Journal-based CME Course: Effect of Nightly Lower Body Negative Pressure on Choroid Engorgement in a Model of Spaceflight-Associated Neuro-ocular Syndrome

Activity ID

9171

Expires

January 20, 2025

Format Type

Journal-based

CME Credit

1

Fee

$30

CME Provider: JAMA Ophthalmology

Description of CME Course

Importance  Astronauts returning from long-duration spaceflight experience ocular remodeling related to cephalad fluid shifts induced by microgravity. It is hypothesized that the absence of diurnal reductions in intracranial pressure in microgravity creates a low but persistent pressure gradient at the posterior aspect of the eye, which results in ocular remodeling and space-associated neuro-ocular syndrome (SANS) over many months.

Objective  To determine whether partial reintroduction of footward fluid shifts during simulated microgravity via lower body negative pressure (LBNP) during sleep attenuates choroid engorgement, an early marker of ocular remodeling related to SANS.

Design, Setting, and Participants  Between May 2019 and February 2020, participants with no major cardiovascular, kidney, or ophthalmic disease completed 3 days of supine (0°) bed rest with and 3 days without 8 hours of nightly LBNP in a randomized, crossover design. This single-center investigation took place at the UT Southwestern Medical Center. All analyses were conducted blinded to condition and time point.

Interventions  Eight hours of nightly LBNP (−20 mm Hg) vs no LBNP.

Main Outcomes and Measures  The primary outcome was the change in choroid area and volume after 3 days of bed rest measured by optical coherence tomography.

Results  Of 10 participants, 5 were female, the mean (SD) age was 29 (9) years, and the age range was 18 to 55 years. Central venous pressure increased from the seated to supine position (mean [SD], seated: −2.3 [2.0] vs supine: 6.9 [2.0] mm Hg; P < .001), leading to choroid engorgement over 3 days of bed rest (Δ area: +0.09 mm² [95% CI, 0.04-0.13]; P = .001; Δ volume: +0.37 mm³ [95% CI, 0.19-0.55]; P = .001). Nightly LBNP caused a sustained reduction in supine central venous pressure (mean [SD], 5.7 [2.2] mm Hg to 1.2 [1.4 mm Hg]; P < .001) and attenuated the increase in choroid area (74%) (Δ: 0.02 mm² [95% −0.02 to 0.06]; P = .01) and volume (53%) (Δ: 0.17 mm³ [95% CI, 0.01-0.34]; P = .05) compared with control.

Conclusions and Relevance  Nightly LBNP reinstated a footward fluid shift and mitigated the increase in choroid area and volume. LBNP during sleep may be an effective countermeasure for ocular remodeling and SANS during long-duration space missions.

Disclaimers

1. This activity is accredited by the American Medical Association.
2. This activity is free to AMA members.

Register for this Activity