Cardiovascular adaptations during sustained acceleration in a short-arm human centrifuge Increases in heart rate, and total peripheral resistance are the main counter-measures during consecutive +g-force exposure

Introduction: During exposure to hyper gravity (+Gz), a massive strain on the cardiovascular system takes place, via blood sequestration in the lower extremities and splanchnic vessels of the pelvis. This blood sequestration leads to a substantial decline in cardiac output (CO) and stroke volume (SV). In order to maintain adequate mean arterial pressure (MAP) , upsurges in heart rate (HR) and total peripheral resistance (TPR) occur as physiologic counter-measures. The objective of this study was to examine how these counter measures react during 2 consecutive rounds of +Gz in a short arm human centrifuge (SAHC). Methods: 20 non-pilot G-force test subjects were exposed to 9 phases of alternating +Gz in an SAHC To measure hemodynamics during the +Gz profile, cardiac output (CO),heart rate (HR), left ventricular ejection time (LVET), mean arterial pressure (MAP), pulse interval (PI), stroke volume (SV), and total peripheral resistance (TPR) were continuously monitored. Results: Out of 20 G-Force test subjects, 14 accomplished all 9 phases of shifting sustained acceleration. The hemodynamics of these 14 successfully maintained a stabile mean arterial pressure (MAP) (13% above baseline values) under conditions of +Gz . This was accomplished via increases in heart rate (HR) (35% above baseline) and total peripheral resistance (TPR) (50% above baseline). Decreases in left ventricular ejection time (LVET) & pulse interval (PI) (24% below baseline) were also significant factors in maintaining MAP. Discussion: The results from this study show that the cardiovascular system can adapt to consecutive +Gz via alternating increases in HR and TPR, as well as decreases in LVET and PI. Through this orchestration of physiologic countermeasures, MAP can be sufficiently maintained, thereby retaining adequate perfusion throughout continued hyper gravitational stress.