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Zofia Czosnyka, John D. Pickard, and Marek Czosnyka

Object

Independent testing of hydrocephalus shunts provides information about the quality of CSF drainage after shunt implantation. Moreover, hydrodynamic parameters of a valve assessed in the laboratory create a comparative pattern for testing of shunt performance in vivo. This study sought to assess the hydrodynamic parameters of the Certas valve, a new model of a hydrocephalus shunt.

Methods

The Certas valve is an adjustable ball-on-spring hydrocephalus valve. It can be adjusted magnetically in vivo in 7 steps, equally distributed within the therapeutic limit for hydrocephalus, and the eighth step at high pressures intended to block CSF drainage. The magnetically adjustable rotor is designed to prevent accidental readjustment of the valve in a magnetic field, including clinical MRI.

Results

The pressure-flow performance curves, as well as the operating, opening, and closing pressures, were stable, fell within the specified limits, and changed according to the adjusted performance levels. The valve at settings 1–7 demonstrated low hydrodynamic resistance of 1.4 mm Hg/ml/min, increasing to 5.1 mm Hg/ml/min after connection of a distal drain provided by the manufacturer. At performance Level 8 the hydrodynamic resistance was greater than 20 mm Hg/ml/min. External programming of the valve proved to be easy and reliable. The valve is safe in 3-T MRI and the performance level of the valve is unlikely to be changed. However, with the valve implanted, distortion of the image is substantial. Integration of the valve with the SiphonGuard limits the drainage rate.

Conclusions

In the laboratory the Certas valve appears to be a reliable differential-pressure adjustable valve. Laboratory evaluation should be supplemented by results of a clinical audit in the future.

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

Object. The aim of the study was to assess how cerebrospinal fluid (CSF) pressure—volume compensation depends on cerebrovascular tone.

Methods. In 26 New Zealand White rabbits, intracranial pressure (ICP), arterial blood pressure, and basilar artery blood flow velocity were measured continuously. Saline was infused into the cranial subarachnoid space to assess CSF compensatory parameters: the resistance to CSF outflow, the elastance coefficient, and the amplitude of the ICP pulsatile waveform. Infusions were repeated on two different levels of CO2 concentration in the arterial blood (PaCO2), at normotension and hypotension, and after the death of the animal.

An increase in PaCO2 from a mean of 27 to 48 mm Hg was accompanied by an 18% increase in the resistance to CSF outflow (p < 0.005) and a 64% increase (p < 0.05) in the elastance coefficient. A decrease in arterial blood pressure from a mean of 100 to 51 mm Hg caused a 25% decrease in CSF outflow resistance (p < 0.01) but did not affect the elastance coefficient. Postmortem, a 23% decrease in the CSF outflow resistance was associated with a 102% decrease in the elastance coefficient.

Conclusions. Cerebrovascular parameters have a limited but significant impact on CSF infusion studies. The vascular component of ICP may be identified as a significant factor contributing to this phenomenon. During infusion studies, physiological parameters influencing vascular conditions should be maintained as stable as possible.

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Nicole C. H. Keong, Alonso Pena, Stephen J. Price, Marek Czosnyka, Zofia Czosnyka, and John D. Pickard

The pathophysiology of NPH continues to provoke debate. Although guidelines and best-practice recommendations are well established, there remains a lack of consensus about the role of individual imaging modalities in characterizing specific features of the condition and predicting the success of CSF shunting. Variability of clinical presentation and imperfect responsiveness to shunting are obstacles to the application of novel imaging techniques. Few studies have sought to interpret imaging findings in the context of theories of NPH pathogenesis. In this paper, the authors discuss the major streams of thought for the evolution of NPH and the relevance of key imaging studies contributing to the understanding of the pathophysiology of this complex condition.

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Zofia Czosnyka, Marek Czosnyka, and John D. Pickard

Abstract

Object. The appearance of numerous B waves during intracranial pressure (ICP) registration in patients with idiopathic adult hydrocephalus syndrome (IAHS) is considered to predict good outcome after shunt surgery. The aim of this study was to describe which physical parameters of the cerebrospinal fluid (CSF) system B-waves reflect and to find a method that could replace long-term B-wave analysis.

Methods. Ten patients with IAHS were subjected to long-term registration of ICP and a lumbar constant-pressure infusion test. The B-wave presence, CSF outflow resistance (Rout), and relative pulse pressure coefficient (RPPC) were assessed using computerized analysis. The RPPC was introduced as a parameter reflecting the joint effect of elastance and pulsatory volume changes on ICP and was determined by relating ICP pulse amplitudes to mean ICP.

Conclusions. The B-wave presence on ICP registration correlates strongly with RPPC (r = 0.91, p < 0.001, 10 patients) but not with CSF Rout. This correlation indicates that B waves—like RPPC—primarily reflect the ability of the CSF system to reallocate and store liquid rather than absorb it. The RPPC-assessing lumbar short-term CSF pulse pressure method could replace the intracranial long-term B-wave analysis.

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Marek Czosnyka, Zofia Czosnyka, Nicole Keong, Andreas Lavinio, Piotr Smielewski, Shahan Momjian, Eric A. Schmidt, Gianpaolo Petrella, Brian Owler, and John D. Pickard

Object

Apart from its mean value, the pulse waveform of intracranial pressure (ICP) is an essential element of pressure recording. The authors reviewed their experience with the measurement and interpretation of ICP pulse amplitude by referring to a database of recordings in hydrocephalic patients.

Methods

The database contained computerized pressure recordings from 2100 infusion studies (either lumbar or intraventricular) or overnight ICP monitoring sessions in patients suffering from hydrocephalus of various types (both communicating and noncommunicating), origins, and stages of management (shunt or no shunt). Amplitude was calculated from ICP waveforms by using a spectral analysis methodology.

Results

The appearance of a pulse waveform amplitude is positive evidence of a technically correct recording of ICP and helps to distinguish between postural and vasogenic variations in ICP. Pulse amplitude is significantly correlated with the amplitude of cerebral blood flow velocity (R = 0.4, p = 0.012) as assessed using Doppler ultrasonography. Amplitude is positively correlated with a mean ICP (R = 0.21 in idiopathic normal-pressure hydrocephalus [NPH]; number of cases 131; p < 0.01) and resistance to cerebrospinal fluid outflow (R = 0.22) but does not seem to be correlated with cerebrospinal elasticity, dilation of ventricles, or severity of hydrocephalus (NPH score). Amplitude increases slightly with age (R = 0.39, p < 0.01; number of cases 46). A positive association between pulse amplitude and increased ICP during an infusion study is helpful in distinguishing between hydrocephalus and predominant brain atrophy. A large amplitude is associated with a good outcome after shunting (positive predictive power 0.9), whereas a low amplitude has no predictive power in outcome prognostication (0.5). Pulse amplitude is reduced by a properly functioning shunt.

Conclusions

Proper recording, detection, and interpretation of ICP pulse waveforms provide clinically useful information about patients suffering from hydrocephalus.