EFFECT OF OZONE ON BRONCHIAL REACTIVITY IN ATOPIC AND NONATOPIC SUBJECTS

Abstract

The effect of exposure to O3 (0.6 ppm, 2 h) on bronchial reactivity was studied in 16 otherwise healthy, nonsmoking subjects with normal pulmonary function. On the basis of medical history and allergen skin testing, 7 subjects were classfied as nonatopic; 9, as atopic. Bronchial reactivity was assessed by measuring the increase in specific airway resistance (SRaw) produced by inhaling histamine or methacholine aerosol before and after sham exposure and after O3 exposure. Nonatopic subjects inhaled 10 breaths of histamine (16 mg/ml solution) and of methacholine (10 mg/ml solution); atopic subjects inhaled 10 breaths of histamine (8 mg/ml solution). In neither group of subjects was the response to histamine affected by sham exposure (P > 0.5). In the nonatopic subjects, the increase in SRaw produced by histamine (6.57 .+-. 1.43 cm H2O/l per s .cntdot. l, mean .+-. SEM) and by methacholine (8.94 .+-. 2.12 cm H2O/l per s .cntdot. l) after O3 exposure were significantly greater than after sham exposure (3.42 .+-. 0.64 and 3.62 .+-. 0.61 cm H2O/l per s .cntdot. l, respectively; P < 0.02). In the atopic subjects, the increase in SRaw produced by histamine after exposure to O3 (10.44 .+-. 3.32 cm H2O/l per s .cntdot. l) was also significantly greater than after sham exposure (4.02 .+-. 1.12 cm H2O/l per s .cntdot. l; P < 0.05). In each group, the increase in bronchial response to histamine or methacholine occurred at a time when baseline SRaw was not changed significantly by O3 exposure, and the increase in bronchial responses returned to control values by the following day. In both groups, premedication with atropine sulfate aerosol (0.1 mg/kg body wt) decreased baseline SRaw and prevented the increase in bronchial response to histamine that occurred after O3 exposure. Brief exposure to 0.6 ppm of O3 increases bronchial reactivity via cholinergic, postganglionic pathways and inducibility of bronchial hyperreactivity by exposure to O3 is not related to atopy.