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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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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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James D. Palmer, John L. Francis, John D. Pickard and Fausto Iannotti

drying out. Cottonoids were not weighed but they were wrung out and their fluid contents aspirated into the suction bottle. Suction of blood and wash was directed into disposable containers; at the end of the procedure all containers were weighed and the dry weight was subtracted to calculate the blood loss. By using the Aquaflow system all wash delivered to the wound was dispensed from 500- or 1000-ml bags under pressure with a pneumatic compression bag. At the end of the procedure all excess wash was aspirated into the suction system. The total volume of wash used

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Richard J. Nelson, Sheila Perry, Tony K. Hames and John D. Pickard

, peak systolic and diastolic velocities, and pulsatility indices. The minimum and maximum depths from which Doppler signals could be obtained were determined by adjusting the range-gate of a 2-mm sample volume in 1-mm steps. Other vessels were identified by varying the depths and angle of insonation. The effects of bilateral carotid artery occlusion were observed. Doppler Ultrasound Studies in Conscious Rabbits With the rabbits under general anesthesia, a 1.5-cm coronal incision was made caudal to the bregma and advanced anteriorly before the periosteum was

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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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John D. Pickard, Margaret Matheson, James Patterson and David Wyper

probability of an ischemic episode after carotid ligation is much higher if CBF falls more than minimally with carotid clamping. 7 Hence, delayed ischemic episodes may reflect the inability of part of the cerebral circulation in some individuals to compensate for periods of hypotension or hypoxia. Two findings are compatible with this concept: the deficit sometimes develops in association with a fall in the patient's blood pressure, and it may be reversed by raising the patient's blood pressure and expanding his blood volume. 8, 15 We have asked the question: what is 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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John D. Pickard and Alonso Pena

subarachnoid space is deeper than normal in IIH, hence the term “meningeal hydrops.” The MRI stigmata of IIH include dilated optic nerve sheaths, dilated sulci, and a partial empty sella, all of which suggest that there is excess extracerebral CSF in IIH, not brain swelling, despite the presence of venous sinus narrowing in many patients. Early studies with brain biopsies were compromised by methodological artifact. 3 Quantitative thin-slice MR studies have confirmed that ventricular size is normal in IIH and that extraventricular CSF volume is significantly increased in

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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