NEW YORK - Chronic obstructive pulmonary disease begins to affect cardiac function at a very early stage, a study published in the New England Journal of Medicine suggests.

While it is well known that severe COPD comes with repercussions on the heart, in the form of pulmonary hypertension and cor pulmonale, it now appears that even the mildest forms of chronic lung disease can adversely affect heart function. In addition, smoking increases the impact of chronic lung disease on the heart, researchers report.

Severe COPD affects the heart through various mechanisms, including loss of pulmonary vascular capacity due to parenchymal destruction, hypoxic pulmonary arterial vasoconstriction, and pulmonary hyperinflation with elevated intrathoracic pressure.

"Whether similar changes occur in milder chronic lung disease, however, remains unknown”, write Dr Graham Barr, of Columbia University in New York City, and colleagues.

To try to answer this question, the researchers measured left ventricular structure and function by magnetic resonance imaging in 2,816 adults aged 45 to 84 years. The study participants also underwent lung function testing and CT evaluation of the lungs.

Half of the subjects had never smoked, 13% were current smokers, and 38% were former smokers.

The main finding of the study was that the extent of emphysema on CT scans (measured as per cent emphysema) and the degree of airflow obstruction correlated with the degree of left ventricular filling impairment, reductions in stroke volume, and decreases in cardiac output.

After adjusting for confounding factors, an increase of 10 percentage points in the extent of emphysema was associated with a 4.1-ml decrement in left ventricular end-diastolic volume, a 2.7-ml decrement in stroke volume, and a decrement of 0.19 l per minute in cardiac output. In contrast, there was no evidence of an association between the extent of emphysema and the left ventricular ejection fraction.

These findings indicate that subclinical hemodynamic changes occur with mild emphysema and airflow obstruction.

In COPD complicated by cor pulmonale, the increased vascular resistance and right heart failure are accompanied by reduced left ventricular filling, left ventricular stroke volume, and cardiac output. Left ventricular ejection fraction (LVEF), on the other hand, usually is preserved.

It is worth noting that the study was conducted in patients without clinical heart disease and who were suffering from mild-to-moderate COPD or emphysema. Patients with restrictive lung disease were excluded from the study.

These findings were stronger among smokers than among former smokers or lifelong nonsmokers. "In conclusion, in this population-based study of subjects without very severe chronic obstructive pulmonary disease, the degree of emphysema and the severity of airflow obstruction were associated with significant decrements in left ventricular filling and cardiac output. The magnitude of these associations was greater among participants with a history of smoking," the authors write.

"The apparent effect of emphysema on left ventricular end-diastolic volume and cardiac output was similar to that of traditional cardiac risk factors previously reported and, among smokers, was greater than that of traditional cardiac risk factors," they conclude.

Reference:

Barr RG, et al. "Percent emphysema, airflow obstruction, and impaired left ventricular filling" N Engl J Med 2010; 362: 217-227.

photo credit: Patrick J. Lynch (Wikimedia Commons)