Modification of the cardiovascular response to hemorrhage by somatic afferent nerve stimulation with special reference to gut and skeletal muscle blood flow

Background: Tissue injury modifies heart rate and blood pressure responses to hemorrhage. The effect of concomitant injury on the hemorrhage-induced r edistribution of cardiac output is much less clear, However, if injury elic its the visceral alerting response of the defense reaction, then a change i n this redistribution of peripheral blood flow might be expected, If such a change compromised the gut circulation, then it might explain the deleteri ous effects of injury on the ability to withstand hemorrhage, Methods: Immature Digs anesthetized with Saffan were bled 30% of blood volu me with or without concomitant somatic afferent (brachial) nerve stimulatio n (to mimic injury), In addition to global cardiovascular and oxygen transp ort variables, blood flow was measured in the cranial mesenteric (gut) and right femoral (skeletal muscle) arteries after a 60-minute stabilization pe riod after surgery, at the end of the 30-minute hemorrhage, and after a 30- minute shock period. Results: Hemorrhage induced the expected cardiovascular and oxygen transpor t changes accompanied by a reduction in skeletal muscle blood flow and a 55 % increase in skeletal muscle vascular resistance, but gut blood flow and v ascular resistance were unchanged. However, in the presence of brachial ner ve stimulation, the pattern of response to hemorrhage was modified, such th at gut blood flow was now reduced and gut vascular resistance increased. Conclusion: The sparing of the gut circulation after hemorrhage was abolish ed in the presence of "injury," This finding is consistent with injury elic iting the defense reaction and may help explain the deleterious effects of injury on resistance to hypovolemia.