REFRACTORINESS FOR ULTRASONICALLY NEBULIZED DISTILLED WATER AND HISTAMINE AFTER HISTAMINE CHALLENGE

Refractoriness for bronchial provocation frequently occurs after different challenge tests used to assess bronchial hyperresponsiveness in asthmatic patients. We investigated whether histamine inhalation could cause refractoriness for bronchoconstriction induced by ultrasonically nebulized distilled water (UNDW) and whether histamine causes tachyphylaxis for a subsequent histamine challenge in nine stable asthmatic patients. Preinhalation of histamine induced a significant diminished bronchoconstrictor response to UNDW cumulative dose of inhaled UNDW causing a 20% fall in forced expired volume in 1 s. The mean increased from 3.5 +/- 0.8 to 11.8 +/- 2.6 (SE) ml after histamine challenge (P < 0.01). However, repeated inhalation of histamine did not change the bronchoconstrictor response to histamine within 1 h after rechallenge (P > 0.5). The magnitude of refractoriness for UNDW inhalation after preinhalation of histamine was correlated to the bronchoconstrictor response to histamine (r = 0.73, P < 0.05). We conclude that inhaled histamine can induce refractoriness for UNDW, which seems to be related to the degree of bronchial hyperresponsiveness.