The prevalence and incidence of venous thromboembolism and other venous disease has been determined as part of a longitudinal study of health and disease in a Michigan community. When these data are extrapolated to 1970 U.S. census figures, a rough estimate of annual incidence of clinically recognized deep venous thrombosis is over 250,000 cases while that of superficial thrombophlebitis is over 123,000. An estimated 24 million US citizens have "significant" varicose veins while 6 to 7 million have stasis changes in the skin of the legs and 400,000 to 500,000 have or have had a varicose ulcer. The relatively high frequency of these conditions in the adult population of Tecumseh, Michigan, indicates that they represent several of the more common medical problems encountered by the practicing physician.

Pericardial effusion, right atrial enlargement and septal displacement are echocardiographic abnormalities that reflect the severity of right heart failure and predict adverse outcomes in patients with severe PPH. These characteristics may help identify patients appropriate for more intensive medical therapy or earlier transplantation.

The echocardiographic manifestations of severe primary pulmonary hypertension reflect abnormalities in hemodynamics and exercise capacity. Prostacyclin has beneficial effects on right heart structure and function that may contribute to the clinical improvement and prolonged survival observed with this drug.