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Biomedical subjects

H Hutten

Publications and source records attributed to H Hutten.

At least 19 recordsLinked to original sources
PubMed1992

Right ventricular conductance to establish closed-loop pacing.

Innovations in pacing technology, which include the addition of rate-responsive features to programmable pacemakers, can improve the quality of life of patients suffering from sick sinus syndrome. Among the strategies providing rate-adaptive cardiac pacing, the most attractive is the physiological restoration of closed-loop chronotropic control. This paper describes how autonomic nervous system (ANS) control information is extracted from dynamic measures of myocardial contractile performance obtained from unipolar conductance measurements using the stimulation electrode in the right ventricular cavity. The pacemaker uses the ANS information to modulate pacing rate and restore normal physiological control of heart rate. A new algorithm, regional effective slope quantity (RQ), for isolating the ANS signal was developed. The resulting signal, ventricular inotropic parameter (VIP), is a normalized parameter proportional to the strength of the ANS inotropic signals to the myocardium. The efficacy of the ANS control concept was evaluated in multi-centre studies. Patients with AV block and VIP-controlled pulse generators performed defined exercise protocols. The ANS-controlled pacing rate and the spontaneous sinus rate were closely correlated. Blood pressure and subjective patient reports further indicated that good control of the cardiovascular circulation was achieved.

Autonomic Nervous System↗
PubMed1992

Intracardiac impedance to determine sympathetic activity in rate responsive pacing.

Modern pacemaker technology renders possible the adaptation of pacing rate to hemodynamic requirements. The most ambitious approach aims at restoration of the physiological closed-loop system by utilizing the information supplied by the autonomic nervous system (ANS) and extracted from myocardial contractile performance. Measurement is accomplished by the impedance method using the stimulation electrode as the measuring electrode. The ventricular inotropic parameter (VIP) has been identified as an ANS dependent parameter. A special detection algorithm, regional effective slope quantity (RQ), with high ANS sensitivity has been developed. Rate adaptation has been achieved by using an individually adjustable inotropic index (II). The concept has been evaluated in a multicenter study using a standardized exercise protocol. The results in patients with AV block demonstrate excellent agreement between spontaneous sinus rhythm and the ANS-controlled stimulation rate during different forms of exercise. Measurement of mean arterial blood pressure (MABP) supports the physiological approach of adapting the pacing rate to various types of hemodynamic challenges.

Algorithms↗
PubMed1992

Autonomic nervous system controlled closed loop cardiac pacing.

A multicenter clinical study is presented, which focuses on the reestablishment of closed loop cardiac control in patients with chronotropic insufficiency. Using the information about sympathetic tone contained in the myocardial contractility, it is possible to reconnect the heart rate to the physiological control mechanisms. Intracardiac impedance is measured with the ventricular electrode and the ventricular inotropic parameter (VIP) is derived from that. The VIP serves directly as input to the control of heart rate by the pacemaker. Over 200 patients have received autonomic nervous system (ANS) controlled pacemakers. The patient-pacemaker system was investigated in different ways. This included standard exercise tests, long-term studies of every day activities over 24 hours, psychological, and pharmacological challenges. To prove the validity of the approach we specifically looked at (1) the appropriateness of changes in paced heart rate with sympathetic tone during exercise, (2) the correlation between heart rate and sinus rate, if detectable, and (3) the correlation between the echocardiographically determined preejection period (PEP) and the VIP controlled heart rate.

Autonomic Nervous System↗
PubMed1992

[Measuring intracardiac impedance for the determination of sympathetic nerve activity in frequency-adapted electrostimulation--Part 2: Clinical results].

The results of a multicenter clinical study involving patients receiving the first ANS controlled rate adaptive pacemaker are presented. In the patients with primary or secondary chronotropic insufficiency, it is possible to reestablish the closed loop control system that includes the baroreceptors, the medulla oblongata, the cardiac output and the mean arterial blood pressure. This system serves to keep the blood pressure constant in the face of changing demands on the circulation. Utilizing intracardiac impedance measurements, the myocardial contractility can be determined, which contains information about the current sympathetic tone, and thus represents an excellent physiological input for a rate adaptive mechanism. The results presented are taken from a study population of over 200 patients. The objective evaluation of this new approach was performed echocardiographically, by ergometry and 24-hour Holter monitoring.

Adult↗
PubMed1992

[Comparative evaluation of equipment: the problem of false evidence. Remarks on the paper by P. März: In electric nerve stimulation is it possible to judge the status of the nerve from the intensity of muscle contraction?].

In a recent comparative evaluation of electric nerve stimulators, data were published for the device of a certain manufacturer that disqualified this stimulator for the claimed application. For this reason, an extensive follow-up examination has been executed. The results of this follow-up examination convincingly show that the data of the stimulator are significantly better than published in the comparative study. It was not possible with this follow-up examination, however, to supply an explanation for the totally erroneous results in the first study. If after all any trustworthiness can be given to that comparative study, it can be emphasized that the examined stimulator compares favourably with those devices that had been declared as especially qualified in the comparative study. In this context, the problem is discussed that is related with the potential of influencing and manipulation as part of comparative evaluation studies.

Evaluation Studies as Topic↗
PubMed1991

Theoretical approach and clinical application of kinetic modelling in dialysis.

Using kinetic modelling for shaping profile dialysis, we present a promising approach to improve the cardiovascular stability of patients during dialysis treatment. In order to obtain an insight into the physiological mechanisms of increased stability, a model considering alterations of electrolytes and water distribution and of acid-base status was developed. This algorithm was used for the evaluation of 114 dialysis sessions, which were performed with highly individualised profiles. Each profile was developed for one patient by trying empirically to prevent episodes of hypotension as well as other clinical problems throughout dialysis. The main advantage of profile dialysis compared to standard bicarbonate dialysis, for example, is a reduced water influx into the cell during the treatment. According to our clinical and theoretical results a correlation between water influx into the cell and time of occurrence of hypotensive episodes in individuals can be assumed. Hypotension usually starts after 0.5 litres of water have entered the intracellular space, regardless of the time necessary for this fluid shift.

Acid-Base Equilibrium↗
PubMed1990

A comprehensive model of the dynamic exchange processes during hemodialysis.

The present model for the mathematical description of exchange processes during hemodialysis includes submodels for potassium, sodium, chloride, acetate, acid-base status (with CO2, bicarbonate and H(+)-ions), water distribution, oxygen, ventilation, and the uremic catabolites urea, creatinine, and vitamin B12. For potassium, sodium and urea a 2-compartment model is used consisting of the extra- and the intracellular space. For chloride, creatinine and vitamin B12 a 3-compartment model is necessary. For the description of acetate kinetics a 1-compartment model consisting of the extracellular space is sufficient. For description of the acid-base balance the model includes three submodels for CO2, bicarbonate, and hydrogen ions. All submodels are made of eight compartments, namely the intracellular and the interstitial space as well as six spaces for the blood. The three submodels are coupled to each other by the chemical reaction of CO2 to HCO3- and a H(+)-ion. Besides this reaction the diffusive exchange between the compartments, the convective transport with the blood and the elimination through the dialyzer and the lung for the molecules and ions are considered. Because of the strong buffer capacity of plasma and intracellular proteins, the functional compartments for hydrogen ions are larger than the anatomical spaces. Also the influence of extracellular pH on the electrolyte distribution at the cell membrane has been considered. With this model, which will be adapted to the patient by more than 45 individual parameters, the mass transfer and the course of concentrations during hemodialysis therapy can be reproduced adequately. Further on the values of some unknown parameters, such as the metabolic rate for acetate in the organism, can be estimated by varying the parameters systematically for several runs of the computer simulation until the simulation results are optimally fitted to measured data.

Acid-Base Equilibrium↗
PubMed1990

A physiological approach to different concepts of rate adaptive cardiac pacing.

Physiological aspects of rate adaptive pacing are dealt with in the context of the cardiovascular control loop with the cardiac output as the controlling quantity and mean arterial blood pressure as the controlled quantity. Different methods proposed or clinically investigated are analyzed with respect to cardiovascular control mechanisms. To qualify as physiologic, the sensor-driven pacing rate must respond to disturbance variables similarly as the sinus node. To achieve this, the feedback signals, which control the cardiac output and are summarized as the sympathetic and parasympathetic innervation of the heart, are prime candidates as input signals for rate control in the presence of chronotropic insufficiency. Since only sympathetic tone can serve to increase contractility and thereby stroke volume and cardiac output in the absence of rate support, its meaningful measurement is the key for physiological sensor-driven rate control. PEP clinically has proved to be a measure of contractility, which represents sympathetic tone as it affects central hemodynamics. PEP-controlled pacing rate adaptation therefore enables restoration of a closed-loop pacing system utilizing those components of the physiological system that are still functioning.

Adaptation, Physiological↗