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Biomedical subjects

J Lewko

Publications and source records attributed to J Lewko.

At least 37 records · Page 2Linked to original sources
PubMed1998

Neural network technique for detecting emergency states in neurosurgical patients.

The problem of reliable detection of life-threatening situations in the neurosurgical patient undergoing treatment in the ICU is still far from reaching a satisfactory solution, although several methods of clinical and instrumental evaluation have recently been developed for the early detection of oncoming signs of danger. Continuous monitoring of intracranial pressure (ICP) provides neurosurgeons with valuable information about the current condition of the patient. However, it is increasingly felt that traditional methods of extracting information from the ICP signal have reached their natural limits, mostly because of difficulties in fitting the appropriate mathematical model to this non-linear and non-stationary process. Successful implementations of artificial neural networks in many medical tasks have encouraged the application of this method of ICP processing. Two problems are considered: the prediction of trends in ICP, and recognition of the configuration of unfavourable symptoms likely to signal danger for the neurosurgical patient. The construction of neural network predictors of ICP trends is based on wavelet pre-processing of the original signal. The approach to the second task involves pre-processing of the ICP with spectral and statistical methods and classification of the extracted features of the current signal on an arbitrarily selected scale of danger.

Brain Diseases↗
PubMed1998

No specific brain protection against thermal stress in fever.

Knowledge about human brain temperature is still very limited, despite evidence demonstrating the critical influence of mild increases in temperature on the ischaemic brain. It has been suggested that in passive and exercise hyperthermia the brain may be protected against thermal damage by a mechanism of selective brain cooling (SBC). It is said to bring about suppression of the temperature of the brain, rendering it significantly lower than trunk and arterial blood temperature. Yet very little is known about the possible role of this mechanism in fever, a condition fundamentally different from "physiological" hyperthermia, especially when it occurs in brain-damaged patients. In our investigation we retrospectively analysed the results of direct recordings of cerebral temperature within the subdural space (Tsd) and within the brain parenchyma (Tbr-16 cases) in 63 unanaesthetized patients following neurosurgical procedures, including 23 with fever > 38 degrees C. The difference between trunk temperature, measured in the rectum (Tre) or in the oesophagus (Tes), and the intracranial temperature, were calculated in all subjects. A statistically significant reduction of these differences, in step with increasing fever, would be compatible with demonstrating a process of selective brain cooling. The offsets Tre-Tsd, Tre-Tbr, and Tes-Tsd were plotted against Tre over a wide range of body temperature and near zero correlation was found. This finding suggests that brain temperature in fever was not selectively suppressed by any specific thermolytic mechanism and that dissipation of the main bulk of cerebral metabolic heat both in normothermia and in fever depends on heat uptake by arterial blood. The results suggest that the brain in fever can be seriously jeopardized by heat stress and no specific cooling mechanism exists, to reduce it below body temperature in feverish neurosurgical patients. Tbr and/or Tsd remained the highest body temperature in 14 out of the 23 patients during fever.

Aged↗
PubMed1994

The relationship between directly measured human cerebral and tympanic temperatures during changes in brain temperatures.

The present study was performed to investigate the relationship between noninvasive measurements of core temperature and intracranial temperature measurements in humans. At 2-3 weeks following minor subarachoid haemorrhage, five patients were studied during open brain surgery. All patients were fully conscious and free of neurological symptoms at the time of surgery. During craniotomies in the frontotemporal region, temperatures between the dura and brain surface were on average 0.58 (SD 0.51) degrees C lower than those near the mesencephalon. During the 60-90 min following the initial exposure of the brain surface to the ambient temperature of 24 degrees C, subdural temperature at the convexity decreased by 0.72 (SD 0.43) degrees C and subdural temperature at the basis decreased by 0.36 (SD 0.17) degrees C. During the same period, mesencephalon temperature decreased by 0.22 (SD 0.10) degrees C. The decreases of cerebral temperatures were followed by a similar decrease in tympanic temperature of 0.28 (SD 0.10) degrees C but by an increase in rectal temperature of 0.22 (SD 0.13) degrees C and an increase in oesophageal temperature of 0.20 (SD 0.20) degrees C. The maximal shift of frontal skin temperature during the same period amounted to +0.04 (SD 0.21) degrees C. The findings would seem to support the thesis that a direct relationship does exist between tympanic and brain temperatures in humans and that of the externally accessible body temperatures, tympanic temperatures giving the best approximation of average cerebral temperature.

Body Temperature↗
PubMed1990

Uncommon causes of intraventricular hemorrhage.

The advent of CT has lead to discovery of a wide variety of unusual causes of intraventricular hemorrhage (IVH) and hence to the shifts in the proportional incidence of its different etiologies. From 96 patients with IVH, 7 uncommon cases of intracerebral hemorrhage (ICH) associated with IVH, including 2 due to anticoagulation treatment, 1 because of thrombolytic therapy, 1 due to thrombocytopenia, 2 as operative complications and 1 due to metastatic brain tumor are presented. In patients with blood disorders-related IVH the clinical presentation was similar to 'stroke in evolution', and the severity of IVH correlated with neurological deficit on admission and outcome of 3/4. All of the patients were treated with external ventricular drainage (EVD), 1 underwent partial evacuation of ICH in addition. 4 (57%) patients, including 3 with coagulation defect deceased. The peculiar aspects of uncommon causes of IVH are discussed on the basis of a review of the literature. The authors suggest that a standardized differentiated protocol should be adopted for the management of every uncommon type of IVH. An active attitude towards the evacuation of blood disorders-related ICHs and IVHs seems to be justified.

Aged↗
PubMed1990

Intraventricular hemorrhage due to rupture of arteriovenous malformations.

From 96 cases of intraventricular hemorrhage (IVH), 7 (7%) were due to rupture of arteriovenous malformation (AVM). 1 patient with a giant AVM had a primary IVH. Others had intracerebral hematoma (ICH) with rupture into the ventricular system. The severity of IVH (SIVH) correlated with neurological deficits on admission and with outcome of 6 (85%) patients and was considered as a reliable radiological prognostic indicator. 1 (14%) patient deceased and 4 (57%) survived with no or minor, 1 (14%) with moderate and 1 (14%) with major disability. Reviewing the literature, the conclusion is made, that in this relatively benign form of IVH, an active neurosurgical attitude regarding immediate evacuation of large ICHs and IVHs and if within reach AVMs is justified.

Adult↗
PubMed1989

External ventricular drainage and passive vs. active neurosurgical intervention in the management of hypertensive intracerebral hemorrhage with rupture into the ventricles.

The mortality rate of hypertensive intracerebral hemorrhages (HICH) with ventricular rupture (VR) has been said to range between 60 and 86%. We report on 33 consecutive cases of HICH associated with VR, which were diagnosed by CT and treated by external ventricular drainage (EVD). Sixteen hemorrhages were in the capsulolenticulostriate area, and 6 were in the posterior fossa. A modification of the usual system of severity grading for intraventricular hemorrhages (IVH) in posterior fossa bleedings is suggested. Extent of IVH correlated with neurological deficit on admission in 29 patients (87%) and with outcome in 26 patients (78%). Following passive neurosurgical policies in which the deterioration of patient's clinical situation indicates the craniotomy, only one intracerebral hematoma (ICH) was partially removed. Twelve patients (36.5%) died, and 12 of the survivors had no or only a minor neurological deficit. The results are compared with those of a series of patients, reported by Hayashi et al., who were treated according to active neurosurgical policies in which the largeness of ICH and IVH indicates the craniotomy, whereby it is concluded that active neurosurgical intervention does not reduce significantly the mortality and morbidity of HICH with VR. The pathophysiological explanation for this is discussed on the basis of a review of reference literature.

Journal Article↗
PubMed1988

Platelet aggregability in patients with common carotid artery ligation.

Increased platelet aggregability is regarded as being a sensitive indicator of the initiation of thrombotic processes. Platelet aggregation was analysed in blood taken from the common carotid artery before and 30 min after its ligation in 3 patients, as well as in the venous blood of 14 patients in the late postoperative period. No tendency towards increasing platelet aggregation was observed in either of the groups investigated.

Adult↗
PubMed1987

Late rheoencephalographic assessment of the cerebral circulation after ligation of the common carotid artery.

A series of 17 patients was investigated following common carotid ligation. The period between operation and examination ranged from 2-7 years. Cerebral circulation was estimated by use of the rheoencephalographic method. Statistical analysis of the reg plot was performed by comparing an age-matched normal population with patients. A comparison was also made of the ligated and nonligated sides for the patients. The following results were obtained: a significant decrease in the amplitude of the reg waves, an extension in the anacrotic part of the wave, and a decrease in the angle of its inclination. This was intensified more on the side of the common carotid ligation. These findings may suggest that after common carotid ligation the cerebral circulation is changed for a long period of time. They would also seem to indicate that postoperatively, the cerebral circulation does not return to normal--if it ever does.

Adult↗
PubMed1987

Some aspects of measuring intracranial pressure.

The problem of measurement of intracranial pressure in the epidural space is discussed in the light of the authors' own experience. Three forms of transducers have been used consecutively: (1) a capsular form which slides into the epidural space, (2) a screw-shaped form, fixed firmly in a burr hole and (3) a cylindrical tape, designed to be fixed in a burr hole with the aid of a protective socket. The zero point may be adjusted during measurement. The merits and disadvantages of these three types of transducer, as well as the practical problems connected with their use are discussed.

Epidural Space↗
PubMedDate not supplied

Pathogenesis of primary internal ophthalmoplegia after head injury.

Primary internal ophthalmoplegia is a rare ocular syndrome after head injury. Its pathogenesis remains unclear and it is only a hypothesis that the pupillomotor fibres on the ventromedial aspect of the oculomotor nerve are slightly contused against the petroclinoid ligament at the moment of impact. We observed a patient after head injury who presented with a fixed, dilated pupil and died within 15 hours of the accident. The postmortem examination revealed an isolated group of fibres on the medial aspect of her oculomotor nerve, which had been torn out of the midbrain. This suggests an alternative explanation in terms of partial injury to the oculomotor nerve to account for primary internal ophthalmoplegia.

Accidents, Traffic↗
PubMedDate not supplied

[Proliferative activity of glial neoplasms of the brain].

The aim of the study including 89 brain gliomas was to determine their proliferative activity assayed with immunohistochemical methods (PCNA and Ki-67) and with the method of AgNORs, as well as to evaluate the correlation between the proliferative activity and features of histological malignancy. The study reveals that the estimation of PCNA, Ki-67 and AgNORs are effective methods for the determination of the proliferative activity of brain gliomas. Statistically significant differences were noted in the proliferative PCNA, Ki-67 and AgNORs between groups of gliomas with lower and higher malignancy, which indicated a distinct correlation between histological malignancy of the tumours and their proliferative activity. High values of PCNA and Ki-67 (> 40%) and AgNORs (> 15) were found to considerably deteriorate prognosis in brain gliomas.

Adult↗
PubMedDate not supplied

[Brain temperature during craniotomy in general anesthesia].

Mild hypothermia may occur spontaneously or, because of its putative neuroprotective effect, may be induced purposefully during neurosurgical procedures. Though the brain is the organ targeted for the purpose of neuroprotection, little is known about its temperature during general anaesthesia and craniotomy. The purpose of this study was to define the relations between core, skin and brain temperature during craniotomy and to compare two modes of inducing thermal insulation in patients during operative procedures. To achieve this we recorded core: rectal (Tre), oesophageal (Tes) and tympanic (Try) temperature, brain temperature in the subdural space (Tsd), and skin temperature on the thigh (Tfe), forehead (Tfr) and sternum (Tst) in 15 patients undergoing standard procedure for aneurysm clipping. In 13 patients the core temperature decreased, whereas skin temperature increased, after induction of general anaesthesia with isofluran. Nevertheless the mean body temperature remained unchanged, thus supporting the view that the cause of the resultant core hypothermia was heat redistribution between the thermal core and the periphery. Special thermofoil proved to be only as effective as a plain cotton blanket in preventing further heat loss during the later phases of the operation. Brain temperature was found to be the lowest core temperature throughout the procedure. It differed by as much as 0.1-1.2 degrees C from rectal temperature (mean 0.75 +/- 0.41 degree C) and reached the level of mild hypothermia (below 35 degrees C) even in those patients in whom rectal temperature indicated the state of normothermia. Furthermore tympanic and oesophageal temperature was on average 0.5 degree C higher than brain temperature. In conclusion, temperature measurements obtained in standard sites do not reflect brain temperature reliably during craniotomy and general anaesthesia. This indicates that the direct measurement of intracranial temperature is necessary for correct estimation of brain hypothermia.

Anesthesia, General↗
PubMedDate not supplied

[Brain temperature in patients with central nervous system lesions].

The knowledge of human brain temperature is still very limited. In this report we investigated the relationship between brain and trunk temperature in neurosurgical patients during normothermia and fever. Another problem addressed was that of possible gradients of temperature within the brain. We carried out direct recordings of temperature in 63 operated, neurosurgical patients with a variety of intracranial pathologies. Flexible, teflon-coated thermocouples were placed intracranially during neurosurgical procedures. Oesophageal, rectal and tympanic temperatures were also monitored. An error of up to 1.3 degrees C is to be expected in single cases if brain temperature is deduced from the rectal or oesophageal temperature. Mean differences between brain temperature and core body temperature measured in the rectum or in the oesophagus, were between 0 to 0.3 degree C. Tympanic temperature (Tty) improved the approximation of brain temperature (Tbr) to within the mean difference between Tbr-Tty close to 0 degree C. Nevertheless Tty also differed from Tbr by as much as 1 degree C in single cases. Brain temperature was the highest body temperature measured, either in normothermia or in fever. Temperature gradients were proved to exist between the warmer brain interior and cooler surface, with maximal differences in temperature reaching 0.6 degree C. This temperature gradient tended to increase along with the rise in intracranial pressure and deterioration of the level of consciousness. Our results suggest that conclusions regarding brain temperature drawn on the basis of other core temperatures, may lead to significant errors, and intracranial temperature measurement is desirable in neurosurgical intensive care. Temperature gradients within the brain may exacerbate its biochemical injury during ischaemia and fever--a combination seen frequently in neurosurgical patients. This may be particularly so, since brain temperature in fever is the highest body temperature in a high proportion of these patients.

Adult↗
PubMedDate not supplied

[Analysis of intracranial pressure signals using artificial neural networks].

Intracranial pressure (ICP) is influenced by an array of predictable and unpredictable factors. Statistical modelling of this signal has only limited applicability because of the significant load of stochastic components. We tested the efficiency of an alternative approach, based on the methodology of artificial neural networks (ANNs) in the on-line prediction of future values of ICP and in the classification of signal properties. Satisfactory accuracy of forecasting was achieved with the ANNs for a 3-minute prediction horizon, while the prediction quality with autoregressive models of statistical origin was proved unsatisfactory. The results obtained with the ANNs were further improved when signal pre-processing with wavelet transform was employed. Nevertheless, even with the ANN methodology, no sudden breakdowns in the ICP signal (which in this respect might be compared to a "catastrophe") can be forecast with any practical applicability. We therefore applied two ANN algorithms, oriented at classification and discrimination of the global properties of the ICP signal. The neural network was expected to discriminate those sets of signal properties, which were assumed to correspond to certain clinical conditions of the patient. In a "dynamic pattern classification" the network was presented with several sections of ICP records. This was combined with information about the assignment of a given record to one of four arbitrary classes of danger. In this mode no data pre-processing was carried out, in contrast to our second approach, in which the signal was pre-processed with statistical analyses and only these intermediate coefficients were fed to the ANN classifier. The results obtained with both classification methods at their present stage of training were similar and approximated to a 70% rate of judgements consistent with expert scoring. Nevertheless, the method based on the assessment of global parameters of the ICP record seems more promising, because it leaves the possibility of extending the set of training data by information from other diagnostic modalities. The study aims towards the development of a pseudo-intelligent computer expert system, which has would be taught salient links between data extracted from the ICP signal and higher- order data, which contributed to the expert score. Hence the system would be able to make decisions on the basis of a reduced set of input information, available from a standard monitoring modality.

Algorithms↗