A SIMPLE METHOD FOR REDUCING CARDIAC-OUTPUT IN THE CONSCIOUS LAMB

A method was developed for reducing cardiac output in a controlled stepwise fashion using awake, intact, unselected lambs. The method involves placing a balloon-tipped (Foley) catheter into the right atrium from a jugular vein isolated by a small neck incision. Systemic venous return and cardiac output are limited by balloon inflation. With each balloon inflation the animal reaches a new and stable cardiac output, which allows the measure of steady-state hemodynamic and metabolic variables. Cardiac oupput was decreased to as low as 20% of the resting cardiac output and maintain a stable preparation. The reductions in cardiac output are quickly reversible by balloon deflation. Animal survival allows repeated study. Data from 5 lambs studied between 26 and 36 days of age are presented. Alterations in O2 consumption, O2 transport, O2 extraction, blood pressure and arterial lactate concentrations are examined in response to decrements in systemic blood flow and are consistent with changes seen in response to a reduction of cardiac output by other methods.