Increased responsiveness to methacholine and histamine after challenge with ultrasonically nebulised water in asthmatic subjects.

Responsiveness to inhaled methacholine was compared before and 40-60 minutes after a challenge with ultrasonically nebulised water (UNH2O) in 16 asthmatic patients. The sensitivity to methacholine increased after UNH2O challenge (p less than 0.001). The mean dose of methacholine producing a 20% fall in forced expiratory volume in one second was 0.4 (95% confidence limits 0.2, 0.8) mumol, compared with 0.9 (95% confidence limits 0.5, 1.6) mumol in the first methacholine challenge. When the study was repeated in six asthmatic patients with histamine substituted for methacholine, five of the patients were significantly more sensitive to histamine after UNH2O challenge. It is concluded that challenge with UNH2O produces an increase in airway responsiveness.