Erik Skinhøj

Autoregulation of Brain Circulation in Severe Arterial Hypertension

Cerebral blood flow was studied by the arteriovenous oxygen difference method in patients with severe hypertension and in normotensive controls. The blood pressure was lowered to study the lower limit of autoregulation (the pressure below which cerebral blood flow decreases) and the pressure limit of brain hypoxia. Both limits were shifted upwards in the hypertensive patients, probably as a consequence of hypertrophy of the arteriolar walls. These findings have practical implications for antihypertensive therapy. When the blood pressure was raised some patients showed an upper limit of autoregulation beyond which an increase of cerebral blood flow above the resting value was seen without clinical symptoms. No evidence of vasospasm was found in any patient at high blood pressure. These observations may be of importance for the understanding of the pathogenesis of hypertensive encephalopathy.

Regional cerebral blood flow in apoplexy without arterial occlusion

IN A PREVIOUS STUDY we reported on regional cerebral blood flow in patients with apoplexy due to occlusion of the middle cerebral artery.l The xenon 133 injection method was used and the studies included observations of the regional flow response of the brain to changes of the arterial blood pressure and of the arterial pC0, and to injection of theophylline. Focal ischemia or focal hyperemia or both were found in all patients, combined with focal vasoparalysis in most of them. This group of middle cerebral artery occlusions was studied with the aim of collecting information on the regional cerebral blood flow and its regulation in a more welldefined group of apoplexies than in earlier reports.2-6 In the present paper, we have aimed at studying another fairly uniform group of apoplexies, i.e., patients without angiographic evidence of arterial occlusion and all with hemiparetic symptoms of more than twenty-four hours’ duration (studies in more transitory attacks will be reported separately).T The flow studies were made at varying time intervals after the acute onset of the disease, and this proved to be of decisive importance for the regional blood flow derangement seen.

Regulation of cerebral blood flow as a single function of the interstitial pH in the brain. A hypothesis.

The relation between pCOz and cerebral blood flow (CBF) has been known for many years. In acute changes in COz the correlation is nearly linear between ApCOz values from 20-60 mm Hg., with an increase in CBF about 2 per cent pr. 1 mm Hg. increase in ApC02. The decrease in oxygen a-v difference follows the same curve. It has been known for many years, too, that this correlation ceases with low oxygen tensions in the brain, Lennox & Gibbs (1932). We have regarded this relationship as a typical homeostatic mechanism of the feedback type as the COz correlation secures the COz producing brain a sufficient blood supply during normal circumstances and the 0 2 correlation acts as a safetyvalve, for example in cases with reduced oxygen capacity of the blood. Some facts, however, are unexplained by this hypothesis:

A Paradoxical Cerebral Hemodynamic Effect of Hydralazine

Hydralazine is shown to have a very complex cerebral hemodynamic effect. It raises the intracranial pressure which, together with its effect upon systemic blood pressure, reduces the cerebral perfusion pressure. In spite of this and a concomitantly induced hyperventilation by hydralazine, CBF increases with some delay. The conclusion is that hydralazine is a cerebral vasodilator acting immediately upon cerebral capacitance vessels but later upon the resistance vessels as well.

Extrastriate cortical areas activated during visual discrimination in man

The regional cerebral blood flow (rCBF) was measured in 254 different regions of the human extrastriate cerebral cortex during rest and during visual shape discrimination. Visual shape discrimination increased the rCBF markedly in the frontal eye fields, the upper part of the prefrontal cortex, the lateral occipital cortex and the superior parietal cortex. Moderate increases of rCBF appeared in the inferotemporal cortex, the parietotemporo-occipital region and scattered in the lateral part of the prefrontal cortex.

Cortical activation during somatosensory stimulation and voluntary movement in man: A regional cerebral blood flow study☆

Abstract Regional cerebral blood flow (rCBF) changes were measured by a 254-channel dynamic gamma camera in 7 human subjects during peripheral nerve stimulation and during voluntary movement. Normal somatosensory evoked potentials (SEPs) were recorded simultaneously from the scalp over the primary cortical projection areas when contralateral digital or ipsi- or contralateral median nerve was stimulated electrically. The voluntary movement was an imitation of the passive thumb twitch which occurred during median nerve stimulation. Focal rCBF increases were observed during nerve stimulation and during voluntary movement in the same area within the middle part of the contralateral central region. This area of cortical activation was localized over the sensory and motor projection areas of the hand and thus involved both the precentral and postcentral gyri. During voluntary movement additional focal increases of rCBF were observed in the upper premotor region, including the supplementary motor area. This area was also activated during contralateral median nerve stimulation. Focal rCBF increases were also observed during contralateral nerve stimulation in the lower central region, just anterior to the primary auditory cortex. This area appears to correspond to the second sensory area (SII) in man. During ipsilateral median nerve stimulation no focal increases of rCBF were observed and also no SEPs were recorded within the analysis time of 200 msec. It is concluded that activation of the contralateral primary cortical sensory and motor areas, as well as the SII area, as shown by focal rCBF increases, reflects generation of the early components of the SEP. The activation of the upper premotor region during median nerve stimulation and during voluntary movement is more likely to be involved in the generation of the later components of the evoked potential and the electrical activity preceding voluntary movement. The same extents of the focal rCBF activation in the contralateral sensorimotor area during peripheral nerve stimulation and during voluntary movements confirm that the precentral gyrus is involved in sensory perception and, similarly, that sensory feedback to the post-central gyrus is a normal component of the execution of voluntary movement.

The Sympathetic Nervous System and the Regulation of Cerebral Blood Flow in Man

Pharmacological blockade of the α adrenergic system by 20 mg phentolemine I.V. was shown not to influence CBF in 14 patients with an intact cerebral autoregulation. If the autoregulation--tested with angiotensin--was impaired for some reason, CBF was found to follow proportionally the blood pressure changes provoked by the blockade. The physiological sympathetic stimulation provoked by distention of the bladder did not alter the CBF (seven patients). The CO2 reactivity was unaffected by the sympathetic α blockade (six patients). It appears from these studies that the sympathetic system does not play any substantial role in regulation of CBF in man, and thus it would seem useless to try to influence the cerebral circulation for therapeutic purposes by systemic application of drugs, which directly or indirectly work via the sympathetic system.

REGRESSIVE LANGUAGE IN SEVERE HEAD INJURY

In a follow‐up study of 50 patients with severe head injuries three patients had echolalia. One patient with initially global aphasia had echolalia for some weeks when he started talking. Another patient with severe diffuse brain damage, dementia, and emotional regression had echolalia. the dysfunction was considered a detour performance. In the third patient echolalia and palilalia were details in a total pattern of regression lasting for months. the patient, who had extensive frontal atrophy secondary to a very severe head trauma, presented an extreme state of regression returning to a foetal‐body pattern and behaving like a baby.