Adaptive Control Strategies for Mitigating Spaceflight Fluid Shifts Using Lower Body Negative Pressure and Non-Invasive Fluid Shift Sensing

Abstract

Entering a microgravity environment induces cephalad fluid shifts that can lead to cardiovascular and renal-hormonal adaptations that can effect astronaut health and performance in space. The current monitoring strategies for fluid shift lack the ability to track regional fluid shift in real-time, which limits countermeasure efficacy. This thesis aims to highlight the investigation and validation of using prototype non-invasive radiofrequency (RF) sensors for regional fluid shift detection. Additionally, the integration of the feedback from these sensors into Lower Body Negative Pressure (LBNP) chambers could allow for the development of an adaptive Lower Body Negative Pressure regulation framework. Coaxial RF sensors were designed and characterized using tissue phantoms, and tested in a human subject study involving controlled LBNP exposure. Reflection coefficients (S₁₁ and S₂₂) were analyzed to detect regional fluid changes in arm and leg tissue. The preliminary results indicated a statistically significant decrease in the arm reflection coefficients (S₁₁) during active LBNP, which is consistent with fluid being pulled towards the lower body. The leg reflection coefficients (S₂₂) were more variable and did not exhibit statistically significant results, suggesting a need for more investigation with placement and sensor sensitivity. This work demonstrates the potential of using wearable RF sensors for non-invasive fluid shift monitoring and lays the foundation for integrating fluid sensor feedback into adaptive LBNP control protocols to improve astronaut health monitoring and countermeasure personalization.