Modeling human orthostatic responses on the Moon and on Mars

• DOI: 10.1007/s10286-018-0527-x
• Publication Date: 2018-04-26T07:14:47Z
• Authors: Paula Beck; Jens Tank; Peter Gauger; Luis E. J. Beck; Hubert Zirngibl; Jens Jordan; Ulrich Limper
• Keywords: Adult; Male; Extraterrestrial Environment; Posture; Mars; Syncope; Cardiovascular Physiological Phenomena; Young Adult; 03 medical and health sciences; 0302 clinical medicine; Heart Rate; Manned space flight; Humans; Inertial resistance; Arterial Pressure; Moon; Parabolic flight; Cardiovascular physiology; Partial gravity; Baroreflex; Middle Aged; Space Flight; Healthy Volunteers; 13. Climate action; Orthostasis; Female; Space Simulation; Gravitation

Since manned missions to the Moon and Mars are planned, we conducted active standing tests with lunar, Martian, terrestrial, and 1.8 loads of inertial resistance (+Gz) modeled through defined parabolic flight maneuvers. We hypothesized that the cardiovascular response to active standing is proportional to the +Gz load.During partial-+Gz parabolic flights, 14 healthy test subjects performed active stand-up maneuvers under 1 +Gz, lunar (0.16 +Gz), Martian (0.38 +Gz), and hyper inertial resistance (1.8 +Gz) while heart rate and finger blood pressure were continuously monitored. We quantified amplitudes and timing of orthostatic response immediately following standing up.The maximum early heart rate increase was 21 (SD ± 10) bpm with lunar, 23 (± 11) bpm with Martian, 34 (± 17) bpm with terrestrial +Gz, and 40 (± 11) bpm hyper +Gz. The time to maximum heart rate increased gradually with increasing loads of inertial resistance. The transient blood pressure reduction was most pronounced with hyper +Gz but did not differ significantly between lunar and Martian +Gz. The mean arterial pressure nadir was reached significantly later with Martian and lunar compared to 1 +Gz. Paradoxically, the time for blood pressure to recover was shortest with terrestrial +Gz.While load of inertial resistance directly affects the magnitude of the transient blood pressure reduction and heart rate response to active standing, blood pressure stabilization is most rapidly attained during terrestrial +Gz. The observation might suggest that the human cardiovascular system is tuned to cope with orthostatic stress on earth.