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Biomedical subjects

A Marmarou

Publications and source records attributed to A Marmarou.

At least 145 records · Page 8Linked to original sources
PubMed1987

Xenon/computed tomography cerebral blood flow measurements. Methods and accuracy.

We performed a series of five baboon experiments to compare cerebral blood flow measured with an improved stable xenon/CT method and the radiolabelled microsphere technique at a PaCO2 of 40 mm Hg. The xenon/CT method was implemented by fitting the arterial xenon uptake with a double exponential function, by measuring the oxygen and carbon dioxide concentrations continuously during each breath and by taking into account the lung-to-brain transit time of xenon. The time of xenon inhalation was extended to 30 minutes to obtain more reliable estimates of CBF in white matter regions. The results indicate an overall correlation coefficient of 0.92 between the two methods and good numeric agreement.

Animals↗
PubMed1987

Brain tissue pH in severely head-injured patients: a report of three cases.

It is well established that low cerebrospinal fluid (CSF) pH and high CSF lactate concentration indicate the development of brain acidosis after severe human head injury. However, there is no direct evidence that tissue acidosis actually occurs. We measured brain extracellular pH (pHe) in three patients undergoing operation for the evacuation of acute subdural hematomas. A pH-sensitive polymer membrane electrode was inserted 500 micron into the cerebral cortex close to the damaged area. The pHe values obtained were correlated with ventricular CSF acid-based parameters and extension of the brain lesion. The CSF pH was higher than the pHe in all cases; the pHe was particularly low in areas of contusion or compression by mass lesion. The effect of focal brain tissue acidosis on clinical course after severe head injury is discussed.

Acid-Base Equilibrium↗
PubMed1987

Contribution of CSF and vascular factors to elevation of ICP in severely head-injured patients.

The authors studied the relative contribution of cerebrospinal fluid (CSF) and vascular parameters to the level of intracranial pressure (ICP) in 34 severely head-injured patients with a Glasgow Coma Scale score of less than 8. This was accomplished by first characterizing the temporal course of CSF formation and outflow resistance during the 5-day period postinjury. The CSF formation and outflow resistance were obtained from pressure responses to bolus addition and removal of fluid from an indwelling ventricular catheter. The vascular contribution to the level of ICP was assessed by withdrawing fluid at its rate of formation and observing the resultant change in equilibrium ICP level. It was found that, with the exception of patients with subarachnoid hemorrhage, CSF parameters accounted for approximately one-third of the ICP rise after severe head injury, and that a vascular mechanism may be the predominant factor in elevation of ICP.

Absorption↗
PubMed1987

A fluid percussion model of experimental brain injury in the rat.

Fluid percussion models produce brain injury by rapidly injecting fluid volumes into the cranial cavity. The authors have systematically examined the effects of varying magnitudes of fluid percussion injury in the rat on neurological, systemic physiological, and histopathological changes. Acute neurological experiments showed that fluid percussion injury in 53 rats produced either irreversible apnea and death or transient apnea (lasting 54 seconds or less) and reversible suppression of postural and nonpostural function (lasting 60 minutes or less). As the magnitude if injury increased, the mortality rate and the duration of suppression of somatomotor reflexes increased. Unlike other rat models in which concussive brain injury is produced by impact, convulsions were observed in only 13% of survivors. Transient apnea was probably not associated with a significant hypoxic insult to animals that survived. Ten rats that sustained a moderate magnitude of injury (2.9 atm) exhibited chronic locomotor deficits that persisted for 4 to 8 days. Systemic physiological experiments in 20 rats demonstrated that all levels of injury studied produced acute systemic hypertension, bradycardia, and increased plasma glucose levels. Hypertension with subsequent hypotension resulted from higher magnitudes of injury. The durations of hypertension and suppression of amplitude on electroencephalography were related to the magnitudes of injury. While low levels of injury produced no significant histopathological alterations, higher magnitudes produced subarachnoid and intraparenchymal hemorrhage and, with increasing survival, necrotic change and cavitation. These data demonstrate that fluid percussion injury in the rat reproduces many of the features of head injury observed in other models and species. Thus, this animal model could represent a useful experimental approach to studies of pathological changes similar to those seen in human head injury.

Animals↗
PubMed1987

Outcome after severe head injury. Relationship to mass lesions, diffuse injury, and ICP course in pediatric and adult patients.

A consecutive series of 330 severely head-injured patients was studied prospectively. All of the patients were treated with the same protocols by the same physicians and staff in the same intensive care unit. All of the patients had intracranial pressure (ICP) monitoring. Of the 330 patients, 100 were in the pediatric age group (0 to 19 years of age) and 230 were in the adult group (20 to 80 years of age). Statistical analyses were performed with regard to outcome, Glasgow Coma Scale (GCS) score, ICP course, and incidence of surgical lesions. The average emergency room GCS score as well as the 24-hour GCS score for each group was the same. The percentage of patients having ICP that was normal, increased but reducible, and increased but not reducible in each group was the same. The pediatric patients had a significantly higher percentage of good outcomes (43%) than the adult patients (28%) (p less than 0.01). They also had a significantly lower mortality rate (24%) than the adult patients (45%) (p less than 0.01). At 1 year following injury, 55% of pediatric patients had a good outcome compared to 21% of adults (p less than 0.001); this trend was evident at 3 months, with the same p value. Pediatric patients with normal ICP had a higher percentage of good outcomes (70%) than the adult patients with normal ICP (48%) (p less than 0.05). There was no significant difference in outcome in pediatric and adult patients with mass lesions or with increased ICP, regardless of whether or not the pressure was reducible. There was a much higher incidence of surgical mass lesions in adult patients (46%) than in pediatric patients (24%) (p less than 0.001).

Adolescent↗
PubMed1987

Pressure-volume index in head injury.

The authors studied intracranial pressure (ICP) and intracranial compliance as defined by the pressure-volume index (PVI) in 34 severely head-injured patients with a Glasgow Coma Scale score of 8 or less. The objective of the research was to determine if there was a correlation between the pressure-volume status and subsequent increase in ICP. The PVI and ICP measurements were obtained serially, and the temporal course of the pressure-volume status and ICP was determined during the 5-day period following injury. Aggressiveness of ICP was quantified by a therapy intensity level scale. A clear relationship between the PVI measured soon after injury and subsequent development of ICP emerged. Following mechanical trauma the PVI is reduced, and the degree of reduction and extent of biomechanical recovery are closely related to outcome and development of raised ICP.

Adolescent↗
PubMed1985

Failure of prophylactic barbiturate coma in the treatment of severe head injury.

In certain subgroups of severely head-injured patients, the mortality rate remains unacceptably high. The authors describe a randomized, controlled trial of prophylactic pentobarbital therapy in a group of these patients. Pentobarbital was started as soon as possible after the head injury, regardless of the intracranial pressure (ICP), and was continued for a prescribed period of time. The study included 53 consecutive head-injured patients over the age of 12 years, who had either an acute intradural hematoma (subdural and/or intracerebral, large enough to warrant surgical decompression), or no mass lesion but whose best motor response was abnormal flexion or extension. All patients in the study were randomly assigned to a control group (26 cases) or a pentobarbital-treated group (27 cases) once the diagnosis had been made and informed consent obtained. All patients were treated with the same protocol of aggressive resuscitation, prompt diagnosis and treatment of mass lesions, and intensive care, with close follow-up monitoring. The randomization was effective in producing a close match between the control and treated groups with respect to age, sex distribution, cause of injury, neurological status, intracranial lesions, prevalence of early systemic insults, midline shift, and initial ICP. Outcome was essentially the same in each group. There was no difference between groups in the incidence of elevated ICP, the duration of ICP elevation, or the response of ICP elevations to treatment. Arterial hypotension occurred in 14 patients (54%) in the treated group and only two patients (7%) in the untreated group. Based on these data the authors cannot recommend the prophylactic use of pentobarbital coma in the treatment of patients with severe head injury. They also believe that its use is accompanied by significant side effects which can potentially worsen the condition of a patient with severe head injury.

Adolescent↗
PubMed1985

Biomechanical and hydrodynamic characterization of the hydrocephalic infant.

The pressure-volume index (PVI) technique of bolus manipulation of cerebrospinal fluid (CSF) was used to measure neural axis volume-buffering capacity and resistance to the absorption of CSF in 16 hydrocephalic infants prior to shunting. The mean steady-state intracranial pressure (ICP) was 11.7 +/- 5.7 mm Hg (+/- standard deviation (SD], representing a modest elevation of ICP in infants. The mean measured PVI was 28.1 +/- 1.5 ml (+/- standard error of the mean (SEM] compared to the predicted normal level for these infants of 12.1 +/- 2.7 ml (+/- SD) (p less than 0.001). This resulted from an enhanced volume storage capacity in the hydrocephalic infants. The PVI was not related to ventricular size in these hydrocephalic infants. Although absorption of the additional bolus of fluid did not occur at steady-state ICP, it was readily absorbed once ICP was raised above a mean threshold pressure of 16.0 +/- 5.0 mm Hg (+/- SD) in 13 of the 16 infants. Above this pressure, the mean CSF absorption resistance was 7.2 +/- 1.3 mm Hg/ml/min (+/- SEM) which is twice the normal values as measured by the bolus injection technique. The biomechanical profile of infantile hydrocephalus described in this study indicates that two factors are required for progression of ventricular volume. While an absorptive defect may initiate the hydrocephalic process, progressive volume storage requires an alteration in the mechanical properties of the intracranial compartment.

Absorption↗
PubMed1984

Mechanism of pseudotumor in Guillain-Barré syndrome.

A patient with pseudotumor cerebri and Guillain-Barré syndrome was studied with serial measurements of pressure-volume index, CSF outflow resistance (Ro), and CSF production rate. The results were comparable to findings in previous cases of idiopathic pseudotumor. Although Ro was elevated and progressively diminished as the pseudotumor syndrome improved, the extent of elevation in Ro was inadequate to account for raised CSF pressure. These results suggest an alternative explanation for pseudotumor based on raised effective venous pressures at points of CSF outflow that are passively reflected in raised CSF pressure. A parallel rise in vascular and CSF pressure may also explain why patients with pseudotumor tolerate such high intracranial pressures.

Adult↗
PubMed1983

Cortical artery pressure in normotensive and hypertensive aneurysm patients.

Cortical artery pressure (CAP) and systemic pressure (SP) were measured in eight normotensive and six hypertensive patients with anterior circulation aneurysms. In the hypertensive patients significant gradients developed between CAP and SP as these pressures were lowered. The relationship between CAP and SP was expressed by the best-fit equation CAP = 1.02 SP -9.27 in the normotensive patients and by CAP = 1.54 SP -65.60 in the hypertensive patients. In the latter, the cycle of decreasing and increasing pressures formed a hysteresis loop suggesting prolonged cortical vasoconstriction despite recovery of systemic pressure. Selective pressure measurements in the distal (D) and proximal (P) segments of the cortical arteries were also obtained. The D/P ratio describes the relative contribution of the collateral circulation to cortical artery pressure. In normotensive patients, the D/P ratio was maintained down to an SP of 48 mm Hg. In hypertensive patients this ratio decreased with lowered SP, and a critical closing pressure of 40 mm Hg was predicted for the distal circulation. These studies described the limited capacity of the cortical circulation to maintain perfusion pressure in hypertensive patients. These responses should be considered when assessing the risks associated with such procedures as carotid ligation or hypotensive anesthesia.

Adult↗
PubMed1983

[Experimental studies of brain edema by infusion edema model-- biophysical changes of edema fluid in white matter of the brain].

The important changes in the area of brain edema are the accumulation and the spreading of edema fluid through the extracellular space in white matter of the brain. In this study, we described the changes of tissue resistance and compliance as the increment of accumulated volume of fluid produced by the slow infusion of normal saline or plasma into white matter of the cat brain. Adult cats (22) were tracheotomized, paralyzed with Galamine (2 mg/kg) and maintained normocapnic, normotensive under nitrous oxide anesthesia. Normal saline or plasma of their own was infused slowly through 25 gauge needle implanted into left frontal white matter by stereotaxic technique. A low compliance pressure gauge transducer was connected to the line for the measurement of inflow pressure. Tissue resistance and compliance for the movement of infused fluid into white matter were delivered from the changes of inflow pressure by adding the 3 microlitter per minutes on top of the resting steady state pressure. Values of tissue resistance in normal white matter, determined at the accumulated volume of 0.05 ml was very high (normal saline infusion: 6.42 +/- 0.61 X 10(3) mmHg/ml/min, plasma infusion: 5.47 +/- 1.43 X 10(3) mmHg/ml/min). But it decreased rapidly followed by more gradual decrease of tissue resistance became more edematous, reaching a plateau of one sixth of initial value at an infused volume of 0.5 ml. Tissue compliance changed by an opposite pattern of rapid increase and plateau to the changes of tissue resistance.

Animals↗
PubMed1983

[Study of brain edema by an infusion edema Model--the method and characteristics of the model].

In this report, we have described the way of making the infusion edema model, physiological changes of various parameters during this procedure, distribution of water content in white and gray matter and the light and electron microscopic findings of this edema model, for the further understanding of vasogenic edema of the brain. To make the infusion edema model, 25-G needle was stereotaxically inserted into the left frontal white matter of the cat brain. Through the polyethylene catheter with three way stop cock, this catheter was connected to the pressure transducer and slow infusion pump. By this way, we can monitor the pressure of infusing fluid into the white matter. Normal saline was infused with initial rate of 0.75 microliter/min for the first 2 hours. The inflow rate was increased to 1.5 microliter/min for the next one hour, and then changed to 3.0 microliters/min for maintenance inflow rate. The total amount of infused volume was 0.5 ml in this study. During making the infusion edema model, blood pressure and PaCO2 changed little. Intracranial pressure slightly increased from 5.8 to 15.1 mmHg. Pressure volume index (PVI) changed from 0.74 to 0.64, suggesting the changes of intracranial compliance. The water content measured by specific gravimetric technique showed nearly the same water contents and distribution of edema fluid in the white matter of the cat as in the cryogenic injury model. Pathological findings of this infusion edema model demonstrated that the infused liquid was accumulated in the extracellular space of white matter without damaging the tight junction, and endothelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

An improved gravimetric measure of cerebral edema.

Significant errors are introduced into the measurement of brain tissue water by the specific gravity technique when the edema fluid contains protein. Protein adds to the tissue solids, increasing the density of the tissue, and masks the proportional increase of brain water. Existing equations relating measured specific gravity and tissue water are not applicable, and a new formula was developed that compensates for the protein component of edema and reduces the experimental error. The new method was applied to the measurement of tissue water in cat brain made edematous by direct infusion of fluids of known composition and volume to test the theory. This technique for improving the gravimetric assessment of brain edema is presented.

Animals↗
PubMed1982

Clinical applications of the pressure-volume index in treatment of pediatric head injuries.

The pressure-volume index (PVI) technique of assessing neural axis pressure-volume relationships was used as an adjunct to managing 22 children with severe head injuries and a Glasgow Coma Scale score of 8 or less. Ventricular cannulation was used to continuously monitor intracranial pressure (ICP). Actual PVI was measured by bolus injection of fluid and compared with predicted values determined from head circumference and spinal axis length in each patient. In 55% of the children, ICP was below 20 mm Hg at initial monitoring. During the course of monitoring, 86% of the children had ICP's exceeding 20 mm Hg. Reduced PVI (less than 80% of predicted normal) proved to be an accurate indicator of impending intracranial hypertension. The PVI proved to be a useful test for assessing the response to therapies for lowering ICP. This study demonstrates that reduced neural axis compliance accompanies intracranial hypertension following severe head injury in children, and that treatment of reduced neural axis compliance may prevent refractory intracranial hypertension.

Adolescent↗
PubMed1981

Microgravimetric analysis of human brain tissue: correlation with computerized tomography scanning.

Microgravimetric technique was used to measure the water content of tumors and adjacent brain. Multiple 1-cu mm samples were obtained from 17 patients with neurosurgical lesions. The site of each sample was located on the appropriate computerized tomography (CT) slice, and the water content correlated with the CT attenuation coefficient. The water content of peritumor white matter in 11 patients with glioblastomas was 5% to 8% H2O/gm tissue greater than the water content of white matter measured in three normal control individuals. These areas corresponded to low CT attenuation coefficients (8 to 15 EMI units). There was no statistically significant differences between the water content of tumors and adjacent white matter, even though the CT attenuation coefficient of the tumor was often at higher value. Low CT attenuation coefficient areas surrounding meningioma, metastasis, and lymphoma always correlated with elevated water content. The greatest water content (84.7% H2O/gm tissue) was found in the white matter surrounding an arteriovenous malformation. There was no correlation between the CT attenuation coefficient of this tissue and the water content in the arteriovenous malformation. This study shows that areas of low CT attenuation coefficient may correlate with measurements of the water content of tissue, but that increased water content may exist without demonstrable changes in the CT attenuation coefficient.

Adenoma↗
PubMed1980

Characterization of clinical CSF dynamics and neural axis compliance using the pressure-volume index: I. The normal pressure-volume index.

The pressure-volume index (PVI) technique was used to measure neural axis compliance, cerebrospinal fluid (CSF) formation (If), and CSF absorption (Ro) in 23 children and 7 adults, all free from intracranial masses, who were undergoing diagnostic or therapeutic procedures. Using bolus manipulation of CSF, If was 0.36 +/- 0.08 ml/min and Ro was 2.8 +/- 0.8 mm Hg/ml/min in both adults and children. PVI, as a measure of neural axis compliance or volume buffering capacity, was 25.9 +/- 3.7 ml for the adults. Measured PVI in the children varied from 8.2 to 30.1 ml but correlated well (r = 0.93) with predicted PVI based on estimates of intracranial and spinal volumes obtained from external measurements. This study provides normal reference data in humans for assessing CSF hydrodynamics and neural axis compliance using the PVI technique in pathological settings.

Adolescent↗