Search PubMed⌕ Search

Biomedical subjects

M R Gaab

Publications and source records attributed to M R Gaab.

At least 73 records · Page 4Linked to original sources
PubMed1990

Brain edema, autoregulation, and calcium antagonism. An experimental study with nimodipine.

We investigated the effects of the calcium entry blocker nimodipine on cerebral autoregulation, BBB, and vasogenic edema in animal experiments. In the first series of rats, ICBF was measured with H2 clearance using a balanced multiwire surface electrode. Variations in blood pressure (SAP), which was measured via femoral catheter, were induced by infusion of norfenefrine (pressure increase) and by hemorrhage (pressure decrease). The effect of SAP on the cerebral microcirculation was evaluated. In control animals receiving nimodipine, a typical autoregulation plateau was found. In rats treated with nimodipine infusion (12-14 micrograms/kg/min), 1CBF was considerably elevated at all blood pressure levels above 50 mm Hg, and in the steep 1CBF/SAP correlation, the autoregulation plateau was almost suspended. In a second series of randomized rats, the effect of nimodipine on BBB was investigated after Evans blue infusion. When a SAP of 180 mm Hg systolic was maintained for 6 min, a diffuse Evans blue staining was seen in 70% of the nimodipine animals (break-through of BBB). In the third series of rats, the effect of nimodipine on cold injury edema was investigated. Nimodipine (1 mg i.p.) considerably decreased the SAP; Edema formation measured by water and Na+ content 24 hr after trauma was then reduced. However, if the decrease in SAP was in part prevented by norfenefrine application, the rats receiving nimodipine developed significantly more edema. Brain water and sodium contents were markedly increased in both hemispheres. The results indicate an interference of nimodipine with cerebral autoregulation, and a BBB disruption may occur at lower SAP. If the BBB is impaired, nimodipine may considerably intensify edema formation. Nimodipine and similar calcium entry blockers should therefore only be used with caution in acute brain damage.

Animals↗
PubMed1990

Oxygen tension, oxygen metabolism, and microcirculation in vasogenic brain edema.

In cold brain injury edema, cerebral pO2, oxygen metabolism, and local CBF were investigated. In randomized groups of 10 rats each, pO2 was measured by polarography using a balanced multiwire surface electrode on the parietal cortex after trepanation. lCMRO2 was approximated by oxygen disappearance rate after sudden complete cerebral circulatory arrest (cervical cuff inflation). Using integrated platinum electrodes, the local CBF was measured by H2 clearance. All data were evaluated on-line by computer. In normal animals we found a regular, normally distributed pO2 histogram in barbiturate and in ketamine anesthesia. Oxygen consumption and local CBF, however, are significantly higher in ketamine narcosis. The local CBF is thereby coupled with metabolic requirements: The more oxygen consumed, the higher the local pO2. In animals 24 hr after cold brain injury, this metabolic coupling is disturbed: In the perifocal edema the pO2 histogram is flat and broad with different mean and median, but with a shifting toward higher oxygen values. Oxygen consumption is reduced; the local CBF, however, is significantly increased with large variations. Also over the contralateral, noninjured hemisphere a decrease in CMRO2 and an increase in pO2 are observed (diachisis). These disturbances with a maximum at 24 hr after injury show a recovery after 72 hr. After infusion of the calcium entry blocker nimodipine a normalization in pO2 distribution was found, combined with an increase in CMRO2. We assume a primary disturbance of oxidative glucose metabolism with uncoupling of metabolic flow control; local CBF and O2 availability are not primarily impaired. Ca2+ may be a main factor in this pathophysiology.

Animals↗
PubMed1989

[Ultra-high, short-term dexamethasone therapy in craniocerebral trauma. Rationale and design of a multicenter study].

In spite of 20 years of discussion the value of corticosteroids in the therapy of head injury still remains controversial. Most animal experiments show an improvement of edema parameters with dexamethasone given immediately after trauma; pharmacological data suggest a further increased "ultrahigh" dosage compared to so-called "high" doses up to now. Simultaneously, the treatment duration might be reduced to 48-72 h after injury. The clinical studies available are not satisfying due to low numbers of patients, insufficient trauma classification and restriction to most severe brain injuries, and do not allow a definite answer. Little side effects and risks, however, were found with clinical steroid trials so far. We therefore perform a new multicenter trial with dexamethasone after head injury, whose design is presented: A sufficient number of patients (n greater than = 240) is recruited according to a priori defined criteria for statistical evaluation. Treatment starts with ultrahigh dosage of 500 mg dexamethasone (Fortecortin) initially not later than 3 h after injury, the treatment duration is limited to 51 h. The selection of patients is based on restrictive criteria of inclusion and exclusion, the age of patients ranges from 15 to 55 years. For maximal statistical separation and for reduction of disturbing factors the representativity of trauma patients is intentionally neglected.

Adolescent↗
PubMed1989

Laser-assisted microsurgical extirpation of a brain stem cavernoma: case report.

A 43-year-old woman presented with progressing signs of a space-occupying brain stem lesion. A computed tomographic scan revealed a hyperdense process located in the pons. Magnetic resonance imaging confirmed the lesion, which had a reticulated core of increased and decreased signal intensity. Vertebral angiography did not show any vascular supply of the process. The patient was operated upon in the lateral park bench position. The lesion, being located close to the exit zone of the trigeminal nerve, could be removed totally with incision of the brain stem and atraumatic vaporization of the tumor tissue with the CO2 laser. Despite the fact that the histopathological examination revealed a cavernous angioma the application of laser energy was judged to be extremely valuable for the surgical procedure. It was concluded that with proper selection of application mode and wattage the CO2 laser may be used for extirpation of vascularized lesions also especially when situated in or close to deep lying vital structures of the brain.

Adult↗
PubMed1988

The influence of nimodipine on cerebral blood flow autoregulation and blood-brain barrier.

Twenty anesthetized rats were randomly assigned to a nimodipine-treated group or a control group of 10 rats each. Local cerebral blood flow (lCBF) was measured by means of a surface electrode using the hydrogen clearance technique. Systemic arterial pressure (SAP) was varied with administration of norfenefrine or by hemorrhage in order to obtain SAP/cerebral blood flow (CBF) curves under different conditions. In the control group, a typical autoregulation curve was obtained with an lCBF plateau between 70 and 120 mm Hg SAP. The nimodipine-treated animals, however, showed only a slight diminution in the slope of the curve but no real plateau, indicating impairment of CBF autoregulation. In another series, 20 anesthetized rats were randomly assigned to a treatment group or a control group of 10 animals each. Intravenous Evans blue dye was used as a tracer for blood-brain barrier (BBB) function. In both groups, SAP was raised to a level of 180 mm Hg with administration of norfenefrine for 6 minutes. Extravasation of significantly more Evans blue dye was observed in the nimodipine group than in the control group, indicating impairment of the BBB. It is concluded that nimodipine may impair CBF autoregulation, allowing damage to the BBB under hypertensive conditions.

Animals↗
PubMed1987

Stable-xenon-CT: effects of xenon inhalation on EEG and cardio-respiratory parameters in the human.

The effects of inhalation of a 33% Xenon-O2 mixture over a period of 5 minutes on EEG and cardio-respiratory parameters were studied in 18 human volunteers. This dosage is similar to that used clinically in Xenon-CT studies. In 4 cases no EEG power change was observed during the study. In the 14 other subjects EEG variations were seen. The most prominent change was an increase in beta EEG power. No change was observed in theta and delta EEG power. The findings seem to correlate with the early induction (excitation) phase of an anaesthetic. Hyperventilation was observed before the study and increased during the Xenon inhalation. Blood pressure remained stable while the heart rate tended to decrease a little. All these changes disappeared rapidly following the termination of the Xenon inhalation. The effects are minimal and should not reduce the clinical value of CBF measurement using the Xenon-CT method.

Administration, Inhalation↗
PubMed1987

EEG changes during five minutes of inhalation of a 33% xenon-O2 mixture.

The effects on the EEG of inhalation of a 33% Xenon O2 mixture over a period of 5 minutes were studied in 18 human volunteers. This dosage is similar to that used in xenon CT studies. In 4 subjects no EEG changes were observed during the study. In the 14 other subjects, EEG variations were detected, the most prominent of which was an increase in beta power. No change was observed in theta and delta power. These findings seem to support an early induction (excitation) phase of anaesthetics. All changes disappeared rapidly following the termination of xenon inhalation. The effects reported are minimal and should not impair the clinical value of CBF measurements using the xenon CT method.

Administration, Inhalation↗
PubMed1987

[Amino acid uptake in brain tumors using positron emission tomography as an indicator for evaluating metabolic activity and malignancy].

Diagnosis and post-therapeutic follow-up of tumour patients necessitates morphological and particularly functional imaging methods. For the latter approach positron emission tomography has proven a valid tool for the measurement of perfusion, of energy consumption parameters such as oxygen extraction, glucose metabolism and amino acid uptake. However, neither perfusion nor energy consumption parameters have yielded unambiguous information on the clinical status of various tumours in respect of their malignancy and their growth status. It is shown in this paper that amino acid uptake seems to be a valid measure for the functional activity of tumour tissue for a broad range of neoplasms. The uptake of 11C-L-Methionine was measured in 33 patients having various brain tumours, and was compared with 6 patients who had an infarction, and with 8 patients suffering from arachnoidal cysts. The amino acid uptake correlated well with the histological grading of the tumours and the clinical status of the patient. The uptake was well differentiated against metabolically inactive lesions. Parallel investigations on the uptake mechanisms of amino acids in an animal model have shown that transport phenomena regulate the uptake rather than protein synthesis rates. However, protein synthesis may nevertheless exercise a control function on the transport process.

Brain Neoplasms↗
PubMed1987

[Local treatment of infections in neurosurgery with gentamicin PMMA chains (Septopal)].

Treatment of infections after neurosurgical operations at the head and vertebral column is lengthy and stressful for the patient. Hence, we implanted--as has been routine in septic bone surgery for a long time--carriers of antibiotics for local antibiotic therapy in the form of Septopal chains. The course of treatment and the results obtained in 16 patients are presented. In all patients the wound cavities were filled with Septopal chains after débridement. In the course of 6-12 days the chains projecting from the skin by a stab incision were extracted sphere by sphere. The treated wound healed immediately in 14 patients; healing was delayed in 2 patients, but there were no complications. Since the use of Septopal chains results in local gentamicin levels which are so high that the conventional classification of germs into gentamicin-sensitive/gentamicin-resistant is of minor importance, the wounds healed without complications even in those patients where the germs had been classified as "resistant" in the routine antibiogram. Thus, Septopal offers the advantage of primary wound closure without secondary contamination or scatter into the environment (intensive-care ward!), shorter treatment time, reduced stress for the patient and more rapid mobilisation.

Adolescent↗
PubMed1987

[Lumbar epidural hematoma and spinal abscess following peridural anesthesia].

Epidural application of local anesthetics or opiates is commonly used for treatment of severe pain or arterial obstruction. We discuss two cases of complications following peridural anesthesia. As an acute complication, a lumbar epidural hematoma developed hours after placement of the catheter and caused sciatic pain and nearly complete paraplegia. The hemorrhage might have been promoted by heparinization. After decompressive hemilaminectomy the patient recovered but was disabled by a persistent paresis. The second patient suffered from renal failure, arterial obstruction, and phantom limb pain. A peridural catheter was kept in place for 6 weeks. Five months later the patient developed severe sciatica. Spinal computed tomography showed compression of the cauda at the L4/5 level (Fig.4) caused by an abscess that was opened and drained. After insertion of a gentamicin - PMMA - chain (Septopal), the wound healed primarily but the patient suffered from persistent pain. The incidence of vessel puncture after insertion of a peridural catheter is about 1%-10%. The risk of hemorrhage, perforation of the dura, and nerve root irritation is increased in scoliotic or elderly patients with a narrow spinal canal. Persistent pain after removal of the catheter is the most important sign. Although paraplegias following peridural catheterization can occur without anticoagulants, even low-dose heparinization is potentially dangerous. The risk of infectious complications after long-term peridural catheterization may be up to 20%. Hematogenous metastatic infection is more common in patients with malignancies or multiple risk factors than continuous immigration of bacteria. Epidural hematomas and spinal abscesses can cause disability and persistent neurological deficit in spite of aggressive surgical and antibiotic therapy.

Abscess↗
PubMed1986

Evaluation of ICP by computerized bedside monitoring: methods and clinical significance.

The recording of intracranial pressure (ICP) is increasingly performed routinely in the hospital setting. Documentation of the pressure course over long time intervals has been performed, until recently, with paper tracings. Objective means of evaluation are lacking, however, for the quantification of pressure-dynamics. We have therefore tested several different statistical and graphical methods of evaluation to improve the efficacy of ICP monitoring. Calculations were done on epidural and transfontanel pressure monitoring. Analyses were performed both on-line and off-line. Graphical methods used included time-plot graphs, histograms, correlations analysis and pulse-amplitude/mean pressure diagrams (PA/Pm); statistical values calculated included mean, variance, standard deviation, coefficient of skewness, coefficient of kurtosis, coefficient of variation and the range. Data obtained from patients with normal intracranial pressure, CSF circulatory disturbances, head injuries, cerebrovascular disorders, and other illnesses allowed for the clear establishment of normal ICP limits, the rapid recognition of pathological pressure changes, the evaluation of therapeutic effects, and also an improvement in the comparability between new measurements and previous recordings. Simultaneously performed on-line evaluation of ICP recordings proved to be a practical means of monitoring both baseline values and therapeutic effectiveness.

Adolescent↗
PubMed1986

A technique for repeated sampling of pure cerebrospinal fluid from the conscious rabbit.

For the study of drug pharmacokinetics' a reliable method for repeated sampling of uncontaminated cerebrospinal fluid (CSF) from a conscious rabbit was established. The subdural space was punctured between a spinous processes of the lumbar vertebrae. A catheter was inserted through a cannula and pushed up to the region of the cisterna magna. After removing the cannula, the distal end of the catheter was sealed and placed subcutaneously until the onset of the experiments. Ten days after the insertion, samples of clear and colorless CSF up to 1 ml could be withdrawn.

Animals↗
PubMed1985

[Effect of the Ca antagonist nimodipine on global and regional cerebrovascular circulation].

The effects of Nimodipine on the global and regional cerebral blood flow were studied in 42 patients with cerebrovascular disorders. In 25 patients with focal deficits such as transitory ischemic attack (TIA), prolonged reversible ischemic neurological deficit (PRIND), and minor stroke due to arteriosclerosis, and in eleven patients with cerebral vasospasm after subarachnoid hemorrhage, the cerebral blood flow was measured by 133Xenon inhalation technique 60 min after oral administration of 40, 60, or 80 mg Nimodipine. In 6 patients with vasospasm the effects of Nimodipine i.v. were examined. The result in twelve patients with minor stroke who were only given placebo (lactose; "test-retest") was identical regional (rCBF) and global (CBF) cerebral blood flow before and 60 min after; placebo, blood pressure, and arterial pCO2 remained constant as well. After Nimodipine, however, the CBF increases, the increase after vasospasm being significant when taking the pCO2 in the Wilcoxon test into account. The rCBF increases much more in the regions with low perfusion rates than in well-perfused areas. This is also observed in the patients with TIA, PRIND, or minor stroke, most clearly after oral administration of 60 mg, whereas regions with normal perfusion rates show little reaction. The blood pressure was lowered, depending on the initial pressure. There was no evidence of a steal phenomenon.

Adult↗