We measured the BNP levels to investigate whether
heart failure can play a role in dyspnea in COPD
patients. It has been reported that BNP can be used to
differentiate heart failure from respiratory diseases,
including COPD, in patients with dyspnea [23]. Furthermore,
COPD patients were reported to have higher
levels of BNP as compared to controls [24]. Although
the Spearman rank correlation test revealed a significant
correlation between BNP levels and dyspnea, the stepwise
multiple regression analysis did not. This does not
explain what elevated BNP levels in subjects with COPD
mean clinically, but the magnitude of this elevation may
depend on the disease severity instead of dyspnea.