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Biomedical subjects

A Eke

Publications and source records attributed to A Eke.

28 records · Page 2Linked to original sources
PubMed1982

Reflectometric mapping of microregional blood flow and blood volume in the brain cortex.

A reflectometric indicator-dilution method has been developed for mapping the parenchymal minute volume flow and blood content over tiny superficial areas of the brain cortex at 625 or 2500 locations, respectively. About 0.4 ml dextran-saline solution was used as nondiffusible indicator and injected into the feline cerebral circulation for each measurement. The subsequent cerebrocortical transit of the hemodiluted bolus was detected as a temporary change in the tissue optical density [OD(t)] and interpreted as indicator dilution, C(t). This gave the data necessary to calculate the microregional blood volume (mrCBV), mean transit time of the bolus (mrMTT), and the microregional blood flow (mrCBF = mrCBV/mrMTT). A two-dimensional record of the OD(t) function was made on Kodak SO 115 film by 16-mm cinematography, as a reflectometric tool, over an exposed area of the brain cortex during the bolus perfusion. Later, the microregional OD(t) functions were retrieved for analysis in a square array from the developed film by computer-controlled, frame-by-frame scanning densitometry. Maps of mrCBF, mrCBV, and mrMTT were presented as square arrays of gray-scaled pixels. The maximal spatial and temporal resolution of the method was 0.015 mm2 (mrCBF), 0.004 mm2 (mrCBV), 6 maps/min (mrCBF), and 600 maps/min (mrCBV).

Animals↗
PubMed1981

Stability of oxygen transmissibility during ischemia.

Simultaneous measurements of oxygen availability (O2a) and partial pressure (PO2) were made by the double noble metal electrode system designed by Erdmann and Krell in an attempt to monitor the oxygen transmissibility (Dk) with respect to time before and after ischemic episodes in the brain cortex. Available current equations can appropriately describe the performance of the electrode in a homogeneous nonconsuming medium, and with some experimental error this electrode system can be used to estimate oxygen transmissibility changes in the brain based on the different characteristics of the O2a (rod-type, flush-ended bare tip) and the PO2 (rod-type, recessed tip) cathodes. Our method monitors the oxygen transmissibility within the diffusion sphere of the bare tip as the ratio of the currents related to O2a and PO2. We find with this system that even prolonged global cerebral ischemia does not alter the oxygen transmissibility of the brain tissue. Therefore, alternation of the oxygen transmissibility can not be a contributing factor to postischemic cerebral malfunction.

Animals↗
PubMed1977

[The protecting action of a combination of vasoactivating substances (CRP) on disturbances of the cerebral blood flow and metabolism and the cortical electrical activity (author's transl)].

The effect of anoxia and direct cortical stimulation was investigated in control, hypotensive and post reinfusional periods, before and after treatment with a combination of coumarin/rutin sulphate sodium salts/proxyphylline (CRP, Theokal). Theokal lowered the mean arterial pressure and a slight NADH oxidation appeared. Blood flow did not change after Theokal in spite of the 30 mm Hg blood pressure drop. This suggests an improved oxygen supply to the cortical cells. The increase in anoxic NADH reaction and the faster reoxidation kinetics of NADH following anoxia provided further evidence for the beneficial effect of Theokal on brain circulation and metabolism. It is to be emphasized that the described action of the drug can be observed only in hemorrhagic shock but not in normal animals.

Animals↗
PubMed1976

In vitro investigation of biological specimens by electron microscopy.

A microchamber was developed for the examination of biological specimens in nearly natural environments, in an electron microscope, at 70kV accelerating voltage.. The chamber can be supplied continually with the sample and with the reagents, which makes it suitable for the study of biochemical reactions, too. Temperature and vapour pressure in the chamber can be controlled and the thickness of the specimen can be varied. Transmission electron micrographs of biological specimens, such as human blood cells, bull gametes and Bacillus subtilis have been obtained. Mobility of microorganisms, which is regarded as a criterion of the wet state, has been observed.

Animals↗
PubMedDate not supplied

Transient metabolic and vascular volume changes following rapid blood pressure alterations which precede the autoregulatory vasodilation of cerebrocortical vessels.

It has been shown by surface fluoro-reflectometry that stepwise decrease of arterial blood pressure causes a biphasic cerebrocortical vascular volume response. After the arterial blood pressure decrease the vascular volume first decreased and later increased. In both parts of the biphasic reflectance change, the cerebrocortical NAD-NADH redox state shifted considerably towards reduction and there was no reoxidation after the onset of cortical vasodilatation. Since a very rapid NADH reduction occurred during the first 30 secs. of the arterial hypotension in parallel with the vascular volume decrease, it is suggested that in the transient phase of arterial hypotension cerebral hypoxia may occur. Furthermore it is suggested that anaerobic tissue metabolites or some unknown NAD-NADH dependent process might dilate the cerebrocortical arterial network during the autoregulatory adjustment of CBF. The participation of the sympathetico-adrenal system in transient brain hypoxia caused by bleeding is a possibility since both the early vasoconstriction and the steep NADH reduction were prevented by the administration of phenoxybenzamine (1 mg/kg) before bleeding.

Animals↗