Refractory period to ultrasonic mist of distilled water: relationship to methacholine responsiveness, atopic status, and clinical characteristics.

Twenty asthmatic subjects had two successive methacholine challenges, two successive challenges with ultrasonically nebulized distilled water (UNDW) and an UNDW followed by methacholine on three separate days. Only ten subjects showed a refractory period to repeated UNDW stimulation. Prior stimulation with UNDW provoked increased methacholine responsiveness in the non-refractory group and a more rapid recovery from methacholine-induced bronchoconstriction in the refractory subset.