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Marek Czosnyka, Zofia H. Czosnyka, Peter C. Whitfield, Tim Donovan and John D. Pickard

formation rate of CSF can be measured in humans with limited accuracy, 7, 10, 16 it has been reported to decrease in healthy persons as they grow older, 16 such that the volume exchange of CSF takes twice as long in the elderly population. It has recently been hypothesized that this leads to accumulation of noxious substances in the CSF, which in turn may contribute to brain atrophy. 19 Indeed, early treatment of Alzheimer disease by implantation of a flow-regulating valve to stimulate increase in CSF production has been postulated. Measurement of the Rcsf is less

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the same as CBF; with due respect, I think there is an error in the title of the paper) contrasts with findings in other studies reporting blood flow volume in hydrocephalus. 2–4 Almost all indicate a decrease in CBF, particularly in periventricular and frontal cerebral areas. Pulsatility index is one of the most misleading variables ever used in cerebral hemodynamic studies. First, it is dependent on arterial pressure pulsatility. A high systolic—diastolic difference of arterial pulse pressure increases PI directly. Second, PI depends on heart rate, cerebral

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Piotr Smielewski, Marek Czosnyka, Peter Kirkpatrick and John D. Pickard

deteriorates with patient recovery and improvement in CO 2 reactivity. 4, 11 This paradoxical observation may result from a linear association between ICP and ABP caused by increases in blood volume in a noncompliant, nonautoregulating brain, such that the CPP does not change significantly. 22, 26 This mechanism could account for the inverse relationship seen between changes in ICP during carotid compression and the baseline ICP found in the present study. Our results show that the THRR correlates with both admission GCS scores and outcome. Three factors may have

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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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Zofia Czosnyka, John D. Pickard and Marek Czosnyka

various lengths are tested. Next, the variability of hydrodynamic parameters with different performance levels was assessed. Additional tests were repeated for a valve integrated with SiphonGuard. The valves were exposed to a magnetic field in 3-T MRI, and safety, stability of adjustment, and volume of artifact on gradient spin echo and T1 scans were assessed. Adjustability and basic hydrodynamic parameters were compared before and after MRI, and no change was noted. Finally, reflux, durability of junctions, and drift of pressure-flow performance over the entire testing

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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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Marek Czosnyka, Piotr Smielewski, Stefan Piechnik, Luzius A. Steiner and John D. Pickard

experimental head injury, it may be observed even when the values of CPP and CBF are normal. 21 Autoregulatory failure, a steep pressure—volume curve, and low cerebrospinal compensatory reserve 22 are all features indicating a potential to rapid deterioration. With a low cerebrospinal compensatory reserve any uncontrolled volume-expanding process may lead to sudden and massive intracranial hypertension. Similarly, if auto-regulation is disturbed, any decrease in CPP, no matter how high the baseline value of CPP has been, will produce a decrease in CBF. In both cases, the

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Peter J. Kirkpatrick, Piotr Smielewski, Marek Czosnyka, David K. Menon and John D. Pickard

also increased in two of these events ( Fig. 4 center ). The close correlation between the signal changes of all parameters suggests that the increased ICP was a consequence of rising CBF and cerebral blood volume. Miscellaneous Of the remaining 12 events (31%), 11 were associated with a rise in ICP and fall in CPP, and one with a rise in CPP. Changes in HbO 2 , Hb, flow velocity, and LDF occurred without any significant time lag ( Fig. 4 right ) and were accompanied by SjO 2 changes in nine cases. The recordings in this group were complex, precluding

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Peter J. Kirkpatrick, Joseph Lam, Pippa Al-Rawi, Piotr Smielewski and Marek Czosnyka

, Delpy DT , et al : Quantitation of cerebral blood volume in newborn infants by near-infrared spectroscopy. J Appl Physiol 68 : 1086 – 1091 , 1990 Wyatt JS, Cope M, Delpy DT, et al: Quantitation of cerebral blood volume in newborn infants by near-infrared spectroscopy. J Appl Physiol 68: 1086–1091, 1990

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whether ventricular size correlates with a positive clinical outcome following shunt placement. Methods. Hydrostatic valves (dual-switch valves) were implanted in 80 patients with NPH at Unfallkrankenhaus, Berlin, between September 1997 and January 2002. One year postoperatively, these patients underwent computerized tomography scanning, and their ventricular size was ascertained using the Evans Index. Among 80% of the patients who showed no postoperative change in ventricular volume, 59% nonetheless had good to excellent clinical improvements, 17% satisfactory