Simplified eucapnic voluntary hyperventilation challenge.

A simplified scheme for eucapnic voluntary hyperventilation ( EVH ) is described that requires only that a source of dry gas containing 5% CO2, 21% O2, and 74% N2 be hyperventilated at 40 L/min or greater. Refrigeration or measurement of end tidal CO2 is not required. When the ventilation pattern of a standardized treadmill exercise challenge in a group of exercise-sensitive asthmatics breathing dry air was matched according to this EVH procedure, the magnitude of the resultant bronchospasm and the exclusive nature of the postchallenge refractory period were similar, since patients in both cases were still fully responsive to methacholine. It is concluded that such an EVH challenge may be used to reproduce the bronchial heat and water fluxes that occur with exercise challenge as well as the consequential challenge-specific refractoriness that follows.