Controlled exposures of volunteers with chronic obstructive pulmonary disease to sulfur dioxide

Twenty-four volunteers with chronic obstructive pulmonary disease (COPD) were exposed to sulfur dioxide (SO2) at 0, 0.4, and 0.8 ppm in an environmental control chamber. Exposures lasted 1 hr and included two 15-min exercise periods (mean exercise ventilation rate 18 liter/min). Pulmonary mechanical function was evaluated before exposure, after initial exercise, and at the end of exposure. Blood oxygenation was measured by ear oximetry before exposure and during the second exercise period. Symptoms were recorded throughout exposure periods and for 1 week afterward. No statistically significant changes in physiology or symptoms could be attributed to SO2 exposure. Older adults with COPD seem less reactive to a given concentration of SO2 than heavily exercising young adult asthmatics. This may be due to lower ventilation rates (i.e., lower SO2 dose rates) and/or to lower airway reactivity in the COPD group.