Yuichi Tada

Intra-operative measurement of cortical arterial flow volumes in posterior circulation using Doppler sonography.

Abstract Little has been reported on the flow volume of cortical arteries in the posterior circulation. During craniotomy in 28 patients, we measured the flow velocity of the arteries using microvascular Doppler sonography and recorded their arterial radii and the insonation angle. The flow velocities and radii were 25.7 cm sec–1 and 0.11 cm for the posterior cerebral artery (PCA), 19.5 cm sec–1 and 0.07 cm for the superior cerebellar artery (SCA), 19.6 cm sec–1 and 0.04 cm for the anterior inferior cerebellar artery (AICA), 14.9 cm sec–1 and 0.05 cm for the posterior inferior cerebellar artery (PICA), 28.3 cm sec–1 and 0.18 cm for the basilar artery, and 18.5 cm sec–1 and 0.16 cm for the vertebral artery, respectively. Since the flow velocities of these arteries were confined in a narrow range compared to the cross-sectional areas, the latter was considered to be the primary determinant for flow volume in these arteries. Based on certain assumptions, we estimated the flow volume of the PCA, SCA, AICA and ICA to be 60, 20, 10 and 10 ml min–1, respectively, which could be regarded as the current reference values for the arterial flow volumes. [Neurol Res 2000; 22: 194-196]

Simulation of therapeutic parent artery occlusion for basilar head aneurysms. Hemodynamic effect of occlusion sites and diameters of collateral arteries.

We simulated parent artery occlusion therapy for basilar head aneurysms to elucidate the hemodynamic changes induced by different occlusion sites and diameters of the posterior communicating arteries (PCom) as collateral pathways. A vascular model of the vertebrobasilar system with a basilar head aneurysm was constructed. Four types of occlusion were simulated: Basilar artery occlusion distal to (Type A), between (Type B) and proximal to (Type C) the superior cerebellar arteries, and bilateral vertebral artery occlusion (Type D). Glycerol solution was perfused into the model, and the half-life of the dye injected into the aneurysm was calculated and regarded as an index of stagnant flow in the aneurysm. The half-life was increased significantly and nonlinearly after parent artery occlusion, depending on the occlusion site and the ratio of two PCom diameters (diameter ratio). Intra-aneurysmal stagnation developed markedly in Type A and Type B in the diameter ratio higher than 0.70 and considerably in Type C in the ratio higher than 0.80. Additional P1 occlusion of the posterior cerebral artery enhanced the stagnation in Type A and B. Since the results are consistent with the published clinical data, the simulation study will be useful for speculating the efficacy of the therapeutic occlusion.

Paraclinoid aneurysms of the internal carotid artery: hydraulic simulation study on their locations and shape of the carotid siphon.

Hemodynamics of paraclinoid aneurysms were investigated focusing on the effects of their locations and shape of the carotid siphon. A transparent silicon model of the carotid siphon was constructed and a model aneurysm was attached to the outside of the curvature at three different sites. Glycerol solution was perfused into the model, and the half-life of the dye injected into the aneurysm was calculated as an index of the stagnant flow. Values of half-life changed significantly depending on the aneurysmal location and the siphon angle. When the siphon angle was 0 degree where C2 and C4 segments were parallel to each other, the half-life value was the lowest in the C2-C3 junction aneurysm, highest in the C3 segment aneurysm and intermediate in the C2 segment aneurysm. While the C2-C3 junction aneurysm maintained low values regardless of the angle, the C3 segment aneurysm values decreased and C2 segment aneurysm values increased with increases in the angle. These changes of half-life occur because the point at which the faster moving fluid component strikes the curved wall changes according to the siphon angle. These results are considered useful to determine the surgical indications, treatment modalities and post-surgical management of the aneurysms.

Hemodynamics in an arterial union—simulation study on therapeutic unilateral vertebral artery occlusion

Hemodynamic changes following unilateral vertebral artery (VA) occlusion were investigated in a rat model. The left carotid artery was resected and anastomosed to the right side in an end-to-side fashion to create a half-ring bypass. The distal side of the bypass was regarded as a union of VAs. Changes in the geometry, histology and hemodynamics in the union were investigated after the recipient artery was ligated. Intimal thickening was most prominently observed in the recipient arterial segment distal to the ligation site, where the lumen was obliterated. However, the portion of the lumen within 2.6 +/- 0.6 (mean +/- s.d.) mm, a distance of 2.9 +/- 0.6 times the internal diameter from the union, was not obliterated. The angle of the union was positively related to the length of this residual lumen. The results of this study explain some of the pathogenesis in unsuccessful aneurysmal thrombosis or brain stem infarction after therapeutic unilateral VA occlusion.

Normal perfusion pressure hyperperfusion in cerebral arteriovenous malformation surgery: model study on the hemodynamics and mechanisms.

A simulation study was undertaken using a compartmental flow model of a large high-flow cerebral arteriovenous malformation to investigate the hemodynamic changes during obliteration procedures. Under certain autoregulatory conditions, marked hyperperfusion (92 ml/100 g/min) could be induced in association with increased wall stress of the arterioles. Narrowing of the autoregulatory pressure range and its shift to a low pressure level are suspected to be among the possible causes of normal perfusion pressure breakthrough phenomenon.