POST-CARDIOPULMONARY BYPASS PULMONARY HYPERTENSION IS AUGMENTED IN LAMBS WITH INCREASED PULMONARY BLOOD FLOW. † 265

Pulmonary hypertension immediately following cardiopulmonary bypass (CPB) is a major source of morbidity in children with congenital heart defects and increased pulmonary blood flow. Plasma levels of endothelin-1 (ET-1), a potent vasoactive substance implicated in pulmonary hypertension, are increased after CPB, suggesting a role for ET-1 in post-CPB pulmonary hypertension. Recently we established a lamb model of increased pulmonary blood flow and pulmonary hypertension following in utero placement of an aortopulmonary shunt. These lambs have altered ET-1-induced responses and increased plasma ET-1 concentrations. To investigate the effects of increased pulmonary blood flow and ET-1 on post-CPB pulmonary hypertension, we characterized and compared the changes in pulmonary vascular tone and plasma ET-1 concentrations, induced by 90 minutes of hypothermic (25°) CPB, in 7 one-month-old lambs with increased pulmonary blood flow (SH) and 6 age-matched control lambs (C). Table