Feb. 18, 2008 One day doctors may recommend using high efficiency particle air (HEPA) filters along with weight loss, smoking cessation, and exercise to improve cardiovascular health, according to researchers in Denmark. In a recent study, they found that using HEPA filters for just two days significantly improved a key measure of cardiovascular health in healthy, non-smoking elderly individuals.
"Reduction of particle exposure by filtration of recirculated air for only 48 hours improved the microvascular function (MVF) in healthy elderly citizens," said Professor Steffen Loft, M.D., D.M.Sc., of the Institute of Public Health in Copenhagen. "This suggests that indoor air filtration represents a feasible means of reducing cardiovascular risk." Abnormal function of the inner lining of small vessels is known to be a predictor of dangerous or possibly fatal cardiovascular events.
The researchers measured MVF and ambient airborne particles in the homes of 21 non-smoking couples aged 60-75 who lived close to heavily trafficked roads. Each couple used air purifiers for two 48-hour periods. During one period, the purifier was equipped with a HEPA filter, and during the other, it ran without it, so that each individual served as his or her own control. The size distribution and number concentration of indoor air particles in each home were continuously monitored.
The researchers then assessed each individual's MVF using a noninvasive finger sensor. Several secondary endpoints were studied in blood and urine samples to assess possible mechanisms of action: markers of inflammation, hemostasis, and oxidative stress.
"Our main finding was a significant improvement in the function of small finger blood vessels after reduction of indoor air particles. This effect most likely indicates a general improvement in the function of the inner lining of small vessels, including those supplying the heart," said Dr. Loft.
The researchers found that HEPA filtration removed about 60 percent of the ultrafine, fine and coarse air particles in homes, and was associated with an 8.1 percent improvement in individual MVF.
"We expected that removing air particles with the HEPA filters would result in improvement of MVF but we were heartened and surprised by the extent it did, considering the modest levels of particles in the indoor air of the homes of the elderly," said Dr. Loft.
None of the secondary endpoints considered showed significant differences after statistical corrections, suggesting that the mechanism underlying the improvement in MVF after air filtration remains unclear, and underscoring the need for further study.
"The results of this study indicate that reduction of particles in recirculated indoor air by filtration significantly improves MVF in a healthy, non-smoking, elderly population," wrote Dr. Loft. "The improvement could not be ascribed to significant reduction in inflammation or oxidative stress by means of biomarkers."
Dr. Loft and his team are now studying the effect of high levels of wood smoke on MVF in healthy subjects. They hope that the mechanisms can be better understood by means of a wider range of secondary endpoints, including expression of important genes, which they are currently developing.
The study was published in the second issue for February of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
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