Space flight associated neuro-ocular syndrome (SANS) is a combination of pathological ophthalmic findings that have been documented in a subset of astronauts that participated in long-duration missions (6+ months) to the International Space Station (ISS). The leading hypothesis for SANS is that the lack of a gravitational vector acting on the body results in a headward body fluid shift that can lead to damage to the eye. Recent research has revealed multiple structural changes in the eye and brain that occur in astronauts with SANS. To help mitigate these structural changes, it is imperative to validate a ground-based analog for spaceflight which can reproduce the structural and physiological changes observed in astronauts.
This experiment will use non-invasive magnetic resonance imaging (MRI) and optical coherence tomography (OCT) to quantify structural and physiologic changes in the brain and eye that occur in prolonged six-degree head-down tilt (HDT) and examine if these alterations can be mitigated using countermeasures.
The experiment includes three specific aims.
(1) Quantify ophthalmic and intracranial alterations in HDT bed rest subjects and postural control subjects compared to pre-bed rest.
(2) Determine if countermeasures can prevent and/or reduce HDT bed rest-induced cerebral and ocular alterations.
(3) Compare alterations in HDT subjects to those already quantified in astronauts that developed SANS.
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This experiment will expose 48 healthy human subjects (four groups; 12 subjects per group) between the ages of 35-55 years to 30 days of bed rest at the Germany Space Agency’s (DLR) :envihab facility. The treatments include: a posture-control group where subjects will remain in strict 6° HDT bedrest with no countermeasures. The three treatment groups will include (1) a posture-control group where subjects will remain in strict 6° HDT bedrest for 18 hours/day with two three-hour sessions in the seated posture, daily, (2) strict 6° HDT bedrest with exercise and veno-occlusive thigh cuffs, and (3) strict 6° HDT bedrest with two three-hour sessions of 25 mmHg lower body negative pressure (LBNP), daily.
Data collected from the subjects in these groups will be compared to data collected from ISS astronauts with SANS.
MRI and optical coherence tomography (OCT) images will be obtained 24 hours before beginning bed rest to establish a baseline, at the conclusion of bed rest to quantify changes resulting from bed rest, and 24 hours post-ending bed rest to observe HDT bed rest-induced adaptation recovery and compare to ISS astronaut data.
The researchers expect significant changes will occur over the 30-day HDT study period, ophthalmic and intracranial changes will be mitigated in the countermeasure treatment groups (veno-occulsive thigh cuff and LBNP), and the changes observed in the control group (strict HDT, no countermeasure) will be similar to the changes observed in astronauts who developed SANS. Some of the parameters to be investigated in this experiment have not been previously measured in astronauts and will provide new insight into the physiologic changes underlying HDT bed rest and inform future research with long-duration space flight astronauts.
Jugular venous outflow
Aqueduct of Sylvius stroke volume
Blood flow volume
Brain tissue volume, gray matter
Brain tissue volume, white matter
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Cerebral spinal fluid center of gravity
Choroidal thickness - peripapillary and sub-macular
Globe volumetric displacement
Intracranial compliance index
Optic nerve diameter
Optic nerve sheath diameter
Peak-to-peak flow amplitude
Retinal nerve fiber layer thickness