Effects of cardiac tamponade on colonic hemodynamics and oxygen uptake.

The local hemodynamic response of the innervated but vascularly isolated colon to decreased systemic perfusion induced by cardiac tamponade was studied in anesthesized dogs as a model of nonocclusive mesenteric ischemia. Increasing levels of pericardial pressure caused progressive decreases in colonic blood flow associated with substantial increases in colonic vascular resistance. These increases in local colonic resistance were proportionately larger than concurrent increases in systemic resistance. The disproportionate response of the colonic resistance vessels was not diminished by colonic (sympathetic) denervation. Reductions of blood flow to 30 ml . min-1 . 100 g-1 resulted in compensatory increases in colonic oxygen extraction such that colonic oxygen consumption remained constant (flow independent) at about 1.5 ml . min-1 . 100 g-1. At blood flows below 30 ml . min-1 . 100 g-1 colonic oxygen consumption was markedly dependent on blood flow. This fundamental relation of colonic oxygen consumption to blood flow was the same whether ischemia was induced by cardiac tamponade, partial mechanical arterial occlusion, or vasoconstrictor (norepinephrine or digoxin) infusion. Furthermore, this relationship was not altered by vasodilation with isoproterenol after the induction of ischemia by any of the above means.