Background Pulmonary hypertension (PH) is a common complication of chronic obstructive pulmonary disease (COPD).Although alveolar hypoxia is considered as a main cause of PH in COPD,structural and functional changes of pulmonary circulation are apparent at the initial stage of COPD.We hypothesized that an inflammatory response and oxidative stress might contribute to the formation of PH in COPD.Methods We measured the levels of interleukin-6 (IL-6) and 8-iso-prostaglandin (8-iso-PSG) in exhaled breath condensate (EBC) and serum in 40 patients with COPD only or in 45 patients with COPD combined with PH.Pulmonary arterial systolic pressure (PASP) was assessed by Doppler echocardiography and defined as PH when the value of systolic pressure was greater than 40 mmHg.Results Compared with the COPD only group,the level of IL-6 in EBC was significantly increased in all 45 patients with COPD combined with PH ((8.27±2.14) ng/L vs.(4.95±1.19) ng/L,P ＜0.01).The level of IL-6 in serum was also elevated in patients with COPD combined with PH compared with the COPD only group ((72.8±21.6) ng/L vs.(43.58±13.38) ng/L,P ＜0.01).Similarly,we also observed a significant increase in the level of 8-iso-PSG in both EBC and serum in the COPD with PH group,compared with the COPD only group (EBC:(9.00±2.49) ng/L vs.(5.96±2.31) ng/L,P ＜0.01 and serum:(41.87±9.75) ng/L vs.(27.79±11.09) ng/L,P ＜0.01).Additionally,the value of PASP in the PH group was confirmed to be positively correlated with the increase in the levels of IL-6 and 8-iso-PSG in both EBC and serum (r=0.477-0.589,P ＜0.05).Conclusion The increase in the levels of IL-6 and 8-iso-PSG in EBC and serum correlates with the pathogenesis of PH in COPD.