Biomedical subjects

M Czosnyka

Publications and source records attributed to M Czosnyka.

At least 127 records · Page 7Linked to original sources

PubMed1995

Cerebrospinal fluid pulse pressure waveform analysis in hydrocephalic children.

Analysis of cerebrospinal fluid pulse pressure was reported to be useful in the assessment of the cerebrospinal pressure-volume compensation. The method for the estimation of high-frequency centroid (HFC) was modified and used to verify the correlation between HFC and other compensatory parameters investigated by means of the lumbar infusion test in 94 hydrocephalic children. The results confirm that in hydrocephalus HFC is positively correlated to cerebrospinal elasticity coefficient, but inversely to mean CSF pressure and pulse wave amplitude. It was also demonstrated that HFC decreased dynamically during the infusion test.

Cerebrospinal Fluid Pressure↗

PubMed1995

Computerised transient hyperaemic response test--a method for the assessment of cerebral autoregulation.

A simple bedside test has been developed to assess the state of autoregulation in subarachnoid haemorrhage patients. Transcranial Doppler was used to measure blood flow velocity in the middle cerebral artery after a brief common carotid compression. Acceleration of blood flow postcompression was interpreted as evidence of intact cerebral autoregulation. A program using the Windows environment was designed for signal analysis of the transient hyperaemic response test (THRT). The flow velocity signal from the TCD was recorded, carotid compression and release automatically detected and the test results immediately displayed and stored in a database. The program was verified in 614 tests; 552 of them were analysed off-line using previously recorded data and 62 on-line during the examination. A significant correlation was found between the results of computerised testing and the patient's neurological state.

Adult↗

PubMed1995

Estimation of laser-Doppler flux biological zero using basilar artery flow velocity in the rabbit.

Laser-Doppler flowmetry has potential for continuous cerebral blood flow (CBF) measurement in man and experimental animals. However, laser-Doppler flux (LDFx) measured when perfusion is absent (the biological zero, 0biol) does not necessarily coincide with the instrument's electrical zero. To evaluate laser-Doppler flowmetry further we have compared LDFx in rabbits with continuous measurement of the maximum flow velocity (FVx) in the basilar artery using Doppler ultrasonography. Arterial blood pressure (ABP), FVx, and LDFx were measured continuously in anesthetized New Zealand White rabbits. ABP was altered by controlled hemorrhage with subsequent reinfusion. 0biol was estimated from regression analysis of FVx vs. LDFx and compared with 0biol obtained after death. There was a strong linear relationship between LDFx and FVx (r = 0.94). The absolute difference between estimated 0biol and true 0biol was 5.24% of control prehemorrhage LDFx. Variations in 0biol (range 4-409) suggest that percent changes in LDFx must be related to 0biol if results between individual animals are to be compared.

Animals↗

PubMed1995

Can cerebrovascular reactivity be measured with near-infrared spectroscopy?

BACKGROUND AND PURPOSE: We used near-infrared spectroscopy (NIRS) to monitor the cerebral oxygenation changes during CO2 reactivity tests. METHODS: Fifty healthy volunteers were examined (age range, 19 to 68 years). The monitored parameters were as follows: transcranial Doppler (TCD) time-averaged middle cerebral artery flow velocity end-tidal CO2 (EtCO2); change in concentration of cerebral oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), and total hemoglobin; mean arterial blood pressure; peripheral arterial oxygen saturation (SaO2); and extracranial tissue perfusion with the use of cutaneous laser-Doppler flowmetry. The examination protocol included both hypercapnia and hypocapnia. The cerebrovascular reactivity indexes were calculated as follows: TCD, relative change in flow velocity per 1 kPa increase in EtCO2; NIRS, absolute change in HbO2, Hb, and total hemoglobin concentration (micromoles per liter) per 1 kPa increase in EtCO2. RESULTS: Mean middle cerebral artery flow velocity was found to be 58 cm/s at a mean baseline EtCO2 of 4.7 kPa. Mean cerebrovascular reactivities were as follows: TCD, 24%/kPa (SEM, 1.1); HbO2, 2.06 mumol/L per kilopascal (SEM, 0.08); Hb, -0.63 mumol/L per kilopascal (SEM, 0.09); and total hemoglobin concentration, 1.44 mumol/L per kilopascal (SEM, 0.1). Statistical analysis revealed significant correlation between reactivities calculated with the use of NIRS and TCD (P < .001). Although some fluctuations were observed in SaO2 and laser-Doppler flux, they were not correlated with either EtCO2 or NIRS. CONCLUSIONS: NIRS signal changes in HbO2, Hb, and total hemoglobin concentration are very sensitive to alterations in EtCO2, which are largely independent of extracranial tissue perfusion. NIRS may be developed as an alternative method for testing cerebrovascular reactivity and may be of particular clinical importance when the ultrasound window is poor.

Adult↗

PubMed1995

An observational study of near-infrared spectroscopy during carotid endarterectomy.

Near-infrared spectroscopy was used to monitor changes in the cerebral oxygenation state in 13 patients during carotid endarterectomy. Variations in the levels of the chromophores (oxygenated hemoglobin (HbO2), deoxygenated hemoglobin (Hb), and oxidized cytochrome (CytO2)), and the total hemoglobin content (tHb) were compared with changes in middle cerebral artery flow velocity measured using transcranial Doppler ultrasonography. Of eight patients who showed a fall in flow velocity on application of the internal carotid artery cross-clamp, seven demonstrated a rapid and closely correlated fall in HbO2 signal, and an increase in Hb. Levels of CytO2 and tHb remained unchanged. During endarterectomy, recovery of the HbO2 and Hb levels toward preclamp baseline values occurred in three of these patients. Intraoperative shunts accelerated recovery of HbO2 and Hb signals in two of three individuals. Release of the internal carotid cross-clamp resulted in a rapid increase in HbO2 and decrease in Hb signal in those patients in whom spontaneous recovery had not occurred; in five instances, a hyperemia evolved with raised flow velocity and HbO2 to above baseline values. Cross-clamping and subsequent reperfusion of the external carotid artery had no effect on any parameter measured. The authors conclude that near-infrared spectroscopy can register changes in cerebral oxygenation during carotid endarterectomy without significant contamination from extracranial tissues.

Adult↗

PubMed1995

Near-infrared spectroscopy use in patients with head injury.

A multimodality recording system was used in 14 ventilated patients with closed head injury to assess the potential use of near-infrared spectroscopy (NIRS) in the neurointensive care unit. Signals of intracranial pressure, cerebral perfusion pressure, peripheral oxygen saturation, jugular venous saturation, and NIRS-derived changes in the chromophores of oxy- and deoxyhemoglobin were digitized and recorded. After a review of 886 hours of continuous monitoring, 376 hours were considered free from artifact and were entered for final analysis. In nine of the patients 38 events were recorded that demonstrated clear changes in cerebral perfusion pressure accompanied by hemodynamic changes in middle cerebral artery flow velocity (transcranial Doppler) and cortical perfusion (laser Doppler flowmetry). Near-infrared spectroscopy showed correlated changes in 37 events (97%) whereas jugular venous saturation monitoring registered only 20 (53%). There was associated peripheral oxygen desaturation in eight cases (21%), intracranial hypertension in 10 (26%), and cerebral hyperemia in eight (21%). The remaining 12 events (32%) appeared to be complex changes of uncertain origin. Iatrogenic factors were identified as causative in 14 cases (37%). The potential application of NIRS in adults and the importance of using multiple parameter recording systems in the interpretation of cerebral events are discussed.

Adolescent↗

PubMed1994

Testing of cerebral autoregulation in head injury by waveform analysis of blood flow velocity and cerebral perfusion pressure.

Thirty five head injured patients were subjected to day-by-day monitoring of intracranial pressure (ICP), arterial blood pressure (ABP) and blood flow velocity (FV) in middle cerebral artery. Parameters describing cerebral autoregulation: flow velocity time average, systolic, diastolic values, pulsatility index (PI), estimate of cerebrovascular resistance (CVR = CPP/FV) etc. were analyzed as functions of CPP (ABP-ICP). The results show that for CPP below 55 mmHg the evidence of exhausted autoregulation can be observed in FV, CVR, PI. The method is helpful in assessment ot the optimal level of CPP in order to reduce the probability of ischaemic brain insults.

Blood Flow Velocity↗

PubMed1994

Shunt audit: a computerized method for testing the performance characteristics of CSF shunts in vitro.

Studies of long-term shunt performance in vivo demonstrate that some 81% fail within 12 years. Such failure is multifactorial in origin: the patient, the surgical technique and the shunt may all prove fallible. Recent studies have shown that there is considerable variability of the performance characteristics of individual shunts when tested for short time periods in relatively simple rigs, and that they do not always behave according to the manufacturers' specifications. We have developed a computerized shunt rig for the long-term evaluation of a valve's performance in vitro using both pressure-flow studies (where flow through the shunt is evaluated for controlled differential pressure across the shunt) and flow-pressure studies (where the differential pressure across the shunt is evaluated for controlled flow rates through the shunt). This rig consists of a pressure transducer, electronic balance, computer-controlled infusion pump and blood pressure systems calibrator that stimulates different wave form patterns. An IBM PC controls all the devices and evaluates the performances characteristics according to various test protocols. Our initial observations with this rig confirm that progressive changes in shunt function occur over long periods of time (weeks).

Cerebral Ventricles↗

PubMed1994

Computer supported multimodal bed-side monitoring for neuro intensive care.

Multimodal monitoring in neuro-intensive care requires computer supported data analysis and archiving. This paper describes a computer system that is able to integrate the results of analysis of intracranial pressure, cerebral perfusion pressure, transcranial Doppler blood flow velocity, jugular bulb oxygen saturation, laser Doppler blood flow, near infrared spectroscopy. A research-oriented software installed in a standard IBM PC equipped with a low-cost analog-to-digital converter allows a broad spectrum of waveform analyses, from calculation of simple mean values to a selective waveform detection and cross-correlation analysis. The architecture for the signal processing algorithm, the principles of system interfacing and data presentation are discussed briefly. Results from two years of multimodal monitoring in neuro-intensive care show that, apart from simple recording of time trends of monitored variables, certain calculated parameters are particularly useful in the continuous assessment of cerebral haemodynamic and compensatory reserves. Such parameters include: transcranial Doppler pulsatility indices, the dependence between blood flow velocity or laser Doppler flux and cerebral perfusion pressure and the correlation coefficient between pulse amplitude and mean intracranial pressure.

Adolescent↗

PubMed1994

Monitoring of cerebrospinal dynamics using continuous analysis of intracranial pressure and cerebral perfusion pressure in head injury.

Cerebrospinal dynamics has been investigated by statistical analysis of results of computerised monitoring of 80 head injured patients admitted to the Intensive Care Unit at Pinderfields General Hospital. One minute average values of intracranial pressure (ICP), systemic arterial pressure (ABP), cerebral perfusion pressure (CPP), amplitude of the fundamental component of the intracranial pressure pulse wave and the short-term moving correlation coefficient between that amplitude and mean ICP (RAP) were recorded. It was found that reduction of CPP down to 40 mmHg was more often caused by decrease in ABP than increase in ICP. Further falls in CPP below 40 mmHg were caused by substantial increases in ICP above 25 mmHg. The relationship between the ICP pulse wave amplitude and CPP showed a significant gradual increase in amplitude with CPP decreasing from 75 to 30 mmHg. For CPP below 30 mmHg there is a sharp decrease in amplitude followed by a change in the coefficient RAP from positive to negative values. This was interpreted as a sign of critical disturbance in cerebral circulation.

Blood Pressure↗

PubMed1994

Frequency-dependent properties of cerebral blood transport--an experimental study in anaesthetized rabbits.

Carotid arterial blood pressure and blood flow velocity in the basilar artery were studied in nine New Zealand rabbits under general anaesthesia. The cerebrovascular impedances for mean and maximal flow velocity were defined as the ratios of the respiratory and pulse waveforms of arterial blood pressure and blood flow velocities. The absolute values of these impedances were expressed and analysed as functions of frequency. Both functions decreased as frequency increased, demonstrating that a pulsatile blood movement need a lower energy expenditure than a continuous one. A minimum absolute value of impedance for flow velocity mean was found near 2.5-4 Hz in each rabbit. The impedance for mean flow velocity could be modelled by a second-order circuit, whereas the distribution of impedance for the maximal velocity had a more uniform character and could be approximated by a first-order model. A method of assessment of changes in cerebrovascular resistance using frequency properties of calculated impedance was proposed.

Animals↗

PubMed1994

Continuous monitoring of cortical perfusion by laser Doppler flowmetry in ventilated patients with head injury.

A method for monitoring cortical perfusion by laser Doppler flowmetry (LDF) in the neurointensive care unit is described. Out of 22 patients with head injuries, reliable and long term recordings were obtained in 16. Laser Doppler flowmetry registered changes in cortical microcirculatory flow in response to spontaneous waves of raised intracranial pressure, and to therapeutic manoeuvres that altered the cerebral perfusion pressure. Comparisons of variations in flux signal with cerebral perfusion pressure provided an indication of the autoregulatory state of the cortical microcirculation, and analysis of raw LDF data demonstrated an autoregulatory breakpoint of cerebral perfusion pressure of 58 mm Hg, below which cortical perfusion failed. Although middle cerebral artery flow velocities were generally tightly coupled with LDF signal changes, episodes of uncoupling were seen. The potential uses and limitations of LDF in the neurointensive care setting are discussed.

Adult↗

PubMed1994

Assessment of cerebral autoregulation with ultrasound and laser Doppler wave forms--an experimental study in anesthetized rabbits.

The aim of the study was to correlate changes in transcranial Doppler blood flow velocity wave form in the basilar artery with cortical red blood cell flux measured with a laser Doppler flowmeter during hemorrhage-induced hypotension in anesthetized and ventilated New Zealand rabbits. Although systolic flow velocity and flux exhibited an autoregulatory threshold at 45 mm Hg, diastolic flow velocity started to fall when mean arterial blood pressure fell below 65 mm Hg. The difference between the mean arterial blood pressure at which diastolic blood flow velocity decreases and the pressure at which mean flux decreases is the difference between systolic and diastolic blood pressure. The increasing divergence between systolic and diastolic flow velocities was reflected in an increase in the amplitude of blood flow velocity pulsations and pulsatility indices. An increase in flux pulsatile wave form was noted as cerebral resistive vessels dilated with hypotension.

Animals↗

PubMed1993

Cerebrospinal compensation in hydrocephalic children.

One hundred and fifteen cases of hydrocephalus in children were analysed. Cerebrospinal compensatory reserve was assessed by a computerized, constant rate, lumbar infusion test. Head circumference and ventricular size were measured and a psychometric examination carried out. A classification of hydrocephalus based on resting cerebrospinal fluid pressure (CSFP) and resistance to cerebrospinal fluid outflow (RCSF) was introduced. Parameters of compensatory reserve were compared in atrophy (low CSFP, low RCSF), normal-pressure hydrocephalus (low CSFP, increased RCSF), non-communicating hydrocephalus (high CSFP, low RCSF) and acute hydrocephalus (high CSFP and increased RCSF). Significant differences were found between the factors describing compensatory ability in these groups. Sixty-two patients could be classified on the basis of resting CSFP and RCSF. Differentiation between the types of hydrocephalus was shown to be more accurate when all variables measured during the pressure-volume test were considered. The patterns of the time courses of CSFP during rate infusion tests in the different types of hydrocephalus are presented.

Cerebrospinal Fluid Pressure↗

PubMed1993

CO2 cerebrovascular reactivity as a function of perfusion pressure--a modelling study.

A mathematical model is described that demonstrated the properties of cerebral vascular resistance and compliance expressed as a function of cerebral perfusion pressure (CPP) and arterial CO2 partial pressure (PaCO2). The hypercapnic induced shift of the lower limit of autoregulation to a higher range of CPP, as shown by this model, is a useful characteristic that facilitates the differentiation between normal and impaired autoregulation described previously in experimental studies. Dynamic properties of cerebrovascular circulation derived from the relationship between pulse wave of CBF waveform and CPP have been analysed at different levels of PaCO2-phenomenon, being often described as dependence of blood flow velocity pulsatility index on the autoregulatory reserve. The model was also used to interpret interhemispheric asymmetry of CBF reactivity to changes in arterial concentration of CO2 in patients with carotid artery stenosis.

Blood Flow Velocity↗

PubMed1993

Management of raised intracranial pressure.

This review has been written at an unfortunate time. Novel questions are being asked of the old therapies and there is an abundance of new strategies both to lower ICP and protect the brain against cerebral ischaemia. In the United Kingdom, the problem is to ensure that appropriate patients continue to be referred to centres where clinical trials of high quality can be undertaken. One of the success stories of the past decade has been the decline in the number of road accidents as a result of seat belt legislation, improvements in car design and the drink/driving laws. Hence, fortunately there are fewer patients with head injuries to treat and it is even more important that patients are appropriately referred if studies to assess efficacy of the new strategies are not to be thwarted. The nihilistic concept that intensive investigation with ICP monitoring for patients with diffuse head injury or brain swelling following evacuation of a haematoma or a contusion has no proven beneficial effect on outcome, requires revision. A cocktail of therapies may be required that can be created only when patients are monitored in sufficient detail to reveal the mechanisms underlying their individual ICP problem. Ethical problems may arise over how aggressively therapy for intracranial hypertension should be pursued and for how long. There has always been the concern that cranial decompression or prolonged barbiturate coma may preserve patients but with unacceptably severe disability. Some patients may be salvaged from herniating with massive cerebral infarction with the use of osmotherapy but is the outcome acceptable? Similar considerations apply to some children with metabolic encephalopathies. Where such considerations have been scrutinised in patients with severe head injury, the whole spectrum of outcomes appears to be shifted so that the number of severe disabilities and persistent vegetative states are not increased. However, it is important to be sensitive to such issues based on experience of the particular cause of raised intracranial pressure in a given age group.

Brain↗

PubMed1992

The hyperaemic response to a transient reduction in cerebral perfusion pressure. A modelling study.

A mathematical model of cerebral blood flow and the cerebrospinal fluid circulation is described which permits the study of phenomena caused by dynamic changes in cerebrovascular autoregulatory or cerebrospinal fluid compensatory reserves. A transient decrease in cerebral perfusion pressure was produced by carotid artery compression. Comparison of the computer simulations with clinical and experimental data, reported elsewhere, suggests that the transient hyperaemic response (THR) is proportional to the strength of the autoregulatory response. The relationships between the magnitude and time course of the THR, and the period and level of reduction in CPP were studied. This model suggests that simple clinical tests based on the examination of THR using transcranial Doppler velocity measurements are of potential value for the non-invasive assessment of the autoregulatory reserve.

Blood Flow Velocity↗

PubMed1992

Computerized infusion test compared to steady pressure constant infusion test in measurement of resistance to CSF outflow.

Resistance to cerebro-spinal fluid outflow is together with intracranial pressure the most important parameter in the investigation of patients with disturbances of CSF dynamics. The methods for determination of resistance are either unreliable or too time-consuming for routine clinical use, which has limited the popularity of this kind of measurement. In this paper a method for computerized acquisition and processing of an infusion test is described. A good correlation to a standard technique is documented.

Adolescent↗