PDE5A and pulmonary arterial hypertension: COPD patients with "out-of-proportion" pulmonary - where resting mPAP was ≥ 35 mmHg in the presence of relatively preserved lung function hypertension - underwent several trials using pulmonary arterial hypertension (PAH)-directed therapy, including prostacyclin agonists, phosphodiesterase type 5 (PDE-5) inhibitors, and nitric oxide-cyclic guanosine monophosphate enhancers.