Health effects of ozone exposure in asthmatics

To investigate whether ambient air quality standards for ozone adequately protect high-risk populations, we assessed pulmonary and biochemical responses of 22 asthmatic volunteers to 2-hour controlled exposures to ozone at concentrations approximating 0.2 ppm, with secondary stresses of heat and intermittent exercise. All subjects had physician-diagnosed asthma; clinically, they covered a range from minimal wheezing to persistent marked abnormality in forced expiratory performance. Control experiments included repeated sham exposures (to purified air with no ozone added) as well as brief exposures to the odor of ozone followed by purified air. No meaningful changes in forced expiratory measures, lung volumes, or single-breath N2 indices were found after ozone exposure relative to control. Symptoms, scored semiquantitatively, increased slightly but not significantly with exposure to ozone. Small but significant (P is less than 0.05) group mean blood biochemical changes occurred with exposure to ozone; these included increased glucose-6-phosphate dehydrogenase and lactate dehydrogenase activities, increased erythrocyte fragility, and decreased concentration of reduced glutathione. Hemoglobin concentration and acetylcholinesterase activity decreased with ozone and decreased to a lesser extent in control studies. Concentrations of ozone readily attainable in smog episodes thus appear to be capable of affecting blood biochemistry in at least some asthmatic persons, in the absence of obvious adverse pulmonary responses. Whether the biochemical effects represent harm to health or a normal response to stress remains to be determined.