The document provides information on pulmonary hypertension and pulmonary circulation. It discusses:
1) The pulmonary circulation begins at the right ventricle and ends at the left atrium, transporting the entire cardiac output to the lungs. It has low resistance and high compliance.
2) Pulmonary artery pressures are normally lower than systemic pressures, with mean pulmonary artery pressure around 10-12 mmHg.
3) Pulmonary vascular resistance is low due to a balance of vasodilator and vasoconstrictor prostaglandins. Resistance primarily occurs in small arteries and arterioles.
4) Pulmonary hypertension is defined as a mean pulmonary artery pressure over 25 mmHg at rest. Its causes