Oscillometry with or without spirometry for methacholine testing

Oscillometry is proposed as a complementary technique to spirometry for methacholine testing. Yet, before being prescribed in conjunction with spirometry, the extent by which the oscillometric readouts are influenced by spirometric maneuvers, especially the deep inspirations, will need to be determined. Herein, 16 very mild-to-mild asthmatics underwent two methacholine challenges on separate visits. On visit 1, the response was tracked by both oscillometry and spirometry, and the challenge was stopped at the provocative concentration causing a decline in forced expiratory volume in 1 s of at least 20%. The same concentration regimen was used on visit 2, but the response was tracked by oscillometry only. The results demonstrated that, except for resistance at 19 Hz, the changes in all oscillometric readouts were greater in the challenge without spirometry (p ≤ 0.02). The maximal change in reactance at 5 Hz (X_rs5), for example, was on average 75.8% greater in the challenge without than with spirometry (p = 0.025). The number of doubling concentrations of methacholine that was needed to reach an equivalent change in X_rs5 was also lower without concomitant spirometry (p = 0.0078). It is concluded that the deep inspirations that are required in spirometry to monitor the response to methacholine decrease the oscillometric response.