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Filtered diesel exhaust may worsen allergy-induced lung impairment more than unfiltered

Filtered air pollution from diesel engines could make allergy-induced lung impairment worse than exposure to unfiltered diesel exhaust, according to new research from the University of British Columbia and the Vancouver Coastal Health Research Institute.

The study, co-authored by Denise Wooding, a master’s student in experimental medicine at UBC, was published online this week in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine.

This surprising result may be due to the fact that some particle-depletion technologies, including the one used by the researchers, increase the amount of nitrogen dioxide (NO2) in the exhaust. NO2, which is subject to national air quality standards, has been shown to impair lung function and may be a cause of asthma in children.

“We previously demonstrated that diesel exhaust augmented allergic responses as well as airflow declines in people who are genetically susceptible, but we wondered if removing particles from the exhaust would lessen these effects,” said senior study author Dr. Chris Carlsten, professor and head of respiratory medicine and the Canada Research Chair in Occupational and Environmental Lung Disease at UBC, and a Principal Investigator at the Centre for Heart Lung Innovation at St. Paul's Hospital. “The take-home message is that technologies that remove particulate matter from diesel exhaust cannot be simply assumed to be beneficial to health, especially in susceptible populations.”

For the study, researchers conducted a randomized, controlled study of 14 non-smoking adults who were sensitive to at least one of three common allergens. All participants at various times were exposed in a laboratory to air with just the allergen, the allergen plus diesel exhaust and the allergen plus filtered diesel exhaust. They all also breathed air with no diesel exhaust or allergen, which served as the control.

After each exposure, the participants underwent a commonly used test called a methacholine challenge to determine how a patient responds to an inhaled allergen. Neither the participants nor those conducting the study were aware of which exposure they had undergone before being tested. The researchers also measured numbers of white blood cells, which marshal the body’s immune response but can “overreact” to allergens, causing breathing problems.

The study found:

  • The particle-depleted diesel exhaust produced by HEPA filtration and electrostatic precipitation—a type of filtration that uses static electricity to remove soot and ash from exhaust fumes—generated higher NO2 levels than unfiltered diesel exhaust.
  • Exposure to filtered diesel exhaust and allergen impaired the amount of air participants could forcibly exhale in one second (FEV1) more than allergen alone and more than unfiltered diesel exhaust and allergen.
  • Increasing levels of white blood cells were associated with declining FEV1 scores, suggesting that white blood cells play a meaningful role in eliciting a reduction in lung function in the context of these exposures.
  • The effects of filtered diesel exhaust on lung function and on white blood cells was more pronounced in those participants who were genetically susceptible to oxidative stress, meaning an imbalance in free radicals and antioxidants in the body.

The study was funded by the Canadian Institutes of Health Research, WorkSafe BC, and the Allergy, Genes and Environment (AllerGen) Networks of Centres of Excellence.

This article originally appeared on the UBC News website.