Hemodynamics of high afterload left heart failure for assist device testing.

The hemodynamic responses to increased afterload of the left ventricle were studied in conscious calves during exercise. The calves were chronically instrumented to measure (or derive) heart rate, stroke volume, cardiac output, iliac, superior mesenteric and renal flows and resistances, mean carotid, aortic, right atrial, pulmonary artery, and left atrial pressures, the systemic and pulmonary pressure gradients, and total systemic and total pulmonary resistances. The calves were also instrumented to produce reversible partial constriction of the ascending aorta and common carotid arteries and for cooling of the cervical vagus nerves. The hemodynamic responses to increased afterload were characterized during treadmill exercise at 2 mph. These responses were compared to the hemodynamic responses to bilateral carotid artery occlusion with and without vagal cooling.