Assessment of Jugular Venous Blood Flow Stasis and Thrombosis During Spaceflight

Abstract

Importance: Exposure to a weightless environment during spaceflight results in a chronic headward blood and tissue fluid shift compared with the upright posture on Earth, with unknown consequences to cerebral venous outflow.

Objectives: To assess internal jugular vein (IJV) flow and morphology during spaceflight and to investigate if lower body negative pressure is associated with reversing the headward fluid shift experienced during spaceflight.

Design, setting, and participants: This prospective cohort study included 11 International Space Station crew members participating in long-duration spaceflight missions . Internal jugular vein measurements from before launch and approximately 40 days after landing were acquired in 3 positions: seated, supine, and 15° head-down tilt. In-flight IJV measurements were acquired at approximately 50 days and 150 days into spaceflight during normal spaceflight conditions as well as during use of lower body negative pressure. Data were analyzed in June 2019.

Exposures: Posture changes on Earth, spaceflight, and lower body negative pressure.

Main outcomes and measures: Ultrasonographic assessments of IJV cross-sectional area, pressure, blood flow, and thrombus formation.

Results: The 11 healthy crew members included in the study (mean [SD] age, 46.9 [6.3] years, 9 [82%] men) spent a mean (SD) of 210 (76) days in space. Mean IJV area increased from 9.8 (95% CI, -1.2 to 20.7) mm2 in the preflight seated position to 70.3 (95% CI, 59.3-81.2) mm2 during spaceflight (P < .001). Mean IJV pressure increased from the preflight seated position measurement of 5.1 (95% CI, 2.5-7.8) mm Hg to 21.1 (95% CI, 18.5-23.7) mm Hg during spaceflight (P < .001). Furthermore, stagnant or reverse flow in the IJV was observed in 6 crew members (55%) on approximate flight day 50. Notably, 1 crew member was found to have an occlusive IJV thrombus, and a potential partial IJV thrombus was identified in another crew member retrospectively. Lower body negative pressure was associated with improved blood flow in 10 of 17 sessions (59%) during spaceflight.

Conclusions and relevance: This cohort study found stagnant and retrograde blood flow associated with spaceflight in the IJVs of astronauts and IJV thrombosis in at least 1 astronaut, a newly discovered risk associated with spaceflight. Lower body negative pressure may be a promising countermeasure to enhance venous blood flow in the upper body during spaceflight.

Figure 1.. Internal Jugular Vein Blood Flow Velocity Waveform Grading Scale

Flow below the baseline (0 cm/s; yellow line) signifies normal flow in the head-to-heart direction, whereas flow above the baseline signifies reverse flow toward the head.

Figure 2.. Internal Jugular Vein (IJV) Cross-Sectional Area and Pressure

Mean IJV cross-sectional area (A) and pressure (B) were measured in the seated, supine and 15° head-down tilt (HDT) positions preflight, on flight days 50 and 150 of spaceflight, with and without lower body negative pressure (LBNP), and 40 days postflight. Seated preflight measurements were used as the reference. Boxes indicate 95% CIs and circles, individual data points.

Figure 3.. Internal Jugular Vein (IJV) Blood Flow Waveform Grading Before, During, and After Spaceflight and Example Ultrasonography Demonstrating the Presence of a Thrombus During Spaceflight

Grade 1 indicates predominantly continuous flow; grade 2, predominantly pulsatile flow that may return to 0; grade 3, no net forward flow (stagnant or equal positive and negative flow); grade 4, retrograde flow. HDT indicates 15° head-down tilt and LBNP, lower body negative pressure (A). Example longitudinal ultrasonographic scans of the left IJV and Doppler ultrasonographic blood flow velocity waveform in one participant showing grade 2 flow preflight measured in the supine position (B), and a thrombus (denoted with an X) with no flow detected through the IJV on flight day 50 on the International Space Station (C). ^aDenotes crew members who presented with an IJV thrombus during spaceflight.