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Biomedical subjects

U Pontén

Publications and source records attributed to U Pontén.

At least 19 recordsLinked to original sources
PubMed1997

MR imaging of experimental subdural bleeding. Correlates of brain deformation and tissue water content, and changes in vital physiological parameters.

PURPOSE: To evaluate morphological and physiological changes during acute lethal subdural bleeding in 2 models of anaesthetized dogs. MATERIAL AND METHODS: In model I, blood from the aorta was led into a collapsed subdural rubber balloon while in model II, the blood was directed into the subdural compartment over the left cerebral frontoparietal lobe. Eight vital physiological parameters were continuously registered. MR imaging visualized the compression and displacement of cerebral tissue, and assessed the dynamic changes in cerebral tissue water. RESULTS: In model I, tissue herniation and compression of cerebral ventricles led to death at a haematoma volume corresponding to 8% of the intracranial volume. In model II, the extravasated blood progressed infratentorially and into the spinal sac with a volume that was 3 times larger than that of the lethal haematoma. Tissue water increased almost linearly during bleeding in both models. CONCLUSION: The high level of mortality after acute subdural haematoma is caused by a reduction in intracranial volume tolerance with a critical decrease in cerebral perfusion pressure, resulting in a fatal cerebral ischaemia.

Animals↗
PubMed1993

Changes in intracranial morphology, regional cerebral water content and vital physiological variables during epidural bleeding. An experimental MR study in dogs.

Epidural bleeding was produced in 8 anaesthetised and heparinised dogs by an artificial system. Changes in vital physiological variables were related to intracranial shifts and tissue water content assessed with MR imaging. Six animals survived while 2 succumbed. In the surviving animals intracranial shifts and compressions remained unchanged from an early stage. The cerebral perfusion pressure was reduced from between 80 and 110 mm Hg to between 40 and 60 mm Hg. Some increase in supratentorial white matter tissue water was observed. In the lethal experiments cerebral perfusion pressure fell to less than 40 mm Hg. Moreover, secondary delayed anatomical changes were seen including hydrocephalus. Increase in cerebral tissue water was more intense and widespread than in the survivors. These findings indicate that the outcome of epidural bleeding is related to cerebral perfusion pressure with secondary deterioration resulting from additional volume loading from increased tissue water and hydrocephalus.

Animals↗
PubMed1993

Progressive brain compression. Changes in vital physiological variables, correlated with brain tissue water content and brain tissue displacement. Experimental MR imaging in dogs.

Continuous recording of vital physiological variables and sequential MR imaging were performed simultaneously during continuous expansion of an epidural rubber balloon over the left hemisphere in anaesthetised dogs. Balloon expansion led to a progressive and slightly nonlinear rise in intracranial CSF pressures and a fall in local perfusion pressures. Changes in systemic arterial pressure, pulse rate, and respiration rate usually appeared at a balloon volume of 4% to 5% of the intracranial volume (reaction volume), together with a marked transtentorial pressure gradient and MR imaging changes consistent with tentorial herniation. Respiratory arrest occurred at a balloon volume of approximately 10% of the intracranial volume (apnoea volume), which was associated with occlusion of the cisterna magna, consistent with some degree of foramen magnum herniation. Increase in tissue water was observed beginning at approximately the reaction volume, presumably due to ischaemic oedema, due to the fall in perfusion pressures.

Animals↗
PubMed1990

Trauma-induced increase of extracellular ascorbate in rat cerebral cortex.

Extracellular (EC) ascorbate concentrations were measured in microdialysates from the cerebral cortex in rats subjected to cortical compression-contusion trauma. The trauma induced a transient, dramatic increase in EC ascorbate compared to the basal level before the insult and compared to control animals. The data support the presence of a releasable intracellular pool of ascorbate in the neocortex. The possibility that ascorbate may influence traumatic brain damage by its proposed neuromodulatory property and/or by its ability to induce lipid peroxidation is considered.

Animals↗
PubMed1990

Neurometabolic monitoring of the ischaemic human brain using microdialysis.

Recent animal research has provided evidence that brain ischaemia is associated with a shift of energy related metabolites (lactate, adenosine, inosine, and hypoxanthine) and several transmitters from the intracellular to the extracellular fluid (ECF). These chemical changes of the ECF reflect the energy crisis of the ischaemic tissue. We have proposed that measurement of these metabolites in the ECF using microdialysis may be a useful technique for detection of secondary ischaemia in neurosurgical intensive care patients. As a first step in the evaluation of such a possible clinical application of microdialysis the aim of this study was to measure energy related metabolites and amino acid transmitters during cerebral ischaemia in man. Microdialysis probes were inserted in tumour-free cortical tissue in the frontal lobe in patients undergoing frontal lobe resection as a treatment for brain tumours. Dialysis samples were collected in 10 minutes fractions before and during frontal lobe resection, thus serving as a simulated ischaemia model. The resection procedure was associated with markedly elevated levels of the energy related metabolites as well as transmitter amino acids. The tissue surrounding the probes was examined histologically, and the degree of oedema was estimated from CT scans. In two of the patients the tissue hosting the probes was oedematous. These patients had markedly higher basal levels of lactate. The main conclusions were (1) that the results support the clinical potential of microdialysis, (2) that lactate may be a sensitive indicator of the metabolic disturbances associated with brain oedema, and (3) that frontal lobe resection may be a useful human brain ischaemia model.

Amino Acids↗
PubMed1990

Rebound of ICP after brain compression. An MRI study in dogs.

The rebound of intracranial pressure (ICP) occurring after decompression of an intracranial mass lesion was studied in an epidural balloon compression model. Intracranial morphology and brain tissue water content were assessed with magnetic resonance imaging (MRI). Fast and slow components of the transverse relaxation time (T2) were used as indicators of brain oedema development. During balloon compression a progressive prolongation of both the fast and the slow T2 components took place. Following deflation of the balloon both components increased rapidly, particularly the slow-T2. The MR scans displayed progressive occlusion of the aqueduct, and obliteration of the ambient and pontine cisterns. The changes in morphology and in water content after decompression had largely the same time course as the development of the rebound of ICP. In contrast, no changes in morphology and tissue water content occurred after hydrostatic brain compression achieved by subarachnoid fluid infusion. The findings suggest that the intracranial pressure rebound is caused by cerebral oedema accumulated during and particularly in the recirculation phase after an ischaemic injury of adequate intensity and adequate duration.

Animals↗
PubMed1990

Changes in cortical extracellular levels of energy-related metabolites and amino acids following concussive brain injury in rats.

The aim of this study was to measure extracellular chemical changes in the cerebral cortex in response to compression contusion trauma in rats. Energy-related metabolites (i.e., lactate, pyruvate, adenosine, inosine, and hypoxanthine) and amino acids were harvested from the extracellular fluid (ECF) using microdialysis and analyzed by high-performance liquid chromatography. The measurements were performed in cortical tissue, where neuronal injury occurs in this model. The severity of the trauma was varied by using different depths of impact: mild trauma, 1.5 mm; severe trauma, 2.5 mm. The trauma induced a dramatic increase in the ECF levels of energy-related metabolites that was conditioned by the severity of the insult. The ECF level of taurine, glutamate, aspartate, and gamma-aminobutyric acid (GABA) also rose markedly, while other amino acids did not change significantly. The results suggest that the trauma induced a transient, profound focal disturbance of energy metabolism in the cortical tissue, probably as a result of mechanically induced disruption of ion homeostasis and reduced blood flow in combination. The data support the potential role of glutamate and aspartate as mediators of traumatic brain injury. However, the concomitantly released adenosine, GABA, and taurine may be protective and ameliorate excitotoxicity. In analogy with the reported cumulative damaging effects of repeated ischemic insults, the observed ECF changes may help explain the vulnerability of traumatized brain tissue to secondary ischemia.

Adenosine↗
PubMed1990

Observations on intracranial dynamics during respiratory physiotherapy in unconscious neurosurgical patients.

The effects of airway care procedures on intracranial dynamics were studied in 12 patients with intracranial lesions. The patients had controlled ventilation and were treated according to a standardized protocol with endotracheal suction and bag squeezing. Intracranial, arterial blood and airway pressures were recorded and cerebral perfusion pressure was calculated. Both methods used for airway care elicited marked changes in intracranial, arterial blood and cerebral perfusion pressures during the treatment session. However, within 1 min after termination of the procedure the different pressure levels returned to pretreatment values except for the intracranial and arterial blood pressure in endotracheal suction. Cerebral perfusion pressure, calculated at different time intervals: 1, 5 and 15 min after the treatment, showed only minor deviations from values before treatment. The mean values varied from 70 to 90 mmHg (9.3 to 12.0 kPa) and the lower limit of the 99% confidence interval of the means was never below 55 mmHg (7.3 kPa). At times complementary administration of sedatives during endotracheal suction was found to induce a drop in arterial blood pressure and cerebral perfusion pressure. In conclusion, patients with severe brain injuries treated on mechanical ventilation are exposed to equal risks when using bag squeezing for airway care as when using traditional endotracheal suction. Regardless of the method used, patients should be adequately sedated before starting the procedure in order to reduce the risk of adverse effects.

Adolescent↗
PubMed1987

Positron emission tomography: an animal model of spinal distribution of drugs after intrathecal administration.

An animal model has been developed in the Rhesus monkey for noninvasive monitoring of CSF transport of drugs by external detectors i.e. positron emission tomography. The model compromises the cannulation of the subarachnoid space (with a spinal needle), and has been used without any damage to the monkey. With the method it was shown that injection rate had a major influence on the transport rate of 68GaCl3 in the CSF. Injection of 0.5 ml over 60 sec gave the highest radioactivity near the injection site, whereas an injection rate of this volume over 10 sec resulted in high radioactivity more rostrally shortly after injection. This method have been of value for the determination of drug kinetics after spinal administration.

Animals↗
PubMed1986

Posttraumatic monitoring of intracranial pressure.

ICP-monitoring is a good guide for surgical and nonsurgical treatment of unconscious patients with severe traumatic brain injuries. Intraventricular and extradural recordings usually are reliable but have systematic differences. Subdural screws tend to underestimate ICP greater than 20 mm Hg. High ICP correlates with poor outcome. Plateau-waves induced by external stimulation indicate a tight brain situation requiring treatment. In critical situations monitoring of the cerebral perfusion pressure is recommended. ICP recordings can never substitute personal supervision of the patient.

Brain Injuries↗
PubMed1986

Magnetic resonance imaging of brain tissue displacement and brain tissue water contents during progressive brain compression. An experimental study in dogs.

Continuous recording of vital physiologic parameters and magnetic resonance imaging (MRI) was performed during continuous expansion of extradural rubber balloons in spontaneously ventilated anesthetized dogs. Initial physiologic changes appeared when the pontine cistern was compressed while respiratory arrest was regularly paralleled by marked tentorial and tonsillar herniation. Local increase in brain tissue water progressed during brain compression and was most marked in white matter of the brain. This was related to the regional decrease in cerebral perfusion pressure. The correlation between the morphologic and physiologic course of events during brain compression has a predictive value.

Animals↗
PubMed1986

Magnetic resonance imaging of water intoxication. An experimental study in dogs.

Sequential magnetic resonance imaging (MRI) was performed to correlate signs of herniation and increase in local brain tissue water content with continuous changes in vital physiologic parameters during progressive water intoxication in anaesthetized dogs. The intracranial pressure increase ultimately resulted in respiratory and cardiac arrest. MRI concomitantly showed an increase in local brain water content starting and dominating in the cerebral cortex but progressing to all parts of the central nervous system. The late appearance of transtentorial pressure gradients and of brain herniation suggests that development of cerebral edema occurs in at least two stages, an intracellular osmotic edema appearing first, being followed by an ischemic edema related to a progressive decrease in local perfusion pressure.

Animals↗
PubMed1986

Magnetic resonance imaging of cerebral compression and local brain tissue water content during continuous extradural bleeding. An experimental study in dogs.

Continuous recording of vital physiologic parameters and magnetic resonance imaging were performed during progressive extradural bleeding in spontaneously ventilated anesthetized dogs. The volume of the bleeding could exceed the intracranial volume by 500 per cent due to the formation of an extradural arteriovenous shunt. The rate of hematoma growth was dependent on the area of stripped dura. Midline shift, herniation and lateral ventricle compression occurred early, corresponding to changes in vital parameters. Local brain water increased non-linearly with white matter preceding gray matter. Water increase started first in the ipsilateral hemisphere followed by the contralateral hemisphere, brain stem and cerebellum. The correlation between local tissue water increase and local perfusion pressure supports the notion of an ischemic brain edema being formed during an extradural bleeding.

Animals↗