CHICAGO (AP) _ Just half an hour of secondhand smoke can impair normal blood flow to the heart, a Japanese study suggests.
The study examined the effects of spending 30 minutes in a hospital's smoking room on 15 nonsmoking men and 15 smokers. The smokers, whose heart arteries already showed damage, were not affected. But in nonsmokers, the result was a reduced ability of heart arteries to dilate, which previous research has suggested may be a precursor to hardening of the arteries.
``This change may be one reason why passive smoking is a risk factor for cardiac disease'' and related deaths in nonsmokers, the researchers said in Wednesday's Journal of the American Medical Association.
The study did not examine whether the changes from the one-time exposure to smoke were permanent.
Previous research in smokers has found similar changes that may be reversible if smokers quit, said Dr. David Faxon, president of the American Heart Association. If exposure continues, ``gradually, as hardening of the arteries sets in, it's irreversible,'' he said.
The study ``really sort of confirms prior information that we've had about the adverse effects of secondhand smoke,'' Faxon said.
In the study, Dr. Ryo Otsuka of Osaka City University Medical School and colleagues used blood pressure tests and an imaging technique called echocardiography to examine the effect on heart arteries' ability to dilate. Measurements were taken before and after exposure to secondhand smoke.
The smoke appeared to impair the functioning of the endothelium, a lining of cells in the arteries that helps regulate dilation. Scientists believe coronary artery disease may begin when the endothelium becomes damaged, leaving the arteries prone to blockages or narrowing.
Stanton Glantz, a University of California at San Francisco professor of medicine, said the findings add fuel to the debate over secondhand smoke.
``People walking into a smoky restaurant, do they want to be clobbering the ability of the arteries in the heart to get blood to the heart, even if it's just for a little while?'' he said.
Seth Moskowitz, spokesman for R.J. Reynolds Tobacco Co., said the study does not change the company's belief that there is no scientific evidence establishing that secondhand smoke is a risk factor for lung cancer, heart disease or any other disease in adult nonsmokers.