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Biomedical subjects

M Czosnyka

Publications and source records attributed to M Czosnyka.

At least 19 recordsLinked to original sources
PubMed2003

Cerebral autoregulation in carotid artery occlusive disease assessed from spontaneous blood pressure fluctuations by the correlation coefficient index.

BACKGROUND AND PURPOSE: Estimation of dynamic cerebral autoregulation from spontaneous fluctuations of arterial blood pressure (ABP) and cerebral blood flow velocity (CBFV) is an attractive monitoring option for cerebral hemodynamic impairment. We evaluated the correlation coefficient index method in patients with severe obstructive carotid disease and compared it with transfer function analysis (frequency domain approach to cerebral autoregulation) and CO2 vasomotor reactivity. METHODS: In 139 patients with severe unilateral carotid stenosis (>or=70%) or occlusion, CBFV (transcranial Doppler) and ABP (Finapres method) were recorded over 10 minutes. Correlations between systolic pressure, diastolic pressure, and mean ABP and CBFV oscillations over 1-minute epochs were averaged over 10 minutes to form the correlation coefficient indexes (Sx, Dx, Mx, respectively). Transfer function parameters (phase shift and gain between ABP and CBFV oscillations) were determined from the entire 10-minute period. CO2 reactivity was assessed by inhalation of 7% CO2. RESULTS: The correlation indexes Dx and Mx were significantly higher ipsilateral to stenosis and increased with degree of stenosis, indicating increasing dependence of CBFV on ABP and thus impairment of cerebral autoregulation. Dx and Mx correlated moderately but highly significantly with transfer function parameters and CO2 reactivity and showed a good level of agreement in detecting pathological values. Patients with a small variance of the 1-minute source correlations of Dx and Mx showed clearly better correlation values. Transfer function parameters and CO2 reactivity but not Dx and Mx were significantly poorer in patients with symptomatic stenosis or occlusion. CONCLUSIONS: The potential of the correlation coefficient indexes Dx and Mx in detecting hemodynamic impairment in patients with carotid stenosis is comparable to that of transfer function analysis and CO2 reactivity testing. In future, a combination of various hemodynamic tests might help to identify patients at risk for ischemic events.

Aged↗
PubMed2003

Pressure-autoregulation, CO2 reactivity and asymmetry of haemodynamic parameters in patients with carotid artery stenotic disease. A clinical appraisal.

OBJECTIVES: Patients with carotid artery stenotic disease and poor cerebral haemodynamic reserve are in increased risk of stroke. Haemodynamic reserve can be estimated by measuring cerebrovascular reactivity induced by breathing CO2 and pressure-autoregulation by analyzing spontaneous slow fluctuation in arterial pressure and MCA blood flow velocity. We evaluated the relationship between clinical status, CO2 reactivity, pressure-autoregulation and other haemodynamic variables derived from Transcranial Doppler ultrasonography in patients with carotid artery disease. METHODS: 38 patients were investigated. Arterial pressure and blood flow velocity were monitored during CO2 reactivity tests. Arterial pressure-corrected and non-corrected indices of CO2 reactivity were calculated to compare an influence of rise in arterial pressure during the test. The pressure-autoregulation index was calculated as correlation coefficient between slow waves in blood flow velocity and arterial pressure. RESULTS: The increase in CO2 produced a consistent rise in arterial pressure and blood flow velocity and weakened the pressure autoregulation. The value of pressure-corrected CO2 reactivity was lower (p<0.0001) than the non-corrected one, indicating that the rise in arterial pressure during the test tends to over-estimate CO2 reactivity. The pressure-corrected reactivity was correlated with pressure autoregulation (r=-0.46; p<0.005). Both CO2 reactivity and pressure-autoregulation index correlated with a degree of carotid artery stenosis. Side-to-side difference of TCD pulsatility index demonstrated a close relationship with the asymmetry of stenosis (r=-0.61; p<0.0002) and symptoms (r=-0.49; p<0.003). CONCLUSIONS: When calculating CO2 reactivity in patients with carotid artery disease, changes in arterial pressure should be considered. Both CO2 reactivity and pressure-autoregulation describe the magnitude of haemodynamic deficit caused by stenosis, pulsatility index expresses the asymmetry of stenosis.

Aged↗
PubMed2003

Validation of a tonometric noninvasive arterial blood pressure monitor in the intensive care setting.

Intra-arterial measurement is considered the gold standard for continuous, beat-to-beat arterial blood pressure monitoring. However, arterial cannulation can be difficult and may cause complications such as thrombosis and ischaemia. Recently, a tonometric system, the Colin CBM-7000 has been developed for noninvasive beat-to-beat measurement of arterial blood pressure from the radial artery. We assessed the level of agreement between the CBM-7000 and invasive radial artery measurements in 15 patients on a neuro-intensive care unit. Agreement of systolic, diastolic and mean arterial pressure values was limited, with approximately 34% of mean arterial pressures differing by over 10 mmHg. In many cases, this was due to a downward drift of the noninvasive measurements over time. Furthermore, there was a tendency to underestimate low pressures and overestimate high pressures. In our opinion, the Colin CBM-7000 cannot be recommended for continuous blood pressure monitoring in the intensive care setting.

Adult↗
PubMed2003

Cerebrovascular pressure reactivity is related to global cerebral oxygen metabolism after head injury.

BACKGROUND: After head injury, impaired cerebrovascular autoregulation has been associated with abnormally high or low cerebral blood flow. The physiological relevance of cerebral blood flow levels is difficult to assess in these patients, whose cerebral metabolic rate for oxygen (CMRO(2)) is known to be abnormal. Investigation of these relations requires quantitative measures of cerebral blood flow and CMRO(2), to allow assessment of oxygen supply and demand relations. OBJECTIVES: To investigate the relation between dysautoregulation and global cerebral oxygen metabolism following head injury. METHODS: Using positron emission tomography, global cerebral blood flow, CMRO(2), and oxygen extraction fraction were determined in 22 patients who were investigated in 26 examinations on days 1 to 11 (mean (SD), 3.5 (2.3)) after head injury. Cerebrovascular pressure reactivity was assessed using a pressure reactivity index, calculated as the moving linear correlation coefficient between mean arterial blood pressure and intracranial pressure. Outcome was assessed six months after injury using the Glasgow outcome scale. RESULTS: Low CMRO(2) was associated with disturbed pressure reactivity (inverse function, R(2) = 0.21, p = 0.018) and there was a correlation between disturbed pressure reactivity and oxygen extraction fraction (quadratic function, R(2) = 0.55, p = 0.0001). There was no significant relation between pressure reactivity and cerebral blood flow. An unfavourable outcome was associated with disturbed pressure reactivity. There was no significant relation between outcome and CMRO(2) or oxygen extraction fraction. CONCLUSIONS: There is a close relation between dysautoregulation and abnormal cerebral metabolism but not blood flow. Further studies are needed to determine whether metabolic dysfunction is a result of or a cause of disturbed pressure reactivity, and to establish if there is a relation between cerebral oxygen metabolism and outcome.

Adolescent↗
PubMed2002

Multi-modal monitoring of acute brain injury.

OBJECTIVE: To review the scientific basis for and utility of the traditional cerebral monitors used currently in neurointensive care, together with research techniques that are soon likely to become used in managing severe head injury and subarachnoid haemorrhage. DESIGN AND CONTENT: Firstly, the pathophysiology of acute brain injury including cerebral haemodynamics, oxygen and metabolism and the role of secondary insults are discussed. Secondly, the importance of assessment of cerebrovascular autoregulation and reactivity is reviewed together with methods for its continuous non-invasive measurement using transcranial Doppler and intracranial pressure/arterial pressure recordings. Thirdly, the respective roles of jugular venous oxygen and brain tissue oxygen monitoring are analysed. Fourthly, the use of cerebral microdialysis is described, together with an overview of its utility. CONCLUSION: Cerebral multimodal monitoring can be helpful for the optimal management of acute brain injury and essential for future exploratory trials of neuroprotective drugs.

Acute Disease↗
PubMed2002

Communicating hydrocephalus: the biomechanics of progressive ventricular enlargement revisited.

BACKGROUND: This article investigates the physical mechanisms involved in the chronic ventricular enlargement that accompanies communicating hydrocephalus (CH)--including its normal and low-pressure forms. In particular, it proposes that this phenomenon can be explained by the combined effect of: (a) a reversal of interstitial fluid flow in the parenchyma, and (b) a reduction in the elastic modulus of the cerebral mantle. METHOD: To investigate this hypothesis, these changes have been incorporated into a finite element computer simulation of CH, in which brain tissue is idealized as a sponge-like material. The fluid pressure in the lateral ventricles and the subarachnoid space has been set to 10 mmHg, while the fluid pressure inside the parenchyma has been set to 7.5 mmHg. The elastic moduli of white and gray matter have been set to the reduced values of 1 and 5 kPa, respectively. FINDINGS: The simulation revealed a substantial ventricular distension (6.5 mm mean outward displacement), which was accompanied by the appearance of stress concentrations in the cerebral mantle. INTERPRETATION: These results support the notion that a relative reduction in intraparenchymal fluid pressure coupled with low tissue elasticity can produce both a significant ventricular enlargement and periventricular solid stress concentrations.

Biomechanical Phenomena↗
PubMed2002

Clinical significance of cerebral autoregulation.

OBJECTIVES: Disturbed cerebral autoregulation is believed to be associated with an unfavourable outcome following head injury. Previously, using ICP monitoring and transcranial Doppler ultrasonography, we investigated whether cerebral response to spontaneous variations in arterial pressure (ABP) or cerebral perfusion pressure (CPP) provide reliable information on cerebral autoregulatory reserve. In the present study we have correlated these methods with clinical findings. METHODS: 188 head injured sedated and ventilated patients were studied daily. Waveforms of intracranial pressure (ICP), arterial pressure and transcranial Doppler flow velocity (FV) were captured over a half to two hour periods. Time averaged mean flow velocity (FV) and CPP were resolved. The correlation coefficient indices between FV and CPP (Mx) and between ICP and ABP (PRx) were calculated over 3 minutes epochs, and averaged for each investigation. RESULTS: The relationship between indices of autoregulation and outcome (favourable-unfavourable) was significant and stronger than the association between admission GCS and outcome. With rigorously maintained CPP-oriented therapy relationship between CPP and outcome became non-significant. Mortality in patients with consistently disturbed autoregulation ranged 47%, while in patients with good autoregulation mortality was 11% (difference: p < 0.0001). CONCLUSIONS: Positive values of indices of autoregulation, expressing positive association between slow waves of CPP and blood flow velocity or ABP and ICP, indicate disturbed autoregulation. These indices correlate with unfavourable outcome following head injury and should be used to guide intensive therapy.

Blood Flow Velocity↗
PubMed2002

Asymmetry of cerebral autoregulation following head injury.

OBJECTIVES: To investigate asymmetry of cerebra autoregulation in head-injured patients with lateral brain contusions. METHODS: Sixty five patients were admitted to Addenbrooke's Hospital suffering from head injuries with mean Glasgow Coma Score 6 (range 3 to 10). The patients were paralyzed, sedated and ventilated to achieve mild hypocapnia. Intracranial pressure (ICP), arterial pressure (ABP) were monitored directly. The left and right Middle Cerebral Arteries were insonated daily and flow velocity (FV) was recorded. Correlation coefficients between slow waves in cerebral perfusion pressure (CPP) and FV were calculated for every 3 minute period. Positive value of Mx denotes a positive association between waves in FV and CPP, therefore deranged autoregulation. Zero or slightly negative value of Mx denotes a good autoregulatory capacity. In each patient all CT scans were reviewed to assess a dominant side of brain contusion and a level of brain compression. RESULTS: The side-to-side difference in FV, pulsatility indices or critical closing pressures, did not correlate with the side of contusion or midline shift. In contrary, the side-to-side difference in Mx indices were significantly (p < 0.05) worse at a side of contusion and at the side of brain expansion in patients presenting with a midline shift (p < 0.05). Of those patients who died in hospital, significantly more presented within meaningful (ABS(Mx) > 0.2) asymmetry in cerebral autoregulation (40% versus 12%; p < 0.05). CONCLUSIONS: Side-to-side difference in cerebral hemodynamic reserve of injured brain is a predictor of fatal outcome following head injury and correlates with the side of contusion or brain expansion.

Blood Flow Velocity↗
PubMed2002

Factors determining mean ICP in hydrocephalic patients with Hakim-programmable valve: implications of the parallel arrangement of the CSF outflow resistance and shunt.

OBJECTIVE: 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. METHOD: 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. RESULTS: 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. CONCLUSION: 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.

Cerebrospinal Fluid Shunts↗
PubMed2002

Shunt testing in-vivo: a method based on the data from the UK shunt evaluation laboratory.

OBJECTIVES: The objective of the UK Shunt Evaluation Laboratory was to perform an independent testing of hydrodynamic performance of hydrocephalus shunts and provide systematic reviewing for neurosurgeons and patients. METHODS: Valves were tested long-term in a computer-controlled rig to evaluate their pressure-flow performance both at baseline and under conditions mimicking phenomena, which may alter CSF drainage in vivo. The operating pressures (Poperating) and hydrodynamic resistances (R) of all types of valves, currently in use in the UK, have been evaluated (Codman: Hakim-Precision, Hakim-Programmable, Uni-Shunt, Accu-flo, Holter. Medtronic PS Medical: Delta, Flow Control, Lumbo-peritoneal. NMT: Orbis-Sigma, Omni-shunt, Hakim Valve. Heyer-Schulte: In-line, Pudenz-Flushing, LowProfile. Radionics ContourFlex. Sophy Programmable). 67 patients, who had improved in the past following shunting but had recent recurrence of their clinical symptoms, were admitted to undergo a computerized infusion test through the shunt pre-chamber or Ommaya reservoir implanted prior to shunting. The criterion used to detect shunt underdrainage was an increase in ICP during constant infusion above (Poperating) + R * Infusion rate + 5 mm Hg. The validity of this formula has been confirmed in a laboratory study. RESULTS: 35 patients met the criteria for shunt underdrainage while in 24 normal drainage was demonstrated. Mean ICP achieved during the test was 24 mm Hg in patients with underdrainage versus 14 mm Hg with normally functioning shunts (p < 0.01). Out of 35 patients 25 improved and 10 were seen again to have the test repeated. In 7 patients shunt was blocked again. Only 3 patients with primarily confirmed shunt underdrainage did not improve following revisions. In 8 patients overdrainage related to body posture was confirmed using tilt-test. CONCLUSIONS: Shunt testing in-vivo is easy, clinically useful and has good prediction power (90%).

Cerebrospinal Fluid↗
PubMed2002

Effects of variation in cerebral haemodynamics during aneurysm surgery on brain tissue oxygen and metabolism.

OBJECTIVES: This study explores the sensitivities of multiparameter tissue gas sensors and microdialysis to variations in blood pressure, CSF drainage and to well-defined periods of ischaemia accompanying aneurysm surgery, and their predictive value for infarction. METHODS: A Neurotrend sensor [brain tissue partial pressure of oxygen (PBO2), carbon dioxide (PBCO2), brain pH (pHB) and temperature] and microdialysis catheter were inserted into the appropriate vascular territory prior to craniotomy. RESULTS: Baseline data showed a clear correlation between PBO2 and mean arterial pressure (MAP) below a threshold of 80 mmHg. PBO2 improved with CSF drainage in 20 out of 28 (Wilcoxon: P < 0.05) cases where data was available. In 26 patients the effects of temporary vascular clipping (TC) (mean duration 16 minutes) were assessed. 2 patients subsequently declared infarction in the region of the probes. PBO2 fell from a mean 3.2 (95% CI 2.4-4.1) kPa to a minimum of 1.5 (95% CI 1.0-2.0) kPa in the non-infarct group. There was a lower baseline PBO2 (mean 0.8 kPa) in the patients who infarcted. PBCO2 mirrored PBO2 changes, whereas pHB did not change significantly in either group. Microdialysis changes associated with decreased PBO2 included a delayed increase in lactate, a raised lactate/pyruvate ratio and more rarely an increased glutamate. These changes were seen in 11 patients but were not predictive of infarction. CONCLUSION: Hypotension during aneurysm surgery is associated with a low PBO2. Multiparameter sensors can be sensitive to acute ischaemia. Microdialysis shows potential in the detection of metabolic changes during tissue hypoxia.

Adult↗
PubMed2002

Laboratory testing of hydrocephalus shunts -- conclusion of the U.K. Shunt evaluation programme.

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.

Cerebrospinal Fluid Pressure↗
PubMed2002

A laboratory model of testing shunt performance after implantation.

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.

Cerebrospinal Fluid Pressure↗
PubMed2002

Should we measure cerebral blood flow in head-injured patients?

Inadequate cerebral blood flow (CBF) after head injury is an important cause of secondary ischaemic damage. Rapid identification of episodes of hypo- or hyperperfusion would allow timely intervention and would possibly improve outcome. Despite a large number of methods to estimate CBF, this concept is only marginally implemented in clinical practice. The methods to detect such episodes are limited for technical reasons, but also because the thresholds of ischaemia and hyperaemia are variable after head injury. Furthermore, we are not always able to manipulate CBF in a controlled manner. Accordingly, it is not surprising that attempts to compare a CBF-targeted strategy with another management option have failed to demonstrate a clear benefit. Methods need to be developed that allow either identification of thresholds for critically low or high CBF in individual patients, allow monitoring oxygen extraction fraction, representing circulatory reserve, or alternatively provide a measure of the volume of ischaemic or hyperaemic brain.

Brain↗
PubMed2002

Continuous monitoring of cerebrovascular autoregulation: a validation study.

BACKGROUND: Continuous monitoring of dynamic cerebral autoregulation, using a moving correlation index of cerebral perfusion pressure and mean middle cerebral artery flow velocity, may be useful in patients with severe traumatic brain injury to guide treatment, and has been shown to be of prognostic value. OBJECTIVE: To compare an index of dynamic cerebral autoregulation (Mx) with an index of static cerebral autoregulation (sRoR). METHODS: Mx was validated in a prospective comparative study against sRoR, using 83 testing sessions in 17 patients with traumatic brain injury. sRoR and Mx were calculated simultaneously during pharmacologically induced blood pressure variations. RESULTS: Mx was significantly correlated with sRoR (R = -0.78, p < 0.05). Nine patients were found to have failure of cerebral autoregulation, with an sRoR value < 50%. If an Mx value of 0.3 was used as the cut off point for failure of cerebral autoregulation, this index had 100% sensitivity and 90% specificity for demonstrating failure of autoregulation compared with the sRoR. An increase in cerebral blood flow velocity correlated significantly with Mx (R = 0.73, p < 0.05) but not with cerebral perfusion pressure (R = 0.41). CONCLUSIONS: Dynamic and static cerebral autoregulation are significantly correlated in traumatic brain injury. Cerebral autoregulation can be monitored continuously, graded, and reliably assessed using a moving correlation analysis of cerebral perfusion pressure and cerebral blood flow velocity (Mx). The Mx index can be used to monitor cerebral blood flow regulation. It is useful in traumatic brain injury because it does not require any external stimulus.

Adult↗
PubMed2001

Bifrontal decompressive craniectomy in the management of posttraumatic intracranial hypertension.

Bifrontal decompressive craniectomy has been used on an ad hoc basis for the treatment of post-traumatic intracranial hypertension for more than thirty years. In this observational study we report the clinical outcome and physiological effects of the procedure in a series of 26 patients with refractory intracranial hypertension treated on a protocol driven basis. Bifrontal decompressive craniectomy was associated with significant reductions in mean ICP from 37.5 to 18.1 mmHg (p = 0.003). In addition, craniectomy reduced the amplitude of ICP waves (p < 0.02) and increased compensatory reserve (p < 0.05). A favourable outcome was achieved in 69% of patients; 8% were severely disabled and 23% died. We conclude that this study provides pathophysiological evidence that bifrontal decompressive craniectomy significantly reduces posttraumatic intracranial hypertension and improves pressure dynamics. Our results support the continued use of bifrontal decompressive craniectomy in selected patients after head injury.

Adolescent↗