Passive and Active Behavior of the Cardiovascular System Under IncreasedGravitational Loads in a Chronically Instrumental Conscious Baboon Model

摘要

Simultaneous recordings of right atrial, left atrial, left ventricular (LV) andaortic pressure (AOP), aortic root flow and LV dimensions were recorded in chronically instrumented baboons at rest and undergoing centrifugation that mimicked military aviation acceleration environments. We separated the early and late hemodynamic responses to increased +Gz loads during acceleration using a rapid onset-rapid return (ROR) (>4.5G/S) centrifugation protocol. +Gz onset resulted in immediate changes in vascular pressure from hydrostatic effects, followed by passive shifting of blood volume to dependent regions causing declines in systemic pressure above the hydrostatic indifference point (HIP) and in venous return. Stroke volume (SV) and mean cardiac power output fell. Distending carotid level pressure routinely fell during acceleration to levels well outside threshold values previously reported for carotid baroreflex function. Active compensation consisted of increases in heart rate, AOP and decreases in aortic flow. Previous +Gz load history had enormous impact on blood pressure regulation during increased +Gz loads and on baseline pressures existing prior to exposure to a second +Gz onset. Animals exposed to a conditioning run that saturated their short-term pressure regulatory mechanisms 5 min before a second +Gz exposure, displayed significantly higher mean aortic root pressures and consistently overshot their baseline operating points during centrifugation. We conclude that hemodynamic consequences of rapid-onset acceleration are extremely complex and may provide conflicting error signal information during compensatory adjustments. Baroreflex, Initial hemodynamic responses, Centrifuge, Late hemodynamic responses, Hypergravity, Military aviation environments.