Microgravity-induced reduced jugular vein flow is more pronounced on the non-dominant side

Abstract

An astronaut developed a left-sided internal jugular vein (IJV) thrombosis while in orbit, likely due to reduced IJV blood flow. We hypothesized that microgravity-induced flow reductions would be greatest on the non-dominant (usually left) side thereby increasing thrombosis risk. A Simulink®-based lumped parameter model (LPM) was used to explore causes of jugular flow reduction and asymmetric thrombosis risk. Vessel behavior is described by combinations of four discrete components: hydrostatic gradients, vessel compliance, flow resistance, and flow inertia. The cranial venous system features drainage pathways through the right IJV, the left IJV and the vertebral plexus. The right jugular vein was modeled as the dominant jugular pathway (60% of total undeformed jugular cross-sectional area). The left side accounted for the remaining 40% of jugular flow. Multiple variables were adjustable in the LPM: body position (supine, prone, head-down tilt), and gravity. A key feature of this LPM is the incorporation of extravascular pressure on the vessels by the weight of tissues.Relative to a supine baseline, simulated total IJV flow changed from an average of 10.7 to 1.7 mL/s in weightlessness. The left and right IJV flow in microgravity was 0.6 and 1.2 mL/s, respectively (33.3% and 66.6% of total jugular venous flow, respectively). Not only was average flow reduced, but the flow pulsatility in the left IJV matched the observations made by Marshall-Goebel et al. in microgravity, where blood flowed forward, but with periodic zero-velocity flow. In microgravity, simulated left IJV was reduced to 33.3% from 40% of total jugular flow because the reduction in vein diameter in response to the transmural pressure changes is non-linear.