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Biomedical subjects

I R Chambers

Publications and source records attributed to I R Chambers.

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

Bilateral ICP monitoring: its importance in detecting the severity of secondary insults.

The aim of head injury management is to prevent secondary insults to the damaged brain. Raised intracranial pressure and low cerebral perfusion pressure are two secondary insults which are important determinants of outcome following severe head injury (SHI). Traditionally ICP is measured in the right frontal region in an attempt to minimise the effects and complications of transducer placement. This assumes that the brain acts like a fluid and that ICP is transmitted equally throughout the intracranial space. Experimental studies suggest that this is not the case: expanding mass lesions are associated with the development of ICP gradients. Ten patients with SHI who had an unilateral mass lesion confirmed on CT were studied. All had bilateral placement of intraparenchymal Camino ICP transducers in the frontal regions. Data from both transducers were recorded every two minutes and stored electronically. The volume of the mass lesion was calculated from the CT scan. Significant and lasting ICP gradients between hemispheres were found in all patients with an acute subdural haematoma (greater than 10 mmHg for longer than 10 minutes). Such differences were not found in patients with intracerebral haematoma or contusions. We would advocate that ICP is recorded IPSILATERAL to the lesion in patients with SHI due to acute subdural haematoma.

Blood Pressure↗
PubMed1998

Clinical evaluation of the Codman microsensor intracranial pressure monitoring system.

INTRODUCTION: The use of the Camino fibre-optic subdural device for measuring Intracranial Pressure (ICP) in patients, has been shown to correlate well with recordings from the "gold standard" intraventricular fluid filled catheter [1]. Following this work, its use has become standard in the clinical monitoring of patients. More recently, laboratory studies have demonstrated accuracy, acceptable drift and high fidelity for the new Codman Microsensor ICP Transducer, a miniature strain gauge mounted on a flexible nylon catheter [3]. Its performance in patients, however, has yet to be fully assessed, in comparative studies. METHODS: Eight patients (5 head injured, 3 with an Intracerebral haematoma) had a Codman Microsensor inserted. A Camino Transducer was fitted immediately adjacent to it. A computerised system was used to continuously record both ICP readings. RESULTS: In total 140,323 recordings were made over a wide range of ICP values. Study periods ranged from 0.5 to 116 hours. In one patient the Codman transducer tracing failed after several days, probably due to fracture of electrical cable close to the interface box. The readings from the two ICP transducers were compared on Time Series, logistic regression and Altman-Bland plots. Drift of the ICP recorded by the Codman microsensor, was noted in 2 patients, 1 in positive direction (maximum 30 mmHg), 1 negative (max. 20 mmHg). In both cases the Camino ICP recording was relatively stable. In 24% of the recordings the Codman microsensor recorded ICP as 5 or more mmHg greater than the Camino, this difference was 10 mmHg or greater in 9% of recordings. Conversely the Camino recording was 5 mmHg or more, than the Codman, in 5% of all recordings, and 10 mmHg or more in 3%. CONCLUSION: These differences could in the majority of cases (excepting the negative drift) be explained by a constant offset of the Codman transducer, as described previously [6]. Further examination of this device is required.

Brain Injuries↗
PubMed1995

Experimental stroke and neuroprotection in the aging rat brain.

BACKGROUND AND PURPOSE: Experimental stroke research has for the most part incorporated the use of young animals despite the importance of aging in cerebrovascular disease in humans. We hypothesized that age-related reductions in the density and function of cortical N-methyl-D-aspartate (NMDA) receptors might limit neuroprotective potential in the elderly. In this study, a model of occlusive stroke in the aging rat brain has been developed and used to establish the effects of age on cerebral infarction and to evaluate the scope for protecting the aging brain during ischemia. METHODS: Focal cerebral ischemia was produced by thermocoagulation of the left middle cerebral artery in adult (11 to 17 months) and aged (28 to 36 months) male Wistar rats. Infarcts were assessed histologically with volumetric analysis of infarct size, hemodynamically by serial cerebral blood flow measurement using the hydrogen clearance technique, and by analysis of specific gravity as an index of brain edema. Neuroprotective potential was assessed using the competitive NMDA receptor antagonist 3-(2-carboxy piperazin-4-yl)propyl-1-phosphonate (D-CPPene). RESULTS: Aging was associated with a significant increase in infarct size, with a mean infarct volume of 40.5 +/- 2.6% of the hemisphere volume in aged rats compared with 30.9 +/- 0.7% in adult rats (P < .01). D-CPPene reduced the mean infarct volume to 33 +/- 1.8% and 20.7 +/- 3.2% in aged and adult rats, respectively (P < .05). Cerebral blood flow fell markedly after infarction, but thereafter D-CPPene-pretreated rats maintained higher cerebral blood flow than untreated animals throughout the duration of the experiment (22.8 +/- 3.2 and 30.1 +/- 5.5 mL.100 g-1.min-1 in treated aged and adult rats, respectively, compared with 11.3 +/- 2.7 and 16.5 +/- 3.2 mL.100 g-1.min-1 in untreated aged and adult groups, 90 minutes after infarction [P < .05]). Pretreatment also reduced cortical edema; mean cortical specific gravity 4 hours after infarction was 1.0381 +/- 0.0013 in untreated aged rats and 1.0391 +/- 0.0014 in untreated adults compared with 1.0458 +/- 0.0031 in treated aged rats and 1.0442 +/- 0.0014 in treated adult rats (P < .05). CONCLUSIONS: Under similar experimental conditions, there was an age-related increase in cerebral infarct size. However, NMDA receptor antagonism was neuroprotective in the aging brain and resulted in a significant reduction in cerebral ischemic damage, less cortical edema, and preservation of cerebral blood flow.

Aging↗
PubMed1994

Cerebral oedema following intracerebral haemorrhage: the effect of the NMDA receptor antagonists MK-801 and D-CPPene.

The effects of pre-treatment with the NMDA receptor antagonists MK-801 and D-CPPene on the development of brain oedema were investigated in a rodent model of intracerebral haemorrhage. In acute experiments (4 hour survival) both drugs caused significant hypotension and had significant anaesthetic effects whilst conferring no protection against oedema formation. In chronic experiments (24 hour survival) MK-801 conferred no protection against brain oedema. With D-CPPene marginal protection against cortical oedema may have been conferred but this result should be interpreted with caution.

Animals↗
PubMed1994

A thermal clearance probe for continuous monitoring of cerebral blood flow.

Cortical thermal clearance provides a practical means of continuous assessment of cerebral blood flow. A probe which can be used to monitor cerebral cortical thermal clearance is described. It has proved a reliable method of predicting oligaemia, showing good correlation between measured thermal clearance and the onset of clinical signs of ischaemia. The limitations are its size, invasiveness, small sample volume and difficulty with quantification. It is a useful additional tool in the management of patients suffering from acute neurosurgical disorders.

Blood Flow Velocity↗
PubMed1994

The effect of age on cerebral oedema, cerebral infarction and neuroprotective potential in experimental occlusive stroke.

A model of occlusive stroke in the aging brain has been developed and used to evaluate the effects of age upon cerebral infarction, cerebral oedema and neuroprotective potential. Focal ischaemia following left middle cerebral artery occlusion has been compared in aged (30 month) and adult (< 17 month) rats, with histological assessment of infarct volume and analysis of specific gravity as an index of cerebral oedema. Aging was associated with a significant increase in cerebral infarct size. The mean infarct volume in aged rats was 40.5% +/- 2.6% of the hemisphere volume, compared to 30.9% +/- 0.7% in adults (p < 0.01). Pre-treatment with the competitive N-Methyl-D-Aspartate (NMDA) receptor antagonist 3-(2-Carboxy Piperazin-4-yl)Propyl-l-Phosphonate (D-CPP-ene) reduced infarct volumes in both age groups to 33.0% +/- 1.8% and 20.7% +/- 3.2% in aged and adult animals, respectively (p < 0.05). There was significantly less oedema of the cerebral cortex in D-CPP-ene pre-treated rats; mean cortical specific gravity 4 hours post-infarction was 1.0381 +/- 0.0013 in untreated aged rats and 1.0391 +/- 0.0014 in untreated adults, compared to 1.0458 +/- 0.0031 in treated aged rats and 1.0442 +/- 0.0014 in treated adults (p < 0.05). At 24 hours post-infarction, D-CPP-ene pre-treated aged rats had a mean cortical specific gravity of 1.0403 +/- 0.0006 compared to 1.0361 +/- 0.0014 in untreated aged animals (p < 0.05). This study has demonstrated an age-related increase in cerebral infarct size, but has shown that the aging brain is amenable to neuroprotection by NMDA receptor antagonism.

Age Factors↗
PubMed1993

Cortical thermal clearance monitoring in surgery for a giant middle cerebral artery aneurysm.

Cortical thermal clearance was used during surgery for clipping of a giant middle cerebral artery (MCA) aneurysm. During prolonged continuous proximal MCA occlusion thermal clearance remained normal, indicating sufficient collateral blood supply. Postoperatively the patient had no neurological deficit. This monitoring technique is a useful guide to the safety of temporary clipping during aneurysm surgery.

Cerebral Arteries↗
PubMed1992

A thermal clearance probe for continuous monitoring of cerebral blood flow.

Thermal clearance has been used as a measure of tissue blood flow for over 60 years. We have developed a probe which can be used to monitor cerebral cortical thermal clearance in patients suffering from acute neurosurgical disorders. Despite its limitations of size, invasiveness, small sample volume, and difficult quantification it has proved a reliable method, showing a good correlation between measured thermal clearance and the onset of clinical signs of ischaemia.

Adult↗
PubMed1992

The effect of immunosuppression on the development of cerebral oedema in an experimental model of intracerebral haemorrhage: whole body and regional irradiation.

The oedema which forms around an intracerebral haemorrhage has a complex aetiology. The immune response may have a role in its formation. There is clinical and experimental evidence that circulating leucocytes and platelets may mediate oedema formation. Global depletion of circulating leucocytes and platelets by whole body irradiation in a rodent model of intracerebral haemorrhage was found to confer protection against both ischaemia and oedema formation. This was not a direct effect of irradiation of the brain. The possible mechanisms for this protection are discussed.

Animals↗
PubMed1991

Closed loop blood pressure control for cerebral perfusion studies.

A method is presented which maintains mean arterial blood pressure at predetermined values during cerebrovascular occlusion studies in a rat model. The system consists of a pressure measurement apparatus, a pump capable of infusing and withdrawing fluids, and a personal computer to control the infusion and withdrawal rate. An evaluation of the system is presented, and potential advantages and difficulties are discussed.

Animals↗
PubMed1990

The effect of immunosuppression with whole body and regional irradiation on the development of cerebral oedema in a rat model of intracerebral haemorrhage.

A lesion simulating intracerebral haemorrhage was produced in the right caudate nucleus of rats immunosuppressed with whole body or regional irradiation. Whole body irradiation produced significant leucopaenia and thrombocytopaenia and conferred protection against cerebral ischaemia and oedema when compared to nonirradiated control animals. Local radiation to the head or torso did not confer protection.

Animals↗
PubMed1990

Pressure measurements during automatic breast compression in mammography.

Breast compression during X-ray mammography results in improved image quality at a lower radiation dose to the patient, and, as a consequence, the Department of Health recommends that automatic breast compression devices are fitted to mammographic X-ray units. However, the degree of breast compression is not standardized and can vary depending on the size of the patient, the particular mammography X-ray unit and the conditions of its use. A pressure measuring system was used to determine accurately the pressure on the breast. This system takes the form of a fluid-filled neonatal cuff connected to a pressure transducer by a fluid line. The pressure measuring system was calibrated and tested, first without and then with the patients, to assess its practical feasibility. The elements of the pressure measuring system, the techniques involved in its calibration and its use on patients in the clinical environment are described here. The system has proved to be a quick and simple method of relating the pressure on the breast to the pressure reading of the mammography X-ray unit.

Automation↗
PubMed1990

A clinical evaluation of the Camino subdural screw and ventricular monitoring kits.

The aim of this study was to compare readings of intracranial pressure from a ventricular catheter with those obtained from a Camino catheter-tipped transducer. The Camino transducer was evaluated in two ways: firstly, when it was inserted by a subdural screw, and secondly, when it was inserted into a ventricular catheter using a ventricular monitoring kit. Data were recorded for 376 hours for the subdural screw method and for 486 hours for the ventricular monitoring kit. Average pressure readings were calculated every 5 minutes (10 half-minute values), and regression analysis was performed. For the subdural screw method, the correlation coefficient was 0.945 (gradient, 1.04; intercept, -5.51. The results from the ventricular monitoring kit showed that the correlation coefficient was 0.901 (gradient, 0.93; intercept, -0.92. The correlation between recordings of ventricular fluid pressure and the Camino recordings obtained from both subdural screw insertions and ventricular monitoring kits was good, with the subdural screw method proving more accurate and reliable in clinical use.

Brain Injuries↗
PubMed1989

An instrument for monitoring the force applied by breast compression devices on mammography x-ray sets.

Automatic breast compression devices are commonly fitted to mammographic x-ray sets. The force exerted by these compression devices should be limited and periodically checked. This article describes the design and construction of an instrument for the routine assessment of the force applied by breast compression devices on mammography x-ray sets. Results obtained on four different mammography x-ray units are presented. In addition, data on the effect of compression plate design on compression force is given for one unit. The instrument has proved to be a simple and quick method of monitoring the force applied by the compression plates on mammographic x-ray units.

Female↗