Recovery of the cortical evoked response following temporary middle cerebral artery occlusion in baboons: relation to local blood flow and PO2.

The degree of recovery of the somatosensory cortical evoked response following a period (15 to 65 minutes) of partial ischemia, produced by temporary occlusion of the middle cerebral artery (MCA), was assessed in baboons and related to the local tissue blood flow and PO2 before, during and after the occlusion. Flow was measured using the technique of two-minute hydrogen clearance. Failure of complete recovery of the evoked response was associated with significantly greater depths of ischemia and tissue hypoxia during occlusion, and with significantly greater and persisting tissue hypoxia after occlusion, than complete recovery.

Changes in regional cortical tissue oxygen tension and cerebral blood flow during temporary middle cerebral artery occlusion in baboons.

Cortical tissue oxygen measured by a platinum cathode, and cerebral blood flow recorded by a hydrogen clearance technique, were measured in 13 baboons before, during and after temporary occlusion of the middle cerebral artery. Mean control pO2 was 23.8 +/- 14 mm Hg and mean flow 51.

Measurements of oxygen tension in the cerebral cortex of baboons.

A polystyrene-covered platinum electrode (100-150 mum diameter) has been used to measure cortical tissue oxygen tension in baboon brains. The method of preparation, calibration, and the importance of small residual current (less than 40 nA) as an attribute of a reliable electrode, are described. With electrodes of this size, there was a large (16 +/- 12nA/torr) and linear current output with pO2 changes.

The effect of intracranial hypertension on cerebrovascular resistance--an experimental study.

Pulse transmission through cortex between a vein and artery in the middle cerebral distribution has been used as an index of vascular resistance in the middle cerebral field in baboons. Following catheterisation of these small vessels, the skull has been reconstituted and the effect of intracranial hypertension produced by cisternal infusion has been studied. An earlier linear relaxation of resistance in relation to rising intracranial pressure has been succeeded by a second phase in which pulse transmission increases quite profoundly despite minimal further increase in intracranial pressure.

Local cerebral blood flow and vascular reactivity in a chronic stable stroke in baboons.

Blood flow in the hemispheres of baboons three years after middle cerebral artery occlusion has been assessed by the hydrogen clearance technique. Blood flow in the infarct itself varied from very low (8 ml/100 gm per minute) to very high (89 ml/100 gm per minute) values and, averaging the values for the infarct as a whole, it was impossible to distinguish average flows in the infarct from those of the normal hemisphere. Flow values in surrounding zones of the infarct remained significantly lower than those of comparable normal hemispheres, and, excluding the infarct, the mean average hemispheral blood flow was 35.

The production and clinical features of a chronic stroke model in experimental primates.

The characteristics of stroke in baboons produced by transcranial occlusion of the middle cerebral artery were studied by clinical examination and serial cinematographic studies, the animals being maintained for three years following the stroke. The characteristic deficit in all animals was an initial, fairly dense faciobrachial weakness with, in a few instances, some accompanying leg weakness for a few days, rapidly improving over the first few months. Some animals retained very evident arm weakness; most animals retained weakness of the face; the majority showed recovery of reaching and placing reactions and some movement in all joints of the upper limb, although fine movements of the fingers remained invariably impaired.

Cerebral blood flow in dementia.

Twenty-four patients of comparable age, blood pressure, and degree of dementia were classified by an "Ischemic Score" based on clinical features into "multi-infarct" and "primary degenerative" dementia. Regional cerebral blood flow (CBF) was measured by the intracarotid xenon 133 method. Both groups showed a decreased proportion of rapidly clearing brain tissue (largely gray matter).

The vasodilator action of angiography with Urografin 60% on the basal vessels of the brain of the baboon.

Angiography under experimental conditions shows that Urografin has a vasodilator action of the order of 8% upon the basal cerebral arteries of the baboon. This action is not seen within the first 4 sec of the angiogram and the dilator effect of a single injection has passed off completely 15 min later. Three successive injections within 7 min show little evidence of cumulative vasodilatation.

Effect of changes in cerebral blood flow on proportion of high and low flow tissue in the brain.

Regional cerebral blood flow was measured by injection of (133)Xenon into the internal carotid artery in 11 patients with cerebrovascular disease. All patients were studied under general anaesthesia, first at normocapnia and then at hypocapnia. The 15 minute isotope clearance curves were analysed by computer by two-compartmental analysis and regional changes in flow and the proportions of fast and slow clearing tissue obtained at two levels of arterial CO(2) tension.

Effect of supratentorial space-occupying lesions on regional intracranial pressure and local cerebral blood flow: an experimental study in baboons.

Cortical blood flow and epidural intracranial pressure have been measured in the two supratentorial compartments of the intracranial space in experimental baboons during the acute expansion of a parieto-occipital epidural balloon. Differential pressures between the two halves of the supratentorial space have been found, and these have been associated with evidence that flow has fallen more quickly in the hemisphere most compressed. The evidence points to a more rapid exhaustion of the autoregulatory capacity in the hemisphere subjected to greater compression, a fall in perfusion pressure to below critical autoregulatory levels occurring slightly before that in the opposite hemisphere, and the establishment of a differential flow pattern for a short time during a critical phase of compression.