MRI Proves That Secondhand Smoke Causes Lung Damage

CHICAGO—For the first time, researchers have identified structural damage to the lungs caused by secondhand cigarette smoke.

The results of the study, conducted by researchers at the University of Virginia School of Medicine in Charlottesville and The Children’s Hospital of Philadelphia in Pennsylvania, were presented at the 2007 annual meeting of the Radiological Society of North America (RSNA).

HELIUM-3 DIFFUSION MRI

“It’s long been hypothesized that prolonged exposure to secondhand smoke may cause physical damage to the lungs, but previous methods of analyzing lung changes were not sensitive enough to detect it,” said Chengbo Wang, PhD, magnetic resonance physicist in the Department of Radiology at The Children’s Hospital of Philadelphia. According to the American Lung Association, 35% of American children live in homes where regular smoking occurs.

Dr. Wang and colleagues used long-time-scale, global helium-3 diffusion magnetic resonance imaging (MRI) to study the lungs of 43 volunteers, including seven current and former smokers and 36 people who had never smoked—18 of whom had a high level of exposure to secondhand smoke.

Helium-3 diffusion MRI differs from conventional MRI in that the patient inhales a specially prepared helium gas prior to imaging, and the scanner is adjusted to collect images showing this helium gas in tissue. MR measures how far the helium atoms move, or diffuse, inside the lungs during a specific time period—1.5 seconds in this study. Using this method, radiologists and physicists can detect changes deep in the small airways and sacs in the lungs, which can break down, become enlarged and develop holes after prolonged exposure to cigarette smoke. Helium-3 diffusion MRI identified this damage by measuring the increased distance the helium atoms move.

“With this technique, we are able to assess lung structure on a microscopic level,” Dr. Wang said.

EVIDENCE OF EARLY LUNG DAMAGE

For the study, measurements were translated into apparent diffusion coefficient (ADC) values for each of the participants. An increased ADC value indicates that the helium atoms were able to travel farther during the measurement time. Fifty-seven percent of the smokers and 33% of the nonsmokers with high exposure to secondhand smoke had ADC values greater than 0.024, suggesting that early lung damage was present. In addition, 14% of smokers, 67% of high-exposure nonsmokers, and 39% of low-exposure nonsmokers had ADC values below 0.0185. Relatively low ADC values in adults are a possible indication of a developing respiratory problem, such as chronic bronchitis or asthma.

“These findings suggest that breathing secondhand smoke can injure your lungs,” Dr. Wang said. “Since legislation to limit public exposure to secondhand smoke is still being considered in many states, we hope that our work can be used to add momentum to the drive to pass such legislation.”

Suggested Reading
Beane J, Sebastiani P, Liu G, et al. Reversible and permanent effects of tobacco smoke exposure on airway epithelial gene expression. Genome Biol. 2007;8(9):R201.
Milner AD, Rao H, Greenough A. The effects of antenatal smoking on lung function and respiratory symptoms in infants and children. Early Hum Dev. 2007 Nov;83(11):707-711.
Stern G, Latzin P, Thamrin C, Frey U. How can we measure the impact of pollutants on respiratory function in very young children? Methodological aspects. Paediatr Respir Rev. 2007;8(4):299-304.
Thomson NC. The role of environmental tobacco smoke in the origins and progression of asthma. Curr Allergy Asthma Rep. 2007;7(4):303-309.
Widome R, Jacobs DR Jr, Schreiner PJ, Iribarren C. Passive smoke exposure trends and workplace policy in the Coronary Artery Risk Development in Young Adults (CARDIA) study (1985-2001). Prev Med. 2007;44(6):490-495.

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