Analysis of Refractory Period after Exercise and Eucapnic Voluntary Hyperventilation Challenge

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Abstract
We compared specific airway conductance (SGaw) and the FEV1 after repetitive exercise or repetitive eucapnic voluntary hyperventilation (EVH) challenges. Replicate challenges were matched in terms of inspired air conditions and minute ventilations (E) in order to determine the degree of refractoriness after each type of challenge in patients with exercise-induced asthma. Ten patients exercised or hyperventilated dry, room temperature air at matched E on two study days. When the patient's FEV1 had returned to 90% of baseline or better, or at 3.75 h if FEV1 had not returned to 90% of baseline, patients repeated the identical exercise or the EVH challenge. Minimum FEV1 values expressed as a percent of predicted FEV1 after the first and second exercise challenges were 52 ± 16 and 58 ± 17, respectively, which were statistically different (p < 0.001; paired t test). Minimum FEV1 values after the first and second EVH challenges were 52 ± 13 and 59 ± 9% of predicted, respectively, which were also statistically different (p < 0.01; paired t test). Seven of 10 subjects demonstrated higher SGaw values after the second exercise challenge compared with the first challenge, whereas eight of 10 subjects showed higher SGaw values after the second EVH challenge compared with the first challenge. Paired t test analysis indicated that percent protection, measured by FEV1, was similar after either type of challenge. We conclude that replicate exercise or EVH challenges with similarly matched inspired air conditions and E induce similar degrees of refractoriness. The EVH challenge techniques should, therefore, serve as a good method for future studies of some of the underlying mechanisms of refractoriness after exercise-induced asthma.