Lo E H
Center for Imaging and Pharmaceutical Research, Massachusetts General Hospital, Harvard Medical School, Charlestown 02129.
Int J Radiat Oncol Biol Phys. 1993 Sep 30;27(2):353-61. doi: 10.1016/0360-3016(93)90247-s.
Stereotactic radiosurgery is being increasingly used to treat intracranial arteriovenous malformations (AVMs). However, successful radiosurgery may involve latent periods of 1-2 years prior to AVM obliteration. This latent period include states of altered flow patterns that may or may not influence hemorrhage probabilities. The probability of hemorrhage is likely to be related to the degree of biomechanical stress across the AVM shunt walls. This paper describes a theoretical analysis of the altered hemodynamics and biomechanical stresses within AVM shunts post-radiosurgery.
The mathematical model is comprised of linked flow compartments that represent the AVM and adjacent normal vasculature. As obliteration of the irradiated shunts occur, changes in flow rates and pressure gradients are calculated based on first order fluid dynamics. Stress on the AVM shunt walls is calculated based on tangential forces due to intramural pressure. Two basic models are presented: a distribution of shunts with fixed thin walls subject to step-function obliteration (Model I), and a distribution of shunts subject to luminal obliteration from slowly thickening walls (Model II). Variations on these models are analyzed, including sequential, selective and random shunt obliteration, and uniform or Poisson distributions of shunt radii.
Model I reveals that the range of pressure alterations in the radiosurgically-treated AVM include the possibility of transient increases in the total biomechanical stress within the shunt walls prior to obliteration. Model II demonstrates that uniform luminal narrowing via thickened walls should lead to reduced transmural stresses. The precise temporal pattern of AVM flow decrease and biomechanical stress reduction depends on the selection of shunts that are obliterated.
(a) The hemodynamic and biomechanical changes appear to be relatively independent of the shunt distribution but highly dependent on the temporal pattern of the obliterative process, (b) uniformly thickened shunt walls should uniformly decrease biomechanical stresses in the latent period prior to complete obliteration, but if uniform obliteration is not achieved, (c) transient alterations in pressure versus stress relationships may lead to temporarily increased biomechanical stress prior to complete obliteration, and (d) reduction in stress may not reach significant levels until the AVM is almost completely obliterated.
立体定向放射外科越来越多地用于治疗颅内动静脉畸形（AVM）。然而，成功的放射外科治疗可能在AVM闭塞前有1至2年的潜伏期。这个潜伏期包括血流模式改变的状态，这可能会也可能不会影响出血概率。出血概率可能与AVM分流壁上的生物力学应力程度有关。本文描述了放射外科治疗后AVM分流内血流动力学改变和生物力学应力的理论分析。
数学模型由代表AVM和相邻正常脉管系统的相连血流腔室组成。随着受照射分流的闭塞发生，基于一阶流体动力学计算流速和压力梯度的变化。AVM分流壁上的应力基于壁内压力产生的切向力来计算。提出了两个基本模型：具有固定薄壁的分流分布，其受到阶跃函数闭塞（模型I），以及分流分布，其受到来自缓慢增厚壁的管腔闭塞（模型II）。分析了这些模型的变体，包括顺序、选择性和随机分流闭塞，以及分流半径的均匀或泊松分布。
模型I显示，放射外科治疗的AVM中压力改变的范围包括在闭塞前分流壁内总生物力学应力短暂增加的可能性。模型II表明，通过增厚壁实现的均匀管腔狭窄应导致跨壁应力降低。AVM血流减少和生物力学应力降低的精确时间模式取决于被闭塞分流的选择。
（a）血流动力学和生物力学变化似乎相对独立于分流分布，但高度依赖于闭塞过程的时间模式，（b）在完全闭塞前的潜伏期内，均匀增厚的分流壁应均匀降低生物力学应力，但如果未实现均匀闭塞，（c）压力与应力关系的短暂改变可能在完全闭塞前导致生物力学应力暂时增加，并且（d）在AVM几乎完全闭塞之前，应力降低可能不会达到显著水平。
