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M Czosnyka

Publications and source records attributed to M Czosnyka.

At least 91 records · Page 5Linked to original sources

Magnetic resonance imaging compatibility testing of intracranial pressure probes. Technical note.

There is increasing recognition that magnetic resonance (MR) imaging and spectroscopy may provide important information in the assessment of patients with acute brain injury. However, optimum care of the acutely head injured patient requires monitoring of intracranial pressure (ICP). Although many monitoring modalities have been integrated into commercially available MR-compatible systems, there have been no reports of commonly used intraparenchymal ICP sensors in an MR environment. The authors describe the use of an ICP micromanometer probe in an MR environment, with a fiberoptic connection that interfaces the probe with a commercially available MR-compatible monitoring system. Phantom studies were performed to demonstrate the safety and compatibility of the modified MR system at 0.5 tesla. The safety of the device was assessed in relation to its interaction with the static, gradient, and radiofrequency fields used in MR imaging. The MR compatibility was documented by demonstrating that its performance was unaffected by the operation of imaging sequences and by showing that there was no degradation of the diagnostic quality of imaging data obtained during ICP monitoring.

Equipment Design↗

A method for a simulation of continuous intracranial pressure curves.

The study introduces a method to simulate continuously an intracranial pressure (ICP) wave form. In a system analysis approach the intracranial compartment was viewed as a black box with arterial blood pressure (ABP) as an input signal and ICP as an output. A weight function was used to transform the ABP curve into the ICP curve. The output ICP waveform was generated using a weight function derived from the transcranial Doppler blood flow velocity (FV) and ABP curves. In order to establish the relationship between TCD characteristics and weight functions simultaneous recordings of FV, ABP, and ICP curves of a defined group of patients were used. A linear function between the TCD characteristics and the weight functions was obtained by calculating a series of multiple regression analyses. Given examples demonstrate the procedure's capabilities in predicting the mean ICP, the pulse and respiratory waveform modulations, and the trends of ICP changes.

Computer Simulation↗

Continuous monitoring of cerebrovascular pressure-reactivity in head injury.

OBJECTIVE: Cerebrovascular vasomotor reactivity reflects changes in smooth muscle tone in the arterial wall in response to changes in transmural pressure or concentration of carbon dioxide in blood. We have investigated whether slow waves in ABP and ICP may be used to derive an index which reflects reactivity of vessels to changes in arterial blood pressure. METHODS: A method for the continuous monitoring of the association between slow spontaneous waves in ICP and AP has been adopted in a group of 98 head injured patients. ABP, ICP and transcranial Doppler blood flow velocity (FV) in the middle cerebral artery was recorded daily (20 to 120 minutes time periods). A Pressure-Reactivity Index (PRx) was calculated as a moving correlation coefficient between 40 consecutive samples of values for ICP and ABP averaged over 5 seconds. A moving correlation coefficient between spontaneous fluctuations of mean FV and CPP (Mx), which was previously reported to describe cerebral blood flow autoregulation, was also calculated. In an additional 25 patients, PRx was calculated and recorded continuously along with mean ICP, ABP and parameters describing ICP waveform. RESULTS: A positive PRx correlated with high ICP (r = 0.366; p < 0.001), low admission GCS (r = 0.29; p < 0.01), and poor outcome at 6 months after injury (r = 0.48; p < 0.00001). During the first two days following injury, PRx was positive (p < 0.05) in patients with unfavourable outcome. The correlation between PRx and Mx (r = 0.63) was highly significant (p < 0.000001). Continuous recordings demonstrated that PRx was able to indicate individual thresholds of vascular reactivity for CPP, ICP, and ventilation parameters. CONCLUSION: Computer analysis of slow waves in ABP and ICP is able to provide a continuous index of cerebrovascular reactivity to changes in arterial pressure, which is of prognostic significance.

Adolescent↗

Increase in transcranial Doppler pulsatility index does not indicate the lower limit of cerebral autoregulation.

INTRODUCTION: Transcranial Doppler pulsatility index was reported clinically to increase when cerebral perfusion pressure decreased, hypothetically marking the lower limit of cerebral autoregulation. We sought to investigate the relationship between pulsatility index, cerenbrovascular resistance, and cerebral perfusion pressure in various states of autoregulation in an animal model of moderate intracranial hypertension. METHOD: Eight New-Zealand White Rabbits were studied with basilar artery blood flow velocity (ultrasound Doppler) and cortical blood flow (laser Doppler) monitored continuously during subarachnoid saline infusion to increase intracranial pressure (< 55 mm Hg). Four animals demonstrated a stable cortical blood flow, and four demonstrated decreasing blood flow when cerebral perfusion pressure decreased. RESULTS: Pulsatility index showed the same pattern of increase when cerebral perfusion pressure decreased, independent on whether cortical blood flow was stable or falling. The percentage rate of increase in the pulsatility index was not different in autoregulating and non autoregulating animals. The rate of decrease in cerebrovascular resistance was significantly lower (p < 0.05) in non-autoregulating than in autoregulating animals. CONCLUSION: The increase in transcranial Doppler pulsatility index when cerebral perfusion pressure falls cannot be interpreted as a phenomenon able to mark the lower limit of cerebral autoregulation.

Animals↗

Assessment of cerebrovascular reactivity in patients with carotid artery disease using near-infrared spectroscopy.

The aim of this study was to assess Near-infrared spectroscopy (NIRS) as a tool for testing CO2 reactivity in patients with carotid occlusive disease. One hundred sixty patients were examined (age range 44 to 85 years). Monitored parameters included transcranial Doppler flow velocity (FV), changes in concentration of oxy-(HbO2) and deoxy (Hb) haemoglobin, cutaneous Laser Doppler blood flow (LDF), endtidal CO2, ABP, and SaO2. Hypercapnia was induced using a 5% CO2 air mixture for inhalation. To estimate the skin flow contribution to NIRS during reactivity testing, the superficial temporal artery was compressed, and the NIRS changes in response to the fall in LDF recorded. FV and HbO2 derived reactivity values were related to the severity of the stenosis (p = 0.0001 and 0.021 respectively). The correlation between the two modalities was significant (r = 0.47, p < 0.000001). The average estimated skin contribution to NIRS changes was 16.5%. Reproducibility of HbO2-reactivity was similar but worse than FV reactivity (19.1% and 13.8% variation respectively). The clinical correlations improved when our method of correction for skin influence was used. NIRS shows potential as an alternative technique for testing CO2 reactivity in patients with carotid disease provided the conditions are carefully controlled and the contribution from extracranial tissue is taken into account.

Adult↗

Indices for decreased cerebral blood flow control--a modelling study.

Time-dependent interactions between pressure, flow and volume of cerebral blood and cerebrospinal fluid were mathematically modelled. The model was designed to simulate blood inflow and storage, arteriolar and capillary blood circulation controlled by cerebral autoregulation, venous blood outflow and storage modulated by intracranial pressure, and cerebrospinal fluid production, storage and reabsorption. The software implementation of the model was used to calculate the response to a gradual decrease in cerebral perfusion pressure corresponding to either systemic hypotension or intracranial hypertension. We computed flow pulsatility index (PI) and short range correlation coefficients between systolic, diastolic and mean flow velocity (FVs,d,m) and mean cerebral perfusion pressure (CPP). In simulation, the changes in cerebral flow produced by intracranial hypertension and systemic hypotension were practically indistinguishable. The relationship between PI and CPP was reciprocal, independent of the state of autoregulation. The short range running correlation coefficients between FVs, FVm and CPP indicated both combined safe CPP range and preserved autoregulation, promising a clear clinical detection of "non-worsening" blood supply conditions. A similar procedure was applied to selected clinical data to illustrate the theoretical considerations.

Adolescent↗

The relationship of vasogenic waves to ICP and cerebral perfusion pressure in head injured patients.

Slow vasogenic waves are characterised by sudden rises and falls in both the mean ICP and its cardiac pulsatile amplitude for periods of up to an hour. On reviewing the on-line computer records of a series of 200 consecutive head injured patients, some 650 waves with increases in mean ICP of at least 15 mm Hg were recognized. The mean ICP, pulsatile amplitude, perfusion pressure, arterial pressure and pulse rates which had been generated every minute were reviewed in each of a 100 randomly selected waves in the hopes of allocating them into defined groups according to precipitating factors. We had expected to find that the majority of waves were precipitated by a preceding fall in cerebral perfusion pressure as a result of a transient arterial hypotension. Only in 19 of the 100 waves did this sequence become apparent and in the remainder, no recognizable precipitating factors were found. In 21 of the records, there was a fall in ICP of at least 5 mm Hg before the onset of the pressure wave.

Blood Pressure↗

Hydrodynamic properties of hydrocephalus shunts.

Hydrodynamic properties of hydrocephalus shunts are not always properly characterized by the manufacturer. Therefore, the choice of the shunt should be made, by matching performance of the shunt to the disturbed profile of CSF circulation of a given patient. The aim of the present shunt evaluation study is to evaluates all types of shunts presently in use in the U.K. and make this information available to neurosurgeons. Ten most common models of valves have been tested to date: Medtronik PS Medical: Delta Valve, Flow Control Valves and Lumbo-Peritoneal Shunt, Heyer-Schulte: In-line, Low Profile and Pudenz Flushing Valve, Codman: Medos-Programmable, Hakim-Precision, Sophy Programmable Valve, Cordis Orbis-Sigma. Our results show the majority of valves have low hydrodynamic resistance (exception: PS Lumboperitoneal, Orbis-Sigma), which increase by 100-200% after connection of a long distal catheter. A few shunts with siphon-preventing mechanism (Delta, Hayer-Schulte Low Profile, Pudenz-Flushing) offer reasonable resistance to negative outlet pressures, however, these valves may be blocked by raised subcutaneous pressure. All programmable valves are susceptible to siphoning. Programmed settings may be changed by external magnetic field.

Cerebrospinal Fluid Pressure↗

Resolving extra- and intracranial signal changes during adult near infrared spectroscopy.

Extracranial tissues have a significant effect on cerebral near infrared spectroscopy (NIRS) measurements in adults. Carotid surgery provides the opportunity to determine the relative contributions from the intra- and extracranial vascular territories. To assist, a specifically gated Laser Doppler flowmetry probe can be inserted between the NIRS optodes to co-monitor cutaneous blood flow associated with external carotid artery (ECA) clamping, whilst transcranial Doppler can be employed to monitor relative changes in the intracranial blood flow seen during internal carotid artery (ICA) clamping. Established criteria for severe cerebral ischemia (SCI) following carotid cross clamping was applied to 703 consecutive patients undergoing carotid surgery for high grade stenosis. Ipsilateral frontal NIRS recorded the difference (Total-deltaHbdiff) in concentrations of oxy- and deoxy-hemoglobin. Interrupted time series analysis following clamping of the ECA and ICA allowed the different vascular components of Total-deltaHbdiff (ECA-deltaHbdiff and ICA-deltaHbdiff) to be identified. Data from 76 patients was suitable. Sixteen (21%) patients fulfilled the criteria for SCI. Patients who demonstrated an ICA-deltaHbdiff of > 6.8 micromol l(-1) all showed SCI. No patient with an ICA-deltaHbdiff < 5.0 micromol l(-1) showed SCI. Thus an ICA-deltaHbdiff threshold of 6.8 micromol l(-1) provided a 100% specificity for SCI, whereas an ICA-deltaHbdiff < 5.0 micromol l(-1) was 100% sensitive for excluding SCI. When Total-deltaHbdiff was used without removing the ECA component, thresholds for SCI could not be resolved. NIRS can provide quantified thresholds for severe ischemia in the adult brain provided the extracranial component is removed.

Aged↗

Posture-related overdrainage: comparison of the performance of 10 hydrocephalus shunts in vitro.

OBJECTIVE: Approximately 10 to 30% of shunt revisions may be attributed to posture-related overdrainage. The susceptibility of various hydrocephalus shunts to overdrainage of cerebrospinal fluid requires independent laboratory evaluation. METHODS: Shunts were tested in vitro by using precise computer-controlled equipment that was able to evaluate pressure-flow performance curves under various conditions. Hydrodynamic resistance and opening, closing, and operational pressures were evaluated for at least 28 days with normal (atmospheric) and decreased (-23 mm Hg, based on the International Standard Organization/Draft International Standard 7197 standard, which simulates conditions in upright body positions) outlet pressures. RESULTS: Ten different models of valves have been tested to date (Medtronic PS Medical Delta valve, flow-control valve, and lumboperitoneal shunt, Heyer-Schulte in-line, low-profile, and Pudenz flushing valves, Codman-Medos programmable and nonprogrammable valves, Sophy programmable valve, and Cordis Orbis-Sigma valve). The majority of these valves produced significantly negative (less than -10 mm Hg) average intracranial pressures in vertical body positions. In conjunction with nonphysiologically low hydrodynamic resistance (with the exception of the Orbis-Sigma valve, Medtronic PS Medical lumboperitoneal shunt, and Heyer-Schulte in-line valve), this may result in overdrainage related to body posture. The clinically reported rate of complications related to overdrainage is probably reduced by the long distal catheter, which increases the resistance of these valves by 100 to 200%. A few shunts (the Delta valve, low-profile valve, and Pudenz flushing valve with anti-siphon devices) offer reasonable resistance to negative outlet pressure, preventing complications related to overdrainage, but all valves with siphon-preventing devices may be blocked by increased subcutaneous pressure. CONCLUSION: Shunts without mechanisms preventing very low intracranial pressure in vertical body positions should be identified and avoided for patients likely to develop complications related to cerebrospinal fluid overdrainage.

Cerebrospinal Fluid Shunts↗

Jugular venous and arterial concentrations of serum S-100B protein in patients with severe head injury: a pilot study.

The objective of this study was to analyse the temporal course of the jugular venous-arterial gradient of S-100B protein after severe head injury and the correlation between the absolute concentrations of serum S-100B protein and outcome, CT findings, and clinical variables. Fifteen patients were included in this pilot study. All patients were treated according to a standard therapy protocol targeted to maintain cerebral perfusion pressure. The serum concentration of S-100 protein was measured daily for five consecutive days after injury by a monoclonal two site immunoluminometric assay. Nine patients showed favourable and six unfavourable outcome after 6 months with a mortality rate of 33% (five patients). The mean gradient between jugular venous and arterial blood was 8.2% (p<0.05). Patients showing an unfavourable outcome had significantly higher jugular venous or arterial S-100 values compared with those with a favourable outcome (jugular venous S-100B 2.78 microg/l v 1.22 microg/l, p<0.05; arterial S-100B 2.48 microg/l v 1.19 microg/l, p<0.05). All patients with an initial or secondary increase in S-100B value of >2 microg/l were found to have an unfavourable outcome. S-100B was found to be an independent predictor of outcome after severe head injury. The persisting increase of S-100B for three to five days even in patients with favourable outcome and no signs of secondary insults might reflect continuing damage to the blood-brain barrier or ongoing glial cell death.

Adolescent↗

Cerebral perfusion pressure in head-injured patients: a noninvasive assessment using transcranial Doppler ultrasonography.

OBJECT: The authors studied the reliability of a new method for noninvasive assessment of cerebral perfusion pressure (CPP) in head-injured patients in which mean arterial blood pressure (ABP) and transcranial Doppler middle cerebral artery mean and diastolic flow velocities are measured. METHODS: Cerebral perfusion pressure was estimated (eCPP) over periods of continuous monitoring (20 minutes-2 hours, 421 daily examinations) in 96 head-injured patients (Glasgow Coma Scale score < 13) who were admitted to the intensive care unit. All patients were sedated, paralyzed, and ventilated. The eCPP and the measured CPP (ABP minus intracranial pressure, measured using an intraparenchymal microsensor) were compared. The correlation between eCPP and measured CPP was r=0.73; p < 10(-6). In 71% of the examinations, the estimation error was less than 10 mm Hg and in 84% of the examinations, the error was less than 15 mm Hg. The method had a high positive predictive power (94%) for detecting low CPP (< 60 mm Hg). The eCPP also accurately reflected changes in measured CPP over time (r > 0.8; p < 0.001) in situations such as plateau and B waves of intracranial pressure, arterial hypotension, and refractory intracranial hypertension. A good correlation was found between the average measured CPP and eCPP when day-by-day variability was assessed in a group of 41 patients (r=0.71). CONCLUSIONS: Noninvasive estimation of CPP by using transcranial Doppler ultrasonography may be of value in situations in which monitoring relative changes in CPP is required without invasive measurement of intracranial pressure.

Adolescent↗

Defining thresholds for critical ischemia by using near-infrared spectroscopy in the adult brain.

OBJECT: Signal changes in adult extracranial tissues may have a profound effect on cerebral near-infrared spectroscopy (NIRS) measurements. During carotid surgery NIRS signals provide the opportunity to determine the relative contributions from the intra- and extracranial vascular territories, allowing for a more accurate quantification. In this study the authors applied multimodal monitoring methods to patients undergoing carotid endarterectomy and explored the hypothesis that NIRS can define thresholds for cerebral ischemia, provided extracranial NIRS signal changes are identified and removed. Relative criteria for intraoperative severe cerebral ischemia (SCI) were applied to 103 patients undergoing carotid endarterectomy. METHODS: One hundred three patients underwent carotid endarterectomy. An intraoperative fall in transcranial Doppler-detected middle cerebral artery flow velocity (%deltaFV) of greater than 60% accompanied by a sustained fall in cortical electrical activity were adopted as criteria for SCI. Ipsilateral frontal NIRS recorded the total difference in concentrations of oxyhemoglobin and deoxyhemoglobin (Total deltaHb(diff)). Interrupted time series analysis following clamping of the external carotid artery (ECA) and the internal carotid artery (ICA) allowed the different vascular components of Total deltaHb(diff) (ECA deltaHb(diff) and ICA deltaHb(diff)) to be identified. Data obtained in 76 patients were deemed suitable. A good correlation between %deltaFV and ICA deltaHb(diff) (r = 0.73, p < 0.0001) was evident. Sixteen patients (21%) fulfilled the criteria for SCI. All patients who demonstrated an ICA deltaHb(diff) of greater than 6.8 micromol/L showed SCI, and in two patients within this group nondisabling watershed infarction developed, as seen on postoperative computerized tomography scans. No patient with an ICA deltaHb(diff) less than 5 micromol/L exhibited SCI or suffered a stroke. Within the resolution of the criteria used an ICA deltaHb(diff) threshold of 6.8 micromol/L provided 100% specificity for SCI, whereas an ICA deltaHb(diff) less than 5 micromol/L was 100% sensitive for excluding SCI. When Total deltaHb(diff) was used without removing the ECA component, no thresholds for SCI were apparent. CONCLUSIONS: Carotid endarterectomy provides a stable environment for exploring NIRS-quantified thresholds for SCI in the adult head.

Adult↗

Changes in transcranial Doppler flow velocity waveform following inhibition of nitric oxide synthesis. Experimental study in anaesthetised rabbits.

BACKGROUND: Analysis of the transcranial Doppler blood flow velocity (FV) waveform is used clinically to detect changes in cerebral haemodynamic profile. Such changes may be initiated both by alterations in microvascular resistance and in the tone of the cerebral arteries. METHODS: The role of endothelial mechanisms was investigated using inhibition of NO synthesis by systemic administration of NG-nitro-L-arginine methyl ester (L-NAME, 6 mg/kg) followed by simultaneous monitoring of both basilar artery FV and cerebrocortical microcirculation (laser Doppler flowmetry, LDF) in anaesthetised, ventilated rabbits over 60 minutes. RESULTS: Arterial blood pressure (AP) increased significantly (p < 0.01) above baseline level in the second minute following L-NAME and remained elevated until the end of experiment. Time average mean and systolic FV decreased immediately following L-NAME injection, with the statistically significant (p < 0.01) decrease from the third minute. Diastolic FV did not show such radical changes. LDF exhibited a slow decrease with time becoming significantly lower than baseline (p < 0.01) at 50 min. CONCLUSION: A gradual decrease in cortical microcirculation preceded by a rapid reaction recorded in the TCD waveform implies that an increase in the tone of the great cerebral arteries is the predominant phenomenon seen during the acute phase of NO synthase inhibition.

Animals↗

A computing system for the clinical and experimental investigation of cerebrovascular reactivity.

We present a computing system for the recording and on-line analysis of analogue signals derived from bedside cerebrovascular monitors in different pathophysiological conditions. These include arterial blood pressure and oxygen saturation, end-tidal carbon dioxide concentration, cerebral blood flow velocities using transcranial Doppler ultrasonography, and concentration changes in cerebral oxy- and deoxyhaemoglobin from near infrared spectroscopy. Configuration and analysis adopts arithmetic expressions of different signal processing functions, various statistical properties for each signal, frequency spectrum analysis using fast Fourier transformation, and correlation/cross-correlation. The software offers off-line analysis of non-invasive tests of cerebrovascular reactivity. Several examples of clinical assessment of cerebrovascular reactivity are presented, including cerebral haemodynamic stress tests which employ carbon dioxide, acetazolamide, the breath holding test, leg cuff inflation and deflation, and transient carotid artery compression. Application within the experimental setting with induced haemorrhagic hypotension can also be used.

Cardiovascular Diseases↗

Non-invasive measurement of cerebral blood volume in volunteers.

Invasive techniques are used for conventional measurements of cerebral blood volume and there is a need for methods which are more readily applicable clinically. We studied 13 healthy volunteers using near infrared spectroscopy and transcranial Doppler sonography. Middle cerebral artery flow velocity (vmca) and changes in cerebral oxygenated haemoglobin (HbO2), deoxygenated Hb (Hb), HbO2 - Hb (Hbdiff) [corrected] and HbO2 + Hb (total haemoglobin; Hbt) were measured at baseline and during graded reduction in arterial oxygen saturation (Spo2) to 85% at hypo-, normo- and hypercapnia. Cerebral blood volume (CBV) values, calculated from regression lines of Hbdiff/SpO2 and HbO2/SpO2 were 5.38 and 4.03 ml 100 g-1 for the two methods, respectively. CBV varied directly with FE'CO2, with mean CBV reactivities of 1.25 and 1.06 ml 100 g-1 kPa-1, respectively. Changes in Hbt were not systematically related to changes in FE'CO2. An increase in vmca and reciprocal decrease in estimated cerebrovascular resistance were observed when oxygen saturation decreased to less than 90-93%. These results suggest that cerebral haemodynamics in individual subjects may be monitored non-invasively providing the methodology is modified to account for hypoxic vasodilatation.

Adult↗

Thresholds for hypoxic cerebral vasodilation in volunteers.

UNLABELLED: The effects of hypoxemia on the cerebral vasculature have been described in animal models, but data from human studies are limited and have often relied on invasive methodology. The ability to detect a threshold for hypoxic vasodilatation in humans may be clinically useful, particularly in patients with impaired intracranial compliance. Because physiology may differ among subjects, it would be advantageous to measure such thresholds using noninvasive bedside techniques that could be readily applied to individual patients. We have attempted to identify thresholds of hypoxic vasodilatation in volunteers using noninvasive methods of measurement. Thirteen healthy volunteers were studied using transcranial Doppler sonography. Time-averaged middle cerebral artery maximal flow velocity (MCA FVx), mean arterial blood pressure, peripheral oxygen saturation (Spo2), and partial pressure of endtidal CO2 were measured at baseline and during graded reduction in arterial Spo2 to 85%, at normocapnia. Flow velocity and estimated cerebrovascular resistance (CVRe) were indexed and plotted against Spo2. There was no significant change in mean arterial pressure during desaturation to 85%, although the mean heart rate increased from 65 to 82 bpm. An increase in MCA FVx and reciprocal decrease in CVRe were observed when Spo2 decreased to below 90%. These results suggest that hypoxemic cerebral vasodilatation may be measured noninvasively and that in normal human volunteers, the threshold is at an Spo2 of 90%, which is greater than that previously reported. IMPLICATIONS: The ability to detect the point at which cerebral blood vessels dilate using noninvasive techniques is clinically advantageous. We have attempted to do this using transcranial Doppler sonography in volunteers whose inspired oxygen concentrations were gradually decreased. Thresholds of cerebral vasodilatation were found to be higher than those previously reported. These thresholds are important with regard to adequate perfusion in various pathologic states.

Adult↗