15 Fakultätsübergreifend / Sonstige Einrichtung
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Item Open Access Signal fidelity requirements for deriving impedance cardiographic measures of cardiac function over a broad heart rate range(1993) Hurwitz, Barry E.; Shyu, Liang-Yu; Lu, Chih-Cheng; Reddy, Sridhar P.; Schneiderman, Neil; Nagel, Joachim H.Our findings indicate that the impedance cardiogram spectrum extends from DC to 50 Hz. Any amplifier with an upper band limit less than 50 Hz can be expected to produce attenuation and distortion of the impedance cardiogram. This signal attenuation may be systematically enhanced under conditions of high heart rate when a greater proportion of signal energy will be in the upper frequency range of the impedance cardiogram spectrum. Therefore, the present study was designed to assess the influence of amplifier bandwidth on dZ/dtmax, stroke volume, and systolic time intervals (LVET, PEP, QZ, QX). Simultaneously measured ΔZ and dZ/dt signals from two impedance cardiographs, with corner frequencies of 120 and 60 Hz for the ΔZ and 50 and 15 Hz for dZ/dt channels, were contrasted over a broad range of heart rate (70–150 bpm). In addition to the analog dZ/dt signals obtained from the instruments, the ΔZ signals were digitally converted to dZ/dt by off-line digital differentiation with a 50 Hz corner frequency. The results demonstrated that the measurements with the 15 Hz corner frequency, when compared with the 50 Hz corner frequency measurements, systematically attenuated the dZ/dtmax amplitude and stroke volume measurements as heart rate increased. The attenuation of dZ/dtmax and stroke volume ranged from about 13% to 26% as heart rate increased from 70 to 150 bpm. When the upper bandlimit was 50 Hz, the dZ/dt signal had greater resolution of waveform events and produced less prolonged systolic time intervals. The 15 Hz amplifier differentially influenced the B point, Z-peak and X minimum, having no apparent effect on the temporal location of the B point, but delaying the Z-peak about 21.7 ms and the X minimum about 7.4 ms. These findings indicate that impedance cardiographs with insufficient upper bandlimits will differentially influence ICG-derived measurements as heart rate varies.Item Open Access Development of individual insulin infusion profiles for open loop infusion systems(1984) Strack, Thomas; Krause, Ulrich; Schulz, Gerhard; Beyer, Jürgen; Beutelspacher, Friedrich; Nagel, Joachim H.The computer program for the open loop infusion device simulated the feed-back structure of a closed loop insulin secretion control by an algorithm based upon a theoretical postprandial blood sugar profile. Fifteen unstable juvenile onset insulin requiring diabetics could be well controlled after two to three days of an intravenous open loop insulin infusion program. The programs consisted of two constant basal rates and superimposed wavy step profile programs activated at the beginning of each meal.The preabsorptive bolus or cephalic phase was an additional tool both for improved postprandial blood sugar control and further reduction of insulin consumption.The programmable insulin infusion device proved as a valuable tool for the study of a sophisticated insulin infusion profile suitable as well for open loop as for closed loop insulin infusion systems.Item Open Access Digital analysis of high resolution fundus images(1992) Nagel, Joachim H.; Cideciyan, Artur V.Fundus photography is a common procedure in ophthalmology providing high resolution images of the inside back portion of the eye to diagnose diseases of the retina and the optic nerve, and to record their progress over time. In many instances, objective, quantitative, reproducible and reliable interpretation of fundus images requires their computerized analysis. A comprehensive system for digital analysis of high resolution fundus images has to address virtuallly all engineering aspects of medical image processing: restoration, segmentation, pattern recognition, and registration. Based on the specific application of investigating the tapetal-like reflex, a retinal reflection uniquely present in carriers of X-linked retinitis pigmentosa (XLRP), novel approaches to the various stages of image processing are presented, and applications in other areas of medical diagnostics are outlined.Item Open Access Differential patterns of dynamic cardiovascular regulation as a function of task(1993) Hurwitz, Barry E.; Nelesen, Richard A.; Saab, Patrice G.; Nagel, Joachim H.; Spitzer, Susan B.; Gellman, Marc D.; McCabe, Philip M.; Phillips, Donna J.; Schneiderman, NeilIn cardiovascular reactivity studies, interpretations of the processes supporting the blood pressure response may become problematic when systolic blood pressure, diastolic blood pressure, and heart rate all increase in response to a behavioral challenge. Therefore, in addition to evaluating these cardiovascular responses, this study examined cardiac output, total peripheral resistance and systolic time intervals derived from impedance cardiogram, electrocardiogram and phonocardiogram recordings during a speech Stressor, a mirror tracing task, and a foot cold pressor test. All of the behavioral Stressors elicited increases in blood pressure and heart rate, with the largest changes occurring during the overt speech. Based on the examination of the response patterns of the underlying hemodynamic variables it would appear that, in both men and women, the blood pressure increase during the speech preparation period was supported by increased cardiac output; the speech itself resulted in a mixed pattern of increased cardiac output and total peripheral resistance; whereas, the mirror tracing and cold pressor tasks produced increased total peripheral resistance. Although men and women produced similar response patterns to the behavioral challenges, sex differences in the estimates of myocardial contractility were observed during rest. These results provide evidence that different behavioral stressors can produce a distinct yet integrated pattern of responses, whose differences may be revealed, when impedance cardiography is used, to derive sufficient response measures for assessing dynamic cardiovascular processes.Item Open Access Die Korrelationstechnik zur Überwachung fetaler Vitalfunktionen(1975) Nagel, Joachim H.; Thull, Roger; Schaldach, MaxDurch die Anwendung neuer Techniken, insbesondere der Korrelationstechnik, soll die Meßwertgewinnung fetaler Vitalfunktionen verbessert, und damit die Effektivität elektronischer Überwachungsgeräte in der Perinatalmedizin gesteigert werden. Im folgenden werden die grundlegenden Untersuchungen über die Erkennung des fetalen QRS-Komplexes im vom Abdomen der Mutter abgeleiteten feto-maternellen EKG dargelegt.Item Open Access Development and application of insulin infusion profiles for therapy of type I diabetics with portable insulin infusion systems(1984) Schulz, Gerhard; Strack, Thomas; Beyer, Jürgen; Krause, Ulrich; Cordes, Uwe; Weber, Thomas; Nagel, Joachim H.; Beutelspacher, FriedrichThe metabolism of insuIin-dependent diabetics (lDDs) cannot always be normalized by the conventional subcutaneous insulin regimen that usually provides only two Injections of reguIar and intermediate-acting insulin per day, but glucose-controlled intravenous insuIin infusion ensures almost normal glycaemia all day long. However, glucose-controlled insulin infusion systems (GCIIS) are available only for inpatient treatment because, at present, in vivo glucose measuring systems are not suitable for portable devices. Thus only open-loop devices are considered for outpatient treatment for brittle IDDs. There is no difficulty in findIng the right dosage for the basic insulin requirement, but control of the postprandial blood glucose increase presents a greater problem since the preprandial blood glucose level should be restored within two hours postprandially, without rlsking severe hypo- or hyperglycaemia. It Is obvious that insulin dosage alone is insufficient for this, but the timing of the insulin infusion may be important. The aim of this study was to clarify the importance of different insulin infusion profiles on daily and postprandial blood glucose levels.Item Open Access Evaluation of a neural-network classifier for PET scans of normal and Alzheimer's disease subjects(1992) Kippenhan, Jonathan Shane; Barker, Warren W.; Pascal, Shlomo; Nagel, Joachim H.; Duara, RanjanThe value of PET as an objective diagnostic tool for dementia may depend on the degree to which abnormal metabolic patterns can be detected by quantitative classification methods. In these studies, a neural-network classifier based on coarse region of interest analyses was used to classify normal and abnormal FDG-PET scans. The performance of neural networks and of an expert reader were evaluated by cross validation testing. When the "abnormal" class was represented by subjects with clinical diagnoses of "Probable Alzheimer's," the areas under the relative-operating-characteristic (ROC) curves were 0.85 and 0.89 for the neural network and the expert reader, respectively. When testing with abnormal subjects represented by "Possible AD" cases, ROC areas for both the network and the expert were 0.81. The neural network out-performed discriminant analysis. It is concluded that PET has potential for the detection of abnormal brain function in dementing diseases, and that the combination of neural networks and PET is a useful diagnostic tool. Despite the low-resolution "view" afforded the neural network, its performance was nearly equivalent to that of an expert reader.Item Open Access Die Entwicklung von Insulininfusionsprofilen zur Therapie insulinpflichtiger Diabetiker mit tragbaren Insulininfusionssystemen(1982) Schulz, Gerhard; Beyer, Jürgen; Strack, Thomas; Krause, Ulrich; Nagel, Joachim H.; Cordes, Uwe; Weber, ThomasWir analysieren den Insulinbedarf von 7 insulinpflichtigen Diabetikem am glukosekontrollierten Insulininfusionssystem und übertrugen die dabei gewonnenen Daten auf ein portables Insulininfusionsgerät, bei dem individuell Insulinabgabeproflle programmiert werden können, bzw. ein System mit einfachen Rechteckprofllen. Unsere Untersuchungen ergaben, daß mit individuell erstellten Insulininfusionsprofilen eine bessere Glättung der Blutzuckerspiegel zu erreichen ist. Bei Berücksichtigung der kephalen Phase der Insulinsekretion kann offenbar sogar Insulin eingespart werden.Item Open Access The insulin requirement of insulin dependent diabetics applying different open loop insulin infusion systems(1981) Schulz, Gerhard; Beyer, Jürgen; Strack, Thomas; Krause, Ulrich; Nagel, Joachim H.-Item Open Access New signal processing techniques for improved precision of noninvasive impedance cardiography(1989) Nagel, Joachim H.; Shyu, Liang-Yu; Reddy, Sridhar P.; Hurwitz, Barry E.; McCabe, Philip M.; Schneiderman, NeilImpedance cardiographic determination of clinically important cardiac parameters such as systolic time intervals, stroke volume, and related cardiovascular parameters has not yet found adequate application in clinical practice, since its theoretical basis remains controversial, and the precision of beat-to-beat parameter estimation has until recently suffered under severe shortcomings of available signal processing techniques. High levels of noise and motion artifacts deteriorate signal quality and result in poor event detection. To improve the precision of impedance cardiography, new techniques for event detection and parameter estimation have been developed. Specifically, matched filtering and various signal segmentation and decomposition techniques have been tested on impedance signals with various levels of artificially superimposed noise and on actual recordings from subjects in a laboratory study of cardiovascular response to a cognitive challenge. Substantial improvement in the precision of impedance cardiography was obtained using the newly developed signal processing techniques. In addition, some preliminary evidence from comparisons of the impedance cardiogram with invasive aortic electromagnetic flow measurement in anesthetized rabbits is presented to address questions relating to the origin of the impedance signal.