Effects of Venoconstrictive Thigh Cuffs on Dry Immersion-Induced Ophthalmological Changes

Abstract

Neuro-ophthalmological changes named spaceflight associated neuro-ocular syndrome (SANS) reported after spaceflights are important medical issues. Dry immersion (DI), an analog to microgravity, rapidly induces a centralization of body fluids, immobilization, and hypokinesia similar to that observed during spaceflight. The main objectives of the present study were 2-fold: (1) to assess the neuro-ophthalmological impact during 5 days of DI and (2) to determine the effects of venoconstrictive thigh cuffs (VTC), used as a countermeasure to limit headward fluid shift, on DI-induced ophthalmological adaptations. Eighteen healthy male subjects underwent 5 days of DI with or without VTC countermeasures. The subjects were randomly assigned into two groups of 9: a control and cuffs group. Retinal and optic nerve thickness were assessed with spectral-domain optical coherence tomography (OCT). Optic nerve sheath diameter (ONSD) was measured by ocular ultrasonography and used to assess indirect changes in intracranial pressure (ICP). Intraocular pressure (IOP) was assessed by applanation tonometry. A higher thickness of the retinal nerve fiber layer (RNFL) in the temporal quadrant was observed after DI. ONSD increased significantly during DI and remained higher during the recovery phase. IOP did not significantly change during and after DI. VTC tended to limit the ONSD enlargement but not the higher thickness of an RNFL induced by DI. These findings suggest that 5 days of DI induced significant ophthalmological changes. VTC were found to dampen the ONSD enlargement induced by DI.

Reduced Regional Cerebral Blood Flow Measured by 99mTc-Hexamethyl Propylene Amine Oxime Single-Photon Emission Computed Tomography in Microgravity Simulated by 5-Day Dry Immersion

“…During 3-day DI, Kermorgant et al (2017) showed an increase in ONSD of about 30%, as measured with ultrasound (Pre-DI: 4.64±0.40mm; DI3: 6.01±0.49mm; p <0.001; Kermorgant et al, 2017 ). In DI5-CUFFS, Kermorgant et al (2021) have found a significant increase of ONSD after 5days of DI by 20% in the control group and 14% in the cuffs group ( Kermorgant et al, 2021 ). These ONSD values are equivalent to an elevation of ICP around 20mmHg, the normal range being between 7 and 15mmHg ( Geeraerts et al, 2008 ).…”

Early Deconditioning of Human Skeletal Muscles and the Effects of a Thigh Cuff Countermeasure

“…After five days of DI, participants were found to have a loss in muscle strength, muscle fiber atrophy, impaired protein balance, and decreased oxidative capacity, regardless of the use of a thigh cuff. In contrast, measurements on cardiovascular and ophthalmological function carried out by our collaborators have shown a beneficial effect of the thigh cuff to prevent the adverse effects of body fluid redistribution induced by 5 days of DI [ 30 , 31 , 32 ].…”

DI-5-Cuffs: Bone Remodelling and Associated Metabolism Markers in Humans After Five Days of Dry Immersion to Simulate Microgravity

“…The main limitation of this study is the low number of subjects in each group ( n = 9). The number of subjects was not specifically powered for bone metabolism criteria, but for change in optic nerve sheath diameter, a primary outcome measure for this protocol (ck Kermorgant et al, 2021 ). This might have been responsible for the lack of significant changes, as seen for example in Glu-OC since statistical difference was achieved with the unique group of 12 subjects in the 1st experiment ( Linossier et al, 2017 ).…”

“…This integrative study was primarily designed to test the efficacy of venoconstrictive thigh cuffs, as countermeasure to limit cephalad fluidshift, on DI-induced deconditioning, in particular for body fluids and related ophthalmological disorders (for results cf. Robin et al, 2020 ; Kermorgant et al, 2021 ). However, several physiological systems interact, including the cardiovascular and musculoskeletal systems.…”