Assessing non-invasive imaging devices to detect temperature differentiation and lymphatic/venous flow to the head and neck during head down tilt, supine, and sitting positions The NIID Study (non-invasive imaging device)
Authors: Melin Matthew , Barnhart Heather , Aviles Frank , Pannunzio Johanna , Sirkis Nathan , Hubbard Chantel , Hardigan Patrick , Ginsburg Sabrina , Mayrovitz Harvey 
Published: September 2023

Abstract

Under the influence of standard developmental physiology on the Earth’s surface (1 gravity equivalent known as “1G”), 70% of body fluids reside below the level of the heart.Fluid shifts towards the cephalic region during microgravity have also been speculated to contribute towards spaceflight associated neuro-ocular syndrome (SANS).Although a significant barrier to spaceflight, the underlying mechanism of SANS is not well understood, partially due to the spaceflight environment and limited medical capabilities including invasive diagnostic testing. Thus, non-invasive approaches to studying real-time fluid shifts in weightlessness could serve as critical areas of research to further SANS study and effective countermeasure protocol development. For continuous fluid shift monitoring and management, the goal is to establish baseline assessments utilizing real time point of care noninvasive imaging devices (NIID). NIID will first need to be quantified and validated through ground-based analogues, with subsequent acquisition of near continuous imaging from arrival in the weightlessness of LEO and during the time of adaptation, which may be variable among crew members. The purpose of this study was to examine temperature differential alterations, superficial venous flow patterns (head, neck, upper torso), and venous flow patterns along the lymphatic ventromedial bundles of the medial calves and thighs. Imaging was obtained in three different positions using three standards of care medical NIIDs: SnapShotTM by Kent Imaging, Scout by WoundVisionTM and LymphScannerTM by Delfin. 30 volunteers were assessed for temperature and lymphatic/venous flow using three different non-invasive devices that can measure temperature, perfusion, and image the lymphatic and venous structures. The volunteers were assessed in the sitting, supine, and 6-degree head down tilt (HDT) positions, with pre/post assessments for the HDT position. Venous and lymphatic flow patterns may vary upon position changes (sitting vs. supine vs. 6-degree head down tilt), and in response to MLD performance in the treatment group. Fifteen subjects per group (N = 30) completed all visits and were used in the full analysis. The sitting and supine position data did not show statistical significance at any of the time points and with the devices used. The HDT data from SnapShot (looking at perfusion, deoxy and oxyhemoglobin) and Wound Vision Scout (thermal imaging) did not show statistical significance between the control and treatment groups at any time points. No significant difference for any of the within-group comparisons were found with the Lymphscanner. A significant reduction in left temple TDC for the treatment group was found at post-30-minutes (5.77, 95% CI: 1.24, 10.30) and post-180-minutes. A significant reduction in right subclavicular TDC for the treatment group was found at post-180-Minutes (5.09, 95% CI: 0.16, 10.03). A significant increase in the left ventromedial bundle for the treatment group was found at post-90-Minutes (5.72, 95% CI: 0.34, 11.10) and post-120-Minutes (5.85, 95% CI: 0.47, 11.23). A significant increase in the right ventromedial bundle for the treatment group was found at post-90 minutes (5.53, 95% CI: 0.21, 10.84).
This is the first HDT spaceflight analogue study, to our knowledge, in which dermal fluid shifts were evaluated using point-of-care noninvasive imaging modalities including Near Infrared Spectroscopy (NIRS), thermography and a subcutaneous edema monitor, with subsequent application of manual lymphatic drainage (MLD) techniques to stimulate dermal lymphatic function as a countermeasure and mitigation therapeutic for intervention in cephalad fluid shifts. Further validating studies are indicated for NIIDs to further quantify fluid shifts in both analogues and weightlessness.