Bronchial hyperirritability in healthy subjects after exposure to ozone

We studied the effect of a 2-hour exposure to 0.6 ppm of ozone on bronchial reactivity in 8 healthy, nonsmoking subjects by measuring the increase in airway resistance (Raw) produced by inhalation of histamine diphosphate aerosol (1.6 per cent, 10 breaths). Before exposure to ozone, histamine increase the mean Raw from 1.2 to 1.8 cm H2O per liter per sec. Immediately after exposure to ozone, the mean baseline Raw was unchanged, but the mean response to histamine was significantly greater than the pre-ozone response (Raw = 3.3 cm H2O per liter per sec; P less than 0.05). For the group, this increase disappeared 1 day after exposure to ozone, although 2 subjects still had a significantly increased response to histamine for more than 1 week after exposure. In 4 subjects, pretreatment with atropine sulfate aerosol (0.1 to 0.2 mg per kg of body weight) blocked the increase in Raw produced by histamine after exposure to ozone. We concluded that brief exposure to 0.6 ppm of ozone produces bronchial hyperirritability via cholinergic postganglionic pathways, probably by damaging airway epithelium and thereby sensitizing bronchial irritant receptors.