Passive effect of reduced cardiac function on splanchnic intravascular volume.

It has been hypothesized that lowered cardiac output due to heart failure results in passive redistribution of intravascular volume from the peripheral circulation to the central circulation and that this redistribution acts to support cardiac output. To test this hypothesis, acute heart failure was induced by rapid atrial pacing to raise heart rate from 148 +/- 6 to 232 +/- 1 beats/min for 5 min, while splanchnic intravascular volume was assessed with radionuclide imaging in eight anesthetized pigs that had undergone prior carotid denervation and vagotomy. Cardiac output decreased from 3,350 +/- 410 to 2,170 +/- 290 ml/min (P less than 0.001), mean arterial pressure decreased from 103 +/- 5 to 84 +/- 4 mmHg (P less than 0.001), left atrial pressure increased from 5.9 +/- 0.6 to 10.8 +/- 0.9 mmHg (P less than 0.001), right atrial pressure increased from 2.4 +/- 0.5 to 4.8 +/- 0.9 mmHg (P less than 0.001), total splanchnic intravascular volume did not change (0 +/- 2 ml), splenic intravascular volume decreased 11 +/- 3% (P less than 0.001), hepatic intravascular volume increased 12 +/- 2% (P less than 0.001), and mesenteric intravascular volume did not change (-3 +/- 2%). Thus, when cardiac output is lowered with pacing-induced acute heart failure, lowered perfusion pressure acts to lower splenic intravascular volume and increased central venous pressure acts to increase hepatic intravascular volume; however, total splanchnic intravascular volume does not decrease to support cardiac filling and cardiac output.