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EFFECT OF OZONE EXPOSURE ON THE DISPERSION OF INHALED AEROSOL BOLUSES IN HEALTHY HUMAN SUBJECTS
Citation:
Keefe, M., W. Bennett, P. DeWitt, AND T. Gerrity. EFFECT OF OZONE EXPOSURE ON THE DISPERSION OF INHALED AEROSOL BOLUSES IN HEALTHY HUMAN SUBJECTS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-91/158 (NTIS PB91231266), 1991.
Description:
Acute exposure of humans to low levels of ozone are known to cause decreases FVC and increases sRaw. hese alterations in lung function do not, however, elucidate the potential for acute small airways responses. n this study we employed a test of aerosol dispersion to examine the potential effects of ozone on small airways in humans. wenty-two healthy non-smoking male volunteers were exposed to 0.4 ppm ozone for one hour while exercising at 20 l/min/m2 (BSA). rior to and immediately following exposure, tests of spirometry (FVC, FEV1, and FEF25-75) and plethysmography (Raw and sRaw) were performed. ubjects also performed an aerosol dispersion test before and after exposure. ach test involved a subject inhaling five to seven breaths of a 300 ml bolus of a 0.5 triphenyl phosphate (TPP) aerosol injected into a 2 l tidal volume. he bolus was injected into the tidal breath at three different depths: at depth A the bolus was injected after 1.6 l of clean air was inhaled from FRC, at depth 8 after 1.2 l; and at depth C after ut with inhalation beginning from RV. he primary measure of bolus dispersion was the expired half-width (HW). econdary measures were the ratio (expressed as percent) of peak exhaled aerosol concentration to peak inhaled concentration (PR), shift in the median bolus volume between inspiration and expiration (VS), and percent of total aerosol recovered (RC). hanges in pulmonary function following ozone exposure were consistent with previous findings. hen corrected for exercise, FVC, FEV1, and FEF25-75 all significantly declined (p<0.001, p<0.002, and p<0.03 respectively) with non-significant increases in Raw and sRaw. W significantly increased following ozone exposure relative to air exposure at all depths (17 ml p<0.05 at depth A, 56 ml p<0.00l at depth B, and 53 ml p<0.005 at depth C). f the other dispersion measures, PR and RC decreased significantly only at depth B (-4.9% p<0.001 and -3.9% p<0.05 respectively). W was only weakly correlated with spirometric measures accounting for less than 25% of the variance. alf-width was not correlated with Raw or sRaw. e conclude that the changes in aerosol dispersion seen with ozone exposure are related to changes in turbulent mixing and/or regional time constants in the small airways thus suggesting a possible ozone effect in that region of the lung.