Mitigating Headward Fluid Shifts With Veno-Constrictive Thigh Cuffs During Spaceflight

Astronauts experience a chronic headward fluid shift in
weightlessness as evidenced by increased cardiac output,
decreased leg volume, a redistribution of venous fluid, and
venous congestion in the upper body. Alterations in
cerebrospinal fluid hydrodynamics and changes in cerebral
venous pressure secondary to the headward fluid shift may
contribute to ocular changes associated with spaceflight-associated neuro-ocular syndrome (SANS). Veno-constrictive
thigh cuffs (VTC; Braslets) provided to Soyuz crewmembers
alleviate symptoms of the headward fluid shift during the first
week of spaceflight and have been documented to reduce
internal jugular vein (IJV) distension during weightlessness.
Application of VTCs designed collaboratively by NASA
Johnson Space Center Cardiovascular and Vision Laboratory
(CVL) and Clemson Textile Laboratory at Clemson University
to improve fit and comfort was documented to mitigate
changes in choroid thickness, intraocular pressure, and IJV
area during posture-induced headward fluid shifts.

VTC are demonstrated to reduce headward fluid shifts in both
ground-based and spaceflight studies, and thus, may be a
countermeasure against development of SANS. In addition,
VTC are a simple mechanical countermeasure currently at a
high technical readiness level (TRL) and are compact and
lightweight, making them compatible with the spaceflight
operations environment