Researchers have found that monitoring blood for tiny particles released by cells lining the lungs may help clinicians diagnose emphysema in its earliest stages. The particles, called endothelial microparticles (EMPs), are shed during the disease process as pulmonary capillaries are injured and die. The findings are published in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine.
“This study confirmed that the levels of EMPs are elevated in the blood samples of smokers, consistent with the concept that emphysema is associated, in part, with the death of cells lining the pulmonary capillaries, and suggesting that the early development of emphysema might be monitored with blood tests to measure EMP levels,” said Ronald Crystal, MD, study author and chairman and professor of genetic medicine at Weill Cornell Medical College.
For the study, the researchers used two lung function tests: spirometry to measure the amount and speed at which a patient exhales; and a lung diffusion test to measure the lung’s ability to diffuse, or transfer, carbon monoxide (DLCO). Patients with early emphysema typically have normal levels of inhalation and exhalation, but exhibit low DLCO.
“One of the key differences between spirometry, which is commonly used in physicians’ offices, and DLCO, which is a more sophisticated test usually used only by pulmonologists, is that spirometry is less sensitive to the changes that occur in the lungs in the early stages of lung disease,” said Crystal. “The DLCO test is much more sensitive and is able to pick up the earliest signs of emphysema.”
The researchers assessed the levels of circulating EMPs in an initial patient population of 92 subjects, including healthy nonsmokers, healthy and symptomatic smokers with normal lung function, and healthy smokers with normal spirometry but low DLCO. Because smoking is known to affect blood vessels in many areas of the body, EMPs were assessed for a specific enzyme that occurs primarily in pulmonary vessels. To confirm their findings, the assessment was repeated in two prospective cohorts, including a group of 92 patients similar to the initial patient population and a group of 15 patients with HIV.
The results show that both symptomatic smokers and healthy smokers with normal spirometry and normal DLCO had mild increases in EMP levels compared to healthy nonsmokers, and there was no difference in EMP levels between healthy and symptomatic smokers. In striking contrast, healthy smokers with normal spirometry but low DLCO had a significant increase in EMP levels.
“The data in these patient populations demonstrated that smokers with normal spirometry and normal DLCO have levels circulating EMPs that are mildly elevated compared to healthy nonsmokers, but smokers who have normal spirometry and reduced DLCO have marked increases in the levels of circulating EMPs,” said Crystal.
He added, “Interestingly, the smokers with the highest EMP levels are healthy smokers with normal spirometry and low DLCO. This suggests that the vascular-based contributions to the development of emphysema may contribute to the early development of the disease, and may identify a point in time where intervention with smoking cessation therapy may prevent the irreversible lung destruction associated with the development of COPD.”
According to the researchers, a blood test to monitor for levels of EMPs may offer an alternative to high-resolution computed tomography (HRCT), which is currently used to identify early-onset emphysema, with varying degrees of success.
Source: American Thoracic Society