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Biomedical subjects

H Hutten

Publications and source records attributed to H Hutten.

At least 37 records · Page 2Linked to original sources
PubMed1997

Influence of ionic shifts during dialysis on volume estimations with multifrequency impedance analysis.

During dialysis the ion concentrations in many body fluids change significantly. The influence of these changes on the accuracy of volume measurements with bioimpedance spectroscopy is investigated by the following procedure: Plasma ion concentrations and impedance spectra (5-500 kHz) are measured during six standard haemodialyses. Intracellular ion concentrations are estimated using a multi-compartment model. Intra- (ICV) and extracellular (ECV) volumes are calculated using a fluid distribution model (FDM) based on Hanai's mixture theory. The input variables of the FDM are intra- and extracellular resistance data that have been fitted from impedance spectra with a Cole-Cole model. Resistivity changes (RCs) due to concentration changes of Na+, K+, Cl-, HCO3- and unspecified intracellular ions are estimated. The FDM is corrected for the RCs. Corrected ICVs and ECVs are calculated and compared with uncorrected values. The range of relative RCs between the start and end of the dialyses is -3.2% to 1.4% in the ECV and -3.7% to 1.7% in the ICV. From the RCs, volume estimation errors of -1.0% to 1.9% (ECV) and -1.2% to 2.1% (ICV) relative to the initial values have been calculated. At the end of dialysis, the percentage of the error with respect to the volume change is < 15% for the ECV but > 20% for the ICV. Consequently, a correction of the FDM for RCs is necessary to obtain more reliable ICV data.

Body Fluids↗
PubMed1997

Effect of postural changes on the reliability of volume estimations from bioimpedance spectroscopy data.

Bioimpedance spectroscopy (BIS) has been suggested for the assessment of fluid shifts between intracellular (ICV) and extracellular volume (ECV) during dialysis. The electrical tissue parameters are estimated by fitting a Cole-Cole model to the impedance data. Those parameters are used for the calculation of ICV and ECV with a fluid distribution model (FDM). We investigated whether postural changes cause artifacts in the volume data measured with a commercial BIS system. This is of importance at the beginning of dialysis, when the patient lies down for treatment. Volume estimations were performed during tilt table experiments with 11 healthy volunteers. Impedance spectra (5 to 500 kHz) were recorded for the total body as well as for body segments (leg and arm) during three phases: (1) 30 minutes resting in a supine position after standing; (2) 30 minutes 70 degrees head up tilt; and (3) a 30-minute resting period in a supine position. ECV and ICV were estimated with a commercially utilized FDM which is based on Hanai's mixture theory. A monoexponential function was fitted to the data for extracting the time constants and the extrapolated steady state values of the volume changes. The ECV and ICV data changed significantly during all three periods, that is, a steady state could not be reached within 30 minutes. During phase 1 the ECV decreased by 1.8 +/- 0.7%, in the tilt phase it increased by 3.8 +/- 1.1%, and in phase 3 it decreased again by 2.9 +/- 1%. The ICV increased by 3.6 +/- 2.4% during phase 1 and decreased by 6.8 +/- 5.1% during tilting; in phase 3 it increased by 4.6 +/- 1.7%. The time constants were 36.4 +/- 12.7 minutes (ECV) and 10.8 +/- 5.4 minutes (ICV) during phase 3. Segmental measurements revealed that the legs contribute significantly to the measured volume changes. The absolute volume changes in ICV and ECV differed significantly in all phases, and the same was found for the time constants during phases 1 and 3. From this discrepancy it is concluded that the measured volume changes are artifacts that are caused by extracellular fluid redistribution. Furthermore, it appears unlikely that the measured fluid shifts actually occur between ECV and ICV in the absence of osmotic changes in the body fluids. The validity of the method for a reliable assessment of volume changes during dialysis appears questionable, as dialysis-induced volume changes lie in the same range as the orthostatically-induced spurious volume changes.

Adult↗
PubMed1996

Evoked epimyocardial electrogram for rejection diagnosis after heart transplantation.

An endomyocardial electrogram (ECG) was reported to be a sensitive and practicable method for rejection monitoring after heart transplantation. Long-term follow up was limited, however, by variations of signals. The repolarization part of ECG signals vary with changes of heart rate. Both can be avoided by using pacemaker-induced signals. For stimulation and sensing of the ventricular-evoked response, a new type of electrode with fractal surface structure was used. Twenty patients undergoing heart transplantation were evaluated. Amplitudes of the depolarization and repolarization part of the ventricular-evoked response signals were analyzed and related to the degree of acute rejection according to histological findings from endomyocardial biopsy. Signals were transferred by Internet and analyzed automatically. In the case of focal moderate rejection (grade 2, International Society for Heart Transplantation grading) and higher degrees of rejection, a significant amplitude decrease was found. This sensitive non-invasive method for rejection monitoring with a high level of reliability provides the possibility of reducing the number of endomyocardial biopsies.

Adult↗
PubMed1996

[Cardiac pacemaker as bridge to cardiac telemonitoring].

Modern pacemakers and electrodes are equipped with supplementary features that can be utilized for many problems related to cardiac diagnosis and therapy management. Especially the recording and computer-assisted analysis of intramyocardial electrograms (IEGM), particularly of ventricular evoked responses (VER), supplies important information. The IEGMs are transmitted with large bandwidth from the implanted pacemaker to an extracorporeal receiver and from there via Internet to a central data processing station, where a specially designed software for IEGM processing is available. An individual password secured account is installed for each user. After signal processing is completed, a comprehensive patient report including trend courses and relevant clinical data is provided and can be utilized by the user for further decisions. Using this basic structure, CHARM (Computerized Heart Acute Rejection Monitoring), a system for non-invasive rejection monitoring after heart transplantation, has been developed and successfully evaluated in a clinical environment.

Computer Systems↗
PubMed1996

Dynamical control of the dialysis process. Part II: An improved algorithm for the solution of a tracking problem.

An efficient algorithm for the optimization of process parameters during dialysis has been developed. By solving a tracking-problem for prescribed time courses of distinguished variables, it is possible to compute optimal concentrations of electrolytes in dialysate as well as an optimal rate of ultrafiltration. These variables are indirectly influencing the status of the patient and can be directly modelled. They are describing the important exchange processes between blood and dialysate as well as between the different distribution spaces within the patient during dialysis. Their time courses are determined by an individually identifiable patient model. The tracking problem was treated as a dynamic optimization problem, and a continuous descent procedure which is usually employed for solving unconstrained static optimization problems has been adapted in such a manner that it is applicable for the solution of this problem. The used method is characterized by its simple mode of application, short solution time and moderate storage need. Especially in cases of contradictional requirements for desired time courses of model outputs the used optimization method performs well.

Algorithms↗
PubMed1996

Paced epimyocardial electrograms for noninvasive rejection monitoring after heart transplantation.

BACKGROUND: Diagnosis of acute heart rejection after transplantation with the help of epimyocardial electrograms has been reported as a sensitive and practicable method. Long-term follow-up has been limited, however, by variations o signal, which can be avoided by using pacemaker-induced signals. METHODS: For stimulation and detection of the ventricular evoked response, a new type of electrode with fractal surface structure was used. Seventeen patients undergoing heart transplantation were included in the study. Amplitudes of the depolarization and repolarization parts of ventricular evoked response signals were analyzed and related to the degree of acute rejection according to histologic findings from endomyocardial biopsy. RESULTS: In cases of focal moderate rejection (grade 2, International Society for Heart and Lung Transplantation grading) and higher degrees of rejection, significant amplitude decreases were found. CONCLUSION: This sensitive noninvasive method for rejection monitoring with a high level of reliability provides the possibility of reducing the number of endomyocardial biopsies.

Biopsy↗
PubMed1995

Development and critical evaluation of an improved comprehensive multicompartment model for the exchange processes during hemodialysis.

An improved comprehensive multicompartment model for the simulation of the most important metabolic state variables in the patient during dialysis is presented. With this approach time courses of urea, creatinine, K+, Na+, Cl-, HCO3-, H+ and CO2 can be predicted. Additionally, osmotic water shifts as well as resting membrane potentials are calculated. The model contains the following extensions compared to classical approaches: For the calculation of osmotic water shifts, not only sodium, but also urea, potassium, chloride and unspecified indiffusable ions are taken into account. Furthermore, hemodynamic aspects are considered by assuming two tissue groups with different perfusion. Thus it is possible to estimate the influence of hemodynamic parameters (e.g. cardiac output or blood flow distribution) on the exchange processes. The model can be adjusted individually by several system parameters. This adjustment is performed by minimizing the sum of the quadratic differences between simulated and measured plasma concentrations of the considered substances. A first validation has been performed successfully with measured data from 18 dialysis patients. After the effective whole-body exchange area of the resting cell membranes for potassium, sodium and chloride had been estimated, rebound effects for those electrolytes could be simulated successfully.

Acid-Base Equilibrium↗