Multispectral imaging of cortical vascular and hemodynamic responses to a shock wave: observation of spreading depolarization and oxygen supply-demand mismatch.

Shunichi Sato,Hiroshi Nawashiro,Izumi Nishidate,Wataru Okuda,Satoko Kawauchi

doi:10.1117/1.jbo.24.3.035005

Abstract

.Blast-induced traumatic brain injury has been a recent major concern in neurotraumatology. However, its pathophysiology and mechanism are not understood partly due to insufficient information on the brain pathophysiology during/immediately after shock wave exposure. We transcranially applied a laser-induced shock wave (LISW, ) to the left frontal region in a rat and performed multispectral imaging of the ipsilateral cortex through a cranial window (). For the spectral data obtained, we conducted multiple regression analysis aided by Monte Carlo simulation to evaluate vascular diameters, regional hemoglobin concentration (), tissue oxygen saturation (), oxygen extraction fraction, and light-scattering signals as a signature of cortical spreading depolarization (CSD). Immediately after LISW exposure, and were significantly decreased with distinct venular constriction. CSD was then generated and was accompanied by distinct hyperemia/hyperoxemia. This was followed by oligemia with arteriolar constriction, but it soon recovered (within ). However, severe hypoxemia was persistently observed during the post-CSD period (). These observations indicate that inadequate oxygen supply and/or excessive oxygen consumption continued even after blood supply was restored in the cortex. Such a hypoxemic state and/or a hypermetabolic state might be associated with brain damage caused by a shock wave.

Highlights

In recent years, the risk of military personnel and civilians suffering from blast-induced traumatic brain injury has been increasing due to frequent attacks using improvised explosive devices.[1,2,3,4] The majority of the patients (>90%) have been categorized as having mild to moderate TBI; most of them do not show any abnormality by conventional structural brain imaging, such as computed tomography
Real-time observation of cerebral responses to a shock wave is crucial for understanding the pathophysiology and mechanisms of blast-induced traumatic brain injury (bTBI), because the initial events caused by a shock wave can trigger cascading processes leading to pathological consequences in the chronic phase
We revealed the vascular type-dependent hemodynamic changes in the cortex from the moment of laser-induced shock wave (LISW) application to the rat brain based on a multispectral imaging approach

Summary

Introduction

The risk of military personnel and civilians suffering from blast-induced traumatic brain injury (bTBI) has been increasing due to frequent attacks using improvised explosive devices.[1,2,3,4] The majority of the patients (>90%) have been categorized as having mild to moderate TBI; most of them do not show any abnormality by conventional structural brain imaging, such as computed tomography. Many of the patients suffer from higher-order brain dysfunction as well as other chronic symptoms, such as headaches, photophobia, and insomnia, which considerably decrease their quality of life.[1,2,3,4] Despite extensive studies, the pathophysiology and mechanisms of such bTBI have not been fully elucidated. This is largely due to, in addition to the complex interactions of the brain with a shock wave, the lack of information on physiological, structural, and functional changes in the brain during and immediately after shock wave exposure in vivo.

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Conclusion