Task Distribution of Body Fluids during Long Duration Space Flight and Subsequent Effects on Intraocular Pressure and Vision Disturbance (Stenger)
Last Published:  03/26/21 03:34:00 PM (Central)
Short Title: Fluid Shifts - Stenger
Responsible HRP Element: Human Health Countermeasures
Collaborating Org(s):
Funding Status: Active - Currently funded and in progress
Procurement Mechanism(s):

The primary hypothesis of this proposal is that long duration space flight will induce a cephalad fluid shift and redistribution of fluid from intra- to extravascular space, resulting in increased facial interstitial thickness. This fluid redistribution will be more significant in a subset of astronauts that will also experience eye morphology changes and vision disturbances.

Specific Aim I: Determine distribution and compartmentalization of fluid volume (intracellular, extracellular, interstitial) during space flight and plasma volume after space flight.

Hypothesis 1: Plasma volume will be decreased post-flight compared to pre-flight.
Extracellular fluid volume will be decreased, intracellular fluid volume will be increased, and total body water will not change during long duration space flight.

Hypothesis 2: Ultrasound measures of fluid shift (interstitial thickness, venous diameter) and near infrared spectroscopy measures of tissue hydration will be elevated in the upper body and decreased in the lower body, during and after long duration space flight.

Specific Aim II: Determine effect of fluid distribution on visual acuity and its surrogates.

Hypothesis 3: Intraocular pressure, measured by tonometry, and optic nerve sheath diameter, a surrogate measure of intraocular pressure, will be increased with long duration space flight. The magnitude of this increase will be related to the magnitude of the measures of cephalad fluid shift.

Hypothesis 4: The magnitude of the changes in visual acuity will be related to the magnitude of the increase in optic nerve sheath diameter and tonometry measures of intraocular pressure.

Hypothesis 5: Recovery of visual acuity will be dependent on the recovery of optic nerve sheath diameter measures to preflight levels.

Specific Aim III: Correlate central venous pressure (CVP) to intraocular pressure as measured by tonometry and its surrogates.

Hypothesis 6: Central venous pressure will be elevated in those subjects who have elevated intraocular pressure after spaceflight, but not in subjects who do not have an elevation in intraocular pressure.

Specific Aim IV: Compare fluid shift measures and eye anatomy between acute 25 head down tilt and measures obtained during long duration space flight.

Hypothesis 7: The degree of pressure and anatomical changes to the eye during acute tilt will predict which subjects experience structural and functional changes during space flight.

Hypothesis 8: Post-bed flight acute tilts will reveal sub-clinical alterations that have occurred due to long duration space flight.

Specific Aim V: Compare the results obtained from space flight with those obtained from acute tilt and chronic head-down bed rest studies to assess whether bed rest is an adequate model of these space flight-induced adaptations. These comparisons will result from data sharing activities with bed rest measurements.

Hypothesis 9: The magnitude of the long duration space flight cephalad fluid shift on measures of fluid re-distribution can be predicted by the magnitude of similar responses during an acute pre-flight head-down tilt test.

Hypothesis 10: Observed magnitude in acute fluid shifts will be similar between spaceflight and bed rest, however the chronic distribution of that fluid between body compartments will be different between space flight and its analog. Changes in eye anatomy and function will be temporary in bed rest, while those observed during and following long-duration spaceflight will persist for months-years in some astronauts.