This study occurs in collaboration with the :envihab facility in the German Aerospace Center (DLR). Four campaigns are now associated with this study. The Aims, Methods, and Results of the second year of this proposal are described below: SPECIFIC AIMS

Specific Aim 1: To determine if donning veno-occlusive thigh cuffs during and for 120 minutes after daily aerobic exercise can be used to (a) reverse headward fluid shift from bed rest for a sustained period of time, and (b) prevent ocular structural and functional changes from developing at the end of bed rest.

Hypothesis 1a: Donning veno-occlusive thigh cuffs during and after daily aerobic exercise will provide an acute and sustained fluid redistribution into the lower extremities (measured using femoral artery conductance and vasculature cross-sectional area) with a corresponding reduction in internal jugular vein cross-sectional area for up to 2 hours after cessation of exercise.

Hypothesis 1b: There will be a decrease in prevalence and magnitude of optic disc edema in subjects performing the exercise countermeasure (CM) outlined in Specific Aim 1 (SA1) compared to subjects in the head-down tilt group who perform no CM. Advanced analyses of optical coherence tomography (OCT) images of the optic nerve head, combined with electrophysiological assessment of ganglion cell function, will unveil functional decline and together may serve as a more sensitive endpoint compared to the visual fields tests currently used in astronauts.

Specific Aim 2: To determine the role of altered vasculature in the development of optic disc edema in this spaceflight analog. [Ed. Note: This spaceflight analog is the :envihab facility at the Deutsches Zentrum für Luft- und Raumfahrt (DLR) in Cologne, Germany.]

Hypothesis 2a: Optical coherence tomography angiography (OCTA) will reveal vascular alterations in the foveal avascular zone (FAZ) area or vascular density in the macula and nerve with intravenous fluorescein angiography showing leakage in subjects demonstrating the greatest degree of retinal thickening.

Hypothesis 2b: There will be a decrease in OCTA and intravenous fluorescein angiography alterations in subjects performing exercise CM outlined in SA1 compared to subjects in the head-down tilt group who perform no CM.

MATERIALS AND METHODS

This study is scheduled to occur at the :envihab facility in the German Aerospace Center (DLR). Previously, six campaigns were associated with this study. The six arms of the study included (1) an upright control, and (2) a 60-day bed rest 6-degrees head-down tilt (HDT) control. All experimental arms included the 30-day 6-degrees bed rest HDT condition combined with four CMs: (1) veno-occlusive thigh cuffs and exercise, (2) lower-body negative pressure (LBNP), (3) a B-vitamin supplement, and (4) a 6-hour upright posture CM. The CM focus of this proposal is #1. During this last year, and due to research resources re-focusing during the COVID-19 pandemic, two arms were removed from this study, the upright control and CM #3. For this proposal, the exercise and veno-occlusive thigh cuff CM will be performed 6 days a week. Each session will include exercise (60 min) that will be sustained at ~60% of pre-bedrest peak oxygen consumption with the veno-occlusive thigh cuff applied at 60 mm Hg for two hours after exercise cessation. Endpoints will be measured before, during, and after the study. These include intraocular pressure (IOP), optical coherence tomography (SPECTRALIS HRA+OCT imaging platform) of the macula and optic nerve, ultrasound measure of neck and lower extremity vessels, optical coherence tomography angiography (OCTA) of the macula and optic nerve, and electrophysiology for ganglion cell function. Intravenous fluorescein angiography (IVFA) will be performed to assess blood:brain vascular integrity at the optic nerve head immediately after cessation of the 30-day bed rest period.

Overall, OCTA, IVFA, and electroretinogram (ERG) endpoints will be assessed across all arms in addition to subjects in the CM #1 group.

RESULTS

This study is scheduled to occur at the :envihab facility at the German Aerospace Center (DLR). There are 4 campaigns. Campaigns 1 and 2 (C1/C2) were scheduled to be comprised of 12 subjects each. For each group of 12, 6 subjects received the upright CM, and 6 subjects received the LBNP CM. C1 ended in December 2021 (12/2021) with data acquired from 12 subjects. C2 just finished in March 2022 (3/2022) with data acquired from 11 subjects (5 upright CM and 6 LBNP CM). One subject (with the upright CM) from C2 was removed from the study due to failure to follow instructions. Data analysis is now underway for the C1 and C2 OCTA, ERG, and IVFA results. Campaigns 3 and 4 (C3/C4) are comprised of 12 subjects each and involve the cuff and exercise CM and HDT control subjects. C3 and C4 are scheduled to begin in the end of 2022, with all data acquired projected in mid-2023.

SPECIFIC AIMS

Specific Aim 1: To determine if donning veno-occlusive thigh cuffs during and for 120 minutes after daily aerobic exercise can be used to (a) reverse headward fluid shift from bed rest for a sustained period of time and (b) prevent ocular structural and functional changes from developing at the end of bed rest.

Hypothesis 1a: Donning veno-occlusive thigh cuffs during and after daily aerobic exercise will provide an acute and sustained fluid redistribution into the lower extremities (measured using femoral artery conductance and vasculature cross-sectional area) with a corresponding reduction in internal jugular vein cross-sectional area for up to 2 hours after cessation of exercise.

Hypothesis 1b: There will be a decrease in prevalence and magnitude of optic disc edema in subjects performing the exercise countermeasure outlined in Specific Aim 1 compared to subjects in the head-down tilt group who perform no countermeasure. Advanced analyses of optical coherence tomography (OCT) images of the optic nerve head combined with electrophysiological assessment of ganglion cell function will unveil functional decline and together may serve as a more sensitive endpoint compared to the visual fields tests currently used in astronauts.

Specific Aim 2: To determine the role of altered vasculature in the development of optic disc edema in this spaceflight analog.

Hypothesis 2a: Optical coherence tomography angiography (OCTA) will reveal vascular alterations in foveal avascular zone area or vascular density in the macula and nerve with intravenous fluorescein angiography showing leakage in subjects demonstrating the greatest degree of retinal thickening.

Hypothesis 2b: There will be a decrease in OCTA and intravenous fluorescein angiography alterations in subjects performing exercise countermeasure outlined in SA1 compared to subjects in the head-down tilt group who perform no countermeasure.

MATERIALS AND METHODS

The six arms of the study include (1) an upright control and (2) a 60-day bed rest 6-degrees head-down tilt (HDT) control. All experimental arms will include the 60-day 6-degrees bed rest HDT condition combined with four countermeasures: (1) veno-occlusive thigh cuffs and exercise, (2) lower-body negative pressure, (3) a B-vitamin supplement, and (4) a 6-hour upright posture countermeasure. The countermeasure focus of this proposal is #1. For this proposal, the exercise and veno-occlusive thigh cuff countermeasure will be performed 6 days a week. Each session will include exercise (60 min) that will be sustained at ~60% of pre-bedrest peak oxygen consumption with the veno-occlusive thigh cuff applied at 60 mm Hg for two hours after exercise cessation. Endpoints will be measured before, during, and after the study. These include intraocular pressure (IOP), optical coherence tomography (Spectralis HRA+OCT) of the macula and optic nerve, ultrasound measure of neck and lower extremity vessels, optical coherence tomography angiography (OCTA) of the macula and optic nerve, and electrophysiology for ganglion cell function. Intravenous fluorescein angiography will be performed to assess blood:brain vascular integrity at the optic nerve head immediately after cessation of the 60-day bed rest period.

RESULTS

This study is scheduled to occur at the :envihab facility at the German Aerospace Center (DLR). Currently, data acquisition has not begun due to delays from the COVID19 pandemic and the inability to perform bed rest and the associated research in an indoor environment. Instead, the focus of the last year has been on coordinating the research plan with the Principal Investigators, the Research Operations and Integration (ROI) element of NASA, and :envihab DLR counterparts. Specifically, the research protocol received approval from the Johnson Space Center Institutional Review Board (IRB) on May 21, 2020. The annual IRB renewal was approved on Jan 25, 2021. All hardware has been purchased with the majority of the equipment shipped to the German Aerospace Center in Cologne, Germany. Together with all Principal Investigators, NASA ROI, and DLR, the Integrated Research Document (IRD) and the integrated study test schedule have been coordinated and developed. As stated above, a tentative timeline for data acquisition has been established that was subject to local COVID19 control. Already, given a spring-time surge in COVID19 cases in Europe, the first campaign has been pushed back to ~September 2021. Given this uncertainty, contingent virtual training programs are being developed to replace in-person technical training, if necessary.