Hemodynamic Simulation Study of Cerebral Arteriovenous Malformations. Part 2. Effects of Impaired Autoregulation and Induced Hypotension

Abstract

Summary:The hemodynamic changes occurring during obliteration procedures for arteriovenous malformations (AVM) have not been fully elucidated, Therefore, we un dertook a simulation study using a compartmental flow model to investigate the role of altered autoregulatory conditions in the development of hyperperfusion during obliteration of large high-flow A VM. Induced hypoten sion was also simulated to evaluate its usefulness in re ducing the incidence and severity of the event. As the A VM flow was decreased during the obliteration proce dures, feeder pressure increased and drainer pressure de creased, with a concomitant increase in the perfusion pressure in the brain tissue surrounding the A VM. Cere bral blood flow (CBF) remained constant at 50 miiOO g-l min -1 in the presence of autoregulation and increased to Microsurgery and intravascular surgery have re cently contributed considerably to progress in the management of formerly inoperable large arteriove nous malformations (A VM) of the brain (Andrews and Wilson, 1987;Drake, 1979;Stein and Solomon, 1990;Vinuela et al., 1991). Reduction of AVM flow volume induced by these therapeutic modalities is known to increase feeder pressure and decrease drainer pressure, both of which elevate the pressure gradient across the nidus as well as the perfusion pressure in the surrounding brain.Under physiological conditions, an autoregula tory mechanism maintains constant cerebral blood Received December 2, 1994; final revision received May 15, 1995; accepted May 15, 1995. Address correspondence and reprint requests to Dr. Shiro Nagasawa at Department of Neurosurgery, Osaka Medical Col lege, Daigaku-cho 2-7, Takatsuki-City, Osaka 569, Japan.Abbreviations used: A VM, arteriovenous malformation; CBF, cerebral blood flow; LAR, lower limit of autoregulatory range; NPPB, normal perfusion pressure breakthrough. 16267 ml 100 g -1 min -1 in its absence. When the lower limit of the autoregulatory pressure range (LAR) was shifted from 60 to 50 or 40 mm Hg, the flow volume increased markedly from 67 to 77 ml 100 g -1 min -I or to 92 ml 100 g -1 min -I after complete obliteration. Decrease in LAR would be a cause of the hyperperfusion. Induced sys temic hypotension was found to be effective in reducing the magnitude of these hemodynamic changes, when in duction was appropriately performed in a stepwise fash ion. A simulation study is useful in clarifying the various hemodynamic changes that develop during the treatment of A VM. Key Words: Arteriovenous malformation Autoregulation-Cerebral hemodynamics-Compart mental flow model-Regional cerebral blood flow Simulation.flow (CBF). However, the brain tissue surrounding a large high-flow A VM is considered to be chroni cally exposed to hypoperfusion, which may result in the impairment of autoregulatory mechanisms. These increased hemodynamic loads are likely to result in an abnormal increase in CBF, with cere bral edema and hemorrhage, in some large high flow AVM. This phenomenon is referred to as nor mal perfusion pressure breakthroug...

Thrombosis and hemorrhage in the acute period following Gamma Knife surgery for arteriovenous malformation

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