Research Program Area: Health & Exposure
We found that small but statistically significant losses in lung function (forced expired volume in one second, FEV1) resulted from exposure to ozone (O ) for 4 hr including exercise for 50% of the time at a ventilation rate averaging 20 1/min. These O3 related losses were not clearly different between volunteers with severe chronic obstructive pulmonary disease (COPD) and otherwise similar healthy older men. However, any measurable loss provokes some concern in patients with severe COPD, because their lung function is greatly diminished by the disease and is impaired additionally by the effects of exercise. Thus the observed lung function losses from O3 must be considered clinically significant for COPD patients. Prudent medical management would require that they avoid O3 exposures capable of causing such effects. The experimental O2 exposure caused no meaningful change in specific airway resistance (SRaw), and small non-statistically-significant increases in reported symptoms. Small equivocally significant decreases in arterial blood oxygen saturation (SaO2) were more apparent in the middle or O3 exposure periods than at the end.
Others' previous studies of healthy older adults exposed to O3 showed responses roughly similar to what we observed (smaller that younger subjects' responses), with roughly similar cumulative O3 doses delivered by shorter exposures at higher concentrations. The present findings in COPD subjects contrast with previous studies of COPD subjects, which showed no clear lung function changes. The difference is explainable in that previous COPD studies employed shorter exposure with cumulative inhaled doses at least 35-40% lower that ours. Previous studies also may have included predominantly chronic bronchitic subjects, who are suspected to be less responsive than this study's subjects with COPD involving substantial emphysema.
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