The absence of gravitational forces experienced during spaceflight produces headward fluid shifts which probably cause Spaceflight Associated Neuro-Ocular Syndrome (SANS). In order to counteract these fluid shifts and prevent SANS, especially when power is limited and a human centrifuge is unavailable, other strategies are needed. One possible strategy is the use of self-generated, lower body negative pressure (LBNP) which meets the low power and safety requirements of deep-space missions. PURPOSE: In this study we explored acute physiologic responses to self-generated LBNP in a horizontal model of simulated microgravity. METHODS: Participants of the study were tested during static 25 mmHg LBNP and compared dynamic self-generating 25 mmHg LBNP chamber as well as upright and supine postures without LBNP. After informed, written consent was obtained, five female and six male subjects’ heart rates and blood pressures were recorded along with cross sectional areas (CSA) of left and right internal jugular veins (IJV) by quantitative ultrasound. RESULTS: Upright IJV CSAs increased significantly when compared to both static and dynamic LBNP. There was a large standard error in the supine posture and no significant differences when comparing the supine posture to the upright posture or either LBNP condition. However, static LBNP reduced IJV CSA by 70% when compared to the supine posture, while dynamic LBNP reduced IJV cross sectional area by 62% compared to supine posture. CONCLUSION: The administered self-generated LBNP and supine LBNP tests and analyses demonstrated that the dynamic, self-generated LBNP may have a similar impact on reducing IJV CSA when compared to traditional static LBNP, thus warranting longer-term tests of self-generated LBNP. In summary, our results suggest that self-generated LBNP at 25 mmHg is as a low-mass, low-volume, unpowered replacement for traditional LBNP hardware (for example, Chibis Suit) during deep-space missions.



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