Current evidence suggests that NASA's spaceflight associated neuro-opthalmological syndrome (SANS/VIIP) risk may be related to an elevation in intracranial pressure (ICP) during spaceflight compared to the upright position on Earth, either consequent to or aggravated by cephalad fluid shifts in microgravity. The key objectives of this project were: (1) to test and assess two commercial devices as mechanical countermeasures for cephalad fluid shifts and modify cerebral and/or ocular parameters, (2) to identify any potential adverse consequences during use or following release of such countermeasures, and (3) to optimize deployment procedures for such countermeasures. Specifically, this project sought to test the Kaatsu thigh cuff muscle training system, as an alternative to the Braslet, and a reconfigured Lymphapress system, originally designed for fluid management in edema patients.
In year 2 of the project we initiated and completed three human experiments. In Experiment 1, we tested n=18 healthy subjects during a -6 degree head-down tilt protocol. Subjects were monitored during two 3-hour sessions (one for each countermeasure, randomized order) consisting of 20-min periods in each of the following orientations, in sequence: +50 degree HUT (head up tilt), supine, -6 degree HDT, -6 degree HDT during countermeasure deployment, -6 degree HDT post-deployment of the countermeasure, supine, and briefly again at 50 degree HUT. All subjects were tested with Kaatsu at 180 SKU deployment pressure and Lymphapress at 34-36 mmHg pressures, in counterbalanced orders. Experiment 2 tested n=12 healthy subjects identically as in Experiment 1, however, with higher countermeasure pressures: Kaatsu at a deployment pressure of 300 SKU and Lymphapress at pressures of 43-45 mmHg. In Experiment 3, the Kaatsu system was tested in n=5 patients in the NeuroICU in collaboration with Dr. Eric Bershad with invasive ICP monitoring for 20 min baseline, 20 min Kaatsu deployment, and 20 min post-deployment at 250 SKU. Neither of the investigated mechanical countermeasure devices caused adverse effects in subjects and were well tolerated throughout trials. Kattsu cuffs were deemed less obtrusive and more practical to deploy due to their small size and compliance. The Lymphapress system was overall less practical to deploy due to its size and mode of application that required subjects to wear large inflatable compression pants—sufficiently so to preclude their use in NeuroICU patients with unstable ICP in Experiment 3.
Experiments 1 and 2 demonstrated significant sequestration of blood in the legs during Kaatsu deployment, whereas Lymphapress deployment did not. No significant changes in cerebral or ocular parameters (cerebral blood volume, cerebral blood flow velocity, intraocular pressure) were observed during or following either countermeasure. We believe the negative findings were in part due to distinct design issues associated with each commercial device.