Cardiac output and organ blood flow in young rabbits during intermittent positive-pressure ventilation

Cardiac output and organ blood flow were measured by a microsphere technique in three groups of healthy young rabbits. In one group, animals were subjected to light sedation and intermittent positive-pressure ventilation. Control animals in a second group were sedated but not ventilated. In a third group, animals were conscious and breathing spontaneously. Cardiac output increased significantly (p less than 0.05) in conscious controls and in one measurement in anesthetized controls. It did not change in ventilated rabbits. Blood flow to the brain increased during study in all three groups and to the eye in both control groups. These elevations in cardiac output and cerebral blood flow were attributed to arousal. Blood flow to the kidney decreased in both anesthetized groups. The blood flow to skin, muscle, ileum and colon decreased significantly in the ventilated animals though not in the anesthetized controls. In both groups, similar reductions were found in the fractional distribution of cardiac output to these areas. It was concluded that ventilation at low pressure had no effect on cardiac output. The occurrence of redistribution of the circulation was deduced from the parallel reductions of regional blood flows and fractions of cardiac output received by some organs together with preservation of cerebral blood flow, though it was obscured in the two control groups by simultaneous increases in cardiac output. The circumstances suggested that this redistribution was due to disturbed homeostasis from arousal. Implications for the newborn were discussed.