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Biomedical subjects

F Brauer

Publications and source records attributed to F Brauer.

13 recordsLinked to original sources
PubMed1992

Can somatosensory evoked potential monitoring predict energy dynamics during controlled hypotension?

Somatosensory evoked potentials and redox (reduction/oxidation ratio) of cytochrome a,a3 were studied simultaneously before, during, and after controlled hypotension used for arteriovenous malformation resection. These studies were also conducted before and after ED-IC (external-internal carotid) bypass procedures for treatment of patients with transient ischaemic attacks. The former served as an acute model and the latter as a chronic model of low blood flow (ischaemia). The use of non-invasive reflection spectrophotometry (for redox studies) in conjunction with somatosensory evoked potentials (SSEP) has demonstrated that metabolic and electrophysiological changes parallel each other during "controlled" hypotension. The authors conclude that an analysis of SSEP changes are valuable in the study of metabolic and functional states of the brain during controlled hypotension.

Animals↗
PubMed1992

The effect of measurement conditions on MCG inverse solutions.

A magnetic inverse solution that uses a single current dipole in a homogeneous volume conductor with realistic torso shape was tested numerically to establish the effect of magnetic noise, number of measurement points, and torso size on the localization accuracy. Seven different sites of cardiological interest were selected as locations for the source dipole. The three components of the magnetic field were calculated as if measured by second order gradiometers, Gaussian noise was added, and Monte Carlo tests performed for inverse solutions using a single field component, or all three combined. It was found that for any of the single component solutions, and a signal-to-noise ratio of 100, 25 measuring points are sufficient for good accuracy; just 12 points are needed if all three components are used together. If, however, the torso size of the inverse solution is different from that of the field data by 10 or 20%, a larger error occurs, even for 56 measurement points and no noise. In this case, the field component orthogonal to the measurement grid, Bz, yields better results than the other two components, or even all three combined. We conclude that a multichannel system measuring the z component of the magnetic field in about 30 locations would be the best choice to locate a dipolar source, provided the torso of the field data is closely matched by the model used in the inverse solution. To this effect, scaling of the torso model can easily be included in the computation. Imaging techniques could be used to accommodate different torso shapes.

Bias↗
PubMed1991

Investigations of phagocytosis concerning the immunological defence mechanism of Mytilus edulis using a sublethal luminescent bacterial assay (Photobacterium phosphoreum).

1. A simple method for the determination of phagocytosis activity using mussel hemocytes by measuring the bioluminescence is presented. 2. The immunological defence activity based on phagocytosis is measured and quantified by a luminescent bacterial assay with Photobacterium phosphoreum. 3. The measuring system allows us to establish the stress of the immunological defence mechanism of organisms exposed to chemicals and polluted rivers or sewage. Results with reference substances and the phagocytosis indices of exposed mussels from Norwegian aquaculture plants compared to those of mussels from the German Wadden Sea are given as examples.

Animals↗
PubMed1990

Models for the spread of universally fatal diseases.

In the formulation of models of S-I-R type for the spread of communicable diseases it is necessary to distinguish between diseases with recovery with full immunity and diseases with permanent removal by death. We consider models which include nonlinear population dynamics with permanent removal. The principal result is that the stability of endemic equilibrium may depend on the population dynamics and on the distribution of infective periods; sustained oscillations are possible in some cases.

Communicable Diseases↗
PubMed1988

Safety limits of controlled hypotension in humans.

Controlled hypotension is a safe and convenient means of allowing a surgeon to perform intracranial aneurysm, arteriovenous malformation and vascular tumor surgery. The mean arterial pressure between 40 and 60 mmHg induces diminished pulsatile arterial pressure, thus preventing rupture of these abnormal vasculatures. It is still possible to maintain cerebral metabolism in the functional level within this 40-60 mmHg blood pressure range. This statement is based on our experience of the physical and neurological outcome of patients after surgery, and on analyses of somatosensory evoked potential and redox of cytochrome a, a3 in the mitochondria of the cerebral cortical cells.

Adolescent↗
PubMed1980

[Post-traumatic alpha-and mu-wave-foci (author's transl)].

28 patients with an activated focus (8-12 c/s focus) in the central region were examined for mu-wave-activity utilizing visual and calculation of the coherence function. Over 60% (18 patients) of these foci were mu-wave-foci. This type of mu-waves was decidedly less sensitive to change in vigilance than physiological mu-waves. Seven foci were alpha-foci and three foci could be classified as neither alpha- nor mu-wave-foci since they did not react to sensory and sensomotoric stimuli. Furthermore, it was demonstrated that the pathological mu-waves and the pathological alpha-waves were very similar in their characteristics.

Adolescent↗
PubMed1978

Heparin activity monitoring during vascular surgery.

Twelve patients undergoing vascular surgery were administered heparin according to preexisting protocols. The response to heparin and the rate of decay were measured by use of the activated coagulation time (ACT). The results showed a significant patient variability to response to and decay of heparin. In addition, a dose-response curve for heparin administration was established in sixteen patients undergoing vascular surgery. The ACT proved to be a simple and accurate monitor of heparin activity. It also made possible a steady state of anticoagulation throughout the duration of the vascular procedure. The reversal of the heparin effect could also be precisely determined by this test.

Aged↗
PubMedDate not supplied

Models for diseases with vertical transmission and nonlinear population dynamics.

Vertical transmission, the direct transfer of a disease from an infective parent to a new born offspring, is an important aspect of many diseases. Most of what is known for vertical transmission models assumes birth rates proportional to population size. We consider models with nonlinear population dynamics and finite carrying capacity and analyze the stability of equilibria in the special case in which the overall birth rate does not depend on infective population size.

Female↗