Diesel Exhaust Has Limited Effect on Lung Function in Chronic Obstructive Pulmonary Disease
Presenter: Nafeez Syed
Fumes from diesel exhaust do not affect the lung function of patients with chronic obstructive pulmonary disease (COPD) any more than healthy individuals.
Diesel exhaust is a key source of traffic-related air pollution and can cause a range of problems from eye irritation to premature death. Epidemiologic evidence suggests a larger association for respiratory mortality than cardiovascular mortality. Controlled studies of pulmonary function and exercise performance show inconsistent findings, and little is known about the acute effects of traffic-related air pollution on cardiorespiratory responses to exercise in COPD patients.
Canadian researchers tested the hypothesis that diesel exhaust would more negatively impact exercise performance and ventilatory responses to exercise in COPD compared with healthy controls. In this double-blind, randomized, crossover, controlled exposure study, 11 healthy never-smokers and 9 ex-smokers with COPD were separately exposed to filtered air and diesel exhaust at a nominal concentration of PM2.5=300 µg/m3 for 2 hours over 3 visits, separated by a minimum of 4 weeks.
Individuals with mild-to-moderate COPD and healthy controls were well-matched for sex, height, mass, and body mass index, although participants with COPD were older (70 years) than controls (56 years) and less fit.
The participants were characterized by pulmonary function tests and an incremental exercise test every 2 minutes until exhaustion. They were then randomized for exposure in a controlled environmental chamber for 2 hours. During controlled exposures, they performed 2 bouts of cycling for 15 minutes at 30% of peak work rate to increase ventilation. Then the participants performed a constant work rate cycling test until exhaustion at 80% of peak cycle work rate within 2.5 hours of exposure.
Researchers used linear mixed-effects models to evaluate the main effects of diesel exhaust on exercise variables and Wilcoxon signed-rank test to compare exercise endurance time between exposures.
“Contrary to our hypothesis, healthy participants showed a greater decline in exercise endurance due to diesel exhaust. In these respiratory responses, both inspiratory duty cycle and operating lung volumes were significantly higher after exposure to diesel exhaust in healthy controls compared with their COPD counterparts,” said Nafeez Syed of The University of British Columbia & Centre for Heart Lung Innovation, St. Paul's Hospital, Vancouver, BC, Canada. There were no negative effects of diesel exhaust on any cardiorespiratory variables in COPD.
The study is limited by the small sample size, and non-residential pre-exposure could not be controlled.
In conclusion, Syed said: “Diesel exhaust did not have a significant adverse effect in mild-to-moderate COPD. We speculate that the negative effects of diesel exhaust in healthy individuals compared with COPD may be due to relatively greater deposition of diesel exhaust particles owing to higher absolute ventilation and possible bronchodilation during diesel exhaust exposure.”
Future work is needed to elucidate the precise mechanisms for the differing effects of diesel exhaust in healthy people versus COPD patients, he said.
Nafeez Syed has no disclosures.