To evaluate the effect of negative ionisation of inspired air on bronchial reactivity, 11 asthmatic children were challenged twice by exercise and 10 were challenged twice by histamine inhalation. The children breathed negatively ionised air (4 X 10(5) - 10 X 10(5) ions/cm3) or control room air in random order in a double-blind fashion. All challenges were matched in terms of basal lung function and the exercise tests were matched in terms of ventilation and respiratory heat loss. Exercise-induced asthma was significantly attenuated by exposure to negatively ionised air, the mean postexercise fall in one-second forced expiratory volume (FEV1) being 29% (SE 5%) of the initial value after the control and 21% (3%) after the ionised air test (p less than 0.02). Ten of the 11 subjects developed less exercise-induced asthma while breathing ionised air. Although the median dose of histamine (cumulative breath units) which caused a constant fall in FEV1 for each individual was higher with the ionised air challenge than with the control challenge the difference was not significant. Five of the 10 subjects were less sensitive to histamine and the other five more sensitive when breathing ionised air. It is concluded that negative ionisation of inspired air can modulate the bronchial response to exercise but the effect on the response to histamine is much more variable.
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