The effect of prolonged spaceflight on cerebrospinal fluid and perivascular spaces of astronauts and cosmonauts

peer reviewedLong-duration spaceflight induces changes to the brain and cerebrospinal fluid compartments and visual acuity problems known as spaceflight-associated neuro-ocular syndrome (SANS). The clinical relevance of these changes and whether they equally affect crews of different space agencies remain unknown. We used MRI to analyze the alterations occurring in the perivascular spaces (PVS) in NASA and European Space Agency astronauts and Roscosmos cosmonauts after a 6-mo spaceflight on the International Space Station (ISS). We found increased volume of basal ganglia PVS and white matter PVS (WM-PVS) after spaceflight, which was more prominent in the NASA crew than the Roscosmos crew. Moreover, both crews demonstrated a similar degree of lateral ventricle enlargement and decreased subarachnoid space at the vertex, which was correlated with WM-PVS enlargement. As all crews experienced the same environment aboard the ISS, the differences in WM-PVS enlargement may have been due to, among other factors, differences in the use of countermeasures and high-resistive exercise regimes, which can influence brain fluid redistribution. Moreover, NASA astronauts who developed SANS had greater pre- and postflight WM-PVS volumes than those unaffected. These results provide evidence for a potential link between WM-PVS fluid and SANS. Copyright © 2022 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution License 4.0 (CC BY)

A re-investigation of the role of utricular asymmetries in space motion sickness

During the first days of spaceflight, about 50-70% of the astronauts experience symptoms of Space Motion Sickness (SMS). It has been proposed that an asymmetry between the left and right otolith organs contributes to an astronaut's individual susceptibility. A recently developed test to measure unilateral utricular function enabled us to re-investigate this so-called otolith asymmetry hypothesis, while using the paradigm of sustained centrifugation as a ground based model for SMS. This latter paradigm has been shown to elicit symptoms similar to those of SMS and is referred to as Sickness Induced by Centrifugation (SIC). In 15 healthy subjects unilateral utricular function was assessed by recording ocular counter rolling during a unilateral centrifugation paradigm. In addition, saccular function was assessed by recording Vestibular Evoked Myogenic Potentials (VEMPs), and horizontal semicircular canal function was assessed using bithermal caloric stimulation. SIC-susceptible subjects showed a marginally higher degree of utricular asymmetry, utricular sensitivity and semicircular canal sensitivity (p < 0.1) than the non-susceptible group. Interestingly, a logistic regression model using both utricular and semicircular canal parameters led to a correct classification of 91% of the subjects. As such, these results suggest that otolith asymmetry is at most one factor - and not present in all susceptible subjects - in defining susceptibility to SMS and SIC. Both the utricular and the canal system might be involved as well. © 2011 - IOS Press and the authors. All rights reserved

Visual Reinforcement of Illusory Rotations: Habituation to Motion Sickness during Centrifugation

Artificial gravity through centrifugation is currently seen as countermeasure with potential against negative effects of spaceflight. However, side effects like increased motion sickness need to be investigated. Habituation protocols abate conflicts by reducing response to rotation with prolonged exposure to mismatches. Visually reinforced habituation may induce less reduction of oculomotor response to rotation than classical habituation

Centrifugation as a countermeasure during bed rest and dry immersion: What has been learned?

We review the studies that have evaluated intermittent short-radius centrifugation as a potential countermeasure for cardiovascular, musculoskeletal, and sensorimotor deconditioning in simulated weightlessness. Methods: The findings from 18 experimental protocols that have used bed rest and dry immersion for comparing the protective effects of centrifugation versus standing upright or walking, and the effects of continuous vs. periodic exposure to centrifugation are discussed. Results: Centrifugation for as little as 30 min per day was found to be effective in mitigating orthostatic intolerance and strength in postural muscle after 5 days of bed rest, but it was not effective in mitigating plasma volume loss. Conclusion: To determine the optimal prescription for centrifugation as a ountermeasure, we recommend further studies using (a) bed rest of longer duration, (b) individualized prescriptions of centrifugation combined with exercise, and (c) functional performance tests

Effects of five days of bed rest with intermittent centrifugation on neurovestibular function

Objectives: We tested whether intermittent short-radius centrifugation was effective for mitigating alteration in balance and gait following bed rest. Methods: Ten male subjects were exposed to 5 days of 6° head-down tilt bed rest with: (a) no countermeasure; (b) daily 1-g centrifugation for a continuous 30-min period; and (c) daily 1-g centrifugation for six periods of 5 min. During and after the bed rest, subjects were asked to scale the severity of neurovestibular symptoms that followed centrifugation or 80º head-up tilt. Following the bed rest, equilibrium scores were derived from anterior-posterior sway while standing on a foam pad with the eyes open or closed while making pitch head movements, and gait was evaluated by grading subjects’ performance during various locomotion tasks. Results: At the beginning of bed rest, one single 30-min period of centrifugation induced more severe neurovestibular symptoms than six periods of 5-min centrifugation. After bed rest, although equilibrium scores and gait performance were not significantly altered, subjects felt less neurovestibular dysfunction with orthostatic stress when centrifugation was used. Conclusion: Centrifugation was effective at reducing the severity of neurovestibular symptoms after bed rest, but this decrease was not different between one or multiple daily sessions

Study protocol, implementation, and verification of a short versatile upright exercise regime during 5 days of bed rest

Objectives: This work provides a reference for future papers originating from this study by providing basic results on body mass, urine volume, and hemodynamic changes to 5 days of bed rest (BR) and by describing acute cardio-respiratory/mechanographic responses to a short versatile upright exercise battery. Methods: Ten male subjects (mean±SEM age: 29.4±1.5 years; height: 178.8±1.5 cm; body mass: 77.7±1.5 kg) performed, in random order, 5 days of 6° head-down tilt (HDT) BR with no exercise (CON), or BR with daily 25 minutes of quiet upright standing (STA) or upright locomotion replacement training (LRT). Results: Plasma volume, exercise capacity and orthostatic tolerance decreased similarly between interventions following 5 days of BR. Upright heart rate during LRT and STA increased throughout BR; from 137±4 bpm to 146±4 bpm for LRT (P<0.01); and from 90±3 bpm to 102±6 bpm (P<0.001) for STA. Conclusion: the overall similarity in the response to BR, and increase in upright heart rate during the LRT sessions suggest early and advancing cardiovascular deconditioning during 5 days of BR bed rest, which was not prevented by the versatile exercise regime