The aim of the study was to investigate the effects of nasal histamine on the intensity of cough reflex and the effects of intensified nasal breathing following the nasal histamine challenge on cough sensitivity (CS) in humans. 20 volunteers (mean age 23, nonsmokers, no history of nasal or respiratory system diseases and atopy) were recruited to the study. Baseline CS was determined in all subjects. 2 days later the subjects (n = 20) were challenged with nasal histamine (8 mg/ml, 0.1 ml) and the number of coughs was determined after four consecutive single-breath inhalations of capsaicin C2 concentration during the period of the most intensive nasal symptoms (sneezing, itching of the nose). The same capsaicin C2 challenge was performed after nasal saline challenge two days later. One week later CS was determined after nasal histamine challenge with subsequent 10 min of intensified breathing (5-6 sniff-like aspirations to total lung capacity per minute) through the nose and mouth in randomized order in ten volunteers, and with a two-day interval between the challenges. The same manoeuvres after intranasal saline challenge were performed in volunteers of the control group (n = 10). The number of coughs after nasal histamine was significantly higher than that after intranasal saline challenge (8(6-10) vs 5(3-7); p = 0.038(. CS was not significantly different between the baseline challenge and challenges after nasal histamine followed by the intensified nasal and mouth breathing ((2.21 (1.8-2.62) vs 2.04 (1.57-2.51) vs 2.05 (1.6-2.5) log(10) of capsaicin concentration in mumol.l(-1); p = 0.09).
Conclusions: During the period of maximum nasal symptoms after nasal histamine challenge the cough response to inhaled capsaicin was enhanced. Capsaicin cough sensitivity measured after a 10-min. intensified nasal breathing after nasal histamine challenge, compared to a previous measurement of CS, remain unchanged.