Effects of acute allergen exposure on posture-induced changes in airway responsiveness to methacholine in asthma

The influence of an allergen challenge on recumbency induced changes in airway responsiveness to methacholine was documented in seven nonsmoking subjects with stable mild asthma (3M, 4F).

All subjects spent four hours (8 to 12 AM) in the supine position before and 24 hours after an allergen challenge that induced a dual asthmatic response. FEV1 was measured hourly in the supine position and a methacholine challenge was done in the sitting position before and after each 4-hour period. None used bronchial antiinflammatory drugs before or during the study.

The mean maximal fall in FEV1 (+/- SEM) was 31.0 +/- 1.1% within one hour of the last allergen inhalation and 27.5 +/- 4.9% between two and eight hours later. Presupine/postsupine session FEV1 (%pred +/- SEM) was unchanged either at baseline or postallergen challenge sessions, with values of 89.3 +/- 2.7/88.3 +/- 5.1 and 86.6 +/- 4.2/87.4 +/- 5.7. Presupine/postsupine PC20 methacholine was slightly reduced but this did not reach statistical significance (P > .05), with a mean PC20 (mg/mL) of 0.83 +/- 1.44/0.52 +/- 1.46 (preallergen session); 0.55 +/- 1.44/0.39 +/- 1.37 (postallergen challenge session). This delta PC20 (baseline/post-session) did not differ between the two sessions (P > .05). The delta PC20 was not correlated with the magnitude of the late asthmatic response to allergen nor the postallergen increase in airway responsiveness.

We conclude that an acute allergen challenge does not significantly increase recumbency-induced changes in airway response to methacholine in patients with mild asthma. The possibility of a significant influence of pro-inflammatory stimuli on recumbency-induced changes in bronchomotor tone in more severe patients or if the stimulus is repeated should be further assessed.