PDE5A and pulmonary arterial hypertension: These inhibitors are categorized based on the PDE subtype they target: PDE5 inhibitors are employed to alleviate erectile dysfunction and pulmonary hypertension by promoting smooth muscle relaxation and enhancing blood circulation; PDE4 inhibitors elevate cAMP levels and are effective for pulmonary diseases such as asthma and COPD by targeting the airways, skin, immune system, and brain.