Experimental assessment of phenoxybenzamine in cerebral vasospasm

Neurological and neurobehavioral assessment of experimental subarachnoid hemorrhage

About 50% of humans with aneurysmal subarachnoid hemorrhage (SAH) die and many survivors have neurological and neurobehavioral dysfunction. Animal studies usually focused on cerebral vasospasm and sometimes neuronal injury. The difference in endpoints may contribute to lack of translation of treatments effective in animals to humans. We reviewed prior animal studies of SAH to determine what neurological and neurobehavioral endpoints had been used, whether they differentiated between appropriate controls and animals with SAH, whether treatment effects were reported and whether they correlated with vasospasm. Only a few studies in rats examined learning and memory. It is concluded that more studies are needed to fully characterize neurobehavioral performance in animals with SAH and assess effects of treatment.

Neurologic evaluation in a canine model of single and double subarachnoid hemorrhage

The pathophysiology of cerebral vasospasm is complex and multifactorial. The present study sought to identify the degree of correlation between cerebral vasospasm as observed angiographically and clinical evaluation of an animal's neurologic status in the canine model following a single and double experimental subarachnoid hemorrhage (SAH) protocol. Nineteen mongrel dogs underwent single or double experimental SAH by percutaneous needle puncture of the cisterna magna and placement of a subarachnoid blood clot in the basal cistern on day 1 and day 4, respectively. At 72 h after each experimental SAH, vertebral angiography was performed and compared to control angiography. Basilar artery diameter measured at multiple positions was expressed as percentage of control diameter. Clinical evaluation of the animals was performed every day throughout the experiments. To assess the degree of neurologic impairment we developed a coma scale that efficiently estimated motor ability, eye response and eating habits of the animals. Vasoconstriction after experimental SAH reduced mean basilar artery diameter to 79.1% (+/- 5.4) of control diameter following single SAH and to 69.0% (+/- 2.1) of control diameter following double SAH. No changes were observed in the neurologic behavior of the animals throughout the experiment. Since a principal characteristic of human cerebral vasospasm is the close correlation between arterial constriction and neurological deficit, we believe that the canine model of SAH, although good in creating cerebral arterial vasoconstriction, does not fully represent the best model of human cerebral vasospasm.

Experimental vasospasm in cultured arterial smooth-muscle cells. Part 1: Contractile and ultrastructural changes caused by oxyhemoglobin

Smooth-muscle cells were cultured from rat aortic media, then oxyhemoglobin and other agents including serotonin, norepinephrine, and angiotensin II were added separately to the medium. Contractile and ultrastructural changes of the cells were examined with electron microscopy during the first 2 weeks of incubation. Oxyhemoglobin not only produced progressive contraction of the arterial smooth-muscle cells, but it also caused ultrastructural changes that resembled myonecrosis. In contrast, there was no evidence of progressive contraction or ultrastructural changes either in control cultures or in cultures with the other vasoactive agents. Although washout of oxyhemoglobin 3 hours after administration prevented continued contraction of the cells, washout 24 hours or longer after administration had no preventive effect. Judging from these results and from the fact that the culture medium was changed every 2 days, it is unlikely that accumulation of exogenous vasoactive agents caused these changes. The contraction and suggestive myonecrosis of the arterial smooth-muscle cells are probably caused by some intrinsic process initiated by oxyhemoglobin. The culture of cerebral arterial smooth-muscle cells requires further technical improvement; nevertheless, these results obtained with the smooth-muscle cells of rat aortic media indicate that arterial smooth-muscle cells in culture provide a promising new experimental model for chronic in vitro study of cerebral arterial spasm. It is suggested from these results that cerebral arteries are particularly prone to vasospasm because of structural differences as compared to noncerebral arteries.

Effect of prostacyclin and adenosine triphosphate on vasospasm of canine basilar artery

Cerebral vasospasm is one of the most important factors influencing morbidity and mortality of intracranial operations or diseases. Platelet aggregation and adhesion is increased in spastic vessels. Degradation of platelets liberates mediators, which in turn increase vasospasm, thus creating a vicious cycle. Healthy vessels cope with this by increasing the synthesis of prostacyclin. The purpose of this study was to increase experimentally the levels of arterial prostacyclin and adenosine triphosphate (ATP) in animals through intraarterial injection of these substances because they are lower in spastic vessels. Prostacyclin promotes antiaggregation and dilatation, increases blood flow, inhibits thromboxane A2, and prevents synthesis of angiotensin II. Most of these effects were done by increasing cyclic adenosine monophosphate (cAMP). After injecting autogenous blood into the cisterna magna of male dogs, both the acute and chronic phases of vasospasm and the degenerative changes in the arterial wall were observed. Injecting ATP increased the severity of vasospasm. During vasospasm it was found that when prostacyclin is used intraarterially, vasodilatation began, but degeneration of the arterial wall could not be prevented. In the group of animals in which both ATP and prostacyclin were used, there was no degeneration of the arterial wall and the basilar artery was seen to be normal when viewed under the electron microscope.

Evaluation of the efficacy of intrathecal nimodipine in canine models of chronic cerebral vasospasm

Previous studies have examined whether calcium antagonists given sublingually, intravenously, or orally affect an experimentally induced vasospasm. This study was designed primarily to determine the efficacy of nimodipine given intracisternally in reversing the cerebral vasospasm produced in dogs by the injection of 4 ml of autogenous blood into the cisterna magna. The magnitude of the vasospasm and the vascular response to nimodipine were determined arteriographically. One group of animals was studied acutely to determine the dose and pharmacodynamic effects of intrathecal nimodipine, a second group was studied 1 to 4 days after the intrathecal injection of blood, and a third group was studied 3 to 6 days after successive injections of cisternal blood given 48 hours apart. Some animals were studied further 24 hours after the nimodipine treatment. Intrathecal administration of 4 ml of 10(-3) M nimodipine promptly and completely reversed the cerebral vasospasm in all groups. This effect lasted at least 4 hours but had disappeared by 24 hours. The intrathecal administration of nimodipine produced a transient drop in blood pressure. In contrast, nimodipine given sublingually (0.28 to 0.58 mg/kg) or intravenously (0.1 mg/kg) produced a persistent hypotensive effect without affecting the vasospasm. The results show that the presence of nimodipine in the cerebrospinal fluid will reverse the blood-induced vasospasm, and suggest that this calcium antagonist administered intrathecally would be an effective emergency treatment of cerebral arterial spasm.

Reversal of cerebral arterial spasm by intrathecal administration of a calcium antagonist (nimodipine)

Specific antagonists to the influx of calcium, necessary for the excitation-contraction coupling process in arterial smooth muscle, are potentially useful in the treatment of cerebral vasospasm but systemic hypotension might limit their clinical applicability. We studied the effect of the calcium antagonist nimodipine (BAY e 9736) on cerebral arterial spasm, intraventricular pressure and blood pressure (BP), when administered into the cerebral ventricles of the dog. Cerebral vasospasm was produced by the injection of autologous blood into the cisterna magna. In a group of 8 dogs, 100 micrograms of nimodipine was injected into the lateral ventricle. The effect of the drug on the basilar artery was monitored angiographically. Nimodipine always relieved spasm, and often the relaxation surpassed the resting vessel diameter. In a control group, the injection of placebo did not relax the spastic arteries. Determinations using gas chromatography of nimodipine in CSF and blood demonstrated that a concentration of 1 microgram/ml in cisternal CSF was sufficient to reduce spasm while concomitant plasma concentrations of 0.004 micrograms/ml did not result in significant BP reduction.

Some inquiries in neuroanesthesia and neurological supportive care

Complications of performing neurosurgery in the sitting position have been well defined, and include cardiac and respiratory effects, air embolism, and pneumocephalus. Prophylactic measures and early diagnosis allow prompt therapy with minimal residual sequelae. All anesthetic agents and techniques alter the intracranial dynamics. A clear understanding of drug effects and the pathology involved allow a rational choice of anesthetic management to maximize the potential for a good outcome. Patients with cerebrovascular disorders frequently have multisystem disease, and careful preanesthetic assessment and preparation ensure a more stable intraoperative and postoperative course. Many chemical and mechanical reactions follow an ischemic hypoxic insult, but appropriate therapeutic intervention and early establishment of cardiorespiratory support measures have shown promise in improving the neurological outcome in these patients.

Experimental cerebral vasospasm. Part 2. Contractility of spastic arterial wall

We studied the mechanical properties of canine basilar arteries subjected to experimental subarachnoid hemorrhage (SAH). Smooth muscle contractility was determined from pressure-diameter curves obtained after subjecting the basilar arteries to three different conditions: Krebs-Ringer solution (KRS), Krebs-Ringer solution containing serotonin (5HT), and saline solution. Pressure-diameter curves obtained in KRS and 5HT are biphasic and have sharp flexions that yield flexion points. The pressure level at the flexion point increases as vasospasm increases. Strong constriction is retained up to that pressure above which the constriction is released abruptly. These data suggest that increasing the intraluminal pressure dilates the spastic artery nonlinearly and that induced hypertension could relieve the cerebral ischemia caused by vasospasm if blood pressure were maintained above the flexion point. The contractile response of spastic arterial wall to serotonin remains unchanged after SAH although the spastic constriction increases progressively and becomes maximal seven days after SAH. The lesser the arterial wall stiffness, the more efficiently it constricts. This means that the diminution of arterial stiffness observed after SAH might be one of the factors promoting the development of vasospasm.

Beneficial effects of adrenergic blockade in patients with subarachnoid haemorrhage

A total of 148 patients presenting within 48 hours of subarachnoid haemorrhage were assigned at random to receive standard management only or standard management and treatment with the adrenergic-blocking agents propranolol and phentolamine (or propranolol alone) for three weeks. One hundred and thirty-four patients completed the study. Assessment at four weeks showed a strong trend for less neurological deficit in the treated group, almost statistically significant (p=0.053) in the women. During the first month the treated group suffered fewer episodes of clinical deterioration consistent with cerebral arterial spasm: thus more treated patients underwent operation and those who did had a better outcome (p=0.030). At one year fewer were dead or disabled (unable to work) in the treated group; a significant difference for women (p=0.030). Possible mechanisms for these actions may include a reduction in pulmonary oedema, prevention of myocardial infarcts, a reduction in plasma renin activity, nd a reduction in cerebral oxygen requirements. It is concluded that early adrenergic blockade benefits patients (particularly women) with subarachnoid haemorrhage for up to one year in terms of lesser neurological deficit. Beta-blocker rather than alpha-blockade appears to be the useful component. A randomised, blind extension of the present study using long-acting propranolol and placebo has shown a significant (p=0.026) decrease in deaths and significantly (p=0.003) fewer poor results in the treatment group.

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.

Roles of subarachnoid blood clots and norepinephrine in cerebral vasospasm

The content of norepinephrine (NE) in the ventricular, basal cisternal and lumbar cerebrospinal fluid (CSF) was determined in 19 patients with ruptured cerebral aneurysms. The cisternal CSF in patients with vasospasm contained a significantly higher level of NE (0.246 +/- 0.0490 ng/ml) compared with those without vasospasm (0.075 +/- 0.001 ng/ml) (p less than 0.001). However, this increase is not considered to be high enough to constrict cerebral arteries, unless there is an increased NE-sensitivity in subarachnoid haemorrhage. Vascular responses to NE in vivo were then studied after reversing blood-induced prolonged vasospasm of the rabbit's basilar artery through a transclival approach as well as a newly developed basal cisternal irrigation model. However, NE in molar concentrations between 1 x 10(-10) and 10(-2) failed to produce further contraction of the artery. In conclusion, the increase in NE with vasospasm might be only a secondary phenomenon, and not a causative factor of vasospasm. Early removal of subarachnoid blood clots seemed to prevent the development of vasospasm.

Cerebrovascular reactivity and metabolism after subarachnoid hemorrhage in baboons

Subarachnoid hemorrhage (SAH) was induced in baboons by puncturing the middle cerebral artery. Four to seven days later cerebral blood flow (CBF) responses to changing PaCO2 and to intracarotid infusion of 1.0, 2.5 and 5.0 micrograms of 5-hydroxytryptamine (5-HT)/kg/min were studied using the intracarotid 133xenon clearance technique. Indices of cerebral metabolism were determined by measuring arterio-venous differences for oxygen, pyruvate, lactate and glucose. The results were compared with those from sham-operated baboons. In the sham-operated group normal CO2 reactivity was seen, and 5-HT infusion did not produce any significant change in CBF or cerebral metabolism. By contrast, the group in which SAH was induced showed a significant decrease in CBF and cerebral oxygen utilization, and attenuated CO2 reactivity.

Effect of nonsteroid anti-inflammatory drugs on subarachnoid hemorrhage in dogs

The effects of two long-acting anti-inflammatory agents on behavioral changes and cerebral vasospasm were evaluated in a canine model of chronic subarachnoid hemorrhage (SAH). The agent with the longest half-life, sudoxicam, clearly reduced both the incidence and the magnitude of the vasopasm, and prevented the usual behavior changes caused by the stimulated SAH. The results obtained with the other agent, naproxen, suggested that it was better than the administration of saline. These agents were studied because of reports indicating that prostaglandins and thromboxane may play a role in the pathogenesis of the effects of SAH and because of nonsteroid anti-inflammatory agents exert pharmacological effects by reducing an excessive synthesis of these lipids. The findings suggest that some of these agents may afford an alternative treatment for the deterious consequences of SAH.