Countermeasures for Visual Impairment in Astronauts (STOP-VIIP)

Safe and Effective Countermeasures to Reduce Intracranial Pressure and Ameliorate Visual Impairment in Astronauts (STOP VIIP)

This study is being done to prevent changes in the vision of astronauts during prolonged residence on the International Space Station or a mission to Mars. This project will provide data about the efficacy of lower body negative pressure to mimic daily upright posture by intermittently lowering central venous pressure while in simulated microgravity (3 days of bed rest). The investigators expect that 3 days of bed rest will increase choroid thickness, and choroid area. The investigators hypothesize that nightly LBNP (-20mmHg) will prevent these changes.

Study Overview

• Status: Completed
• Conditions: Space Flight Associated Neuro-ocular Syndrome
• Intervention / Treatment: Other: Lower body negative pressure

Detailed Description

The visual impairment observed in many astronauts after long duration spaceflight aboard the International Space Station is considered the most important mission-threatening medical problem identified in the last decade of the space program. Between 2012 and 2014, NASA and NSBRI have spent $3-4 million/year investigating the clinical course and underlying mechanisms of this condition, termed the Visual Impairment Intracranial Pressure Syndrome (VIIP) because of its theoretical association with elevated intracranial pressure and central venous pressure. During the previous funding cycle, the investigators for this application performed the first invasive measures of intracranial pressure during acute (head down tilt bedrest and parabolic flight) and chronic (24 hours HDT bedrest) changes in gravitational gradients simulating spaceflight in healthy humans. Novel observations made from those studies determined that 1) there is a large range of central venous pressure experienced normally during changes in posture in daily life; 2) these changes occur within seconds of postural transients from upright to supine and then are stable over time in that position; 3) with acute assumption of simulated microgravity (HDT bedrest), intracranial pressure and central venous pressure goes up slightly from the supine position, but over the next 24 hours, returns toward, and sometimes below the supine value because of spatial compensation within the brain; 4) during true microgravity (parabolic flight), the acute reduction in central venous pressure reduces cerebral outflow resistance and ICP decreases compared to the supine position, though remains above the upright position in 1G.

The current hypothesis is that the VIIP syndrome is Not due to a pathologically elevated central venous or intracranial pressure. However, because there is not the usual reduction in pressure typically seen in the upright position on earth, the incessant, low level elevation in ICP (i.e., greater than upright, but less than supine) leads to adaptive changes in the eye which ultimately result in globe flattening, choroidal folds, and visual impairment. Preliminary data suggest that the use of lower body negative pressure (LBNP) can lower ICP while in the head down position, towards the values observed upright. The investigators propose that applying LBNP during sleep in space would be a practical strategy to restore a relevant (though reversed) circadian variability in central venous pressure that would then prevent adaptive changes in the eye. The investigators propose the following hypothesis:

Hypothesis 1: Repeated administration of LBNP at night will cause a safe, sustained reduction in central venous pressure while asleep. This restoration of effective circadian variability in central venous pressure will prevent structural changes in the eye induced by microgravity. To test this hypothesis, the long-term efficacy of nightly LBNP (6-8 hrs) to simulate the upright position and prevent structural changes in the eye during four days of bedrest. Comprehensive, non-invasive state-of-the-art imaging will be used to examine the structure of the visual apparatus, using optical coherence tomography combined with invasive direct measurement of CVP.

• Study Type: Interventional
• Enrollment (Actual): 10
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Texas
    • Dallas, Texas, United States, 75390
      • UT Southwestern Medical Center

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 55 years (Adult)
• Accepts Healthy Volunteers: Yes
• Genders Eligible for Study: All

Description

Inclusion Criteria:

• age 18-55

Exclusion Criteria:

• cardiovascular disease
• ophthalmological disease

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Single

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
No Intervention: Control; 4 days of strict bed rest
Experimental: Lower body negative pressure; 4 days of strict bed rest with nightly lower body negative pressure at -20mmHg	Other: Lower body negative pressure; lower body negative pressure at -20mmHg delivered via a custom designed sleeping sack

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in choroid area	The change in choroid area measured by optical coherence tomography.	Baseline, after 3-days of bed rest
Change in choroid volume	The change in choroid volume measured by optical coherence tomography.	Baseline, after 3-days of bed rest

Collaborators and Investigators

• Sponsor: University of Texas Southwestern Medical Center
• Investigators: Principal Investigator: Benjamin Levine, MD, UT Southwestern Medical Center

Study record dates

Study Major Dates

• Study Start (Actual): March 1, 2019
• Primary Completion (Actual): March 1, 2020
• Study Completion (Actual): March 1, 2020

Study Registration Dates

• First Submitted: August 9, 2021
• First Submitted That Met QC Criteria: August 16, 2021
• First Posted (Actual): August 23, 2021

Study Record Updates

• Last Update Posted (Actual): September 8, 2021
• Last Update Submitted That Met QC Criteria: August 31, 2021
• Last Verified: August 1, 2021

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Nervous System Diseases; Eye Diseases; Neurologic Manifestations; Sensation Disorders; Vision, Low; Vision Disorders
• Other Study ID Numbers: STU 102015-057

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No