AN ACUTE ANIMAL-MODEL THAT SIMULATES THE HEMODYNAMIC SITUATIONS PRESENT DURING +G(Z) ACCELERATION

Air combat maneuver acceleration (G) profiles with onset/ offset patte rns that occur faster than the response characteristics of the human c ardiovascular system may lead to regulatory instability and, ultimatel y, acceleration-induced loss of consciousness (G-LOC) incidents. We ha ve developed an acute animal model that simulates the hemodynamic situ ations seen under acceleration to study the effects of complex G envir onments on individual reflexogenic areas. This preparation allowed us to individually isolate the effects of high gravity on venous return a nd cardiac preload, arterial baroreflexes and splanchnic capacity. Thi s report describes the preparation and presents examples of the types of +Gz simulations possible and recordings of the responses of the ani mals. Further, we tested the hypothesis that the volume of blood displ aced from the cephalic regions of the circulation and the rate of disp lacement into the splanchnic capacitance with G onset is affected by d istending pressure at the carotid/aortic baroreceptor sites. Early res ults from 7 dogs show that resistance to flow into the splanchnic beds is affected by changes in distending pressure occurring at arterial b aroreceptor sites. When pressure distending the carotid/aortic barorec eptors was increased, resistance to flow into the abdominal vascular b eds was decreased. This result suggests that sudden increases in +Gz l oads occurring during the overshoot phase from a previous G-peak may r esult in reduced tolerance.