Microgravity-Induced Fluid Shift and Ophthalmic Changes
Abstract
:1. Introduction
2. The Visual Impairment and Intracranial Pressure (VIIP) Syndrome
CPG Class | Definition | No. of Affected Crewmembers |
---|---|---|
Non Cases |
| 2 |
1 | (repeat Optical Coherence Tomography (OCT) and visual acuity in 6 weeks)
| 2 |
2 | (repeat OCT, cycloplegic refraction, fundus exam and threshold visual field every four to six weeks x six months, repeat Magnetic Resonance Imaging (MRI) in six months)
| 8 |
3 | (repeat OCT, cycloplegic refraction, fundus exam and threshold visual field every four to six weeks x six months, repeat MRI in six months)
| 1 |
4 | (institute treatment protocol as per CPG)
| 4 |
Unclassified |
| 19 |
Ophthalmic Condition | Total Affected |
---|---|
Optic nerve sheath distension | 6/7 (86%) |
Nerve fiber layer thickening | 6/7 (86%) |
Optic disc edema | 5/7 (71%) |
Posterior globe flattening | 5/7 (71%) |
Hyperopic shift in one or both eyes by >+0.50 diopters | 5/7 (71%) |
Choroidal folds | 4/7 (57%) |
Elevated postflight CSF pressure (indicative of increased ICP) | 4/7 (57%) |
Cotton wool spots | 3/7 (43%) |
Decreased intraocular pressure (IOP) postflight | 3/7 (43%) |
Tortuous optic nerve | 2/7 (29%) |
3. Fluid Redistribution in Microgravity
3.1. Reduced Gravity Environments
3.2. Simple Physical Systems
3.3. Human Beings in Space and the Cephalic Fluid Shift
3.3.1. Hydrostatic and Biomechanical Effects on Humans in Spaceflight and Simulated Spaceflight
- The height of the fluid column,
- The initial fluid volume,
- The volume, saturation potential and material properties of fat, muscle and other porous tissues,
- The bones, cartilage and other tissues that may limit volumetric expansion,
- The water storage capacity and compliance of vascular and extravascular systems,
- The presence of semipermeable membranes that separate fluid volumes, such as the blood/brain barrier, and
- The distribution of all these components along the height of the body.
3.3.2. Experimental Data on the Impact of Cephalic Fluid Shift
4. The Ocular Environment in Spaceflight
4.1. Intracranial Pressure Dynamics, Ocular Blood Flow and Biomechanics
4.2. The Spacecraft Environment and Other Potential Factors in the Development of VIIP
- Low humidity and high CO2 concentrations, with periods of exposure to low total pressure and 100% O2 during extravehicular activity,
- Increased radiation levels with the potential of exposure to high energy ‘cosmic ray’ radiation,
- A high salt diet resulting from a change in taste acuity, and
- A disrupted circadian rhythm.
5. Concluding Remarks
Nomenclature and Abbreviations
A | Mean cross-sectional area inside the blood vessel |
COP | Colloid Osmotic Pressure |
CPG | Clinical Practice Guidelines |
CRA | Central Retinal Artery |
CSF | Cerebrospinal fluid |
CWS | Cotton wool spots |
d | Diameter |
GCR | Galactic Cosmic Rays |
g | Gravitational or net acceleration |
ge | Gravitational acceleration at sea level on earth |
h | Axis along which gravity acts |
ĥ | Local axis aligned with the height of the body |
Hb | Total height of the body |
Ht | Total height of the tubular balloon |
HDT | Head-Down Tilt |
ICP | Intracranial Pressure |
IIH | Idiopathic Intracranial Hypertension |
IOP | Intraocular Pressure |
ISS | International Space Station |
m | Mass |
MCA | Middle Cerebral Artery |
MR | Magnetic resonance (imaging) |
OCT | Optical coherence tomography |
OA | Ophthalmic artery |
OD | Oculus dexter (right eye) |
ON | Optic nerve |
OND | Optic nerve disc |
ONS | Optic nerve sheath |
ONSD | Optic nerve sheath diameter |
OS | Oculus sinister (left eye) |
OV | Ophthalmic vein |
pcsf | Cerebrospinal fluid pressure |
PV | Plasma Volume |
Q | Mean volumetric flow rate |
RBC | Red blood cell |
SPE | Solar particle event |
SRB | Solid Rocket Boosters |
SSME | Space Shuttle Main Engines |
V | Mean velocity |
VIIP | Visual Impairment and Intracranial Pressure |
W | Weight |
Δph | Hydrostatic pressure gradient |
ρ | Density |
Acknowledgments
Author Contributions
Conflicts of Interest
References and Notes
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Nelson, E.S.; Mulugeta, L.; Myers, J.G. Microgravity-Induced Fluid Shift and Ophthalmic Changes. Life 2014, 4, 621-665. https://doi.org/10.3390/life4040621
Nelson ES, Mulugeta L, Myers JG. Microgravity-Induced Fluid Shift and Ophthalmic Changes. Life. 2014; 4(4):621-665. https://doi.org/10.3390/life4040621
Chicago/Turabian StyleNelson, Emily S., Lealem Mulugeta, and Jerry G. Myers. 2014. "Microgravity-Induced Fluid Shift and Ophthalmic Changes" Life 4, no. 4: 621-665. https://doi.org/10.3390/life4040621