Severity of emphysema, measured by CT, is a strong independent predictor of all-cause, cardiovascular and respiratory mortality in current and former smokers with or without chronic obstructive pulmonary disease (COPD), according to a study published online Jan. 18 in American Journal of Respiratory and Critical Care Medicine.
Airway wall thickness in patients with severe emphysema is also associated with mortality from respiratory causes, according to the researchers.
“Given the magnitude of CT examinations performed worldwide each year, predictive effects of such measures on mortality risks are of substantial importance,” wrote Ane Johannessen, PhD, post-doctoral researcher at Haukeland University Hospital in Bergen, Norway, and colleagues.
Findings were based on a community-based cohort of 947 ever-smokers with and without COPD who were followed for 8 years. All participants underwent spirometry and CT scanning. Degree of emphysema was categorized as low, medium or high based on the percent of low attenuation areas on CT.
The authors explained that most COPD patients are assessed through spirometry alone, but that chest CT makes it possible to subgroup COPD patients into predominantly emphysematic and airways disease phenotypes.
Overall, 462 patients had COPD, reported Johannessen and colleagues. Results showed that 4 percent of subjects with a low degree of emphysema died, compared with 18 percent and 44 percent of subjects with medium and high degrees of emphysema, respectively.
Survival in the low emphysema group was 19 months longer than survival in the middle and high emphysema groups for all-cause mortality after adjusting for sex, COPD status, age, body mass index, smoking and measures of lung function. Compared with subjects in the low emphysema group, subjects with a high degree of emphysema had 33 months and 37 months shorter survival for respiratory mortality and cardiovascular mortality, respectively.
In speculating as to precisely why emphysema predicts respiratory mortality, the authors pointed out that emphysema has been shown to have a relationship with forced expiratory volume decline, inflammatory markers, white blood count, low muscle mass and osteoporosis. The exact nature of these relationships—whether emphysema is the cause or if certain conditions are part of the disease process—is unclear.
Increasing emphysema levels significantly predicted shorter survival. Airway wall thickness was not an independent predictor of mortality, though increased airway wall thickness reduced survival time in patients with more severe emphysema, according to the authors.
“Accurate prediction of mortality is important because it helps identify patients in whom the implementation of specific therapeutic measures may improve outcome,” wrote Johannessen and colleagues.