, sex, or baseline lung function values. Further, the level of ventilation achieved during cold-air testing did not differ significantly (Table 2), whether expressed in absolute terms or as a fraction of predicted MBC, calculated as FEVj X 35.
Of patients with positive methacholine responses, 17 had negative cold-air responses, 20 showed a decrement in FEVx from 10 to 19 percent with cold air, and 26 showed decreases of FEVx that exceeded 20 percent (Table 2). These subgroups did not differ significantly in terms of age, sex, or baseline FEVls and also did not differ significantly in terms of the ventilation achieved during cold-air testing, although there was a tendency for those with the greatest cold-air responses to have achieved the greatest levels of ventilation. in detail
Among patients who responded to methacholine, PC*) differed according to cold-air sensitivity. Patients with negative cold-air tests had a mean PCao of 4.76 mg/ml (SEM = 0.48), those with cold-air responses of 10 to 19 percent of control FEV! had a mean PC, of 3.45 mg/ml (SEM = 0.50), and those with cold-air responses of at least 20 percent of baseline FE Vx had a mean PC^ of 1.55 mg/ml (SEM = 0.29). The last figure was significantly different (p<0.05, unpaired t test) from either of the other two, which were not significantly different. There was a significant correlation between log PC20 and change in FEWl after cold-air testing (r = – .53, p<0.001) among methacho-line-positive patients (Fig 1). The relationship remained significant when methacholine-negative, cold-air-positive patients were added by arbitrarily assigning them a PC20 of 10 mg/ml (Fig 1, r= —0.48, p<0.001).
Table 2—Cold-Air Responses and Ventilation Achieved During Cold-Air Tests
|Dose||N||Age, yr||FEVj, % pred||Ve/MBC,%t||Ve,L/min|
|PCao >8 mg/ml|
|PCao —8 mg/ml|
Figure 1. Relationship of methacholine sensitivity to cold-air sensitivity. Ordinate, methacholine PC*, on a logarithmic scale; abscissa, change in FEV, noted with cold-air challenge. Each point represents a single patient; closed circles, those with PC*, ^8 mg/ ml; open circles, those with PC* >8 mg/ml who have been arbitrarily assigned PC*,10 mg/ml.