Research Program Area: Health & Exposure
We hypothesized, on the basis of epidemiologic and animal toxicologic findings, that exposure to ozone (03) in air pollution can acutely impair cardiovascular function in susceptible human populations. We tested this hypothesis in ten hypertensive and six healthy male volunteers aged 40-78 years. Each subject, after catheterization of the right heart and a radial artery, was exposed in an environmentally controlled chamber to filtered air (FA) on one day and to 0.3 ppm 03 on the following day, for three-hour periods with intermittent exercise. Relative to FA, 03 exposure induced little change in cardiac index, pressures and resistances in the central, pulmonary, or peripheral circulations, cardiac enzymes, homeostatic hormones (norepinephrine, epinephrine), or arterial oxygen saturation, as measured at rest after exposure. Stroke volume and central venous pressure showed small changes associated with 03 exposure, which were statistically but not clinically significant. During 03 exposure, heart rate increased relative to FA, even though ventilation rate did not increase. Post-03-exposure resting heart rate also increased. Ozone exposure elicited statistically and clinically significant respiratory effects, i.e., increased the mean alveolar-arterial oxygen gradient by 10 mm Hg (P < 0.01) increased respiratory symptoms slightly but significantly (P < 0.05) and decreased mean forced vital capacity and FEVl by ~5% (P < 0.01). These effects did not differ significantly between hypertensive and healthy subjects. This study, although limited by a non-ideal design and small sample, suggests that direct acute effects of moderate 03 exposure on cardiac function are unlikely in typical ambulatory healthy or hypertensive middle-aged and older men. However, 03 exposure can impair gas exchange, thereby indirectly increasing the hemodynamic load on the cardiovascular system. This, in turn, increases oxygen demands of a stressed myocardium, to a degree that may be clinically important in some patients with preexisting cardiopulmonary impairment.
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