Brain natriuretic peptide levels in middle aged subjects with normal left ventricular function in relation to mild-moderate COPD

Background: Levels of plasma brain natriuretic peptide (BNP) have been shown to be elevated in chronic obstructive pulmonary disease (COPD) especially in connection with cor pulmonale (CP) and the late stages of the disease. BNP is also raised in left sided heart failure which sometimes coincides with COPD. Whether BNP is elevated in subjects with mild-moderate stable COPD and normal left ventricular function is not clear. Objective: To investigate BNP levels in subjects with mild-moderate COPD and normal left ventricular function. Methods: This was a cross sectional study of 450 subjects from a population-based respiratory questionnaire survey. All subjects were examined with echocardiography and spirometry and blood samples were drawn for BNP measurements. Subjects with left sided heart disease (n=26) or echocardiographic signs of elevated filling pressure (n=75), COPD stages III and IV (n=5) or missing data (n=13) were excluded. Results: In the final study population (n=331) spirometry identified 86 subjects with COPD (GOLD stage I, n=65 and GOLD stage II, n=21). In comparison with the rest of the study population subjects with COPD were significantly older, longer and with a male predominance. In a multivariate linear regression analysis with log-normalized (lnBNP) as the dependent variable a significant correlation was found with age, left atrial volume, body surface area and haemoglobin, but not with any pulmonary variables. Even when comparing groups no significant difference could be found between the plasma levels of lnBNP in normal subjects (1.8±0.7 mean±SD, pmol/L) subjects and in COPD subjects (1.9±0.7, P=0.47). Conclusions: In a population with normal left ventricular function no significant differences in BNP levels between stable mild-moderate COPD subjects and normal individuals could be found.