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Venous Congestion Countermeasure Study (Venous_Congestion_CM)
Research Area:
Biomedical countermeasures
Ocular physiological phenomena
Species Studied
Scientific Name: Homo sapiens Species: Human


During long-duration space flight, changes to ocular structures and visual function occur which is hypothesized to be the result of the chronic headward fluid shift that is induced by weightlessness. A variety of countermeasures aimed at reversing the headward fluid shift have been tested in ground-based studies. However, no countermeasure has been implemented during spaceflight because it is unknown which countermeasure, single or in combination with another, would be the most effective. Lower body negative pressure (LBNP), venoconstrictive thigh cuffs (VTC), and an impedance threshold device (ITD) breathing are countermeasures that partially reverse headward fluid shift. LBNP counteracts headward fluid shift by drawing the fluid from the upper body and shifting it into the legs. VTC reduces blood volume from the central circulation and ITD lowers intrathoracic pressure and augments venous return.

Although LBNP, VTC, and ITD have been shown previously to partially reverse the headward fluid shift, no single countermeasure has successfully reversed values to those observed in the upright position. LBNP, VTC, and ITD individually represent specific and unique physiological strategies to reduce headward fluid shift. When these countermeasures are combined, a flexible and sustained strategy can be developed to increase the magnitude and duration of effects.

The objectives of this three-part study were to determine if an individual countermeasure or a combination of countermeasures can reduce the headward fluid shift induced when moving from the upright to the supine posture, and determine the effectiveness of using a countermeasure during sleep. This experiment evaluated the following specific aims:

  1. Determine which countermeasure, individual or a combination, is most effective at reversing a seated-to-supine posture headward fluid shift and be able to sustain the reversal for 45 minutes.
  2. Determine if the effective countermeasure(s) in specific aim one, is also able to reverse the cerebral spinal fluid (CSF) shift.
  3. Determine if daily use of LBNP during sleep, up to eight hours per day, can prevent the headward fluid shift induced changes during three days of head-down tilt bed rest.

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Hearon CM, Dias KA, Babu G, et al. Effect of Nightly Lower Body Negative Pressure on Choroid Engorgement in a Model of Spaceflight-Associated Neuro-ocular Syndrome: A Randomized Crossover Trial. JAMA Ophthalmology. 2022;140(1):59–65

Cerebrospinal fluid
Venous pressure
Intraocular pressure

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Data Information
Data Availability
Archive is complete. Data sets are not publicly available but can be requested.
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Aqueductal cerebral spinal fluid pulsatility
Brain volume
Cardiac output
Central venous pressure
Cerebral spinal fluid, velocity
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Mission/Study Information
Mission Launch/Start Date Landing/End Date Duration
Ground 05/01/2009 In Progress

Additional Information
Managing NASA Center
Johnson Space Center (JSC)
Responsible NASA Representative
Institutional Support
National Aeronautics and Space Administration (NASA)
Proposal Date
Proposal Source
Directed Research