Several previous studies detected elevated levels of ET-1 in EBC in interstitial pulmonary disease [38], in non small cell lung cancer patients (NSCLC) [39], and in unstable bronchial asthma [40], similar to those observed in our COPD patients, while in the present, we found significantly higher EBC levels of ET-1 in COPD with PAH. Here, EDN1 is linked to chronic obstructive pulmonary disease.