Advanced venous flow dynamics and return mechanisms during physiological stress and aging

Abstract

Human veins are dynamic vessels responsible for managing return of blood to the heart. Unlike arteries, veins are structurally limited, creating exceptional hemodynamic susceptibility to hydrostatic forces and pressure generating forces. The precise extent of venous flow regulating mechanisms to these forces have implication for disease pathogenesis yet have been historically limited by technological tools. Thus, the purpose of this thesis is addressing the responses to hydrostatic volume stress, muscle pump activation and healthy aging through the piezoelectric lens of vector flow imaging ultrasound through a series of projects. First, progressive hydrostatic volume stress is applied to the internal jugular vein to address regional flow complexity and volume expansion behaviour. The internal jugular vein presented step-wise volume expansion in a trapezoidal shape and increasing flow complexity, increasing the risk for flow stasis and thrombus formation. Second, hydrostatic volume stress is used to compare artery-adjacent and non-adjacent veins to probe the existence of an arterial pump. During relevant hydrostatic driving forces, artery-adjacent veins demonstrated a preservation of venous flow, suggestive of a newly described mechanism of venous and an elegant conservation of mechanical energy within the cardiovascular system. Third, a comparison of younger and older adults leveraged differences in venous compliance to investigate flow complexity features during muscle pump activation during hydrostatic volume stress. Older adults were found to utilize their lower compliance to maintain venous ejection efficiency, whereas younger adults experienced great turbulence and vorticity flow features for the same venous outflow. Finally, venous valves were explicitly investigated during progressive hydrostatic volume stress and muscle pump activation to describe flow complexity features. Healthy valves generated efficient forward jets with downstream disturbed, low-shear zones, and volume stress amplified regional differences, underscoring the role of valve geometry in venous hemodynamics. Together, these studies establish new mechanistic links between venous structure, hydrostatic and muscle pump forces, and aging, advancing understanding of venous flow regulation and its implications for thrombotic risk and cardiovascular health.