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Biomedical subjects

M Czosnyka

Publications and source records attributed to M Czosnyka.

At least 109 records · Page 6Linked to original sources
PubMed1997

Continuous assessment of the cerebral vasomotor 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 the concentration of carbon dioxide in blood. We investigated whether slow waves in arterial blood pressure (ABP) and intracranial pressure (ICP) may be used to derive an index that reflects the reactivity of vessels to changes in ABP. METHODS: A method for the continuous monitoring of the association between slow spontaneous waves in ICP and arterial pressure was adopted in a group of 82 patients with head injuries. ABP, ICP, and transcranial doppler blood flow velocity in the middle cerebral artery was recorded daily (20- to 120-min 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 for a period of 5 seconds. A moving correlation coefficient (Mean Index) between spontaneous fluctuations of mean flow velocity and cerebral perfusion pressure, which was previously reported to describe cerebral blood flow autoregulation, was also calculated. RESULTS: A positive PRx correlated with high ICP (r = 0.366; P < 0.001), low admission Glasgow Coma Scale score (r = 0.29; P < 0.01), and poor outcome at 6 months after injury (r = 0.48; P < 0.00001). During the first 2 days after injury, PRx was positive (P < 0.05), although only in patients with unfavorable outcomes. The correlation between PRx and Mean index (r = 0.63) was highly significant (P < 0.000001). 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↗
PubMed1997

Hydrodynamic properties of hydrocephalus shunts: United Kingdom Shunt Evaluation Laboratory.

BACKGROUND: Although about 80% of properly diagnosed patients with hydrocephalus improve after implantation of any model of shunt, the remaining 20% may develop further complications because of inadequate shunt performance. Therefore, hydrocephalus shunts require careful independent laboratory evaluation. METHOD: Computer supported shunt testing, based on the new International Standard Organisation directives, characterises various aspects of pressure-flow performance of shunts such as variability with time, susceptibility to reflux, siphoning, temperature related behaviour, external pressure, the influence of a strong magnetic field (for example, MRI), presence of pulsation in differential pressure, particles in drained fluid, etc. RESULTS: Seven different models of valves, representing most common constructions, have been tested so far. Most contemporary valves have a hydrodynamic resistance which is too low. 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%. Most shunts are very sensitive to the presence of air bubbles and small particles in drained fluid. Few shunt models offer reasonable resistance to negative outlet pressure, preventing complications related to overdrainage. Valves with an antisiphon device may be blocked by raised subcutaneous pressure. All programmable valves are susceptible to overdrainage in an upright position. CONCLUSION: The behaviour of a valve during such testing is of immediate relevance to the surgeon and may not be adequately described in the manufacturer's product information.

Cerebrospinal Fluid Shunts↗
PubMed1997

Contribution of mathematical modelling to the interpretation of bedside tests of cerebrovascular autoregulation.

OBJECTIVES: Cerebral haemodynamic responses to short and longlasting episodes of decreased cerebral perfusion pressure contain information about the state of autoregulation of cerebral blood flow. Mathematical simulation may help to elucidate which of the indices, that can be derived using transcranial Doppler ultrasonography and trends of intracranial pressure and blood pressure, are useful in clinical tests of autoregulatory reserve. METHODS: Time dependent interactions between pressure, flow, and volume of cerebral blood and CSF were modelled using a set of non-linear differential equations. The model simulates changes in arterial blood inflow and storage, arteriolar and capillary blood flow controlled by cerebral autoregulation, venous blood storage and venous outflow modulated by changes in ICP, and CSF storage and reabsorption. The model was used to simulate patterns of blood flow during either short or longlasting decreases in cerebral perfusion pressure. These simulations can be considered as clinically equivalent to a short compression of the common carotid artery, systemic hypotension, and intracranial hypertension. Simulations were performed in autoregulating and non-autoregulating systems and compared with recordings obtained in patients. RESULTS: After brief compression of the common carotid artery, a subsequent transient hyperaemia can be interpreted as evidence of intact autoregulation. During longlasting sustained hypoperfusion, a gradual increase in the systolic value of the blood flow velocity waveform along with a decrease in the diastolic value is specific for an autoregulating cerebrovascular system. CONCLUSION: Modelling studies help to interpret both clinical and experimental cerebral haemodynamic phenomena and their dependence on the state of autoregulation.

Blood Flow Velocity↗
PubMed1997

Laboratory testing of the Spiegelberg brain pressure monitor: a technical report.

OBJECTIVES: The Spiegelberg brain pressure monitor is a low cost intracranial pressure monitoring system that has been used clinically for some time, mainly in Germany. To provide a rigorous bench comparison of the Spiegelberg monitor with the Camino pressure monitor an evaluation programme has been carried out in the UK Shunt Evaluation Laboratory. DESIGN: Drift over 72 hours and with temperature, a frequency response, and the accuracy of measurement of both static and pulsatile pressures have been tested simultanously in Camino and Spiegelberg transducers using a computerised rig. RESULTS: Long term zero drift was less than 0.7 mm Hg in both transducers. The Spiegelberg monitor showed no temperature drift whereas the Camino monitor had a drift of around 0.3 mm Hg/degrees C. The Spiegelberg monitor underread mean pressures <40 mm Hg by <1 mm Hg, but the error increased to 4.7 mm Hg at 100 mm Hg. The frequency bandwidth of the Spiegelberg monitor was 4 Hz at a low pressure. Underreading of the amplitude increased with the mean pressure, with a delay of about 0.1 s in the detection of the peaks of pulse waveform. CONCLUSION: The Spiegelberg transducer had excellent accuracy for static intracranial pressure measurement, but complex waveform analysis may be biased by its limited dynamic response.

Clinical Laboratory Techniques↗
PubMed1997

Clinical evaluation of near-infrared spectroscopy for testing cerebrovascular reactivity in patients with carotid artery disease.

BACKGROUND AND PURPOSE: Near-infrared spectroscopy (NIRS) derives information about the concentrations of oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) from measurements of light attenuation caused by these chromosphores. The aim of this study was to assess NIRS as a tool for testing CO2 reactivity in patients with carotid artery disease. METHODS: One hundred patients with symptomatic carotid occlusive disease were examined (age range, 44 to 83 years). The severity of stenosis ranged from 30% to 100% (median, 80%) on the ipsilateral side and 0% to 100% (median, 30%) on the contralateral side. Monitored parameters included transcranial Doppler flow velocity, changes in concentration of HbO2 and Hb, cutaneous laser-Doppler blood flow, endtidal CO2, arterial blood pressure, and arterial oxygen saturation. Hypercapnia was induced with the use of a 5% CO2/air mixture for inhalation. To estimate the contribution of skin flow to NIRS during reactivity testing, the superficial temporal artery was compressed, and the NIRS changes in response to the fall in laser-Doppler blood flow were recorded. Finally, reproducibility of reactivity testing was assessed in 10 patients who were subjected to repeated examinations over 3 days. RESULTS: Flow velocity- and HbO2-derived reactivity values were related to the severity of the stenosis (P = .0001 and P = .017, respectively). The correlation between the two reactivity modalities was significant (r = .49, P < .000001). The median estimated contribution of skin flow to NIRS changes was 15.8%. Another variable affecting HbO2 signal changes during the CO2 challenge was arterial blood pressure (P = .025). Reproducibility of HbO2 reactivity was similar to flow velocity reactivity (14.3% and 18.6% variation, respectively). CONCLUSIONS: NIRS shows potential as an alternative technique for testing CO2 reactivity in patients with carotid disease provided that conditions are carefully controlled. Marked changes in arterial blood pressure may render the NIRS reactivity indices unreliable, and the contribution from extracranial tissue must be taken into account when significant.

Adult↗
PubMed1997

Evaluation of the transient hyperemic response test in head-injured patients.

The transient hyperemic response test has been shown to provide an index of cerebral autoregulation in healthy individuals and in patients who have suffered a subarachnoid hemorrhage. In this study, the test was applied to patients who had received a severe head injury, and the value of the test was assessed by comparing its result with the individual's clinical condition (Glasgow Coma Scale [GCS] score), cerebral perfusion pressure (CPP), transcranial Doppler wave form-derived index for cerebral autoregulation (relationship between the CPP and the middle cerebral artery flow velocity), and outcome (Glasgow Outcome Scale [GOS] score). Forty-seven patients, aged 16 to 63 years, with head injuries were included in the study. Signals of intracranial pressure, arterial blood pressure, flow velocity, and cortical microcirculatory flux were digitized and recorded for a period of 30 minutes using special computer software. Two carotid compressions were performed at the beginning of each recording. The transient hyperemic response ratio (THRR: the ratio of the hyperemic flow velocity recorded after carotid release and the precompression baseline flow velocity) was calculated, as was the correlation coefficient Sx used to describe the relationship between slow fluctuations in the systolic flow velocity and CPP throughout the period of recording. No significant changes in CPP were found during compression. There was a significant correlation between the THRR and the Sx (r = 0.49, p < 0.0001). The hyperemic response proved to be lower in patients who exhibited a poor clinical grade at presentation (GCS scores < 6, p = 0.01) and lower in patients achieving a poor outcome (GOS scores of 3, 4, and 5, p = 0.003). Loss of postcompression hyperemia occurred when the CPP fell below 50 mm Hg. The carotid compression test provides a simple index of cerebral autoregulation that is relevant to the clinical condition and outcome of the severely head injured patient.

Adolescent↗
PubMed1996

Significance of intracranial pressure waveform analysis after head injury.

The authors have investigated the relationships between the amplitude of the ICP pulse wave, the mean values of ICP and CPP, and the outcome of 56 head injured ventilated patients. The ICP was monitored continuously using a Camino transducer (35 patients) or subdural catheter (21 patients). The mean Glasgow Coma Score was 6 (range 3-13; 5 patients had a GCS > 8 after resuscitation). Patients were grouped according to their Glasgow Outcome Score assessed at 12 months after injury. The amplitude of ICP pulse waveform was assessed using the fundamental harmonic of the pulse waveform (AMP) to avoid distortion caused by different frequency responses of the pressure transducers used in the study. Statistical analysis revealed that in patients with fatal outcome the ICP pulse amplitude increased when the mean ICP increased to 25 mmHg and then began to decrease. The upper breakpoint of the AMP-ICP relationship was not present in patients with good/moderate outcome. The moving correlation coefficient between the fundamental harmonic of ICP pulse wave and the mean ICP (RAP: R-symbol of correlation between A-amplitude and P-pressure) was introduced to describe the time-dependent changes in correlation between amplitude and mean ICP. The RAP was significantly lower in patients who died or remained in the vegetative state. In 7 patients who died from uncontrollable intracranial hypertension RAP was oscillating or decreased to 0 or negative values well before brain-stem herniation. The combination of an ICP above 20 mmHg for a period longer than 6 hours with low correlation between the amplitude and pressure (RAP < 0.5) was described as an predictive index of an unfavourable outcome.

Adolescent↗
PubMed1996

A feedback-controlled pump produces stable hypotension in anaesthetised rabbits.

A method is described for the reliable production of controlled hypotension in experimental animals. Reduction in arterial blood pressure was obtained in rabbits by withdrawing arterial blood using a computer-driven pump operating within a feedback control system. Arterial blood pressure, blood flow velocity in the basilar artery (measured using transcranial Doppler), and anterior cortical microcirculation (measured using laser Doppler) were monitored. The aim of the experiments was to compare stability of hypotension produced using arterial blood pressure or basilar flow velocity as feedback control variables. Basilar artery flow velocity provided the most stable profound hypotension and during reinfusion when animals were not autoregulating. However, arterial blood pressure provided the most accurate stepwise control in autoregulating animals.

Anesthesia↗
PubMed1996

Laboratory testing of three intracranial pressure microtransducers: technical report.

Three comparatively priced intracranial pressure (ICP) microtransducers are now available, each characterized by the manufacturer as having very low zero drift over long periods, an excellent frequency response, and a low measurement error. The three microtransducers, coded Transducer A (Camino OLM ICP monitor; Camino Laboratories, San Diego, CA), Transducer B (Codman Microsensor ICP Transducer; Codman & Shurtlef Inc., Randolph, MA), and Transducer C (ICP Monitoring Catheter Kit OPX-SD [4F]; InnerSpace Medical, Irvine, CA), were examined in a pressure-flow test rig designed for assessment of hydrocephalus shunts. All three microtransducers compiled with the manufacturers' specifications and gave high-quality readings under test conditions. However, some differences were noted; Transducer C had the lowest 24-hour zero drift (drifts in all transducers were < 0.8 mm Hg). The temperature drift was very low in Transducer B and C, but Transducer A had a significantly higher drift (0.27 mm Hg/degrees C). Transducer A had a static error < 0.3 mm Hg, Transducer B < 2 mm Hg, and Transducer C < 8 mm Hg. Frequency detection in Transducers A and B were very good (bandwidth, > 30 Hz), whereas Transducer C had a limited bandwidth of 20 Hz. Transducer B scored the best overall, but all three scored satisfactorily during bench testing.

Cerebrospinal Fluid Pressure↗
PubMed1996

Early effects of mannitol in patients with head injuries assessed using bedside multimodality monitoring.

OBJECTIVE: We have employed bedside multimodality methods to assess the influence of a slow (20 min) bolus of hypertonic mannitol on cerebral hemodynamics in comatose patients with head injuries. METHODS: Middle cerebral artery flow velocities (FV) and cortical microcirculatory flows were measured in comatose patients with head injuries after the administration of 200 ml of 20% mannitol. A comparison was made with the effects of an identical bolus of isotonic saline. Fourteen patients with diffuse head injuries and with raised intracranial pressure were selected, and mannitol infusion studies were conducted when clinically indicated (n = 23). Using transcranial doppler and laser doppler flowmetry (LDF), indices of estimated cerebrovascular resistance (eCVR) were calculated for the macro- (eCVR-FV) and micro- (eCVR-LDF) circulation. RESULTS: During mannitol infusion, a significant rise in cerebral perfusion pressure was detected (+10%, P = 0.03) as a result of a fall in intracranial pressure (-21%, P = 0.001). Increases in both FV (+13%, P < 0.001) and LDF (+14%, P = 0.002) occurred only after the administration of mannitol and persisted beyond completion of infusion. The effect on FV and LDF decayed exponentially, with a time constant of 34.0 and 38.0 minutes, respectively, and was independent of the pressure autoregulatory status. There was a tendency for eCVR-FV and eCVR-LDF to decrease. No significant effects resulted from the administration of saline. CONCLUSION: Bedside multimodality monitoring may provide a useful means for assessing the effects of therapy in the comatose patient. The mechanisms by which mannitol reduces intracranial pressure in patients with head injuries are discussed.

Blood Flow Velocity↗
PubMed1996

Testing of cerebrospinal compensatory reserve in shunted and non-shunted patients: a guide to interpretation based on an observational study.

OBJECTIVE: To design a computerised infusion test to compensate for the disadvantages of Katzman's lumbar infusion method: inadequate accuracy of estimation of the resistance to cerebrospinal fluid outflow and poor predictive value in normal pressure hydrocephalus. METHODS: Accuracy was improved by intracranial pressure signal processing and model analysis for measurement of cerebrospinal compensatory variable. These include the CSF outflow resistance, brain compliance, pressure-volume index, estimated sagittal sinus pressure, CSF formation rate, and other variables. Infusion may be made into the lumbar space, ventricles, or, when assessing shunt function in vivo, the shunt chamber. RESULTS AND CONCLUSIONS: The computerised test has been used for five years in a multicentre study in 350 hydrocephalic patients of various ages, aetiologies, and states of cerebrospinal compensation. The principles of using the test to characterise different types of CSF circulatory disorders in patients presenting with ventricular dilatation, including brain atrophy and normal and high pressure hydrocephalus, are presented and illustrated. Previous studies showed a positive correlation between cerebrospinal compensatory variables and the results of shunting, but such a prediction remains difficult in idiopathic normal pressure hydrocephalus, particularly in elderly patients. The technique is helpful in the assessment of shunt malfunction, including posture-related overdrainage, over-drainage related to the nocturnal B wave activity, and proximal or distal shunt obstruction. The appendix presents an introduction of the mathematical modelling of CSF pressure volume-compensation included in computerised infusion test software.

Cerebrospinal Fluid Shunts↗
PubMed1996

Monitoring of cerebral autoregulation in head-injured patients.

BACKGROUND AND PURPOSE: Disturbed cerebral autoregulation has been reported to correlate with an unfavorable outcome after head injury. Using transcranial Doppler ultrasonography, we investigated whether hemodynamic responses to spontaneous variations of cerebral perfusion pressure (CPP) provide reliable information on cerebral autoregulatory reserve. METHODS: We studied 82 patients with head injury daily. Waveforms of intracranial pressure (ICP), arterial pressure, and transcranial Doppler flow velocity (FV) were captured during 2-hour periods. Time-averaged mean FV (FVm) and the FV during cardiac systole (FVs) were resolved. The correlation coefficient indices between FVm and CPP (Mx) and between FVs and CPP (Sx) during spontaneous fluctuations of CPP were calculated during 3-minute epochs and averaged for each investigation. RESULTS: Mx and Sx correlated with CPP (r = -.34, P = < .002; r = -.2, P = NS. respectively), with ICP (r = .46, P < .0001; r = .34, P < .003, respectively), with admission Glasgow Coma Scale score (r = -.34, P < .0025; r = -.38, P < .0008, respectively), and with outcome after head injury (r = .41, P < .0002; r = .48, P < .00009, respectively). In patients who died, cerebral autoregulation was severely disturbed during the first 2 days after injury. CONCLUSIONS: Indices derived from spontaneous fluctuations of FV waveform and CPP describe cerebral vascular pressure reactivity. They correlate with outcome after head injury and therefore may be used to guide autoregulation-oriented intensive therapy.

Adolescent↗
PubMed1996

Assessment of cerebral autoregulation using carotid artery compression.

BACKGROUND AND PURPOSE: A simple method of testing cerebral autoregulation by observing transcranial Doppler changes in middle cerebral artery flow velocity (FV) during a brief ipsilateral carotid artery compression (the transient hyperemic response test) was studied in 11 normal healthy volunteers. The aim of this study was to assess the reliability of the method and to compare derived autoregulatory indices with those of a standard noninvasive test of autoregulation, Aaslid's leg-cuff test. METHODS: Volunteers were subjected to repeated carotid compressions and leg-cuff tests at different levels of CO2. Hypercapnia was induced using inhalation of a mixture of 5% CO2 in air. Hypocapnia was induced by moderate hyperventilation. To assess the influence of the duration of carotid compression, a series of carotid compressions lasting 3, 4, 5, 7, and 9 seconds were performed in random sequence. Monitored parameters included ipsilateral FV, end-tidal CO2, and arterial blood pressure. The transient hyperemic response ratio (THRR), calculated as the maximum increase of FV divided by baseline values after release of the carotid compression, was taken as the autoregulation index. This index was compared with the rate of autoregulation index derived from the leg-cuff test. RESULTS: Both tests were significantly associated with end-tidal CO2 (ANOVA, P < .000001 for both carotid compression and cuff test). There was a linear correlation between THRR and autoregulation index (r = .86). However, the reproducibility of the THRR was more consistent than for the autoregulation index from single tests (13% versus 46%, respectively; P < .0001). Although the influence of the duration of carotid compression on THRR values was significant for carotid compressions lasting up to 5 seconds, there was no relation to the relative magnitude of FV drop during the compression. CONCLUSIONS: Brief (> 5 seconds) carotid artery compression provides an index of cerebral autoregulation that is reproducible and is affected by CO2 tension in a fashion similar to autoregulatory indices derived from a standard leg-cuff test. The simplicity of the method provides a potentially useful addition to other noninvasive autoregulation tests for clinical assessments, particularly when repeated measurements are required.

Adaptation, Physiological↗
PubMed1996

Relationship between transcranial Doppler-determined pulsatility index and cerebrovascular resistance: an experimental study.

Clinical studies with transcranial Doppler suggest that the pulsatility of the flow velocity (FV) waveform increases when the distal cerebrovascular resistance (CVR) increases. To clarify this relationship, the authors studied animal models in which the resistance may be decreased in a controlled manner by an increase in arterial CO2 tension, or by a decrease in cerebral perfusion pressure (CPP) in autoregulating animals. Twelve New Zealand white rabbits were anesthetized, paralyzed, and ventilated. Transcranial Doppler basilar artery FV, laser Doppler cortical blood flow, arterial pressure, intracranial pressure, and end-tidal CO2 concentration were measured continuously. Cerebrovascular resistance (CPP divided by laser Doppler cortical flux) and Gosling Pulsatility Index (PI, defined as an FV pulse amplitude divided by a timed average FV) were calculated as time-dependent variables for each animal. Four groups of animals undergoing controlled manipulations of CVR were analyzed. In Group I, arterial CO2 concentration was changed gradually from hypocapnia to hypercapnia. In Group II, gradual hemorrhagic hypotension was used to reduce CPP. In Group III, the short-acting ganglion blocking drug trimetaphan was injected intravenously to induce transient hypotension. Intracranial hypertension was produced by subarachnoid saline infusion in Group IV. During the hypercapnic challenge the correlation between the cortical resistance and Doppler flow pulsatility was positive (r = 0.77, p<0.001). In all three groups in which cerebral perfusion pressure was reduced a negative correlation between pulsatility index and cerebrovascular resistance was found (r = -0.84, p<0.001). The authors conclude that PI cannot be interpreted simply as an index of CVR in all circumstances.

Animals↗
PubMed1996

Multimodal monitoring and assessment of cerebral haemodynamic reserve after severe head injury.

This article contains an overview of selected clinical techniques employed for neurointensive care monitoring and testing of cerebral autoregulation of patients following severe head injury. Multiple modalities are used for monitoring of cerebral haemodynamic reserve, including intracranial pressure, cerebral perfusion pressure (CPP), blood flow velocity (FV) in the middle cerebral artery (MCA), jugular bulb oxygen saturation, laser-Doppler cortical flowmetry, near infrared spectroscopy of cerebral cortex, tissue oxygenation, and microdialysis. Large volumes of information demand specialised computer support for sensible interpretation and filtration of artifacts. Methods of testing of cerebral autoregulatory reserve based on transcranial Doppler ultrasonography are reviewed. Repetitive or continuous assessment is important in practice as autoregulatory reserve may fluctuate in time. Static and dynamic rates of autoregulation show sensitivity to carbon dioxide-induced vasodilatation, but fail to correlate with outcome following head injury. The carotid artery compression test, useful for assessment of patients after subarachnoid haemorrhage, has yet to prove its usefulness in head injury. Continuous waveform analysis of MCA FV and CPP correlates with coma score after resuscitation and outcome and hence may be considered as a robust method for the assessment of autoregulation in ventilated head trauma patients.

Cerebrovascular Circulation↗
PubMed1995

Identification of the cerebrospinal compensatory mechanisms via computer-controlled drainage of the cerebrospinal fluid.

The constant rate infusion test is still widely used for the diagnosis of hydrocephalus in children. The increased resistance to reabsorption of the cerebrospinal fluid (CSF) is considered the most important factor in the improvement seen after shunting. However, the classic infusion test has some disadvantages: the compensatory model is identified in the conditions of raised intracranial pressure, which may provoke some uncontrolled changes in cerebral blood volume in the mechanism of vasomotor response; also non-linear effects in reabsorption mechanisms may have a significant influence. The controlled drainage of CSF can be considered as a form of pressure-volume testing if the volume of the drained fluid is precisely measured. The main advantage of the method is the possibility of estimating unknown parameters in practically physiological conditions (with only slightly decreased pressure). This paper presents a new method for the identification of an electrical model of cerebrospinal volume compensation. The method has been described theoretically, verified on the simulator and introduced into clinical practice at the Medical Academy in Warsaw and the Children's Health Center in Miedzylesie.

Adolescent↗