Furthermore, we detected HIF2α expression in the serum of patients enrolled in the study with HPH and found that serum HIF2α in patients with COPD and HPH patients was higher than that in patients with COPD but without HPH and in the healthy control group (Figure 4A), and serum HIF2α expression was highly positively correlated with PASP (Figure 4B). Here, EPAS1 is linked to chronic obstructive pulmonary disease.