Biomedical subjects

M Czosnyka

Publications and source records attributed to M Czosnyka.

134 records · Page 8Linked to original sources

PubMed1992

Experimental aspects of cerebrospinal hemodynamics: the relationship between blood flow velocity waveform and cerebral autoregulation.

The dynamic relationships among mean flow velocity, its pulsatile amplitude (FVa), cortical cerebral blood flow (CBF), and cerebral perfusion pressure (CPP) were studied in normal rabbits and rabbits with subarachnoid hemorrhage using 8-MHz pulsed transcranial Doppler ultrasound and hydrogen clearance under conditions of systemic hypotension and intracranial hypertension. A two-slope relationship was observed between FVa and CPP with a break point that correlated closely with the lower limit of CBF autoregulation in each animal. Below this CPP break point, FVa varied directly with CPP, and above the break point FVa varied inversely with CPP. In this experimental model, an inverse correlation between FVa and CPP indicates intact CBF autoregulation, whereas loss of that correlation implies exhaustion of autoregulatory reserve. Simultaneous recording and computation of FVa, CPP, and the correlation coefficient between FVa and CPP may be a means of monitoring CBF autoregulation in clinical practice.

Animals↗

PubMed1990

Early pathomorphological changes and intracranial volume-pressure: relations following the experimental sagittal sinus occlusion.

Saggital sinus occlusion was produced in cats. The intracranial volume-pressure relations were studied using the lumbar infusion tests. Right after occlusion ICP rised from 7.1 +/- 1.8 to 12.4 +/- 4.1 mmHg. The values of outflow resistance and volume-pressure response increased also and remained significantly unchanged with only slight decrease of the volume-pressure response. The morphometric study of the surface veins showed the dilatation of the veins draining to the occluded saggital sinus for about 10-20%. No signs of the blood-brain barrier disruption were observed.

Animals↗

PubMed1990

A computer system for the identification of the cerebrospinal compensatory model.

A computer system, based on IBM PC, was designed for the cerebrospinal compensatory model identification. The intracranial pressure (ICP) signal, registered during the lumbo-lumbar infusion test is analyzed by means of the spectral analysis algorithm in order to measure precisely the pulse wave amplitude. The amplitude and the mean ICP level, calculated repetetively within the period of about 8 seconds, are stored on the disk and form the basis for further model identification. Three different methods of identification were applied. They enable one to estimate the fundamental model parameters, such as: resistance to the cerebrospinal fluid resorption, pressure-volume index, baseline pressure, rate of formation of the cerebrospinal fluid. Statistical evaluation of the results of the infusion test analysis obtained by means of the system described in two groups of hydrocephalic patients (children and adults) is presented.

Adult↗

PubMed1990

Comparison between classic-differential and automatic shunt functioning on the basis of infusion tests.

Infusion tests were performed in order to examine cerebrospinal compensatory ability in two groups of patients with impaired compensation, subjected to shunt implantation. The functioning of the classic differential shunts was compared to the automatically (Orbis-Sigma) functioning shunts. The reference group, with intact compensatory parameters is also presented. The influence of different types of shunts on the intracranial compensation ability was compared. Automatic shunts produce less decrease in the resorption resistance of CSF in the post-shunted examination than the classic differential shunts. Classic differential shunts disturb the mono-exponential character of the pressure-volume relationship in a higher degree than automatic shunts. Shunt functioning models were proposed as well as the method of detection of eventual recovery to the normal resorption reserve. This method can be applied only to patients with automatic shunts.

Adult↗

PubMed1989

The role of cerebrospinal compensatory parameters in the estimation of functioning of implanted shunt system in patients with communicating hydrocephalus (preliminary report).

Twelve patients presenting with communicating hydrocephalus were studied. In 9 cases where the mean ICP level remained below 10 mmHg the symptoms of normal pressure hydrocephalus were observed. All of the patients were treated by shunt system implantation. The clinical and psychological state, cranial computerized tomography and parameters of the cerebrospinal compensatory mechanisms, evaluated using the constant rate infusion test were compared before and after treatment. In most of the patients (11) the pathologically enlarged ventricles persisted. Only in three cases no clinical improvement was noticed. In this group the resistance to the cerebrospinal fluid absorption and the fluid formation rate were estimated as normal. In the group with improvement the normalization of the resistance (4), decrease in the cerebrospinal fluid formation rate (4) and decrease in the cerebrospinal system elasticity (1) can be pointed out as factors responsible for improvement manifested after shunting. Therefore the resorption resistance and the formation of cerebrospinal fluid should be considered as predictive factors in the shunt implantation in hydrocephalic patients, and play an important role in the diagnosis of this entity.

Adult↗

PubMed1988

Analysis of intracranial pressure waveform during infusion test.

An analysis of intracranial pressure (ICP), based on an examination of the temporary correlation between the changes in amplitude of the pulse wave and the mean ICP level, is presented. The paper contains a discussion of the preliminary results of the method when applied to the analysis of ICP as monitored during infusion tests in a group of 24 children. Infusion of a certain volume of CSF is a good example of an uncompensated volume process, introduced externally into the intracranial space. Results allow an interpretation of the short term correlation coefficient RAP (correlation coefficient between ICP and variations of the amplitude of fundamental component of the pulse wave AMP), as a steady state index. According to this interpretation, the presented analysis enables the observation of a loss of equilibrium during the test. Other phenomena can also be observed, for instance a recovery to equilibrium after the test, nonlinearities of amplitude-pressure relationship, vasomotor reflexes etc.

Adolescent↗

PubMedDate not supplied

[Characteristics of intracranial volume-pressure relationship in hydrocephalic children with reference to age].

The purpose of the study was establishing of the effect of child's age, and thus the biomechanical properties of cranial coverings, on the parameters characterizing the intracranial space in the infusion test. The results of the infusion tests performed as a supplementary diagnostic examination in 59 cases of infantile hydrocephalus were subjected to statistical analysis. The studied material and the methods used for its processing no significant differences were found in the mean values of the biomechanical parameters of intracranial space were found between the group of younger children (aged up to 2 years) and older children (over 2 years). This finding may be important in the interpretation of the results of the infusion test, since it was not found that the biomechanical properties of the cranial coverings had any significant effect on the results of this test.

Age Factors↗

PubMedDate not supplied

[Evaluation of intracranial volume compensation analyzing changes of harmonic components of intracranial pressure pulse wave].

Intracranial pressure (ICP) pulse wave was analysed during infusion tests performed in hospital (hydrocephalus) and in cats. Pulse wave changes were evaluated calculating the high frequency centroid index (HFC) in the HFC, found to be a very valuable parameter in intracranial volume-pressure situation evaluation. The HFC decrease occurred much earlier than the rise of ICP in both clinical and experimental studies. Thus the HCF index should be very usefull in clinical evaluation of intracranial volume-pressure relation disturbances.

Adolescent↗