Experimental aortic stenosis and corresponding left ventricular hypertrophy in sheep.

Left ventricular hypertrophy (LVH) is an independent cardiac risk factor. A simple standard experimental model of inducing LVH for further studies using experimental aortic stenosis in sheep was performed. The aim of this study is to describe animal-specific requirements as well as perioperative therapy, postoperative care, and the use of echocardiography for routine follow-up examinations. Supracoronary aortic banding was performed in 55 female sheep at an age of 6 to 8 months. General anesthesia and an antero-lateral thoracotomy were used. The objective was to achieve pressure gradients of 20 to 30 mm Hg. In addition a 4th intercostal space rib window was created to improve echocardiographic vision. The operations were completed successfully in all animals. Intraoperatively, little severe arrhythmia occurred. During the follow-up interval of 8 +/- 1.3 months, 8 animals died, due to incomplete perforation of the ascending aorta (3), chronic heart failure (2), pericardial cyst (1), and respiratory failure and infection (2). All remaining animals were amenable for further studies. Severe LVH was diagnosed with routine echocardiography on follow-up. Thus, experimental aortic stenosis in sheep is a safe and relatively simple technique to generate stable LVH. Echocardiography is an easy tool for follow-up evaluations. Due to low complication rates, the sheep model is well suited for further research in LVH.

Backscattering peak of hexagonal ice columns and plates.

The backward cross section of hexagonal ice crystals of arbitrary orientation is calculated for visible light by means of a ray-tracing code. It is shown that backscattering of the tilted crystals is caused by a corner-reflector-like effect. A very large peak of backscattering is found for a tilt of 32.5 degrees between the principal particle axis and the incidence direction. This peak is caused by multiple total internal reflections for part of the rays that are incident upon the skewed rectangular faces. Slant lidar measurements for remote sensing of cirrus clouds are proposed.

Shape characterization of a large nonspherical particle by use of its Fraunhofer diffraction pattern.

We characterize the shape of a large nonspherical particle by means of the two-dimensional Fourier transformation of its diffraction pattern, called the S function. The main properties of S functions are considered. Some ways in which to retrieve the geometric parameters of a particle by use of its S function are discussed. In particular, the parameter of nonsphericity of a particle is defined by means of the S function.

Mixed graphical models for simultaneous model identification and control applied to the glucose-insulin metabolism.

In this paper a method for model identification of biological systems described by stochastic linear differential equations using a new computational technique for statistical Bayesian inference, namely mixed graphical models in the sense of Lauritzen and Wermuth, is presented. The model is identified in terms of biological model parameters and noise parameters. This non-linear estimation problem is solved by means of an exact inference algorithm. The parameter estimates are given as a-posteriori distributions which can be interpreted as fuzzy possibility distributions. For model-based simulations of the underlying biological system the model parameters are represented as uncertain parameters with the distributions obtained from the estimation procedure. We apply the presented methods to a model for the glucose-insulin metabolism: the Karlsburg model for type I diabetes.

Scattering of light by a red blood cell.

The optical parameters of a red blood cell suspended in the blood plasma and, namely, the scattering and absorption cross sections and the scattering phase function describing the small-angle distribution of the scattered light are calculated. Dependence of the optical parameters on all possible values of size, shapes, orientations, hemoglobin concentration, and oxygenation degree is considered. The data are calculated with the so-called straight-ray approximation. The accuracy of the approximation is estimated by comparison with the Mie theory. © 1998 Society of Photo-Optical Instrumentation Engineers.

[The value of magnetic resonance tomography using gadolinium-DTPA in the diagnosis of the post-lumbar disk surgery syndrome]. / Wert der Kernspintomographie mit Gadolinium-DTPA bei der Diagnostik des lumbalen Postdiscotomie-Syndroms.

Our results have shown that MR tomography - especially if gadolinium-DTPA is used as a contrast medium - is an excellent method to differentiate between the various possible causes of the post-discotomy syndrome. In particular, it is definitely possible to differentiate between a relapsed hernia of an intervertebral disc and a postoperative development of cicatricial tissue which is practically inevitable. This differentiation is of vital importance to the clinician, because a second operation should be performed only in case of a relapse, whereas cicatricial tissue is best left alone, because no matter how carefully the operation is performed with preparation of the neural structures, even more extensive cicatricial plates are bound to develop. Instability of the vertebral column in the operated disc segment, or other causes of complaints, can be identified via MR equally well if not better than by other means. Hence, the method should be the method of choice in postdiscotomy syndrome, since it facilitates the difficult choice between conservative therapy and reoperation.

[Magnetic resonance tomography studies with contrast media in post-discotomy syndrome]. / Kernspintomographische Untersuchungen mit Kontrastmitteln beim Postdiskotomie-Syndrom.

The syndrome encompassing failed back-surgery is a relatively uniform combination of complaints caused by a variety of pathological changes in the lumbar spine, alone or in various combinations. The MRI's capability of detecting these factors is described. MRI can detect recurrent disc herniations and separate them from intradural and/or extradural scar formation. With further experience, MRI might also be able to assess instability of the lumbar spine motion segments. MRI is not very helpful in detecting neural lesions or facette syndromes. For this kind of pathology, advances in diagnosis will depend on the further improvement of neuro- and electrophysiological tests. The same applies to the diagnosis of cases of spinal stenosis. The size of the spinal canal can be measured by MRI as well as by other modalities. These results just point out the risk of disease - not the disease itself.

[Talocrural angle and ankle joint mobility in Germans and Japanese]. / Talokrural-Winkel und Sprunggelenksbeweglich-keit bei Deutschen und Japanern.

1980 Krämer and Gudat introduced the talo crural angle, which provides exact measurement of the mobility of the ankle joint. In field studies in Germany we found a greater range of mobility in female compared with male persons. With advancing age range of mobility decreased in both sex. Same examinations in Japan were performed to determine influence of genetic and way of life pattern.

[Significance of nuclear magnetic tomography in the diagnosis of lumbar disk displacements]. / Bedeutung der Kernspintomographie in der Diagnostik lumbaler Bandscheibenverlagerungen.

In a prospective study we determined the validity of MRI (Magnetic Resonance Imaging) in lumbar disc herniations. MRI and CT were compared in 34 patients who underwent operation and 8 patients who underwent discography and intradiscal injection. By this study we determined the validity of CT and MRI being more than 90%.

[Analysis of the NMR signal for biological information in spinal diagnosis]. / Analyse des NMR-Signals auf biologische Information in der Diagnostik der Wirbelsäule.

Discs of 23 patients and volunteers were examined for the purpose of obtaining T1 and T2-relaxation times. First of all, the signal characteristics of the surface coil were evaluated. The relaxation times of 100 discs were then measured by using standard spin echo sequences. There was a correlation between age and T2-values for healthy discs (R = -0.744). This was not found in case of degenerated discs. The mean value of T1 for healthy discs was found to be 825 ms. The results show a possibility of using relaxation measurements in routine diagnosis for the early identification of disc degeneration.