Millions of Smokers May Have Undiagnosed Lung Disease
More than one-half of long-term smokers and ex-smokers who are considered disease-free because they passed lung-function tests have respiratory-related impairments when more closely evaluated with lung imaging, walking, and quality-of-life tests. Many of those people likely have the earliest stages of COPD, an incurable progressive disease that is the third leading cause of death in the United States.
"The impact of chronic smoking on the lungs and the individual is substantially underestimated when using lung-function tests alone," says James D. Crapo, MD, a professor of medicine at National Jewish Health and senior author of the study, which was published online ahead of print June 22 in JAMA Internal Medicine. "Lung disease is common in smokers whose lung-function tests fall within population norms."
COPD is diagnosed by having people blow as hard and as long as they can into a device called a spirometer, which measures how much air they can blow out in one second and how much total air they can force out of their lungs. Individuals' results are compared with population norms and adjusted for age, size, and gender.
The researchers evaluated 8,872 people aged 45 to 80 who had smoked at least a pack of cigarettes a day for 10 years (10 pack-years) or the equivalent. Most had smoked considerably more, 35 to 50 pack-years. About one-half of the participants were considered disease-free based on their lung-function tests.
When researchers considered other criteria including impairments in physical function, respiratory symptoms, CT scans, use of respiratory medications, and respiratory-specific quality of life, they found that 55% of the "disease-free" study participants had some form of respiratory-related impairment.
CT scans found emphysema or airway thickening in 42% of the disease-free participants. Twenty-three percent had significant shortness of breath compared with 3.7% of never smokers. Fifteen percent walked less than 350 meters in six minutes, compared with 4% of never smokers. The disease-free smokers also had considerably worse quality of life than neversmokers, with 25% of them having scores on questionnaires that exceeded a threshold considered clinically significant.
"Smokers who have 'normal' lung-function tests often have significant respiratory disease. Many of those smokers likely have the early stages of chronic obstructive pulmonary disease," says Elizabeth Regan, MD, PhD, lead author and an assistant professor of medicine at National Jewish Health. "We hope these findings will help debunk the myth of the healthy smoker and highlight the importance of smoking prevention and cessation to prevent lung disease and other long-term effects of smoking."
Recent research has shown that lung CT screening of smokers with smoking histories of at least 30-pack years can lead to early detection of lung cancer and reduce deaths by 20%. Early detection of COPD may also enable early treatment that can improve symptoms, functional abilities, and quality of life. Crapo and Regan say they hope the findings will encourage long-term smokers to get lung CT screenings to detect early stages of lung cancer and COPD.
— SOURCE: National Jewish Health