A total of 231 normal male human subjects were exposed for 4 hr to air, ozone, nitrogen dioxide, or sulfur dioxide; to sulfuric acid, ammonium bisulfate, ammonium sulfate, or ammonium nitrate aerosols; or to mixtures of these gaseous and aerosol pollutants. Only one concentration of each pollutant was used. This study, therefore, represents a preliminary survey, intended to allow direct comparison of studies to plan future research. During exposure each subject had two 15-min exercise sessions on a treadmill at 4 mph and 10% grade. Environmental conditions were mildly stressful, i.e., temperature = 30 degrees C and relative humidity = 60%. A battery of 19 measurements of pulmonary function was performed just prior to exposure (air control); 2 hr into the exposure, following the first exercise session; 4 hr into the exposure, following the second exercise session; and 24 hr after exposure. Significant differences were noted in specific airway resistance (SRAW), forced vital capacity (FVC), and forced expiratory flow at 50% of FVC (FEF50) and in related measurements in those experimental groups exposed to ozone or to ozone plus aerosols. None of the aerosols alone, nitrogen dioxide or sulfur dioxide alone, or mixtures of nitrogen dioxide or sulfur dioxide with aerosols produced significant effects. A distribution analysis of subject responsivity to ozone gave a normal distribution among subjects not exposed to ozone, and a distribution shifted to the right and skewed to the right among those exposed to ozone alone or in mixture, with no evidence of bimodal distribution of ozone sensitivity.
Of 31 young, health male volunteers who participated in this study 15 were exposed to air (control) and 16 to 0.75ppm (2.15mg/m3) SO2 for 2 hr at 21 degrees C and 60% relative humidity. At the end of the first hour, the subjects exercised for 15 min on a treadmill at 6.4 kmph, with a 10% grade. Methods employed in evaluation of pulmonary function included body plethysmography, spirometry, and multigas rebreathing test. From the battery of 15 pulmonary function parameters, only the pattern of airway resistance changes was significantly altered by SO2 exposure, although spirometric parameters followed a similar pattern. Eight of the SO2-exposed ubjects, with one or more positive allergen skin tests, appeared to be significantly more reactive to SO2 than skin test-negative subjects. All subjects remained asymptomatic. The small number of changes observed appeared to be reversible and do not suggest a significant health hazard to normal human subjects exposed to SO2 under these conditions.
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