arXiv subjects

Kuniyasu Niizuma

Publications and source records attributed to Kuniyasu Niizuma.

4 recordsLinked to original sources

arXiv2026

Development of a 4D Cerebral Microvascular Imaging Platform for Mouse Stroke Model

In ischemic stroke, changes in cerebral hemodynamics during both the ischemic and reperfusion phases strongly influence stroke outcomes. However, these hemodynamic changes remain incompletely understood. To address this challenge, we devised an imaging platform that enables time-resolved ultrasound microvascular imaging during the experimental induction of ischemia and reperfusion in a mouse model. The platform leverages our previous ultrasound imaging framework combined with continuous mechanical scanning, which acquires whole-brain blood-flow signals within 5 s. The experiments demonstrated that the proposed platform can visualize both local and whole-brain hemodynamic responses to the induction of ischemia and reperfusion, suggesting its potential for rapid and continuous whole-brain hemodynamic assessment in small-animal models.

eess.SY↗

arXiv2025

Multiscale modeling of blood circulation with cerebral autoregulation and network pathway analysis for hemodynamic redistribution in the vascular network with anatomical variations and stenosis conditions

Cerebral hemodynamics is fundamentally regulated by the Circle of Willis (CoW), which redistributes flow through communicating arteries to stabilize perfusion under anatomical variations and vascular stenosis. In this study, we develop a multiscale circulation model by coupling a systemic hemodynamic framework with a cerebral arterial network reconstructed from medical imaging. The model incorporates a cerebral autoregulation mechanism (CAM) and enables quantitative simulation of flow redistribution within the CoW under normal, anatomically varied, and stenotic conditions. Baseline simulations reproduce physiological flow distributions in which communicating arteries remain nearly inactive, showing negligible cross-flow and agreement with clinical measurements. In contrast, anatomical variations reveal distinct collateral activation patterns: the anterior communicating artery (ACoA) emerges as the earliest and most sensitive functional collateral, whereas the posterior communicating arteries (PCoAs) exhibit structure-dependent engagement. Progressive stenosis simulations further demonstrate a transition from a complete CoW to a fetal-type posterior cerebral artery (PCA) configuration, characterized by early ACoA flow reversal followed by ipsilateral PCoA activation, consistent with experimental and transcranial Doppler observations. Finally, a path-based quantitative analysis is introduced to illustrate how the cerebral vascular network dynamically reconfigures collateral pathways in response to structural changes. Overall, the proposed framework provides a physiologically interpretable, image-informed tool for investigating cerebral flow regulation through functional collaterals within the CoW, with potential applications in the diagnosis and treatment planning of cerebrovascular diseases.

physics.med-ph↗

arXiv2020

Physiologic Blood Flow is Turbulent: Revisiting the Principles of Vascular Hemodynamics

Contemporary paradigm of vascular hemodynamics considers normal blood flow to be pulsatile laminar flow. Transition to turbulence can cause diseases such as atherosclerosis or brain aneurysms. Recently, we demonstrated the existence of turbulence in experimental models of brain aneurysm; in the aneurysm sac as well as in the main artery. Thus, we were intrigued to explore if such a long-standing assumption of the laminarity of blood flow could be challenged. We have used methods and tools from chaos theory, hydrodynamic stability theory and turbulence physics to explore the existence of turbulence in normal vascular blood flow. We used Womersley exact solution of the Navier-Stokes equation with the HaeMed database of physiologic blood flow measurements, to offer reproducible evidence for our findings, as well as evidence from Doppler ultrasound measurements from healthy volunteers. The tools we used to investigate the properties of blood turbulence are well established in the fields of chaos theory, hydrodynamic stability and turbulence dynamics. We show, evidently, that blood flow is inherently chaotic and turbulent and not laminar. We propose a paradigm shift in the theory of vascular hemodynamics which requires rethinking the hemodynamic-biologic links governing physiologic and pathologic processes.

physics.flu-dyn↗

arXiv2020

Non-Kolmogorov Turbulence and Inverse Energy Cascade in Intracranial Aneurysm: Near-Wall Scales Suggest Mechanobiological Relevance

The genesis, growth and rupture of intracranial aneurysm (IA) are open questions in neurovascular medicine until the present moment. The complexity of aneurysm mechanobiology and pathobiology staggeringly combine intertwining biological and physical processes that are tightly connected. Recently, transition to turbulence in IA blood flow is thought to play a central role in IA growth and rupture as it can be directly linked to endothelial dysfunction. However, the problem of turbulence brings unprecedented complications to the topic. We found turbulence in IA to be of non-Kolmogorov type. For the first time, we detected inverse kinetic energy cascade in blood flow and in non-Kolmogorov turbulence. Here, we hypothesize that the near-wall turbulence undergoing inverse energy cascade have scales that could affect the mechano-signaling of endothelial cells. Our findings could be a paradigm shift in the contemporary theory of aneurysm hemodynamics.

physics.med-ph↗