On the importance of vascular architecture in selective vulnerability of the basal ganglia.

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1. A series of measurements of pressure drop occurring at arterial branchine, were conducted using model branches with various geometries, and the effect of branching on distal blood supply was studied. It was revealed that in blood circulation, the pressure drop due to branching is important where a small artery divide off with a large branching angle from a large trunk.2. The pallidum in the basal ganglia was found to be fed by small arteries which divide off from a large trunk and run a long course until they enter the brain parenchima. These features suggest that the pressure drop at the entrance of arteries feeding the palliddum is significant and may play an important role in determining the regional blood flow under carbon monoxide poisoning, where peripheral resistance is maximally reduced and systemic hypotension is superimposed.3. The arteries feeding the putamen were considerably large compared with those of pallidum and they enter the brain parenchima immediately after branching from a trunk. These features of vascular architecture indicate that the arteries in the putamen are exposed to high pressure, and may relate to selective involvement of this part in hypertensive hemorrhage.4. The pattern of arteries distributed in the brain was found to be a "fractal" characterized by two fractal dimensions (1.78 and 1.29). The randomness of it is quantitatively represented by the fractal dimension.