Evaluating countermeasures in spaceflight analogs

Abstract

Countermeasures are defined as solutions to prevent the undesirable physiologic outcomes associated with spaceflight. Spaceflight analogs provide a valuable opportunity for the evaluation of countermeasures because they allow for the evaluation of more subjects, more experimental control, and are considerably less expensive than actual spaceflight. The various human analogs have differing strengths and weaknesses with respect to the development and evaluation of countermeasures. The human analogs are briefly reviewed with a focus on their suitability for countermeasure evaluation. Bed rest is the most commonly used analog for evaluating countermeasures. While countermeasures are typically developed to target one or maybe two particular physiologic issues, it is increasingly important to evaluate all of the organ systems to discern whether they might be unintended consequences on nontargeted tissues. In preparation for Mars exploration it will be necessary to fully integrate countermeasures to protect all organ systems. The synergistic and antagonistic effects of multiple countermeasures needs to be the focus of future work.

Hypoxia Aggravates Inactivity-Related Muscle Wasting

“…The bed rest experimental model, initially established as an earth-based analog to explore the effects of space-travel related microgravity ( Deitrick et al, 1948 ), is especially valuable as it provides a unique insight into the integrative physiological deconditioning in response to whole body unloading. Bed rest investigations that were performed over the last half-century clearly showed that whole body inactivity generally provokes muscle atrophy of the lower limbs at an initial rate of about 2–3% per week ( Pavy-Le Traon et al, 2007 ; Narici and de Boer, 2011 ; Ploutz-Snyder, 2016 ). Thus, previous work suggests that a ∼7–12% reduction of the thigh and calf muscle mass can be expected following 3 weeks of bed rest-induced inactivity ( Kawakami et al, 2000 , 2001 ; Akima et al, 2001 ; Kubo et al, 2004 ).…”

High-Intensity Exercise Mitigates Cardiovascular Deconditioning During Long-Duration Bed Rest

“…Space agencies are thus investigating adverse health effects of long-term missions and their possible countermeasures in order to reduce detrimental consequences for astronaut health (Aubert et al, 2016 ; Bergouignan et al, 2016 ; Frippiat et al, 2016 ; White et al, 2016 ; Lang et al, 2017 ). Space analogs simulating prolonged gravity changes therefore play a crucial role (Ploutz-Snyder, 2016 ). Bed rest with −6 degrees head-down tilt (HDT) is one of the best conditions to mimic the effect of long-term weightlessness on the human body—even within the limitations of this model.…”

“…Despite research spanning at least four decades on weightlessness-associated cardiovascular alterations (Pavy-Le Traon et al, 2007 ; Hargens and Vico, 2016 ), the exact time courses of changes in hemodynamic regulation and autonomic cardiovascular control induced by long-term spaceflight are not fully understood (Liu et al, 2015 ; Aubert et al, 2016 ). Moreover, several countermeasures for cardiovascular deconditioning have already been tested (e.g., volume loading, lower-body negative pressure, hypergravity; Wang et al, 2011 ; Stenger et al, 2012 ; Jeong et al, 2014 ; Li et al, 2017 ), but exercise is the most investigated countermeasure (Blaber et al, 2009 ; Petersen et al, 2016 ; Ploutz-Snyder, 2016 ). However, despite the consensus on physical activity as a countermeasure, the type and intensity of the exercise are undergoing further investigation.…”

Breast Cancer Cells in Microgravity: New Aspects for Cancer Research

“…Therefore, there is little or no genetic memory in organisms on how to respond to force changes in the low gravity range. Hence, it is likely that terrestrial life adapting to µ g will reveal many novel mechanisms that could be helpful in biomedical research [ 8 , 9 , 10 ].…”