CARDIOVASCULAR ADAPTATIONS DURING SUSTAINED ACCELERATION IN A SHORT-ARM HUMAN CENTRIFUGE AMONGST G-FORCE NAIVE INDIVIDUALS

摘要

Introduction The purpose of this investigation was to examine the endogenous physiological cardiovascular counter measures active during 2 rounds of alternating +Gz s in a short arm human centrifuge (SAHC). We hypothesized that the hemodynamic mechanisms at play during initial +Gz, such as increases in heart rate (HR) and total peripheral resistance (TPR), would react to a second +Gz phase profile in the same manner. Methods 20 subjects, were exposed to two rounds of +Gz in a SAHC. The G force profile followed a plan of nine phases of varying +Gz exposure. Each subject began with a baseline +0Gz exposure, followed by step by step +Gz phase profile of+1Gz-+2Gz-+1Gz. The second round was identical to the first round of +Gz. Each phase lasted for four minutes. During this experiment, non-invasive cardio-vascular parameters were recorded. The parameters examined were cardiac output (CO), heart rate (HR), mean arterial pressure (MAP), stroke volume (SV), systolic/diastolic blood pressure (sys/dia BP), and total peripheral resistance (TPR). Results From the 20 subjects, 14 successfully completed the entire +Gz profile. In the first round of+Gz, amongst these 14 subjects,HR increased to 34% & TPR to 51% over baseline levels, in order to offset a 28% decrease in CO. In the second round of +Gz, HR & TPR increased to over 35% and 45% over baseline respectively, whereas CO decreased to 32% below baseline. Discussion The results from this study showed that the physiological counter-measures active during a first exposure to +Gz arc just as active in a subsequent second exposure to +Gz.