SUMMARY A computer model was developed to describe regional cerebral blood flow and tissue oxygen ation with autoregulation during focal ischemia produced by occlusion of the middle cerebral artery (MCA). This steady state model described the distribution of blood flow in the cerebral arterial system including the circle of Willis as well as the pial arterial anastomoses, and included a simplified form of autoregulation based on the local control of pressure and flow in the pial and intracerebral arteries, respectively. Preliminary simulation studies with the model yielded the following results. Less effective autoregulation was predicted by the model at low blood pressure in focal ischemia. Passive dilatation of the pial vasculature produced a leftward shift in the autoregulatory curve. Simulations with occlusion of the MCA revealed the ultimate importance of the pial anastomoses in providing adequate blood and oxygen supply in the ischemic territories including the specially vulnerable lenticulostriate area. The volume of the ischemic (p0 2 < 1 mmHg) brain tissue in the MCA-cortex estimated by using a concurrent Krogh cylinder model was 50% when the pial anastomoses were 80 /nm in diameter and the ischemic area disappeared at 170 /xm diameter. With relatively small anastomoses (< 200 m) the model demonstrated intracerebral steal during intracerebral vasodilation. Passive dilation of the pial arteries including the pial anastomoses caused the steal to disappear and to reverse. These results suggest that both autoregulatory shift and steal reversal can be explained by passive dilatation of the pial vasculature. Stroke, Vol 13, No 5, 1982 EXPERIMENTAL OBSERVATIONS suggest that a pressure changes. One way to test this or any hypoth general determinant of the severity of acute cerebral esis is to do more laboratory experiments, as we have ischemia in response to occlusion at the middle cere in progress. Another important test of a hypothesis is bral artery (MCA) is the competence of the collateral to analyze it for its internal consistency. The essential circulation. '^ During obstruction of the MCA, the ma intellectual discipline required is the reduction of jority of the ipsilateral hemisphere can receive blood qualitative thoughts to mechanisms which can be flow only through the pial anastomoses from the quantified. These can then be related to each other in a branches of the anterior and posterior cerebral arteries.computer simulation, thereby testing the hypothesis Similarly, retrograde flow through the lenticulostriate with the best available experimental data. If this simu branches of the MCA supplies the internal brain struc lation yields results which seem reasonable according tures (caudate nucleus, putamen, etc.) via the same to order of magnitude the hypothesis is thereby some pial anastomoses. Experimental evidences support that what strengthened, while if the order of magnitude is the severity of ischemia in this region plays a central unreasonable this would imply a defect in the hypoth role in th...

A prospective investigation on the short-term effects of various sedation regimens on 549 nonhospitalized magnetic resonance (MR) patients was performed. The drugs evaluated were chloral hydrate, pentobarbital, midazolam, and diazepam (fentanyl was used for enhancement after any of these drugs). The overall safety and efficacy were quite good with all the regimens. Overall, 84% of children slept less than 8 h after the examination, 90% were drowsy and/or unsteady for less than 8 h after they awoke, and 97% resumed their usual activities by 24 h. Significant hyperactivity was seen only with pentobarbital and occurred in 8.4% of children over 8 years of age. The multiple-dose regimen of pentobarbital and fentanyl had a significant short-term effect on the children less than 8 years of age, with 35% sleeping longer than 8 h after the MR. Ten children who had needed the multiple-dose pentobarbital regimen or who had failed prior pentobarbital sedation presented for repeat sedation. Midazolam was effective in 9 of these 10 children.

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The purpose of this work is to obtain a better understanding of transient oxygen release, diffusion and consumption in the capillaries and tissue of cerebral grey matter by describing the different aspects of the convectiondiffusion system in a mathematical model. Insight into the problem can be gained by the formulation and solution of a detailed mathematical model. ANATOMY