Human Performance in Altered-Gravity Environments
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Texas A&M University, United States
Astronauts undergo important physiological deconditioning in space due to the weightless environment. Some of the most common issues include bone loss, muscle atrophy, cardiovascular deconditioning, spaceflight-associated neuro-ocular syndrome, and neurovestibular alterations. Currently, several countermeasures are in place that have notably reduced the detrimental effects of weightlessness, but they require significant crew time and resources. New approaches, possibly combining novel and current countermeasures are needed, especially for longer missions such as a trip to Mars where astronauts will not have the ground support usually provided when landing on Earth.
Artificial Gravity (AG) has often been proposed as a multi-system countermeasure capable of mitigating most of the physiological deconditioning occurring in reduced gravity levels, particularly if combined with exercise (Clément 2017; Clément, Charles, and Paloski 2016). Artificial gravity has never been tested in space as a countermeasure, but multiple ground studies have shown its benefits in various physiological systems, including cardiovascular, neurovestibular, and musculoskeletal systems. Despite the potential benefits, many questions still remain about its implementation. Aspects such as the appropriate gravity level, centrifuge configuration, radius, angular velocity, exposure time, exercise modality, exercise protocol, or safety concerns are still unanswered, and require further investigation.
Our artificial gravity research program at the Bioastronautics and Human Performance group at Texas A&M University focuses on investigating human performance in altered-gravity environments to inform future AG implementation as a spaceflight countermeasure. We are using both experimental and computational approaches to develop quantitative models to predict partial-gravity dose-response relationships (i.e. the relationship between a physiological response and the magnitude of G-level) and test the new models in experiments with human subjects. Our current and future research platforms include a short-radius centrifuge, a tilting bed-platform, parabolic flights, and a reduced-gravity treadmill.
In our previous research efforts, we conducted a human experiment using a short-radius centrifuge to quantify the effects of gravity level and cycling exercise intensity on multiple aspects of human physiology, including cardiovascular responses, foot forces, and comfort. This was the first study to characterize and quantify the transient cardiovascular response in human subjects to a combination of multiple levels of artificial gravity and exercise intensity in a short-radius centrifuge. All subjects tolerate well the centrifugation protocol, and our quantitative results showed that the addition of artificial gravity to exercise could provide a greater cardiovascular benefit than exercise alone (Diaz Artiles 2015; Diaz, Heldt, and Young 2015; Diaz, Trigg, and Young 2015). Using these experimental data, we developed and validated a unique lumped-parameter model of the cardiovascular system that includes both the effects of gravity gradient and ergometer exercise. Identical centrifugation and exercise profiles were simulated and compared to the experimental data and results show that the model is capable of reproducing the cardiovascular changes due to both centrifugation and exercise, including the dynamic responses during transitions between the different phases of the protocol (Diaz Artiles 2015; Diaz Artiles, Heldt, and Young 2016).
Current and future research efforts include a human experiment using the tilt-platform to study cardiopulmonary responses to ergometer exercise in multiple simulated hypo-gravity conditions (Berg and Diaz Artiles 2017; Perez, Navarro Tichell, and Diaz Artiles 2018). Tilt paradigms are commonly used to simulate hypo-gravity conditions. The principle is to recreate the fluid shift from the lower extremities towards the upper part of body that occurs when the gravitational force is partially or completely removed. A head-down tilt (HDT) of -6 degrees is widely accepted as a microgravity analog. Similarly, we can recreate the partial fluid shift conditions at different gravity levels by using the appropriate tilt angles (Head-up tilt or HUT) and considering the gravitational component in the head to-toe direction (Gz) We are particularly interested in the following environments: microgravity: -6° head down tilt; Moon: +9.5° head up tilt (HUT); Mars: +22.3° HUT; and upright. These four conditions will provide a good quantitative set of data to generate the gravitational dose-response curve of the cardiopulmonary system during exercise in the hypo-gravity domain.
Additionally, we are implementing a comprehensive sensitive analysis of our cardiovascular model using Latin Hypercube Sampling/Partial Rank Correlation Coefficient (LHS/PRCC) techniques to study output changes due to subject variability. Simulations are also being conducted under different gravitational conditions, both constant gravity environments as well as artificial gravity created by a short-radius centrifuge, which generates a strong gravity gradient along the body Gz direction. (Alonso and Diaz Artiles 2018). Results from this study will provide quantitative information about the effect of individual differences on cardiovascular responses to orthostatic stress. Additional modeling efforts include the extension of the current capabilities of this model by introducing pulmonary and metabolic effects, as well as long-term effects, including time-dependencies in model parameters and blood volume regulation mechanisms.
References
Alonso, Diego A. and Ana Diaz Artiles. 2018. “Understanding Gravitational Effects on the Cardiovascular System Using a Lumped-Parameter Model: Sensitivity Analysis.” in 2018 NASA Human Research Program Investigators’ Workshop, Galveston, TX.
Berg, E. W. and Ana Diaz Artiles. 2017. “Exercise in Altered Gravity for Increased Health during Space Exploration.” in 2017 NASA Human Research Program Investigators’ Workshop. Galveston, TX.
Clément, Gilles. 2017. “International Roadmap for Artificial Gravity Research.” Npj Microgravity 3(1):29.
Clément, Gilles R., John B. Charles, and William H. Paloski. 2016. “Revisiting the Needs for Artificial Gravity during Deep Space Missions.” Reach 1:1–10.
Diaz, Ana, Thomas Heldt, and Laurence R. Young. 2015. “Cardiovascular Responses to Artificial Gravity Combined with Exercise.” IEEE Aerospace Conference Proceedings 2015–June.
Diaz, Ana, Chris Trigg, and Laurence R. Young. 2015. “Combining Ergometer Exercise and Artificial Gravity in a Compact-Radius Centrifuge.” Acta Astronautica 113:80–88.
Diaz Artiles, Ana. 2015. “Exercise under Artificial Gravity – Experimental and Computational Approaches.” PhD Thesis, Massachusetts Institute of Technology, Cambridge, MA.
Diaz Artiles, Ana, Thomas Heldt, and Laurence R. Young. 2016. “Effects of Artificial Gravity on the Cardiovascular System: Computational Approach.” Acta Astronautica 126:395–410.
Perez, Francisca, Patricia Navarro Tichell, and Ana Diaz Artiles. 2018. “Cardiopulmonary Responses to Exercise in Altered-Gravity Environments.” in 2018 NASA Human Research Program Investigators’ Workshop, Galveston, TX.
Keywords:
centrifuge,
computational modeling,
Artificial gravity,
cardiovascular responses,
Orthostatic intolerance,
Gravitational dose-response curves,
Human experiments,
Human spaceflight,
Space countermeasure,
Exercise
Conference:
39th ISGP Meeting & ESA Life Sciences Meeting, Noordwijk, Netherlands, 18 Jun - 22 Jun, 2018.
Presentation Type:
Extended abstract
Topic:
Astronaut health
Citation:
Diaz Artiles
A
(2019). Human Performance in Altered-Gravity Environments.
Front. Physiol.
Conference Abstract:
39th ISGP Meeting & ESA Life Sciences Meeting.
doi: 10.3389/conf.fphys.2018.26.00032
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Received:
02 Dec 2018;
Published Online:
16 Jan 2019.
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Correspondence:
Prof. Ana Diaz Artiles, Texas A&M University, College Station, United States, adartiles@tamu.edu