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Biomedical subjects

R Kern

Publications and source records attributed to R Kern.

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

Visual position stabilization in the hummingbird hawk moth, Macroglossum stellatarum L. II. Electrophysiological analysis of neurons sensitive to wide-field image motion.

Response properties of neurons in the cervical connectives of the hummingbird hawk moth, Macroglossum stellatarum L., were determined. All neurons described in this account respond directionally selectively to motion in large parts of the visual field of either eye. They respond maximally to bilateral stimulation, preferring either motion as induced on the eyes during translatory movements of the animal or when it turns around one of its body axes. Cells most sensitive to rotational motion either respond best to rotation of the patterns around the vertical axis of the animal or around its longitudinal body axis. Neurons most sensitive to translational pattern motion respond best to either simulated translations of the animal along its vertical or along an oblique axis. Most types of neurons respond tonically and do not habituate. The sensitivity to motion stimuli is not evenly distributed within the receptive field of any investigated neuron. Part of these neurons might play a role in visual position and course stabilization.

Animals↗
PubMed1998

[Stereolithography models vs. milled 3D models. Production, indications, accuracy].

Anatomic, life-like, three-dimensional models have a definite place in cranio-maxillofacial surgery. Our experience with 541 computer tomographic (CT)-based three-dimensional (3D)-models for diagnostic purposes, preoperative planning and model operations in our department was gained using stereolithographic and milled models. The question of which production method is preferable is a matter of controversy in the literature. Both methods are based on CT and magnetic resonance imaging data, but the differences in production give rise to specific advantages and disadvantages. For comparison we scanned two measurement models, fabricated milled and stereolithographic models, and analyzed the differences concerning accuracy and shape of specific structures. The scan distance (feed) is the limiting factor for the accuracy for both methods. Milled models show the highest precision in the plane of CT scanning--the more oblique the measurements became to this plane, the greater the decrease in accuracy. Hollows and undercuts can only be produced by splitting the model. Stereolithographic models show higher deviations with randomly distributed errors. The mean deviation was 0.81 mm on stereolithography and 0.54 mm on milled models. The accuracy of both methods is sufficient for clinical use. In routine cases the milling method seems to be superior because of shorter production time and lower costs. In special cases, where hollows and fine structures play a major role, stereolithography is the method of choice.

Humans↗
PubMed1998

Increased expression of a hemimethylated oriC binding protein, SeqA, in an aphA mutant.

In Escherichia coli, the origin of DNA replication, oriC, becomes transiently hemimethylated at the GATC sequences immediately after initiation of replication and this hemimethylated state is prolonged because of its sequestration by a fraction of outer membrane. This sequestration is dependent on a hemimethylated oriC binding protein such as SeqA. We previously isolated a clone of phage lambda gt11 called hobH, producing a LacZ fusion protein which recognizes hemimethylated oriC DNA. Very recently, Thaller et al. (FEMS Microbiol. Lett. 146 (1997) 191-198) found that the same DNA segment encodes a non-specific acid phosphatase, and named the gene aphA. We show here that the interruption of the aphA reading frame by kanamycin resistance gene insertion, abolishes acid phosphatase (NAP) activity. Interestingly, in the membrane of the null mutant, the amount of SeqA protein is about six times higher than that in the parental strain, suggesting the existence of a regulatory mechanism between SeqA and NAP expression.

Acid Phosphatase↗
PubMed1997

[Quantitative determination of left ventricular myocardial perfusion with electron beam computerized tomography].

Myocardial perfusion is one of the most important functional parameters of the heart. Presently various indirect methods are used to determine coronary blood flow or myocardial perfusion as inertgas-, thermodilution-, Doppler catheter- and radiopharmacological techniques. Electron-beam-computed-tomographical technology is able to perform CT data acquisition with a very short exposure time of 50 ms. Using this method it is not only possible to determine left ventricular volumes but also to measure myocardial perfusion in ml/100 g/min. The measurement of the left myocardial perfusion is performed using the short axis view. This position is obtained by moving the table 25 degrees to the patient's right and 15 degrees caudally. To determine the position of the left ventricle, a localization scan is obtained in multi-slice-mode using all for target-rings, thus obtaining 8 tomographic levels over 68 mm (each tomographic level having a slice thickness of 7 mm, with an interslice gap of 4 mm between each two adjacent tomographic levels). In this short axis position, using the multi slice flow mode with 3 target-rings and after administration of 50 ml of contrast medium intravenously with a flow of 3 ml/s, 6 tomographic levels are imaged. Each tomographic level is obtained 13 times at 80% of the R-R-interval at each 2 or 3 heart beat (ECG-gated). The left ventricular myocardial contrast enhancement is measured by drawing manually the outline of the left ventricular myocardium using time-density-software of the Imatron workstation. For calculation of the myocardial perfusion the so-called "slope method" is used and the results are expressed as the maximum slope of enhancement of the myocardium divided by the difference of the precontrast and peak CT-value in the left ventricle. The global myocardial perfusion is calculated as a mean of all evaluated tomographic levels. In this study left ventricular volumes as enddiastolic volume endsystolic volume and stroke volume were measured and ejection fraction and cardiac output calculated. The measurements were performed in the log axis view. This view is obtained by moving the table 15 degrees to the patients left in a horizontal position. In this long axis position 6 tomographic levels are imaged using the multi-slice-cine-mode with 3 target-rings after administration of 50 ml of contrast medium intravenously with a flow of 3 ml/s. Each tomographic level is obtained 13 times starting at 0% of the R-R-interval (ECG-triggering). The exposure time is 50 ms with an interscan time delay of 8 ms. In 9 studied patients of whom one had 3 significant coronary artery stenotic lesions (> 50%), 2 patients had each 2 non significant stenotic lesions (< 50%) and 6 revealed nearly normal coronary angiograms. The mean global myocardial perfusion was 70 ml/100 g/min (min.32 and max. 116 ml/100 g/min). This mean value of 70 ml/100 g/min is reflecting 5% of the cardiac output supposing that the mean heart weight of these patients was 300 g. In this study the mean of the left ventricular muscle mass determined by the use of EBCT was 130 g. A comparative evaluation of coronary angiographic findings in these patients with the measured myocardial perfusion values revealed, that is not sufficient to look only at the absolute values of the measured myocardial perfusion. Furthermore it seems to be necessary to interpret these perfusion values with respect to the calculated cardiac output. Additional studies of well defined patients groups are necessary to determine normal values of myocardial perfusion at rest in patients with and without coronary artery disease. This seems to be important as comparative analysis of myocardial scintigraphic and EBCT-studies is difficult because of methodical inherent differences. The results of this study suggest that despite the presence of some beam hardening artifacts it is possible to measure myocardial perfusion using EBCT in patients with suspected coronary artery disease in the

Aged↗
PubMed1997

[Electron beam computerized tomography (EBCT) of the heart].

Using electron-beam computed tomography (EBCT) with short exposure times of 100 or 50 ms and the capability of acquiring up to 2 x 17 images/s it is possible to study most of the important morphological and functional determinants of the heart. Various examples of studies in acute and chronic cardiac diseases are shown to demonstrate the use of EBCT to determine quantitatively left ventricular volumes (ml), myocardial mass (g), wall thickness changes over the cardiac cycle (mm/s), myocardial perfusion (ml/ 100 g/min) and the extent of coronary calcification (calcium score) and qualitatively the state of the proximal 4-6 cm of the subepicardial coronary arteries. The knowledge of these determinants seems very useful in excluding cardiac dysfunction, in the early recognition of cardiac disease and in the evaluation of the haemodynamic severity of coronary artery stenotic lesions. Further interdisciplinary studies are necessary to assess the clinical validity of these cardiac determinants, especially myocardial perfusion, using this advanced CT technology.

Aged↗
PubMed1997

Edge detection by landing honeybees: behavioural analysis and model simulations of the underlying mechanism.

The mechanism of edge detection in the honeybee was investigated by examining the effects of combining different kinds of visual cues that define an edge. Free-flying bees were trained to land at three different types of edges which were defined by texture and relative motion cues either in isolation or in combination with each other. Bees are able to detect and land at the three types of edges, but do so with different frequencies. In contrast to the naive expectation that edges jointly defined by two cues can be detected better than those defined by a single cue in isolation, the combination of the cues does not increase and may even decrease the detectability of an edge. When bees land at an edge the orientation of their body axis is strongly affected by the visual cues defining this edge. Model simulations were performed to test whether the experimental findings can be explained on the basis of a single edge detection mechanism sensitive to both types of visual cues. In the model, the information from both types of cues is sensed by two fields of movement detectors that receive their input signals from two adjacent patches in the visual field. The output of all detectors subserving either patch is pooled by integrating cells. The signals of the two integrating cells subserving the two adjacent patches are compared at a subtraction stage. The resulting signal is then rectified and forms the output signal of the model. The model simulations closely resemble the experimental results, thus providing evidence that edge detection by the bee could be mediated by a single mechanism.

Animals↗
PubMed1997

Vascular air embolism: location, frequency, and cause on electron-beam CT studies of the chest.

PURPOSE: To determine the frequency and location of venous air emboli that occur with the use of electron-beam computed tomographic (CT) studies of the chest. MATERIALS AND METHODS: Findings from 677 patients who underwent chest electron-beam CT with intravenous administration of contrast material were reviewed. Unenhanced CT studies were performed in 127 (18.8%) of these patients while the intravenous cannula was in place but before injection of contrast material. RESULTS: Air emboli were observed on CT studies in 79 (11.7%) of 677 patients. Emboli were small (up to three air bubbles less than 1 cm in diameter) in 70 (10.3%) patients and were moderate (more than three air bubbles or bubbles 1-2 cm in diameter) in nine (1.3%) patients. Air emboli were located in the main pulmonary artery (n = 54 [8.0%]), superior vena cava (n = 12 [1.8%]), right ventricle (n = 10 [1.5%]), subclavian or brachiocephalic vein (n = 6 [0.9%]), and right atrium (n = 5 [0.7%]). Seven patients (1.0%) had emboli in more than one location. Air emboli were depicted on unenhanced CT scans of seven (5.5%) of 127 patients. No association was found between the frequency of air embolism and injection flow, injection site, or amount or type of contrast agent. CONCLUSION: Intravenous administration of contrast material may cause small to moderate-sized air emboli. Knowledge of the common locations of emboli can help radiologists distinguish them from image artifacts or paravasal air collections.

Brachiocephalic Veins↗
PubMed1996

[Functional studies of swallowing with electron beam computerized tomography].

Functional evaluation of swallowing disorders requires rapid imaging modalities. Videofluorography and cinematography are the gold standard, but they have their limitations: no transverse plane imaging is achieved and structural resolution for exact topographic analysis is limited. Three cases preselected by videofluorography were studied to evaluate whether electron beam tomography (EBT) permits more detailed dynamic imaging of swallowing disorders focusing on the mesonasopharyngeal segment, the hypopharynx and the upper esophageal sphincter (UES). Immediately after videofluorographic examination of the oropharyngeal deglutition, EBT is performed. The patient is in a supine position and while the patient swallows a 20 ml bolus of water or diluted iodine containing contrast agent, a sequence of 20 images per level is scanned. The levels, which are determined by using the scout view, are oriented parallel to the hard palate either at the level of the hard palate to image the mesonasopharyngeal segment or just above the hyoid bone to focus on the hypopharynx or at the location of the UES. The scan technique is a single-slice cinemode with a slice thickness of 3 mm (exposure time 100 ms, interscan delay 16 ms, 130 kV, 620 mA). The following structural interactions that we have so far been unable to image can be clearly demonstrated with EBT: (1) during normal swallowing, the mesonasopharyngeal segment is completely and symmetrically closed by the soft palate and Passavant's cushion; (2) lateral hypopharyngeal pouches can be located more precisely; and (3) disorders of the UES can be differentiated into functional or morphologically caused disorders (e.g., goiter or cervical osetophytes). Videofluorography and cinematography are still the gold standard in functional evaluation of swallowing disorders. However, EBT permits dynamic imaging of pharyngeal deglutition in a preselected transverse plane and can give useful additional information concerning functional anatomical changes in the pharynx during swallowing. Further clinical evaluation is needed.

Adult↗
PubMed1996

Co-ordination between membrane oriC sequestration factors and a chromosome partitioning protein, TolC (MukA).

oriC DNA in the hemimethylated (but not in the fully methylated) state reacts with an Escherichia coli K-12 outer membrane preparation. This reaction is drastically reduced when the membrane preparation of a seqA null mutant is used. An in vitro reconstitution of the activity was undertaken by adding a partially purified SeqA protein to a seqA mutant membrane without success. A possible reason for this failure might be a profound modification of the outer membrane of the seqA mutant (as revealed by the fact that membrane from the mutant sediments more slowly than that from the wild type during ultracentrifugation). There is also a reduction in the content of OmpF protein. Moreover, one of the minor outer membrane proteins involved in partitioning of newly synthesized chromosomes, the ToiC (MukA) protein, was also found to be downregulated in the seqA mutant. This is also true of the hobH mutant grown in a high-osmolarity medium. Mutants of both seqA and hobH stop dividing after hyperosmotic shock, forming filaments (as observed in dam mutants).

Bacterial Outer Membrane Proteins↗
PubMed1996

Differentiation of delayed kidney graft function with gadolinium-DTPA-enhanced magnetic resonance imaging and Doppler ultrasound.

RATIONALE AND OBJECTIVES: The authors differentiate acute tubular necrosis from transplant rejection in patients with delayed kidney graft function using gadolinium (Gd)-DTPA enhanced magnetic resonance (MR) imaging. METHODS: Twenty-four patients after renal transplantation (10 with normal graft function, 14 with delayed graft function) underwent conventional and Doppler sonography and MR imaging examination after bolus application of Gd-DTPA. Within a time period of 512 seconds, 39 single-slice MR images were obtained. Measurements of signal intensity in three regions of interests (cortex, medulla, renal pelvis) resulted in a graphic description of the dynamics of the contrast enhancement. The time between the start of the scan and the peaks of the curves was measured. RESULTS: In patients with normal graft function the curves reached the peaks between 39 and 55 seconds (cortex), 44 and 61 seconds (medulla), and between 161 and 318 seconds (renal pelvis). Six patients with acute tubular necrosis showed normal values for the curves 1 and 2 but markedly prolonged time for curve 3 (between 420 and 512 seconds). In all patients with histologically proven transplant rejection, the peaks of all curves were not reached before the ends of the scans. CONCLUSION: The authors' preliminary results suggest that MR imaging seems to be a sensitive, noninvasive diagnostic tool to differentiate acute tubular necrosis from transplant rejection in the critical early postoperative period.

Adult↗
PubMed1996

Ultrafast computed tomography and three-dimensional image processing of CT sialography in patients with parotid masses poorly defined by magnetic resonance imaging.

The purpose of this study was to determine the efficacy of ultrafast computed tomography (UF CT) in patients with parotid masses poorly defined by magnetic resonance imaging (MRI) and to evaluate the diagnostic potential of three-dimensional (3-D) UF CT sialography when compared with conventional CT sialograms. Thirteen patients with clinical suspicion of a parotid mass, in whom MRI was degraded by motion, underwent UF CT of the parotid region. Two radiologists independently assessed the CT and MR with respect to tumor localization, intraglandular tumor location, tumor margin characteristics, and infiltration of surrounding tissue. In 9 patients, CT sialography was performed using 3-D image processing. Anatomical details and pathologic findings were assessed by three readers using a numerical grad and compared with the findings derived from conventional CT sialography. Histopathologic specimens were obtained in all cases and correlated with the radiographic findings in a consensus manner following the blinded interpretations. UF CT and (suboptimal) MRI provided the same diagnostic information for the evaluation of tumor localization, and intraglandular location. UF CT was superior to MRI in the detection of tumor infiltration, and definition of tumor margins in 2 cases (15%), resulting in a substantial difference in treatment. Three-dimensional CT sialography offered significant improvement in demonstration of anatomic detail (2.5 +/- 0.2 vs 1.5 +/- 0.1, respectively) and pathologic findings (2.6 +/- 0.1 vs 1.3 +/- 0.2, respectively) when compared with conventional CT sialography. UF CT is a viable alternative in uncooperative patients with parotid masses. UF CT 3-D sialography has the potential to allow more precise pre-surgical planning and contributes to the diagnosis and therapy planning of parotid masses.

Adult↗
PubMed1996

Internally standardized simultaneous assay of gallopamil enantiomers in human plasma by means of high performance liquid chromatography.

A high performance liquid chromatographic method with internal analogue standardisation for the simultaneous assay of the gallopamil enantiomers in human plasma after administration of racemic gallopamil is described. The method comprises extraction from alkalinized plasma into an n-hexane/2-propanol phase (95:5), back extraction into 1 N hydrochloric acid and extraction into n-hexane/ 2-propanol (95:5) after addition of 5 N sodium hydroxide. Separation of the optical antipodes was achieved by the use of a chiral phase (Daicel Chiralcel OD-H) and quantification by means of fluorescence detection. A limit of detection of about 0.2 ng/ml was determined for both enantiomers. Under routine conditions the limit of determination (variation coefficient < 20%) was about 0.5 ng/ml for (R)- and (S)-gallopamil. The method is not impaired by the known metabolites. The suitability of the method for clinical pharmacology studies is demonstrated with samples obtained from healthy subjects. First results of kinetic studies in humans showed that the (R)-enantiomer dominates after oral administration of racemic gallopamil.

1-Propanol↗
PubMed1994

Parental strand recognition of the DNA replication origin by the outer membrane in Escherichia coli.

The outer membrane of Escherichia coli binds the origin of DNA replication (oriC) only when it is hemimethylated. We report here the results of a footprinting analysis with the outer membrane which demonstrate that its interaction with oriC occurs mainly at the left moiety of the minimal oriC, where 10 out of 11 Dam methylation sites are concentrated. Two regions, flanking the Integration Host Factor (IHF) sites, are preferentially recognized at the minimum membrane concentration at which oriC plasmid replication is inhibited in vitro. We have identified the putative proteins involved in hemimethylated oriC binding and cloned one of the corresponding genes (hobH). The purified LacZ-HobH fusion protein specifically binds oriC DNA at the same preferential sites as the membrane. A mutant of the hobH gene reveals partial asynchronous initiation of DNA replication.

Amino Acid Sequence↗
PubMed1994

Magnetic resonance assessment of age-related development of the sphenoid sinus.

Magnetic resonance images of the sphenoid sinus in 401 patients under 15 years old were reviewed to establish normal age-related standards. T1-weighted sagittal and T2-weighted axial scans were evaluated for bone marrow conversion, development of pneumatization, spatial enlargement and septation of the sphenoid sinus. The sphenoid sinus had a uniformly low signal intensity (red bone marrow) on T1-weighted images in all children less than 4 months old. Signal intensity changes from hypointense to hyperintense (bone marrow conversion) started at the age of 4 months. Onset of pneumatization was observed in 12% of the patients at age 13-15 months. By age 43-48 months, 85% of the patients showed pneumatization of the anterior part of the sphenoid bone. Pneumatization was complete in all patients older than 10 years. Enlargement of the sinus showed a characteristic profile in each dimension. Median septation was observed irregularly with age, with a maximum of 77%. Septum variants were noticed between 4.5% and 20%. Because paediatric sinus disease is a challenging problem in children, these results may be useful as baseline standards of normal age-related development of the sphenoid sinus during childhood.

Adolescent↗