Hun K. Park

Advances in ICP monitoring techniques

Abstract With the advent of newer devices for measuring intracranial pressure (ICP) and cerebral metabolism, more alternatives continue to rise aiming to control ICP. This manuscript presents a proposed analysis of different ICP monitoring devices in order to make appropriate selection of them in our clinical setting including general and pediatric applications. A systematic review of the literature was made analyzing the technical advances in ICP monitoring. The recent in vitro and in vivo tests as well as mathematical/computer models were reviewed. Practical applications of principles were discussed and compared based on the mode of pressure transformation. A ventricular catheter connected to an external strain gauge transducer or catheter tip pressure transducer device is considered to be the most accurate method of monitoring ICP and enables therapeutic CSF drainage. The significant infections or hemorrhage associated with ICP devices causing patient morbidity are clinically rare and should not deter the decision to monitor ICP. Parenchymal catheter tip pressure transducer devices are advantageous when ventricular ICP cannot be obtained or if there is an obstruction in the fluid couple, though they have the potential for significant measurement differences and drift due to the inability to recalibrate. Subarachnoid or subdural fluid-coupled devices and epidural ICP devices are currently less accurate. With an increasing miniaturization of the transducers, fiberoptic systems have been developed, however, there is a problem of measurement accuracy during the period of patient monitoring and external calibration should be performed frequently to ensure constant accuracy. Ventriculostomies continue to have a pivotal role in ICP control. With a rational understanding of the applications and limitations of the different ICP monitoring devices, the outcome for critically ill neurological patients is optimized.

Brain retraction injury.

Abstract This paper reviews the literature of the brain retraction injury during the last century. The review focused on the instrument characteristic as well as the physiopathological and histopathological damage of the brain induced by brain retraction. It was found that lesions were induced by cerebral ischemia. We conclude that a better monitoring system needs to be developed to avoid brain injury.

Biomechanical properties of calvarium prosthesis.

Abstract There are many materials available for the reconstruction of calvarial defects. Even though their biomaterial properties are well known, the biomechanical properties as part of the calvarium have not been investigated. In this article, calvarial implants are reviewed with their historic development into modern cranioplasty. Materials for trephined skulls are classified by their category. Individual parameters to describe their mechanical properties are collected and revealed in detail. The laboratory testing methodology for cranioplasty material is introduced to understand each parameter. At last, we discuss an engineering technique to look into the implant behavior. Since there is no standard goal for the biomechanical and biomaterial point of view for cranioplasty, this article suggests the finite element method for evaluation of the implant behavior and the degree of damage upon the impact injury. [Neurol Res 2001; 23: 267-276]

Cerebral cortex blood flow and vascular smooth muscle contractility in a rat model of ischemia: A correlative laser Doppler flowmetric and scanning electron microscopic study

Abstract The present study was undertaken to ascertain the role of smooth muscles and pericytes in the microcirculation during hyperperfusion and hypoperfusion following ischemia in rats. Paired external carotids, the pterygopalatine branch of the internal carotids and the basilar artery were exposed and divided. Reversible inflatable occluders were placed around the common carotids. After 24 h, the unanesthetized rat underwent 10-min ischemia by inflating the occluders. Continuous cortical cerebral blood flow (c-CBF) was monitored by laser Doppler flowmetry. The measured c-CBF was below 20% of control (P < 0.001) during ischemia. A c-CBF of 227.5 ± 54.1% (P < 0.001) was obtained during reperfusion hyperemia. A c-CBF of 59.7 ± 8.8% (P < 0.001) occurred at the nadir of postischemic hypoperfusion, and this was followed by a second hyperemia. The cytoarchitecture of the vascular smooth muscles and pericytes was assessed by scanning electron microscopy. Samples were prepared using a KOH-collagenase digestion method. In control rats, arteriolar muscle cells showed smooth surfaces. Capillary pericytes were closely apposed to the endothelium. Immediately after reperfusion, transverse membrane creases were observed on the smooth muscle surfaces. During maximal hyperemia the creases disappeared. When c-CBF started to decrease the creases became visible again. Throughout the postischemic hypoperfusion the creases remained. Capillary endothelial walls became tortuous in the late phase of hypoperfusion. During the second hyperemia most arteriolar muscle cells showed smooth surfaces. Some pericytes appeared to have migrated from the vascular wall. The morphological changes of smooth muscle membranes suggest that they are related to specific perfusional disturbances during ischemia and reperfusion.

Intervertebral foraminal ligaments of the lumbar spine: anatomy and biomechanics

Abstract The anatomical existence of the transforaminal ligaments has been studied extensively. However, there are very few studies examining how the transforaminal ligaments could be involved in the causation of nerve root compression and the low back pain syndrome. In this article, the authors review earlier studies in an attempt to find anatomical and biomechanical correspondence between the intervertebral foraminal ligaments of the lumbar spine and the low back pain syndrome.

Biomechanical properties of high-density polyethylene for pterional prosthesis

Abstract The pterional approach is the most popular surgical technique in aneurysm and skull base tumor removal. Reconstruction of the temporal contour deformity due to craniotomy requires graft implantation. Porous high-density polyethylene (PHDPE) as a craniofacial and pterional implant material recently became available. However, material properties of the pterional implant are not yet known. In order to measure the biomechanical properties of PHDPE, we implemented the tensile test, the three-point bending test and the water displacement method for density measurement. Elastic modulus varies from 227 to 307 MPa. Density range is 0.68 and 0.7 depending on the size of pores. The data can be used to study the character of the porous high-density polyethylene implant, how it resists stress or fatigue in combination with conventional plating systems.

CNS child abuse: Epidemiology and prevention

Abstract The problem of child abuse and the central nervous system implications are reviewed from a multidimensional approach. Statistics regarding prevalence, risk factors, epidemiological considerations, and physiological aspects are studied. The incidence is reviewed in the United States and in other countries where incidence and social services are also described. Implications for prevention efforts are considered. [Neurol Res 2002; 24: 29-40]

Application of finite element analysis in neurosurgery

Abstract With the rapid development of computer equipment, approximation by analytical solutions has become popular in mathematical modeling. Finite element (FE) analysis uses numerical methods to solve problems with physical phenomena, and these can be applied to various geometrically complex materials, such as brain. The FE formulation can provide such diverse domains as heat conduction, torsion of elastic material, diffusion and fluid flow, and it can view different objects of study in the neurosurgical field. In this article, the various applications of FE methods are introduced to illustrate the usefulness of the technique and the link between the external biomechanical aspect and internal phenomena in brain research.

Analysis of pellet implant for cranioplasty

Cranioplasty for large cranial defects greater than 10 cm/sup 2/ is a still challenge to neurosurgeons because of insufficient materials and strength. Polymethylmethacrylate (PMMA) generates chemical heat and fumes that cause tissue necrosis and delayed bone growth. Hydroxyapatite (HA) is not recommended for larger cranial defects. Large defects may not provide appropriate underlying cerebral protection from direct trauma even after cranioplasty. In this study, we investigated cranial prosthesis with pellet structures that facilitate stress redistribution upon impact.

Biomechanical simulation for 3 layer calvarial prosthesis

In this study, we conducted biomechanical study about behavior of large cranioplasty upon post-operative impact injury. Previous studies utilized a surface model of single layer with thickness of adult skull as 7 mm in the parietal bone. The finite element model used four-node and three-node quadrilateral shell elements. The overall model consists of 2,168 solid elements, and 4,736 shell elements. The dynamic behavior of the model was tested on the composite materials similar to normal adult skull in three layers (inner, outer and diploe layer). This structure resembles characteristics of calvarial implant differently upon impact. In order to overcome limitation of previous model, we designed a physiological model and analyzed dynamic behavior with new implant materials. The composite implant with two popular materials and middle polymer layer was evaluated and compared with bony material.