An acute animal model that simulates the hemodynamic situations present during +Gz acceleration.

Air combat maneuver acceleration (G) profiles with onset/offset patterns that occur faster than the response characteristics of the human cardiovascular system may lead to regulatory instability and, ultimately, acceleration-induced loss of consciousness (G-LOC) incidents. We have developed an acute animal model that simulates the hemodynamic situations seen under acceleration to study the effects of complex G environments on individual reflexogenic areas. This preparation allowed us to individually isolate the effects of high gravity on venous return and cardiac preload, arterial baroreflexes and splanchnic capacity. This report describes the preparation and presents examples of the types of +Gz simulations possible and recordings of the responses of the animals. Further, we tested the hypothesis that the volume of blood displaced from the cephalic regions of the circulation and the rate of displacement into the splanchnic capacitance with G onset is affected by distending pressure at the carotid/aortic baroreceptor sites. Early results from 7 dogs show that resistance to flow into the splanchnic beds is affected by changes in distending pressure occurring at arterial baroreceptor sites. When pressure distending the carotid/aortic baroreceptors was increased, resistance to flow into the abdominal vascular beds was decreased. This result suggests that sudden increases in +Gz loads occurring during the overshoot phase from a previous G-peak may result in reduced tolerance.