CENTRAL VASCULAR FLOW PATTERNS IN THE ALLIGATOR ALLIGATOR MISSISSIPIENSIS

Many different flow patterns have been described through the central c irculation of crocodilian reptiles. We tested the hypothesis that the vagus nerve stimulation promotes right-to-left (R-L) shunting in the a lligator. Flow patterns were investigated before and during stimulatio n of the intact left vagus nerve using three methods. 1) Atrial and ao rtic Po-2 were measured simultaneously and continuously by gas probes. 2) Atrial outflows were tracked with a blood tracer (helium). 3) Flow s were assessed with echocardiography. Four different flow patterns we re observed before vagal stimulation: left ventricular (LV) blood flow ed into both the right (RAo) and left (LAo) aortas, whereas right vent ricular (RV) blood flowed only into the LAo; both aortas received a mi xture of LV and RV blood; only LV blood perfused both aortas; and RV b lood flowed into both aortas, but LV blood flowed only into the RAo. D uring vagal stimulation, both aortas received a mixture of LV and RV b lood in half of the animals, and in the other half, both aortas receiv ed RV blood, but LV blood flowed only into the RAo. Doppler and contra st echocardiography demonstrated swirling flow in the foramen of Paniz za and the base of the LAo during systole. These data indicate that va gal stimulation either maintains or produces R-L shunting, flow patter ns are variable, and blood can swirl in the foramen of Panizza and LAo base.