Physiological responses to diesel exhaust exposure are modified by cycling intensity

Background Outdoor exercisers are frequently exposed to diesel exhaust (DE) that contains particulate matter (PM) air pollution. How the respiratory and metabolic responses to exercise are affected by DE exposure and how these responses change with exercise intensity are unknown. Purpose This study aimed to determine the respiratory and metabolic responses to low- and high-intensity cycling with DE exposure containing high levels of PM. Methods Eighteen males age 24.5 ± 6.2 yr performed 30-min trials of low-intensity (30% of power at V˙O2peak) and high-intensity (60% of power at V˙O2peak) cycling as well as rest. Each trial was performed once while breathing filtered air (FA) and once while breathing DE (300 μg·m−3 of PM2.5) for a total of six trials, each separated by 7 d. During the trials, minute ventilation (V˙E), oxygen consumption (V˙O2), CO2 production (V˙CO2), RER, and perceived exertion for lungs (RPELungs) and legs (RPELegs) were measured. Work of breathing, respiratory muscle V˙O2, ratio of O2 consumption to power output, and gross efficiency were estimated. Results The RER was significantly lower (0.02 lower, P = 0.008), and the RPELungs (0.9 greater, P = 0.001) and the RPELegs (0.6 greater, P = 0.017) were significantly greater, in DE compared with FA. During low-intensity exercise, V˙E (44.5 ± 8.9 vs 40.5 ± 8.0 L·min−1, P < 0.001), V˙O2 (27.9 ± 5.4 vs 24.9 ± 4.4 mL·kg−1·min−1, P = 0.001), and V˙CO2 (25.9 ± 5.3 vs 23.5 ± 4.5 mL·kg−1·min−1, P = 0.006) were significantly greater in DE. This pattern was not seen during high-intensity cycling. Conclusions Respiratory and metabolic responses to low-intensity, but not high-intensity, cycling in DE exceed FA. Practically, the greater responses during low-intensity exercise in DE could have implications for individuals with cardiopulmonary disease. Also, the elevated RPE during DE could impair performance in self-paced exercise.