Autonomic control of the regional hemodynamic response to scald

Ultrasonic flow probes were placed around the ascending aorta and each femoral artery of dogs to record cardiac index and femoral blood flow, respectively. Intravenous hexamethonium (n = 5) produced 30% decreases in systemic mean arterial pressure and in cardiac index, and a 14% increase in femoral blood flow, effects that waned over time, consistent with the half-life of the agent. Without hexamethonium, hind paw scalding with boiling water for 5 sec (n = 5) caused a marked increase in ipsilateral femoral artery blood flow (70.7 +/- 8.9 ml/min pre-burn vs 243.7 +/- 23.7 ml/min 5 min post-burn) that persisted for the 3 hr observation period. Contralateral femoral blood flow, systemic mean arterial pressure, and cardiac index were unchanged. Compared to burn only dogs, pre-burn treatment with hexamethonium (n = 6) blunted the femoral vasodilator response to burn (78.8 +/- 9.7 ml/min pre-burn vs 116.5 +/- 7.5 ml/min 5 min post-burn). These data suggest that postganglionic autonomic nerves are at least partially responsible for mediation of the regional vasodilator response to thermal injury.