VCAM1 and pulmonary arterial hypertension: In conclusion, we were able to infer that R-hirudin treatment may be able to attenuate pulmonary arterial hypertension and thrombosis, improve APE, and protect lung tissues by improving cardiopulmonary function and vascular endothelial function, alleviating oxidative stress injury and inflammatory response, dose-dependently regulating MMP-9, VCAM-1, p-ERK1/2/ERK1/2 and p-P65/P65 expression, and inhibiting apoptosis.