Biomedical subjects

D Gense de Beaufort

Publications and source records attributed to D Gense de Beaufort.

3 recordsLinked to original sources

PubMed1992

[Methods for measuring spinal cord blood flow].

This study aimed to review the techniques used most currently for measuring spinal cord blood blow flow (SCBF) in animals, i.e. the hydrogen clearance, labelled microspheres, 133Xe clearance and 14C-antipyrine autoradiographic methods. All four techniques may only be used in animals, because of their invasiveness. Flow figures varied greatly with the method, the spinal level at which measurements were carried out, and the species of animal. However, results tend to suggest that SCBF is very similar to cerebral blood flow in that it is controlled by chemical, autoregulatory and metabolic factors. Approaches to measuring SCBF in man may be made using stable xenon-enhanced computed tomographic imaging (Xes-CT) in the same way as for measuring cerebral blood flow. The calculation of SCBF is based on Fick's principle transformed by Kety and Schmidt. After a reference CT section has been obtained, twelve 8 mm thick sections are carried out whilst the patient breathes a 30% xenon-70% air/oxygen mixture. This series of views enables the SCBF to be calculated in four steps. Quantitative analysis in eight human subjects gave a mean SCBF of 58.8 +/- 5.96 ml x 100 g-1 x min-1. However, this method has a low signal to noise ratio. Moreover, the qualitative analysis of the parametric views of flow demonstrate tissue heterogeneity, partly due to the patient's movements (breathing movements). However, the method is non invasive, safe, and reproducible. As it can measure very low values of blood flow, the study of ischaemic spinal lesions is made possible, although some technical and software improvements are still required.

Adult↗

PubMed1991

[CT X-ray measurement of cerebral blood flow by stable xenon. Methodology and applications].

The measurement of cerebral blood flow by stable xenon computerized tomography is a tridimensional method that offers an excellent spatial resolution. The quantitative estimation of the cerebral blood flow is based on Fick's principle, transformed by Kety and Schmidt, using stable xenon as indicator, which is an inert and freely diffusible gas. The limitations of this method are related to the necessity for the patient to remain completely immobile during the examination, the low signal/noise ratio and the impossibility of measuring cerebral metabolism. By contrast, this method represents a real advantage in the diagnosis and prognosis of cerebral pathology: it allows the acquisition of a precise cartography of superficial and deep regional blood flows; it can reveal zones under the functional perfusion threshold thank to its capacity to measure very low blood flows; it allows the obtention of additional information in pathologies of tumoral, ischemic or degenerative origin by measuring the partition coefficient. Moreover, this technique is reliable, non invasive and reproducible. Advantages of such measurement are illustrated in revealing epileptic foci in partial seizures resistant to medical treatment, in the prognosis of cerebrovascular accidents and in the therapeutic evaluation of drugs used in animal experiments.

Blood Flow Velocity↗

PubMed1990

Measurement of cerebral blood flow by the stable xenon computerized tomography method.

Measurement of cerebral blood flow (CBF) by computerized tomography (CT) is a three-dimensional method with better spatial resolution than the two-dimensional methods. Its principle was first described by Drayer et al. in 1978, with stable xenon (Xes) as CBF indicator. CBF quantitation is based on Fick's principle transformed by Kety and Schmidt when the indicator is a diffusible inert gas. Xes concentrations in cerebral parenchyma and arterial blood are the initial parameters in Kety's equation; they are expressed as variations in attenuation coefficient. Examinations are performed with a Somatom DRH (Siemens) apparatus. Xes (35%) is inhaled from a closed circuit ventilation system which enables xenon to recirculate. From a console connected to the inhalator the operator can command gas preparation, start examination, acquire and transfer data. A reference ("native") section is cut at the site chosen on the topogram. Twelve sections, each 8 mm thick, are then performed while the patient inhales, during 6 minutes, the mixture: air-35% xenon + 65% oxygen. The series of images which enable the CBF parametric image to be calculated is treated in four stages: 1. Xenon concentrations in arterial blood are calculated from the Xes values measured in the air exhaled at the end of expiration. 2. All contrasted sections are visualized on the image monitor after subtraction of the background noise. 3. The CBF parametric image is calculated by Koeppe's optimization method (linear calculation of least squares), using a PDP 11/44 processor. 4. The CBF parametric image is treated to give the CBF value expressed as ml.100 g.min. The method has its limitations: it depends on the limited signal/noise ratio and on the patient's complete immobility; cerebral metabolic rates cannot be measured. But these limitations are largely outweighed by major advantages: the CT/Xes method is non-invasive, safe and reproducible. Owing to its excellent spatial resolution, it provides very accurate maps of superficial and deep regional blood flows. As it measures very low blood flows and can give partition coefficient values, it is of considerable help in the study of ischaemic and degenerative cerebral pathologies.

Adult↗