Evidence of alveoli changes similar to those seen in the lungs of long-time smokers was found in 27% of nonsmokers who were exposed to secondhand smoke for at least 10 years versus 4% for nonsmokers who were not so exposed (P=0.047), said Chengbo Wang, Ph.D., a magnetic resonance physicist at Children's Hospital of Philadelphia.
Dr. Wang, who reported the finding at the Radiological Society of North America meeting here, said the lung changes were present even though there were no clinical signs of COPD.
The finding may have more "public policy than public health implications," said co-investigator Talissa Altes, M.D., of the University of Pennsylvania and Children's Hospital.
She said there are no clear "effective treatments for preclinical COPD, but we do know that the only way to slow the disease is to stop smoking. So I think the clear message for these people is that they should avoid smoke exposure."
But on a policy level, she said, the finding supports legislative efforts to limit smoking in public places.
Drs. Altes and Wang conducted the research while training at the University of Virginia in Charlottesville, which, Dr. Altes said, was "the heart of tobacco country."
They recruited 60 volunteers -- 23 people who had never smoked and who had a low exposure to secondhand smoke, 22 people who had been exposed to secondhand smoke from a family member or work environment for at least 10 years, and 15 current or past smokers.
Lung structure was assessed with hyperpolarized helium diffusion MRI, an investigational technology that uses software designed by Dr. Wang.
The hyperpolarization process "doesn't change the chemical structure of helium, it simply makes it visible on MRI," said Dr. Altes.
The patients "inhale the hyperpolarized helium while lying in the MRI," she said. Changes in alveoli size are measured by calculating the distance the helium atoms travel in the alveoli, she said. Healthy lungs have small alveoli so the helium travels a shorter distance than it does in the lungs with damaged enlarged alveoli.
This distance is calculated as an apparent diffusion coefficient or ADC.
Normal lungs were defined as an ADC of 0.024 (mean value in nonsmokers plus 2 times the standard deviation).
Of the 15 past or active smokers, 67% exhibited depressed lung function, she said. Compared with those not exposed to secondhand, smoke the difference was also statistically significant (P<0.001), she said.
Katarzyna Macura, M.D., Ph.D., of Johns Hopkins, who moderated the session, said the results should be considered "preliminary." She said she would have liked to see animal studies to elucidate and confirm the apparent structural differences.
Moreover, she said the study was too small to provide evidence of a cause and effect.
Dr. Altes said other researchers have induced emphysematous changes in animal lungs, but, although the changes correlate with emphysema, the animal studies do not prove that tobacco smoke caused those changes.
Asked why so many people exposed to secondhand smoke did not have evidence of lung damage -- 73% had normal ADC values -- Dr. Altes said she found that number very provocative because "the number of people who did have evidence of lung damage, 27%, correlates nicely with the number of smokers who go on to develop COPD (15% to 30%)."
Dr. Altes said "27% may reflect the proportion of the population that is sensitive to tobacco smoke."
|The study was primarily funded by the Flight Attendant Medical Research Institute, with additional support from the National Heart, Lung, and Blood Institute, the Commonwealth of Virginia Technology Research Fund, and Siemens Medical Solutions.
Zalman S. Agus, MD Emeritus Professor
University of Pennsylvania School of Medicine