Z Czosnyka

Publications (32)57.61 Total impact

• Article: Impact of duration of symptoms on CSF dynamics in idiopathic normal pressure hydrocephalus.

  Z Czosnyka, B Owler, N Keong, T Santarius, O Baledent, J D Pickard, M Czosnyka
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  ABSTRACT: Cerebrospinal fluid (CSF) pressure-volume compensation may change over time as part of normal ageing, where the resistance to CSF outflow increases and the formation of CSF decreases with age. Is CSF compensation dependent on duration of symptoms in idiopathic normal pressure hydrocephalus (iNPH)? We investigated 92 patients presenting with iNPH. Mean age was 73 (range 47-86). There were 60 men and 32 women. They all presented with gait disturbance and ventricular dilatation. Memory deficit occurred in 72% and urinary incontinence in 52% of patients. All patients underwent computerized CSF infusion tests. Sixty-four shunted patients were available for follow-up, and their improvement was expressed using the NPH score. Mean intracranial pressure (ICP) was 10.1±5.1 mmHg, and mean resistance to CSF outflow was 17.3±5.2 mmHg/(ml/min). Mean duration of symptoms was 24±19 months (range from 2 weeks to 86 months). Baseline ICP, magnitude of ICP pulse waveform, brain compliance and improvement after shunting (72% of patients improved) did not exhibit any dependency on the duration of symptoms. The resistance to CSF outflow showed a strong tendency to decrease in time with the duration of symptoms beyond 2 years (R= -0.702; P<0.005). This is a preliminary observation, and it suggests that for patients with duration of symptoms longer than 2-3 years, the threshold for normal resistance to CSF outflow should be duration-adjusted.
  Acta Neurologica Scandinavica 06/2011; 123(6):414-8. · 2.47 Impact Factor
• Article: Evaluation of the cerebrovascular pressure reactivity index using non-invasive finapres arterial blood pressure.

  M Kasprowicz, E Schmidt, D J Kim, C Haubrich, Z Czosnyka, P Smielewski, M Czosnyka
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  ABSTRACT: A pressure reactivity index (PRx) can be assessed in patients with continuous monitoring of arterial blood pressure (ABP) and intracranial pressure (ICP) as a moving correlation coefficient between slow fluctuations of these two signals within a low frequency bandwidth. The study aimed to investigate whether the invasive ABP monitoring can be replaced with non-invasive measurement of ABP using a Finapres plethysmograph (fABP) to calculate the fPRx. There is a well-defined group of patients, suffering from hydrocephalus and undergoing CSF pressure monitoring, which may benefit from such a measurement. 41 simultaneous day-by-day monitoring of ICP, ABP and fABP were performed for about 30 min in 10 head injury patients. A Bland-Altman assessment for agreement was used to compare PRx and fPRx calculations. Performance metrics and the McNemary test were used to determine whether fPRx is sensitive enough to distinguish between functioning and disturbed cerebrovascular pressure reactivity. The fPRx correlated with PRx (R(Spearman) = 0.92, p < 0.001; bias = -0.04; lower and upper limits of agreement: -0.26 and 0.17, respectively). The fPRx distinguished between active and passive reactivity in more than 89% cases. The fPRx can be used with care for assessment of cerebrovascular reactivity in patients for whom invasive ABP measurement is not feasible. The fPRx is sensitive enough to distinguish between functional and deranged reactivity.
  Physiological Measurement 09/2010; 31(9):1217-28. · 1.68 Impact Factor
• Article: How does CSF dynamics change after shunting?

  G Petrella, M Czosnyka, N Keong, J D Pickard, Z Czosnyka
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  ABSTRACT: Hydrocephalus is much more complex than a simple disorder of cerebrospinal fluid (CSF) circulation. Shunting primarily corrects disturbed fluid flow which may have an impact on cerebral blood flow and metabolism. We studied hydrocephalic patients before and after shunting to characterize changes in their CSF compensatory parameters. We selected 25 patients and studied them retrospectively. All patients had ventriculomegaly and clinical symptoms of normal pressure hydrocephalus. After shunting, they were still presenting with some adverse symptoms, mainly headaches, slow improvement or no improvement of ventriculomegaly. Therefore, they underwent further infusion studies to assess shunt function. In all cases, the shunts were confirmed to be draining CSF adequately. Parameters of CSF dynamics: baseline intracranial pressure (ICP), resistance to CSF outflow, cerebrospinal elasticity, content of vasogenic pressure waves (pulse, respiratory and B waves) and compensatory reserve assessed as moving correlation coefficient between mean CSF pressure and pulse amplitude (RAP), were compared before and after shunting. Mean ICP and resistance to CSF outflow decreased (P < 0.003) after shunting. All vasogenic pressure waves decreased (P < 0.005). Compensatory reserve (RAP) significantly improved (P < 0.005). A functioning shunt has an important impact on CSF circulation and pressure-volume compensation. Infusion studies can demonstrate the return of disturbed CSF dynamics to normal values even if clinical or radiological changes are not dramatic.
  Acta Neurologica Scandinavica 06/2008; 118(3):182-8. · 2.47 Impact Factor
• Article: Clinical testing of CSF circulation.

  Z Czosnyka, M Czosnyka, A Lavinio, N Keong, J D Pickard
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  ABSTRACT: Since shunting is almost a purely mechanical treatment that radically affects pressure-volume compensation, patients' cerebrospinal fluid hydrodynamics compensation should be examined before a shunt is implanted. Apart from an opening pressure and a resistance to cerebrospinal fluid outflow, pulse amplitude of intracranial pressure and the content of vasogenic waves are useful to gauge cerebrospinal fluid dynamics. Infusion studies, although invasive, may help with the decision about surgery. They also provide basic information for further management of shunted patients, when complications, such as shunt blockage, under- and over-drainage, arise.
  European Journal of Anaesthesiology - Supplement 02/2008; 42:142-5.
• Article: Cerebrospinal fluid dynamics: disturbances and diagnostics.

  A Lavinio, Z Czosnyka, M Czosnyka
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  ABSTRACT: The pathophysiology of hydrocephalus can be modelled and described in terms of altered biomechanical parameters. Shunting is aimed to correct the patient's cerebrospinal fluid dynamics, compensating for inadequate cerebrospinal fluid re-absorption or insufficient volume buffering reserve. Computerized infusion studies implement intracranial pressure and arterial pressure signal processing and model analysis to allow the estimation of cerebrospinal dynamics variables such as cerebrospinal fluid outflow resistance, brain compliance and pressure-volume index, estimated sagittal sinus pressure, cerebrospinal fluid formation rate, compensatory reserve and cerebral vasoreactivity. Infusion studies can assist in the prognostication of normal pressure hydrocephalus and in the diagnosis of idiopathic intracranial hypertension. The technique is also helpful in the assessment of shunt malfunction, including posture-related over-drainage and shunt obstruction.
  European Journal of Anaesthesiology - Supplement 02/2008; 42:137-41.
• Article: Coupling of sagittal sinus pressure and cerebrospinal fluid pressure in idiopathic intracranial hypertension--a preliminary report.

  J D Pickard, Z Czosnyka, M Czosnyka, B Owler, J N Higgins
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  ABSTRACT: Narrowing of the cranial dural venous sinuses has been implicated as contributing to elevated intracranial pressure in idiopathic intracranial hypertension [IIH]. Such narrowing may be either a fixed stenosis or secondary to raised ICP. We have investigated whether narrowing of the venous sinuses may reflect direct coupling between cerebrospinal fluid pressure and sagittal sinus pressure. Nine patients with the clinical features of IIH [8F, 1M; mean age 41 (range 22-55)] were studied as part of their standard clinical investigations by simultaneous lumbar CSF infusion study and direct retrograde cerebral venography whereby a catheter is placed within the sagittal sinus under fluoroscopic guidance. In all cases, both CSF pressure (Pcsf) and sagittal sinus pressure (Pss) were elevated with Pcsf slightly exceeding Pss (27.0 +/- 2.3 mm Hg. 25.2 +/- 7.5 mm Hg; difference P = 0.026; correlation R = 0.97, P = 0.0032). There was a gradient of pressure along the sagittal and transverse sinuses. CSF infusion provoked rises in both Pcsf and Pss (R = 0.97, P < 0.0007). During drainage of CSF after the test (8 cases), Pcsf decreased to values lower than Pss (-3.26 +/- 3.9 mm Hg; P = 0.0097). There was excellent correlation between slow waves of Pcsf and Pss (mean R = 0.9) and between baseline pulse amplitudes of both pressures (R = 0.91; P = 0.03). In the 9 patients studied with IIH, Pcsf and Pss were coupled both statically (mean values) and dynamically (vasogenic components). During drainage, both pressures decreased until probably central venous pressure was reached and then Pcsf decreased further while Pss remained constant. This suggests that, in many cases of IIH, there is functional obstruction of venous outflow through the dural sinuses. Raised Pcsf partly obstructs venous sinus outflow, thereby increasing Pss which, in turn, leads to a further rise in Pcsf, et sequor. This vicious cycle can be interrupted by draining CSF.
  Acta neurochirurgica. Supplement 02/2008; 102:283-5.
• Article: Pulse amplitude of intracranial pressure waveform in hydrocephalus.

  Z Czosnyka, N Keong, D J Kim, D Radolovich, P Smielewski, A Lavinio, E A Schmidt, S Momjian, B Owler, J D Pickard, M Czosnyka
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  ABSTRACT: There is increasing interest in evaluation of the pulse amplitude of intracranial pressure (AMP) in explaining dynamic aspects of hydrocephalus. We reviewed a large number of ICP recordings in a group of hydrocephalic patients to assess utility of AMP. From a database including approximately 2,100 cases of infusion studies (either lumbar or intraventricular) and overnight ICP monitoring in patients suffering from hydrocephalus of various types (both communicating and non-communicating), etiology and stage of management (non-shunted or shunted) pressure recordings were evaluated. For subgroup analysis we selected 60 patients with idiopathic NPH with full follow-up after shunting. In 29 patients we compared pulse amplitude during an infusion study performed before and after shunting with a properly functioning shunt. Amplitude was calculated from ICP waveforms using spectral analysis methodology. A large amplitude was associated with good outcome after shunting (positive predictive value of clinical improvement for AMP above 2.5 mmHg was 95%). However, low amplitude did not predict poor outcome (for AMP below 2.5 mmHg 52% of patients improved). Correlations of AMP with ICP and Rcsf were positive and statistically significant (N = 131 with idiopathic NPH; R = 0.21 for correlation with mean ICP and 0.22 with Rcsf; p< 0.01). Correlation with the brain elastance coefficient (or PVI) was not significant. There was also no significant correlation between pulse amplitude and width of the ventricles. The pulse amplitude decreased (p < 0.005) after shunting. Interpretation of the ICP pulse waveform may be clinically useful in patients suffering from hydrocephalus. Elevated amplitude seems to be a positive predictor for clinical improvement after shunting. A properly functioning shunt reduces the pulse amplitude.
  Acta neurochirurgica. Supplement 02/2008; 102:137-40.
• Article: Interaction between hydrocephalus shunt and pressure waves

  Z Czosnyka, M Czosnyka, G Petrella, HK Richards, JD Pickard
  Cerebrospinal Fluid Research. 01/2007;
• Article: Intracranial baroreflex yielding an early cushing response in human.

  E A Schmidt, Z Czosnyka, S Momjian, M Czosnyka, R A Bech, J D Pickard
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  ABSTRACT: The Cushing response is a pre-terminal sympatho-adrenal systemic response to very high ICP. Animal studies have demonstrated that a moderate rise of ICP yields a reversible pressure-mediated systemic response. Infusion studies are routine procedures to investigate, by infusing CSF space with saline, the cerebrospinal fluid (CSF) biophysics in patients suspected of hydrocephalus. Our study aims at assessing systemic and cerebral haemodynamic changes during moderate rise of ICP in human. Infusion studies were performed in 34 patients. This is a routine test perform in patients presenting with symptoms of NPH during their pre-shunting assessment. Arterial blood pressure (ABP) and cerebral blood flow velocity (FV) were non-invasively monitored with photoplethysmography and transcranial Doppler. The rise in ICP (8.2 +/- 5.1 mmHg to 25 +/- 8.3 mmHg) was followed by a significant rise in ABP (106.6 +/- 29.7 mmHg to 115.2 +/- 30.1 mmHg), drop in CPP (98.3 +/- 29 mmHg to 90.2 +/- 30.7 mmHg) and decrease in FV (55.6 +/- 17 cm/s to 51.1 +/- 16.3 cm/s). Increasing ICP did not alter heart rate (70.4 +/- 10.4/min to 70.3 +/- 9.1/min) but augmented the heart rate variance (0.046 +/- 0.058 to 0.067 +/- 0.075/min). In a population suspected of hydrocephalus, our study demonstrated that a moderate rise of ICP yields a reversible pressure-mediated systemic response, demonstrating an early Cushing response in human and a putative intracranial baroreflex.
  Acta neurochirurgica. Supplement 02/2005; 95:253-6.
• Article: Clinical testing of CSF circulation in hydrocephalus.

  Z Czosnyka, M Czosnyka, B Owler, S Momjian, M Kasprowicz, E A Schmidt, P Smielewski, J D Pickard
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  ABSTRACT: INTRODUCTION: Recent 'NPH Dutch trial' has re-emphasised the importance of the resistance to cerebrospinal fluid (CSF) outflow (Rcsf) in the diagnosis of hydrocephalus. We re-evaluated the clinical utility of the physiological measurements revealing CSF dynamics. The results were summarized from our previous publications. The Computerised Infusion Test was designed to perform quick and low-invasive assessment of CSF dynamics described by parameters as Rcsf, brain compliance, elasticity coefficient, estimated sagittal sinus pressure, CSF formation rate and other variables. Overnight ICP monitoring with quantitative analysis of CSF dynamics was used in those cases where infusion study was unreliable or producing results close to the borderline. We found that the threshold of normal and increased Rcsf should be age-matched because in patients older than 55 Rcsf increases 0.2 mm Hg/(ml/min) per year (p < 0.04: N = 56). Rcsf was positively correlated with cerebral autoregulation (R = 0.41; p < 0.03; N = 36) indicating that in patients with symptoms of NPH but normal Rcsf underlying cerebrovascular disease is more frequent. Computerized infusion tests and overnight ICP monitoring are useful diagnostic technique alone or in conjunction with other forms of physiological measurement.
  Acta neurochirurgica. Supplement 01/2005; 95:247-51.
• Article: The relationship between CSF circulation and cerebrovascular pressure-reactivity in normal pressure hydrocephalus.

  Z Czosnyka, F van den Boogaard, M Czosnyka, S Momjian, L Gelling, J D Pickard
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  ABSTRACT: Previously, we documented association between CSF circulation and transcranial-Doppler derived autoregulation in non-shunted patients suffering from hydrocephalus. In the present study we sought to investigate the relationship between the resistance to CSF outflow and pressure-reactivity both in shunted and non-shunted NPH patients. Sixty-eight patients (47 non-shunted and 21 shunted) with NPH have been examined as a part of routine diagnostic procedure. Resistance to CSF outflow (Rcsf) was measured using a ventricular constant rate infusion test. Cerebrovascular pressure-reactivity was assessed as a moving correlation coefficient (PRx) between coherent 'slow waves' of ICP and arterial blood pressure (ABP). This variable has previously been demonstrated to correlate with the autoregulation of CBF in patients following head injury. Results. In non-shunted patients cerebrovascular pressure-reactivity (PRx) was negatively correlated with Rcsf (R = -0.5; p < 0.0005). This relationship was inverted in shunted patients: a positive correlation between PRx and Rcsf was found (R = 0.51; p < 0.03). Cerebrovascular pressure-reactivity is disturbed in patients with normal resistance to CSF outflow, suggesting underlying cerebrovascular disease. This result confirms our previous finding where transcranial Doppler autoregulation was investigated. After shunting the pressure-reactivity strongly depends on shunt functioning and deteriorates when the shunt is blocked.
  Acta neurochirurgica. Supplement 01/2005; 95:207-11.
• Article: Link between vasogenic waves of intracranial pressure and cerebrospinal fluid outflow resistance in normal pressure hydrocephalus.

  S Momjian, Z Czosnyka, M Czosnyka, J D Pickard
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  ABSTRACT: Recent studies on normal pressure hydrocephalus (NPH) have pointed to a possible link between the disturbance in CSF circulation and cerebrovascular factors. We investigated the quantitative relationship between the resistance to CSF outflow (Rcsf) and vasogenic waves of ICP in patients with normal pressure hydrocephalus. Forty-five patients with NPH were investigated by an infusion study. The magnitudes of vasogenic ICP components: pulse, respiratory and slow vasogenic waves were assessed, and compared with Rcsf. Both baseline respiratory and slow waves of ICP were positively correlated with Rcsf. The respiratory wave at baseline was a single independent predictor of Rcsf (r = 0.66, p < 0.0002). All vasogenic components increased significantly during the infusion test. The magnitude of the increase was positively correlated with Rcsf. The vasogenic ICP waves, notably the respiratory wave of ICP, correlate with the resistance to CSF outflow.
  British Journal of Neurosurgery 03/2004; 18(1):56-61. · 0.88 Impact Factor
• Article: Pattern of regional white matter CBF in normal pressure hydrocephalus during infusion test

  S Momjian, BK Owler, Z Czosnyka, M Czosnyka, A Pena, JD Pickard
  Cerebrospinal Fluid Research. 01/2004;
• Source

  Available from: bmj.com

  Article: Calculation of the resistance to CSF outflow.

  M Czosnyka, Z Czosnyka, S Momjian, E Schmidt
  Journal of Neurology Neurosurgery &amp Psychiatry 10/2003; 74(9):1354; author reply 1354-5. · 4.76 Impact Factor
• Article: Continuous assessment of cerebral autoregulation: clinical and laboratory experience.

  M Czosnyka, P Smielewski, Z Czosnyka, S Piechnik, L A Steiner, E Schmidt, I Gooskens, M Soehle, E W Lang, B F Matta, J D Pickard
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  ABSTRACT: The method for the continuous assessment of cerebral autoregulation using slow waves of MCA blood flow velocity (FV) and cerebral perfusion pressure (CPP) or arterial pressure (ABP) has been introduced seven years ago. We intend to review its clinical applications in various scenarios. Moving correlation coefficient (3-6 min window), named Mx, is calculated between low-pass filtered (0.05 Hz) signals of FV and CPP or ABP (when ICP is not measured directly). Data from ventilated 243 head injuries and 15 patients after poor grade subarachnoid haemorrhage, 38 patients with Carotid Artery stenosis, 35 patients with hydrocephalus and fourteen healthy volunteers is presented. Good agreement between the leg-cuff test and Mx has been confirmed in healthy volunteers (r = 0.81). Mx also correlated significantly with the static rate of autoregulation and transient hyperaemic response test. Autoregulation was disturbed (p < 0.021) by vasospasm after SAH and worse in patients with hydrocephalus in whom CSF circulation was normal (p < 0.02). In head injury, Mx indicated disturbed autoregulation with low CPP (< 55 mmHg) and too high CPP (> 95 mmHg). Mx strongly discriminated between patients with favourable and unfavourable outcome (p < 0.00002). This method can be used in many clinical scenarios for continuous monitoring of cerebral autoregulation, predicting outcome and optimising treatment strategies.
  Acta neurochirurgica. Supplement 01/2003; 86:581-5.
• Article: Hysteresis of the cerebrospinal pressure-volume curve in hydrocephalus.

  M Kasprowicz, M Czosnyka, Z Czosnyka, S Momjian, P Smielewski, H Juniewicz, J D Pickard
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  ABSTRACT: The objective was to study the displacement of the cerebrospinal fluid pressure-volume curve during the descent relative to the ascent of intracranial pressure recorded during the cerebrospinal fluid constant rate infusion test. This phenomenon can be interpreted as the hysteresis of the pressure-volume curve. The cerebrospinal fluid dynamics were tested in fifty-eight patients with clinical symptoms of hydrocephalus. After finished infusion, ICP was recorded until it returned to steady state level. Pressure-volume curves were plotted separately for ascending and descending phases of the test. The parameters of CSF compensation were estimated on the basis of mathematical mono-exponential model of CSF circulation. The pressure-volume curve post-infusion was visibly shifted upward in 69% of tests. Those who demonstrated the upward shift of the pressure-volume curve had greater an elastance coefficient of the cerebrospinal space (with shift: E1 = 0.26 +/- 0.14; without shift: E1 = 0.17 +/- 0.06; p < 0.05). Magnitude of the shift was positively correlated with pulse amplitude of ICP (r = -0.763; p < 0.0001). The accuracy of clinical examination of the pressure-volume compensatory reserve, which take into account both compression and decompression phase of the study, may be affected by this phenomenon.
  Acta neurochirurgica. Supplement 01/2003; 86:529-32.
• Article: Laboratory testing of hydrocephalus shunts -- conclusion of the U.K. Shunt evaluation programme.

  Z Czosnyka, M Czosnyka, H K Richards, J D Pickard
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  ABSTRACT: 16 models of valves, currently in use in the U.K., have been tested long-term in the U.K. Shunt Evaluation Laboratory according to the protocol based on the new ISO 7197 standard. Valves tested were: Medtronic PS Medical: Delta Valve, Flow Control and Lumbo-Peritoneal Shunt, Heyer-Schulte Nero-Care: In-line, Low Profile and Pudenz Flushing Valve, Codman: Codman-Hakim Programmable, Hakim Precision, Accu-Flo, Holter, Uni-Shunt, and siphon-preventing device -- SiphonGuard, NMT: Orbis-Sigma Valve, Omni-Shunt and Hakim Valve, Sophysa: Sophy Programmable Valve, Radionics: Contour-Flex Valve. The majority of the valves had a non-physiologically low hydrodynamic resistance (with the exception of Orbis-Sigma, PS Lumbo-Peritoneal and Heyer-Schulte In-Line). This may result in overdrainage both related to posture and during nocturnal cerebral vasogenic waves. A long distal catheter increases the resistance of these valves by 100-200%. Drainage through valves without siphon-preventing mechanism is very sensitive to body posture. This may produce grossly negative intracranial pressure after implantation. A few shunts (Delta, Low Profile and Pudenz-Flushing with Anti-Siphon Devices) offer a reasonable resistance to negative outlet pressure, and hence potentially might prevent complications related to overdrainage. On the other hand, valves with siphon-preventing devices may be blocked by raised subcutaneous pressure (exception: SiphonGuard, but this device may block the drainage because of its faulty design). In most of the silicone-diaphragm valves, closing pressure varied and reached values lower than that specified by the manufacturer (exception: Heyer-Schulte Pudenz Flushing Valve). All programmable valves are susceptible to overdrainage in the upright body position. Programmed settings may be changed by external magnetic fields. Most shunts are very sensitive to the presence of small particles in the drained fluid. The behavior of a valve revealed during such testing is of immediate relevance to the surgeon and may not be adequately described in the manufacturer's product information. These results are also relevant to the assessment of shunt function in-vivo using an infusion test.
  Acta Neurochirurgica 07/2002; 144(6):525-38; discussion 538. · 1.52 Impact Factor
• Article: A laboratory model of testing shunt performance after implantation.

  R Taylor, Z Czosnyka, M Czosnyka, J D Pickard
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  ABSTRACT: Constant rate infusion tests are used clinically to test shunt function in vivo in hydrocephalic patients. The criteria for appropriate shunt function have never been validated in the laboratory. Nine of the most commonly used types of hydrocephalus valves construction were selected and tested in a model of the CSF circulation incorporating increased resistance to CSF outflow [24 mmHg/(ml/min)] and decreased hydrodynamic compliance (<2 ml/mmHg), that are typical conditions in hydrocephalus. The aim was to document the pressure response to constant rate infusion of a model of CSF circulation with different valves and to define which measures are useful in shunt testing in vivo. The pressure-course of simulated CSF pressure was established and proved to be equivalent to clinical results. The baseline CSF pressure failed to correlate with shunt operating pressure for medium pressure valves (R = 0.14, p > 0.05). End-equilibrium pressure recorded during infusion correlated strongly with the opening pressure (R = 0.94, p = 0.0001) and the shunt's resistance (R = 0.86, p = 0.0026). The infusion test is able to assess shunt function. End-equilibrium pressure recorded during the test has been confirmed to correlate with the shunt's performance.
  British Journal of Neurosurgery 02/2002; 16(1):30-5. · 0.88 Impact Factor
• Article: Factors determining mean ICP in hydrocephalic patients with Hakim-programmable valve: implications of the parallel arrangement of the CSF outflow resistance and shunt.

  R Taylor, Z Czosnyka, M Czosnyka, J D Pickard
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  ABSTRACT: Measurement of CSF pressure is used clinically to test shunt function in vivo in hydrocephalic patients. Criteria for appropriate shunt function have never been validated. Hakim-Programmable valve was tested in a model of CSF circulation with variable resistance to CSF outflow (from 12 to 50 mm Hg/ml/min), increased hydrodynamic compliance (> 1.5 ml/mm Hg), and constant perfusion of a rate of 0.4 ml/min, i.e. conditions typical for hydrocephalus. The main question was how the simulated CSF pressure was influenced by the shunt setting and the residual resistance to CSF outflow. Measured baseline CSF pressure correlated well with shunt operating pressure only when high resistance to CSF outflow (50 mm Hg/(ml/min)) was used. For the medium resistance (20 mm Hg/(ml/min)) operating pressure was strongly affected by system's absorption capacity. For low resistance (12 mm Hg/(ml/min)) operating pressure through the valve was independent on valve's settings and no fluid drainage through the valve was recorded. Patients with moderately elevated resistance to CSF outflow (12-18 mm Hg/(ml/min)) cannot possibly react to changes of the valve's settings above 100 mm H2O. Mean CSF pressure results both from shunt setting and patient's own re-absorption capacity.
  Acta neurochirurgica. Supplement 01/2002; 81:23-6.
• Article: A randomized, controlled study of a programmable shunt valve versus a conventional valve for patients with hydrocephalus.

  Z Czosnyka, M Czosnyka, J Copeman, J D Pickard
  Neurosurgery 12/2000; 47(5):1250-1. · 2.79 Impact Factor