The role of mechanical factors in the pathogenesis of short-term and prolonged spasm of the cerebral arteries

Interrelationships among wall structure, smooth muscle orientation, and contraction in human major cerebral arteries

Human major cerebral arteries were fixed under pressure in the brain or after excision and ligation. They were sectioned and stained for light microscopy. Sterological point counting was used on mid-plane longitudinal sections of ten segments to determine that the media occupied 52.0% +/- 6.39 (SD) of the arterial wall and that the smooth muscle comprised 72.0% +/- 4.76 (SD) of the media. In arterial segments containing nine planar bifurcations, areas of varying muscle orientation and composition were identified and mapped out. A circumferential alignment of smooth muscle was consistently found in the cerebral branching systems except for the bifurcation region proximal to the apex at major bifurcations where the regular pattern was replaced by multilayered multidirectional smooth muscle. Theoretical models relating smooth muscle contraction to arterial caliber in cylindrical segments are outlined. In the extreme case of complete closure of an artery, our prediction is that for a typical cerebral arterial media the outermost muscle cells should have to contract to 42% of their relaxed length. The possible importance of medial smooth muscle patterns in the pathogenesis of cerebrovascular lesions is discussed.

A new model of subarachnoid hemorrhage in experimental animals with the purpose to examine cerebral vasospasm

Using 20 rabbits, we tried to establish a new model of experimental subarachnoid hemorrhage (SAH) for examining both acute and chronic cerebral vasospasm. A cranial opening was drilled, and a puncture made on the posterior branch of the middle cerebral artery. A second puncture was made in the superior sagittal sinus for additional withdrawal of subarachnoid blood. The bleeding thus induced resulted in arterial spasm which was studied by using serial electrocorticograms, cerebral blood flow measurement with 133Xe, and videomicroscopy of the small pial vessels at various intervals. After death of the animals, the brains were observed to identify the extention of the bleeding. It was indeed obvious that large amounts of subarachnoid blood clots had accumulated. This investigation showed that the rabbit can be used as a new experimental model of SAH. With a two-puncture method, it is possible to simulate the clinical phenomenon of a ruptured aneurysm, that seems to produce acute and chronic cerebral vasospasm. For the latter, the accumulation of blood clots in the basal surfaces plays an important role. The three methods of observation, videomicroscopy, cerebral blood flow measurements, and electrocorticography appeared to provide useful information in the study of biphasic vasospasm in the rabbit.

Regional cerebral blood flow in the acute stage of experimentally induced subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) was induced in 13 adult mongrel cats by a slow injection of fresh autogenous blood into the cisterna magna. Serial determinations of regional cerebral blood flow (rCBF) in the cortex and deep-seated areas (internal capsule, thalamus, and caudate nucleus) were made during the following 2 hours, while intracranial pressure (ICP) was maintained at normal values. A decrease in rCBF was observed in all the areas examined. This reduction followed a characteristic triphasic pattern with an initial steep decline immediately after the SAH. The clinical implications of these findings are discussed.

Cerebral arterial constriction after experimental subarachnoid hemorrhage is associated with blood components within the arterial wall

Sequential cisternal blood injections in dogs reproduce some of the morphological and physiological features seen in man after subarachnoid hemorrhage-induced vasospasm. This study reports the morphological features observed in cerebral vessels in areas exposed to subarachnoid blood. Subarachnoid hemorrhage was produced in dogs by two cisternal injections of non-heparinized autologous blood 48 hours apart. Dogs were sacrificed 48 hours after the second injection. Angiographic narrowing of the basilar artery was routinely present 48 hours after the second injection, and there was a good correlation between angiographic vasospasm and a narrowed arterial lumen at postmortem examination. All basilar arteries showed structural changes with electron microscopic examination; these included endothelial cell vacuoles, early smooth-muscle cell necrosis, intimal changes, and adventitial erythrocytes, leukocytes, and mast cells. The finding that accompanied vessel constriction most uniformly was packing of the adventitial cerebrospinal fluid spaces with erythrocytes. Angiographically visible spasm was resistant to vasodilators. These data suggest that infiltration of blood elements into the arterial wall is an important concomitant feature of morphological and angiographic vasospasm.

Experimental cerebral vasospasm: resolution by chlorpromazine

Vasospasm of the cat basilar artery was produced by electrical, mechanical, or chemical stimuli or by subarachnoid hemorrhage. The vasospasm induced by these stimuli was relieved by the topical application of chlorpromazine to the vascular wall. Chlorpromazine appears to be a nonspecific vasoparalytic agent. Unlike previously used substances, it is effective in resolving vasospasm caused by mechanical as well as chemical irritation.

Experimental cerebral vasospasm after subarachnoid hemorrhage. Participation of adrenergic nerves in cerebral vessel wall

Distribution and morphology of nerves in basilar-artery-induced vasospasm were investigated electronmicroscopically. Small cored vesicles were transformed, decreased and disappeared gradually after development of vasospasm induced by blood-CSF mixture incubated 5--10 days. These changes were not induced by fresh arterial blood, lysed platelets in saline and mechanical stimulation. In the portion with severe vasospasm induced by incubated blood-CSF mixture, nerve distribution was rich and uniform in all portions of the adventitia. In the portion with slight vasospasm, nerves were extremely scanty in the innermost area of the adventitia, within 10 mu from the outer edge of the media. The severity of experimental vasospasm became definitely lighter and the duration shorter after bilateral cervical sympathectomy. These findings indicate that nerves, especially the adrenergic axon in the innermost area of the adventitia, may play an important role on the genesis of late vasospasm. The difference in nerve distribution may be a factor influencing individual differences in frequency or severity of vasospasm.

Aseptic meningitis and hydrocephalus after posterior fossa surgery

In an attempt to define the tissue of origin of substances causing aseptic meningitis and secondary hydrocephalus after posterior fossa surgery, analysis of several marker substances from blood, brain, tumour and muscle in the CSF was performed early in seven postoperative patients. No clear pattern emerged which could relate the substances, CSF reaction, and meningeal scarring. The effects of various factors such as contrast studies, drainage, and steroids were also not clear. Review of the literature reveals that all four tissues can cause inflammation. Certain facts about the anatomy of the basilar cisterns and arachnoid villi probably make them logical sites for problems in CFS circulation. Children, for several reasons, are most susceptible to this complication. The complexity of factors in human cases suggests that the problem should be studied in an animal model.

Vasospasmogenic substance produced following subarachnoid haemorrhage, and its fate

Fresh blood and supernatants of blood-CSF mixtures incubated for 1 to 15 days were applied to the basilar artery of adult cats, and the degree of constriction was measured with a surgical microscope. The constriction due to fresh blood was weak and transient. It seems possible to assume that serotonin isolated from platelets participates greatly in the transient vasoconstriction induced by fresh blood. Supernatants of blood-CSF mixtures incubated for three days had weak activity in comparison with the powerful and long-lasting activity of those incubated for seven days. Furthermore, mixtures incubated for 15 days had little or no activity. This change in the vasoconstrictive activity was similar to, and coincides chronologically with clinical late spasm following subarachnoid haemorrhage 34. We investigated the vasospasmogenic substance in the seventh day mixture. Heat coagulation, ultrafiltration, sephadex G-100 gel-chromatography, disc-electrophoresis, and Spectrophotography show that extracellular oxyHb has a strong spasmogenic activity. In the 15th day mixture, oxyHb is spontaneously converted to metHb. Experimentally, oxyHb has a strong vasoconstrictive activity, and metHb has no vasoconstrictive activity. We have had success in oxidizing oxyHb into metHb with sodium nitrite, thus preventing experimental vasospasm.

Experimental cerebral vasospasm after subarachnoid hemorrhage: development and degree of vasospasm

Vasospasm of the basilar artery in 57 cats was induced by application of fresh blood, or a blood and cerebrospinal fluid (CSF) mixture incubated at 37 degrees C for 2 to 16 days. In animals treated with fresh blood or mixtures incubated for over 15 days, the severity of induced vasoconstriction is slight and duration short. Mixtures incubated 5 to 10 days induced severe and prolonged vasoconstriction. This incubation period for blood and CSF mixtures inducing severe vasospasm coincides with the developmental period of vasospasm after the onset of subarachnoid hemorrhage in our clinical experience. The prolongation of severe vasoconstriction induced by mixtures incubated for 7 days with clotted components is definitely greater than one induced by a mixture without clotted components. This experimental study suggests the existence of a vasospasmogenic substance in the blood in the subarachnoid space. Activity begins about 3 days after subarachnoid hemorrhage, increases strongly at 5 to 10 days, and disappears after 15 days.

Prolonged vasospasm produced by the breakdown products of erythrocytes

The cause of cerebral vasospasm has been generally attributed to the vasoconstrictive substances released from platelets. The role of extravasated erythrocytes in vasospasm has never been well analyzed. To elucidate this point, the basilar arteries of cats were exposed and subjected to topical application of various blood fractions in their fresh state and after prolonged incubation for 1 to 7 days. Incubation was done to test stability of the vasoconstrictors. Severe vasospasm was induced by application of fresh and incubated fractions of lysed erythrocytes. Fresh, intact erythrocytes had no vasoactivity, but by incubation they lysed and gained vasoconstrictors. Vasospasm induced by lysed erythrocytes both in their fresh state and after prolonged incubation never relaxed, and tended to increase in severity during observation up to 24 hours. Fresh serum and platelet-rich plasma had vasoconstrictors, but they were lost after incubation. Apparently platelet-induced vasoconstriction is of short duration and contributes only to the early phase of vasospasm. Later, 12 to 24 hours after hemorrhage, iron pigments released by lysis of extravasated erythrocytes (oxyhemoglobin or methemoglobin) irritate the arterial wall and induce prolonged vasospasm. It is emphasized that the study of cerebral vasospasm should be focused on the role of the breakdown products of extravasated erythrocytes.

Experimental head injury in the rat. Part 3: Cerebral blood flow and oxygen consumption after concussive impact acceleration

Cerebral blood flow (CBF) and oxygen consumption (CMRO2) were determined during timmediate posttraumatic period in rats subjected to concussive impact acceleration. According to previous studies an impact of 9 m/sec velocity elicited typical and marked symptoms of experimental concussion and often a prolonged comatose state, accompanied by cerebral metabolic signs of energy failure. During the immediate concussive response there was an increase of the CBF, followed within the next few minutes by a decrease to about one-third of normal flow, and then by a tendency toward normalization of flow 20 to 40 minutes posttrauma. Simultaneous measurements of cerebral oxygen extraction indicated an increase of the CMRO2 during the first minute. During the ischemic phase oxygen extraction increased but the lowest CBF values were only partially compensated for, and normal oxygen availability could not be maintained. The combined data, including cerebrospinal fluid pressure measurements, indicated primary cerebrovascular effects of the concussive trauma. These vasomotor effects may induce critical cerebral ischemia and thus profoundly influence posttraumatic cerebral function, and cause irreversible damage.

Experimental subarachnoid hemorrhage from a middle cerebral artery. Neurologic deficits, intracranial pressures, blood pressures, and pulse rates

Devices to produce experimental subarachnoid hemorrhage (SAH) can be implanted in animals. After SAH is produced by the puncture of a middle cerebral artery (MCA) in awake cats, neurologic deficits develop that are not as severe as those caused by MCA occlusion. Biphasic increases of epidural pressure occur and are related to the extent and distribution of the hemorrhage. Ischemic changes are more severe if the flow of blood through the MCA is interrupted.

Changes in the subarachnoid space after experimental subarachnoid haemorrhage in the dog: scanning electron microscopic observation

The possible changes in the subarachnoid space after subarachnoid haemorrhage were studied in animals by using a scanning electron microscope (SEM). About 1 ml/kg of autogenous blood was injected intracisternally in 36 adult mongrel dogs to investigate changes in the subarachnoid space, over periods ranging from immediately after the injection to as long as 6 months. We have come to the conclusion that the injected blood disappears in about one to two weeks; the fibrosis or thickening of the arachnoid membrane appears in one to three weeks, and then returns to normal in a month in instances of rapid recovery, but there are some cases in which fibrosis persists for a long period and becomes chronic. The fact that an increase of fibrous tissue was found in the parietal region, where the injected blood had hardly reached, appears to indicate that the fibrosis is not always limited to the site of the haemorrhage but can occur in remote regions. We also discuss the usefulness of the SEM in the observation of the subarachnoid space, and the finding that vascular specimen preparations can be made by perfusing the brain with 2-10% phosphate-buffered formaldehyde solution.

An in vitro study of prolonged vasospasm of a rabbit cerebral artery

Longitudinal stretch of the rabbit basilar artery produces local injury followed by prolonged circular constriction. After stretching and rapid release in vitro localized constrictions promptly occurred. This could be prevented by prior treatment with cyanide or calcium-free solution. Once produced, constrictions persisted for more than 72 hours. Previously induced constriction was not reversed by treatment for two hours with cyanide or by removing calcium. Histological observation indicated that constricted areas were associated with a discrete circumferential rupture of the internal elastic lamina and disruption and thinning of the underlying media. Specific catecholamine fluorescence at the adventitio-medial junction was unchanged in constricted areas. The relationship between smooth muscle cell length and resting tension of artery segments with and without constrictions was compared. Segments with constrictions had a shorter muscle length for any given resting tension, which confirms that constriction was not due to passive collapse of the vessel wall. These findings suggest that injury of cerebrovascular smooth muscle may result in essentially irreversible vasoconstriction. Such a mechanism could contribute to the pathogenesis of prolonged cerebral vasospasm after SAH or traumatic injury to the cerebrum.