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Testing Mechanical Countermeasures for Cephalad Fluid Shifts

Principal Investigator:
Gary E. Strangman, Ph.D.

Harvard Medical School-Massachusetts General Hospital

Current evidence suggests that NASA’s visual impairment and intracranial pressure (VIIP) risk may be associated with an elevation in intracranial pressure (ICP) during spaceflight, consequent to (or aggravated by) cephalad fluid shifts in microgravity. From recent data, it occurs in >50% of astronauts, to varying degrees, and can lead to long term visual changes. Although its cause is unknown, its importance is high enough to motivate studies of potential countermeasures. The key objectives of this proposal are therefore: (1) to test and help validate mechanical countermeasures for cephalad fluid shifts as a potential treatment of elevated ICP, (2) identify any potential adverse consequences during use or following release of such countermeasures, and (3) help optimize deployment procedures for such countermeasures.

The Russians currently use Braslet, an elastic thigh band, to help sequester blood in the legs and alleviate symptoms resulting from cephalad fluid shifts. While promising, this device has not been tested as a VIIP countermeasure. Lower body negative pressure (LBNP) is an alternative approach, which draws fluid into the legs using a vacuum mechanism. Both have drawbacks, however. Braslet devices are only made in Russia and have limited calibration options. LBNP is bulky and hence only one such device would be available in-flight at a time, limiting the number of astronauts who could use it each day, or the duration of use. In place of the Braslet, we will test the Kaatsu thigh cuff system, which is used for enhanced muscle training on Earth. Instead of the LBNP alternative, we will investigate use of a LymphaPress compression garment configured to progressively compress fluids from the lower ribcage towards the knee. In Experiment 1, we will conduct tests using both potential countermeasures in healthy subjects undergoing head-down tilt (HDT) to elevate ICP by +10 mmHg, and in neurointensive care unit (NeuroICU) patients with invasive ICP devices implanted to monitor and treat elevated ICP. We will establish the ICP, cerebral blood flow, intraocular pressure, structural eye parameters, and cerebral vascular parameter changes associated with application and release of each countermeasure. This will also involve calibration of our non-invasive versus invasive cerebral measurements. In Experiment 2, we will determine if gradual discontinuation of device usage may be safer than abrupt discontinuation. In Experiment 3, we will seek to quantify the relationship between exposure time to the countermeasure and cerebral responses during exposure as well as post-release.

Together, these studies will help identify which countermeasure is the most promising treatment for, or mitigator of, cephalad fluid shifts and elevated ICP. This project will increase the technology readiness level of mechanical countermeasures for VIIP from CRL 4 to CRL 7.

NASA Taskbook Entry

Technical Summary

Our objective is to test two qualitatively distinct countermeasures for VIIP, based on the assumption that VIIP is caused—or influenced—by cephalad fluid shifts. Both systems are commercial: (1) the Kaatsu cuff system, developed for muscle strength training, and (2) the LymphaPress Optimal system, developed for lymphedema patients. Studies will be conducted at Massachusetts General Hospital (MGH) as well as at Baylor College of Medicine/NSBRI Center for Space Medicine on both healthy subjects undergoing head-down tilt (HDT) as well as NeuroICU patients with invasive ICP measurement devices. The project specific aims are as follows:

Aim 1:  Identify and characterize cerebrovascular and/or ophthalmological parameters altered by cephalad fluid shifts that are mitigated by mechanical countermeasures.

Aim 2: Identify and characterize any rebound effects or other adverse occurrences when use of the mechanical countermeasure device is discontinued.

Aim 3: Quantify the effect of two mechanical countermeasures on their ability to reduce invasively-measured continuous ICP.

Aim 4: Determine if gradual countermeasure discontinuation is safer than abrupt discontinuation.

Aim 5: Quantify the relationship between countermeasure exposure time vs. ICP reduction (and rebound).

Earth Applications

Management of intracranial hypertension, intracranial pressure and pressure related vision pathology is a billion dollar industry. If successful, these countermeasures may provide clinicians with a new tool to help investigate and/or modulate intracranial hypertension.