Pial Microcirculation in Subarachnoid Hemorrhage

Abstract

Pial Microcirculalion in Subarachnoid Hemorrhage• Microsurgical and microscopic methods were employed in guinea pigs to expose, observe, and measure response characteristics of cerebral cortical pial microvessels and microcirculation to traumatic and nontraumatic experimental subarachnoid hemorrhage. Bleeding produced by vascular micropuncture was associated with a 44.3% arteriolar constriction. Topical application of homologous blood alone produced a 33.2% vasoconstriction. Observed microcirculatory flow characteristics subsequent to such microvascular changes were consistent with those known to be associated with cerebral cortical infarction. These changes could be prevented or reversed by topical application of the alpha adrenergic blocker, phenoxybenzamine. Topical pretreatment with the beta adrenergic blocker, propranolol, prevented blood-induced spasm, but did not reverse such spasm once it had been established. A chemo-mechanical mechanism is suggested as underlying the vasoconstriction associated with rupture of pial microvessels. It is thought that consideration of such microvascular characteristics, in conjunction with those known to be associated with larger intracranial vessels, adds to current knowledge of the pathophysiology of subarachnoid hemorrhage and may be extrapolated to bear future clinical import.Additional Key Words microvessels phenoxybenzamine propranolol image splitting vasospasm adrenergic blocker• It has been known for many years that rupture of intracranial aneurysms is associated with angiographically demonstrable cerebral vasospasm, 13 which can be confirmed visually at the operating table.2 Similar spasm has been noted in patients with traumatic subarachnoid hemorrhage, 46 and is seen less frequently with arteriovenous malformations and other disorders.2 It is clear, however, that blood experimentally introduced into the subarachnoid space by a variety of methods produces spasm of large intracranial arteries. "11 Vasospasm has been a deterrent to the surgical therapy of intracranial aneurysms, being associated with profound neurological deficits and death.1 ' 2t 12~17 Such a grave clinical problem has led to many laboratory investigations on the pathophysiology of blood-induced large vessel spasm.7 ' 9i "• 18~25 The regulation of blood supply to cerebral cortical tissue capillary beds is not exclusively a function of these large arteries, and is at least partially relegated to the precapillary resistance and distributing vessels of the pial microcirculation. systematically examine, by direct in vivo microscopy, pial microcirculatory changes in these states. MethodsForty-five young guinea pigs of both sexes, weighing 400 to 500 gm, were anesthetized with pentobarbital (40 mg per kilogram i.m.). The animals were usually not re-injected with pentobarbital after surgery, so that they were under light anesthesia at the time when their cerebral cortical vessels were studied. Using the Zeiss operating microscope a tracheostomy, right common carotid cannulation, and left pariet...

Cerebral microcirculatory failure after subarachnoid hemorrhage is reversed by hyaluronidase

“…The physiological deformation of erythrocytes as they travel through capillaries has been studied since the 1960s 3,4 and is a phenomenon conserved across many mammalian species, including humans. 35 RBC shape is thought to influence oxygen transport by erythrocytes in capillaries and alterations in RBC deformability can contribute to the pathology of a variety of human diseases.…”

Are We Barking Up the Wrong Vessels?

“…27 Based on these findings, the term early brain injury was created to describe the events associated with cerebral ischemia before the occurrence of large artery spasms. 33 That blood surrounding cerebral vessels may cause acute vasoconstriction was already shown by Herz et al in 1975. They removed the dura and studied pial microvessels using in vivo microscopy and noted that both micropuncture and directly applying blood to pial arterioles resulted in pial artery spasms.…”

“…They removed the dura and studied pial microvessels using in vivo microscopy and noted that both micropuncture and directly applying blood to pial arterioles resulted in pial artery spasms. 34 Later, it was shown that subarachnoid vessels develop similar spasms in experimental models of SAH. For example, Bederson et al 35 used histology in rats to demonstrate acute vasoconstriction immediately after experimental SAH; this vasoconstriction was independent of CPP and led to decreased CBF, increased hemorrhage size, persistently elevated extracellular glutamate levels, and poor general outcome.…”

“…Herz и соавт. в 1975 г. Они удаляли твердую мозговую оболочку и изучали микрососуды мягкой мозговой оболочки с помощью микроско-пии in vivo, при этом отмечали, что микропункция и непосредственное влияние крови на пиальные артерии вызывают их спазм [34]. Позже в экспериментальных моделях САК было показано, что в сосудах субарах-ноидального пространства развивается аналогичный спазм.…”

“…Кроме того, применение донаторов NO после экспериментального САК расширяет суженные церебральные артерии и снижает выраженность эксайтотоксичности [46]. В дополнение к NO другие механизмы могут играть определенную роль в развитии микровазоспазма после [34]. Позже в экспериментальных !…”