EDMONTON, ALBERTA—Chronic obstructive pulmonary disease (COPD) carries with it an increased risk of cardiovascular disease. A new study suggests a possible explanation for this connection: Moderate to severe airflow obstruction is accompanied by low-grade systemic inflammation, which in turn is associated with cardiac injury.[1]

The study examined data from 6,629 participants in the Third National Health and Nutrition Examination Survey who were 50 or older. The extent of airflow obstruction was determined in all participants, and a Cardiac Infarction Injury Score (CIIS) was calculated from each patient’s electrocardiography results. C-reactive protein (CRP) levels were evaluated, along with other markers of systemic inflammation.

CRP, AIRFLOW OBSTRUCTION, AND CARDIAC INJURY

Spirometry revealed airflow obstruction in 31% of participants. (Those without airflow obstruction served as controls.) Nineteen percent of participants were smokers. Levels of CRP, leukocytes, platelets, and fibrinogen were all higher in the persons with airflow obstruction than in controls, with the highest levels occurring in those with the most severe airflow obstruction.

CIIS increased with the severity of airflow obstruction; mean scores were 6.5 among controls, 7.9 among participants with mild obstruction, 10.0 among those with moderate obstruction, and 11.2 among those with severe obstruction. In addition, those with severe airflow obstruction were 2.1 times more likely to have electrocardiographic findings of a previous myocardial infarction than were controls. After subgroup analysis excluded patients with pulmonary hypertension and those who used digitalis—two possible confounding factors—airflow obstruction was still associated with an increased CIIS.

Not surprisingly, CRP levels and CIIS were significantly correlated; airflow obstruction had an additive effect on both measures. Participants with high CRP levels and severe airflow obstruction had a CIIS that was an average of 5.88 U higher than that of controls with low CRP levels.

S. F. Paul Man, MD, one of the study authors and a Professor of Medicine at the University of Alberta in Edmonton, noted that pulmonary inflammation is well known in COPD. “We postulate that pulmonary inflammation leads to systemic inflammation, but we don’t know the exact mechanism of this,” he said.

Even small reductions in forced expiratory volume in one second can increase the risk of cardiovascular morbidity and mortality. When airflow obstruction occurs along with elevated CRP levels, the risk of cardiac injury increases almost twofold.

Dr. Man pointed out that although the current study demonstrates an association between airflow obstruction and systemic inflammation, it was an analysis of population-based data, and thus “we have not proven the causality between COPD and systemic inflammation represented by molecules such as CRP. Our kind of study generates a hypothesis that has to be further tested,” he concluded.

—Gale Jurasek

References
1. Sin DD, Man SFP. Why are patients with chronic obstructive pulmonary disease at increased risk of cardiovascular diseases? The potential role of systemic inflammation in chronic obstructive pulmonary disease. Circulation. 2003;107:1514-1519.

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