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Marek Czosnyka, Hugh K. Richards, Helen E. Whitehouse and John D. Pickard

T ranscranial Doppler (TCD) ultrasonography allows repeated, noninvasive studies of dynamic changes in cerebral blood supply. Although the mean blood flow velocity (FV) cannot be translated easily into volume blood flow, 20 additional information on cerebral hemodynamics may be derived from TCD pulsatility. Many authors have demonstrated the usefulness of various indices of pulsatility in the diagnosis of carotid artery stenosis 30 and other cerebrovascular diseases, 23 for the assessment of cerebral vasospasm after subarachnoid hemorrhage, 32 and for the

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Marek Czosnyka, Hugh K. Richards, Zofia Czosnyka, Stefan Piechnik and John D. Pickard

T he immediate effect of an increase in the volume of cerebrospinal fluid (CSF) depends on the brain's modulus of elasticity and baseline intracranial pressure (ICP). The phenomenon of pressure—volume compensation has been studied for many years. 2, 14, 19, 20, 22, 26 In conjunction with the model of CSF absorption (being proportional to the pressure difference between the CSF and the sagittal sinus, known as Davson's law 13 ), it has formed the foundation for the mathematical modeling of CSF pressure—volume compensatory mechanisms. 2, 10, 14, 22, 26, 31, 44

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Andrea Lavinio, Sally Harding, Floor Van Der Boogaard, Marek Czosnyka, Peter Smielewski, Hugh K. Richards, John D. Pickard and Zofia H. Czosnyka

and published in the peer-reviewed literature. Artifact volume was expressed in cm 3 and graded according to the following scheme: 0, no artifact; 1, artifact less than the size of the device; 2, artifact same as the size of the device; 3, artifact slightly larger than the size of the device; and 4, artifact larger than twice the size of the device. This particular technique of artifact assessment has been used in several prior publications and therefore serves as an appropriate comparison. All image display parameters were carefully selected to facilitate a valid

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Peter J. Hutchinson, Mark T. O'Connell, Pippa G. Al-Rawi, Lynn B. Maskell, Rupert Kett-White, Arun K. Gupta, Hugh K. Richards, David B. Hutchinson, Peter J. Kirkpatrick and John D. Pickard

heterogeneity of the brain, particularly along the course of a 30-mm-membrane catheter. In fact, in one patient the glucose concentration obtained using the 10-mm membrane was higher than that measured using the 30-mm membrane. One explanation for this may be that the whole of the 10-mm membrane was located in well-perfused tissue, whereas the distal part of the 30-mm membrane dialyzed a volume of tissue with lower glucose levels. Several types of perfusion fluids have been applied in clinical microdialysis, including saline, Ringer's solution, artificial cerebrospinal fluid

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Ming-Yuan Tseng, Peter J. Hutchinson, Hugh K. Richards, Marek Czosnyka, John D. Pickard, Wendy N. Erber, Stephen Brown and Peter J. Kirkpatrick

, Lundar T , Finset A : Cognitive outcome after aneurysmal subarachnoid hemorrhage: time course of recovery and relationship to clinical, radiological, and management parameters . Neurosurgery 60 : 649 – 657 , 2007 17 Jennett B , Bond M : Assessment of outcome after severe brain damage . Lancet 1 : 480 – 484 , 1975 18 Kassell NF , Peerless SJ , Durward QJ , Beck DW , Drake CG , Adams HP : Treatment of ischemic deficits from vasospasm with intravascular volume expansion and induced arterial hypertension . Neurosurgery 11 : 337