Weightlessness Associated Cephalad Fluid Shifts; The Potential to Evaluate Venous and Lymphatic Dysfunction

Introduction, Objectives, and/or Purpose: INTRODUCTION
Spaceflight crew exposure to weightlessness in low earth orbit (LEO) results in a 2-liter fluid shift from the legs to the head, neck, and upper torso within 6-10 hours, with mild to moderate adaptation over the following 4 days. Invasive and noninvasive methods have been utilized to measure transcapillary fluid shifts in a head down tilt (HDT) spaceflight analogue, central venous pressure catheter measurements in orbit and internal jugular venous duplex ultrasound in both parabolic flight and on the International Space Station (ISS). Point of care (POC) evaluations using non-invasive, decreased mass/weight, validated tools may further improve the evaluation and understanding of cephalad fluid shifts, venous distension, and lymphatic dysfunction contributing to Spaceflight Associated Neuroocular Syndrome (SANS) and other physiological maladaptation’s due to weightlessness. Thermography has been used for evaluation of chronic venous insufficiency (CVI), lymphedema, and deep tissue injuries (pressure injuries). Near InfraRed Spectroscopy (NIRS) and Long Wave Infrared Thermography (LWIT) has been utilized to assess physiological measurements and responses in intact skin and open ulcers. Thermography has an established orbital use as a noncontact handheld inspection tool for Shuttle wing evaluations. POC devices have continued to decrease in size, mass/weight with improved image signal acquisition, tissue differentiation and increased pixel count. A spaceflight analogue IRB approved study was recently completed with 30 volunteers at Nova Southeastern University (NSU) that utilized thermography, NIRS and dermal fluid percent content (Delfin monitor) to evaluate cephalad fluid shifts and response to manual lymphatic drainage (MLD).

OBJECTIVES/PURPOSE
The goal of the study was to evaluate POC devices and image changes associated with 3 fluid shift inducing positions (6-degree HDT, supine and upright), and to determine if MLD may be an effective countermeasure to impact analogue positional fluid shifts.

Methods: Thirty consented subjects meeting inclusion/exclusion criteria were randomized into a control or treatment group. All participants were assessed in the sitting position for 30 minutes, supine for 1.5 hours and 6 degrees head down tilt for 3 hours (validated simulated spaceflight analogue). Each position was assessed on a different date to reduce any position-related carryover effects. Baseline vitals and imaging using NIRS, LWIT, and dermal fluid content were taken immediately after assuming the designated position. Subsequent image assessments and vital signs were taken every 30 minutes thereafter. At completion of the established timepoints, reassessment images were taken prior to moving out of the designated position. Participants in the treatment group received 15 minutes of an established MLD protocol to the head, neck, and upper torso prior to moving out of position. Immediately post MLD, reassessment images were taken, followed by a final assessment 30 minutes after MLD to assess for potential changes and resolution of any symptoms experienced in any of the positions. Vital sign data and images from the various POC devices were evaluated by independent trained reviewers to assess for notable changes in perfusion (hemoglobin/deoxyhemoglobin), temperature and percent fluid over time and for each study position.

Results: NOTE: currently collecting data and will be analyzing data in July/August. Results not available at time of abstract submission.

Conclusion(s): Pending further conclusion...

POC imaging involves emerging technologies that offer low mass/weight handheld noncontact devices with clinical applications for CVI, lymphedema and early detection of skin temperature thermal pattern abnormalities. POC has high potential for application and use in spaceflight analogue testing, on parabolic flights, ISS, and other spacecraft for fluid shifts (acute and chronic), SANS, and crew core body temperature (CBT) evaluations. Ideally, these devices will help guide or establish countermeasures specifically to address fluid shifts pre-flight, during flight and post-flight with the potential to have significant “spinoff” applications for fluid shift recognition in wound care and lymphedema clinics to improve outcomes through recognition and improved treatment protocols.