Browsing by Author "Nagel, Joachim H."

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Open Access
Analyse bioelektrischer Potentiale in der Perinatologie
(1979) Nagel, Joachim H.; Schaldach, Max (Prof. Dr.-Ing.)
Das Ziel der vorliegenden Arbeit besteht in der Entwicklung eines physikalischen Verfahrens, das eine zuverlässige Schlag-zu-Schlag Erfassung des Kardiotokogramms gewährleistet, und damit einen Beitrag zur Verbesserung der Überwachungsmöglichkeiten des Feten, vor und während der Geburt, leistet. Die aus der Arbeit gewonnenen Kenntnisse sind nicht auf die perinatale Meßtechnik allein beschränkt, sondern lassen auch in vielen anderen Bereichen der medizinischen Diagnostik, so z.B. in der Kardiologie und in der Intensivmedizin, Verbesserungen gegenüber dem gegenwärtigen Stand der Meßtechnik erwarten.
Open Access
Assessment and diagnostic applications of heart rate variability
(1993) Nagel, Joachim H.; Han, Kedu; Hurwitz, Barry E.; Schneiderman, Neil
Though heart rate (HR) is one of the basic parameters in medical diagnostics, precise and reliable assessment of its variability is still an engineering and physiological challenge. Measurement of HR and its changes over time, as in a stress test, is a routine diagnostic procedure to evaluate the cardiovascular condition of a patient. Prenatal monitoring, with its unique problems regarding noninvasive acquisition of reliable fetal data, heavily relies on diagnostic HR analysis.
Open Access
Beam/ray imaging
(1988) Nagel, Joachim H.
The diagnosis of disease is facilitated by imaging internal structures of anatomy and metabolic processes. The basic medical imaging techniques are radiographic (X-ray) imaging, nuclear medicine (gamma-ray) imaging, magnetic resonance imaging (MRI), ultrasound (US) imaging, and endoscopy. With the exception only of ultrasonic imaging, these techniques use electromagnetic waves as information carriers or measuring probes. According to the nature and wavelength of the radiation used and the properties of its interaction with tissue, including its ability to penetrate, specific diagnostic applications and imaging principles have been developed for each type of radiation.
Open Access
Biotelemetry
(1988) Nagel, Joachim H.
Telemetric transmission of functional and physiological information offers many advantages in medical diagnostics and patient surveillance. The telemetric data link avoids direct connections to the recording or monitoring equipment, which are sometimes embarrassing and restraining, thus leaving the patients freely movable. They can be monitored in their natural environment and during work. Accordingly, the measurement does not influence the physiologic system under study, thus avoiding severe artifacts. This advantage is especially important in behavioral studies involving both humans and animals. Implantable telemetry systems transmit internal physiologic signals, or serve to control and program implanted devices, such as stimulators and drug infusion systems, without the need of transcutaneous wire connections which always carry the risk of infection.
Open Access
Coherent ensemble averaging techniques for impedance cardiography
(1990) Hurwitz, Barry E.; Shyu, Liang-Yu; Reddy, Sridhar P.; Schneiderman, Neil; Nagel, Joachim H.
EKG synchronized ensemble averaging of the impedance cardiogram tends to blur or suppress signal events due to signal jitter or event latency variability. Although ensemble averaging provides some improvement in the stability of the signal and signal to noise ratio under conditions of nonperiodic influences of respiration and motion, coherent averaging techniques were developed to determine whether further enhancement of the impedance cardiogram could be obtained. Physiological signals were obtained from sixteen male and female subjects during resting conditions, while delivering a speech and while undergoing submaximal bicycle exercise. Results indicated that improved resolution of dZ/dt signal events could be obtained using coherent ensemble averaging. Although some improvement in precision of event location was obtained, most enhancement of the impedance cardiogram occurred in measurement of the amplitude of the dZ/dt maximum (ejection velocity) during speaking and exercise conditions. Validated increases in dZ/dt maximum exceeding 20% were obtained in some subjects with coherent averaging, suggesting that the diagnostic utility of impedance cardiography can be improved by using this technique.
Open Access
The cold pressor test : vascular and myocardial response patterns and their stability
(1993) Saab, Patrice G.; Llabre, Maria M.; Hurwitz, Barry E.; Schneiderman, Neil; Wohlgemut, William; Durel, Lynn A.; Massie, Clifford; Nagel, Joachim H.
The purposes of the present study were to compare the cardiovascular response patterns evoked by three versions of the cold pressor test (either forehead stimulation or hand or foot immersion) and to determine the reproducibility of the responses over a 2-week interval. Blood pressure, heart rate, stroke volume, cardiac output, total peripheral resistance, and systolic time intervals were obtained during rest and during the cold pressor test in 42 young men. Across conditions, the pressor response was supported by peripheral resistance increases with concomitant stroke volume decreases. Although the response patterns were generally similar across sites, exceptions were apparent for heart rate. Forehead stimulation was characterized by no significant change in heart rate, whereas limb (hand or foot) immersion was associated with significant heart rate acceleration. The responses elicited by the three cold pressor test conditions were reliable and showed little evidence of attenuation over the test-retest interval.
Open Access
Compensation for patient motion in nuclear medicine renal studies by fast correlation image registration
(1993) Georgiou, Michalis F.; Nagel, Joachim H.; Cideciyan, Artur V.; Sfakianakis, George N.
A computer method has been developed to compensate for patient motion which degrades nuclear medicine renal dynamic studies. The method is based on a fast correlation algorithm which accomplishes decoupling of the registration variables translation, rotation and scaling, and converts rotations into cyclic shifts using polar transformations of the images in the Fourier domain. The method has been implemented into a fully automated program which compensates for translational and rotational differences between images acquired while the patient was immobile and images acquired after the occurrence of motion. Preliminary results indicate the usefulness of the program as a clinical tool for salvaging renal scintigraphic studies with patient motion, thus preventing erroneous interpretations or repeat of the examinations.
Open Access
A continuous representation of heart rate
(1992) Han, Kedu; Nagel, Joachim H.; Schneiderman, Neil
Analysis of heart rate variability (HRV) often requires a continuous representation of the inherently discrete heart rate measurement. In combination with a suitable cardiac pacemaker model, e.g. the integral pulse frequency modulator (IPFM), the cardiac event series can be considered as an irregular sampling of a continuous input to the pacemaker model, m(t). Continuous representation of heart rate can thus be achieved by a reconstruction of the input function m(t) from the cardiac event series. Two such representations of the heart rate, the instantaneous heart rate (IHR) and the low pass filtered event series (LPFES), have previously been assumed to be consistent with the IPFM model. Simulations show, however, that the LPFES actually is not consistent with the model. The IHR representation, although consistent with the model, suffers from discontinuities which are both unphysiological and inadequate for subsequent signal processing. A solution to the problem has been developed by introducing M(t), the continuous integral of m(t). The samples of M(t) are specified by the cardiac event series and continuous representation of M(t) is achieved by cubic spline interpolation. The input to the cardiac pacemaker model m(t), or in other words, the representation of the heart rate is given by the derivative of M(t).
Open Access
Continuous representation of unevenly sampled signals : an application to the analysis of heart rate variability
(1994) Nagel, Joachim H.; Tkacz, Ewaryst J.; Reddy, Sridhar P.
The various methods for continuous representation of heart rate were tested on artificial signals as well as on real patient data. The limitation for the tests on real HR data is, that no error for the HR representation can be calculated for the values between measurements since thes 'are unknown. It can clearly be seen that only two of the methods for continuous representation of HR actually retain the original HR values: IHR and DECON. By improvements of the algorithm used for the deconvolution method in terms of higher computational precision, the errors obtained with this technique can be further reduced. But even in its current state, DECON is clearly superior to all the other techniques and can serve to judge the quality of all simplified techniques for the continuous representation of heart rate.
Open Access
The correlation of maternal and fetal heart rates : an important aspect of CTG interpretation
(1986) Nagel, Joachim H.
The heart rate is a rather poor indicator of the physiological condition both in the fetus and in the mother. Even such simple measurements as maternal blood pressure recording can provide additional information. However, for an accurate analysis of the feto-maternal coupling at least cardiac output and maternal oxygen saturation should be monitored. Nevertheless, our investigations have shown that for routine use even the MHR provides sufficient information to improve the interpretation of the CTG quite considerably. The correlation analysis of fetal and maternal heart rates facilitates diagnosis, particularly in borderline cases, and may help to prevent misinterpretation of the CTG. Since the provision of an additional MHR channel in perinatal monitors is very simple and inexpensive, future systems should not be without one.
Open Access
Decomposition of heart rate variability by adaptive filtering for estimation of cardiac vagal tone
(1991) Han, Kedu; Nagel, Joachim H.; Hurwitz, Barry E.; Schneiderman, Neil
Heart rate fluctuations resulting from respiration and other influences upon the cardiovascular system are encoded into the patterns of heart rate variability (HRV). The fluctuations due to respiration are called respiratory sinus arrhythmia (RSA). Since RSA is primarily mediated through the autonomic nervous system (ANS), it is of interest to separate RSA from other influences to assess the underlying ANS function. On the other hand, the RSA may obscure heart rate responses to external manipulations in psychophysiological tests. A method of partitioning the HRV signal which can provide quantitative estimate of RSA as well as true heart rate responses without respiratory disturbances for psychophysiological studies is developed. The analysis of HRV signal is performed using an adaptive filtering system. With the simultaneously recorded respiration signal as a reference input, the HRV signal can be separated into two components, RSA and fluctuation due to other influences. After the separation, the variance of RSA, an estimate of cardiac vagal tone (ECVT), is readily obtained. The performance of the system was evaluated using artificial test signals as well as real HR V data. As a time domain approach, the method is simple, fast and robust.
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, Friedrich
The 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.
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.
Open Access
Diagnosis and modelling of Alzheimer's disease through neural network analyses of PET studies
(1990) Kippenhan, Jonathan Shane; Nagel, Joachim H.
The back-propagation neural network algorithm was applied to the analysis of regional patterns in cerebral function, as demonstrated in positron emission tomography (PET). A trained network was able to successfully distinguish PET scans of normal subjects from PET scans of Alzheimer's Disease patients. It is concluded that the combination of PET and neural networks is a useful diagnostic tool for Alzheimer's Disease. A new paradigm for back-propagation learning is discussed which emphasizes its similarity to template matching. It is demonstrated that, under certain circumstances, the back-propagation network can be used as an estimation tool, as well as a classification tool, i.e., a trained neural network can indicate the criteria by which its classifications are performed.
Open Access
Dialogfähiges programmierbares Infusionssystem
(1980) Nagel, Joachim H.; Müller, Heinz; Schubert, Wolfgang; Thull, Roger; Schaldach, Max
Einige wichtige Medikamente können nicht oral verabreicht werden, weil sie aufgrund ihrer chemischen Struktur im Magen-Darm-Trakt entweder nicht absorbiert oder so verändert werden, daß sie ihre Wirksamkeit verlieren. Andere Medikamente müssen so exakt dosiert werden, daß eine orale Gabe wegen der aus den Halbwertszeiten resultierenden Konzentrationsschwankungen nicht in Frage kommt. Diese Probleme können nur mit Hilfe eines Infusionssystems gelöst werden, das in der Lage ist, den jeweiligen Medikamentenbedarf direkt in das Blut oder das Körpergewebe abzugeben. Hit Hilfe der kontinuierlichen gesteuerten oder geregelten Infusion läßt sich eine optimale Medikamentenkonzentration aufrecht erhalten. Zur Abgabe kleinster Medikamentenmengen wurde eine extrakorporale, tragbare Infusionseinheit entwickelt, die zunächst für die programmierte Insulindosierung bei der Diabetes-Therapie zur Anwendung kommt.
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, Neil
In 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.
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.
Open Access
Digital signal processing of the fetal heart sound
(1982) Kartmann, Peter; Schlotter, Claus M.; Zhou, Li Gao; Nagel, Joachim H.; Schaldach, Max
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Open Access
Der Einfluß verschiedener Insulininfusionsprofile auf Blutzuckerführung und Insulinverbrauch bei der Therapie von Typ-I-Diabetikern mit nichtrückgekoppelten, portablen Insulininfusionssystemen
(1983) Strack, Thomas; Schulz, Gerhard; Beyer, Jürgen; Krause, Ulrich; Nagel, Joachim H.; Beutelspacher, Friedrich
Der Stoffwechsel insulinpflichtiger Diabetiker kann nicht immer durch die konventionelle subkutane Therapie befriedigend eingestellt werden. Blutzuckerkontrollierte Infusionssysteme hingegen sind zur Zeit nur für die klinische Diabetestherapie verwendbar, da in vivo messende Blutglukosesonden für portable Infusionssysteme nicht zuverlässig genug arbeiten. So kommen vorläufig nur nichtrückgekoppelte Insulininfusionssysteme für die ambulante Behandlung des Typ-I-Diabetes mellitus in Betracht. Ein größeres Problem stellt die Kontrolle des postprandialen Blutzuckeranstiegs dar: Der Nüchternblutzuckerwert sollte innerhalb von 2 Stunden wieder erreicht werden, und zwar ohne das Risiko schwerer Hypoglykämien in dieser Zeit. Offenbar ist dies nicht nur ein Problem der Insulindosis, sondern auch eine Frage des Infusionsprofils selbst.
Open Access
Elektronische Simulation der Reizausbreitung im Herzen
(1980) Müller, Heinz; Nagel, Joachim H.; Schaldach, Max
Das beschriebene Gerät erweist sich als wertvolles Hilfsmittel zur Veranschaulichung der Reizausbreitung im Herzen im Zusammenhang mit den meßbaren Potentialen. Durch Anschluß eines Schrittmachers kann dessen Verhalten bei verschiedenen Rhythmusstörungen des Herzens sowie bei Störfällen beobachtet werden.