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Biomedical subjects

M Schaldach

Publications and source records attributed to M Schaldach.

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

[Physical mechanisms of solid-protein interactions in the interface between amorphous silicon carbide and fibrinogen].

State of the art in biomaterial research and implant design is a compromise between functionality and biocompatibility. Consequently the results often have disadvantages with respect to both aspects. In regard to biocompatibility the activation of the clotting system by alloplastic materials is of great significance, because it necessitates anticoagulant therapy. Further improvements of implant technology require an understanding of the interactions between blood and implants. Therefore a microscopic model of thrombogenesis at alloplastic surfaces will shortly be presented, which relates thrombogenicity of a material to the electronic structure of its surface. The requirements for high hemocompatibility, which result from this model--especially in regard to the density of states and the conductivity at the surface--are fulfilled by an amorphous alloy of silicon and carbon (a-SiC:H). The advantage of amorphous materials is that they do not obey stoichiometric rules. Thus they allow a continuous adjustment of the electronic parameters without fundamental changes of their mechanical and chemical properties. The theoretical results where checked by total internal reflection intrinsic fluorescence spectroscopy (TIRIF) as well as thrombelastography experiments (TEG). In comparison to conventional materials like titanium or LTI carbon the TEG-clotting time of a-SiC:H-coatings is prolonged in excess of 200%. As a consequence a-SiC:H is well suited as a hemocompatible coating material for hybrid structuring of cardiovascular implants.

Biocompatible Materials↗
PubMed1990

Cardiovascular laser application.

With the invention of the laser, many clinical disciplines have taken advantage of this new energy source. Its precision, intensity and energy density is superior to all other known surgical devices. Based on the principle of light amplification from a photon-emitting resonator, the monochromaticity, collimation and coherence provide the high-energy density of the laser beam for medical applications. The state-of-the-art and future potential of laser use in cardiovascular diseases will be reviewed. Most of the work in this field has been accomplished during the past decade with numerous research projects. Although many technical advances have been made, so far the results in cardiovascular medicine are in the areas of vessel anastomosis, ablation of conduction passes for arrhythmia therapy, and angioplasty. In this paper, special attention will be given to the recent success in XeCl excimer laser application for photodecomposition of tissue with a goal of improved recanalization. The high-power density of the XeCl excimer laser provides significant advantages for the disruption of both embolic and calcified plaque. Regardless of the type of tissue ablated, gross, histologic, and ultra-structural analysis confirmed the absence of thermal injury in luminar recanalization as well as in animal studies. Progress in the manufacture of catheters, with multiple very small diameter fibers, led to the decisive breakthrough in clinical laser angioplasty. Peripheral as well as coronary arteries have been successfully recanalized followed by balloon dilatation. The ease of application and the success achieved thus far have resulted in an optimistic assessment for laser medicine.

Angioplasty, Balloon↗
PubMed1990

Artificial heart valves: improved blood compatibility by PECVD a-SiC:H coating.

Implants are steadily increasing in importance as substitutions for body functions. With the present state of the art, the limitations of the application of cardiovascular implants are due to insufficient performance of biomaterials. Present research in this field is being concentrated on efforts to improve the thrombus resistance of conventional materials by coating with semiconducting materials to actively influence the electrochemical interaction between the condensed matter and blood proteins. Based on an electrochemical model of the interaction of fibrinogen with an artificial surface and the resulting requirements for improving hemocompatibility, a coating of amorphous hydrogenated silicon carbide deposited by plasma-enhanced chemical vapor deposition (PECVD) is presently under evaluation as a special coating material for cardiovascular prostheses and is herein described. In particular, first results are published concerning the optimum deposition parameters in the PECVD process and cell culture tests. Experimental results of comparative partial thromboplastin time studies serve the purpose of proving the validity of the electrochemical reaction model referring the hemocompatibility of implantable materials to their semiconducting surface properties. The aim of this article is to demonstrate a feasible method for an antithrombogenic surface modification based on doped amorphous silicon carbide films that is in full conformance to the above mentioned model.

Biocompatible Materials↗
PubMed1990

Automatic adjustment of pacing parameters based on intracardiac impedance measurements.

The selection of the parameters used for rate control is determined not only by technical feasibility, but also by patient considerations. Technical feasibility considerations include long-term stability and reliability of the sensor, as well as susceptibility to interference. The patient considerations relate to the patient's physical state, including the various physiological and pathologic conditions. The rate response must be in proportion to circulatory demand. The specificity of the rate response is of particular importance for the patient with low cardiac reserve. The development of future pacemakers aims at providing additional patient benefits, with a reduction of the effort associated with initial parameter selection and patient follow-up. This will be achieved by utilizing a better understanding of the integration of the control mechanisms for the entire cardiovascular system under physiological and pathological conditions. To support the development of the future pacemakers, we must utilize realistic multiparametric models of the cardiovascular system. These models will assist the evaluation of potential algorithms for integrating multisensor signals into a single pacing rate. The parameterization and validation of these models are important issues to be addressed. Intracardiac impedance measurements in conjunction with microprocessor controlled signal processing and improved lead technology provide a great variety of practical applications for physiological control of the pacing rate and the automatic adjustment of pacemaker parameters. The concepts of an "intelligent" pacemaker capable of automatic control in response to changes in the pacing requirements under a variety of physiological and clinical conditions are presented.

Cardiac Pacing, Artificial↗
PubMed1990

Sputter-deposited TiN electrode coatings for superior sensing and pacing performance.

The sensing and pacing performance of pacemaker electrodes is characterized by the electrochemical properties of the electrode/tissue interface affecting tissue reactions and the kinetics of the ionic exchange. The usually smooth metallic electrode surface results in a high pass filter characteristic. To better match the electrode's filter characteristic to the spectral content of the depolarization signal, various combinations of electrode shape, material and surface structure have been researched. The electrode with sputter-deposited TiN coating presented in this report has been designed to meet the demand for low acute as well as chronic thresholds and superior sensing performance not only with respect to spontaneous activity but also regarding the detection of the evoked response. The clinical results obtained with this electrode prove the excellent pacing and sensing properties resulting from minimized polarization losses and optimized filtering of the signal to be detected, respectively. The acute and chronic clinical advantages over previous concepts are attributed mainly to the biocompatibility of the material used and the microcrystalline surface structure achieved by the coating process. The design concept of the new electrode is presented together with the clinical results obtained. While the advancements in microelectronics and battery technology have certainly formed the basis for the development of pulse generators featuring an ever increasing versatility of functions at the same or even smaller pacemaker dimensions, from a point of view of pacing system performance the development of improved electrode concepts as the one presented must be regarded as equally indispensable.

Biocompatible Materials↗
PubMed1990

[Mechanical aspects of the development of artificial heart valves].

The development of an antithrombogenic coating permits a hybrid design for artificial heart valves. A substrate material optimized for its application is coated to meet the electrochemical requirements of improved hemocompatibility. But future progress in artificial heart valves requires an improvement in design as well as of the material. The basis of both aspects is the determination of such fundamental mechanical properties as the elasticity and plasticity of the valve ring and the deformation and fraction behaviour of the occluder. Analytical and numerical calculations of various different models result in different requirements for the substrate of ring and occluder. A combination of high elastic temper and low resistance to flow requires a ring material with a Young's modulus of 40 GPa or more, and a 0.2% proof stress to (Young's modulus)2/3 ratio of 0.3 MPa1/3. The best occluder materials should have a Young's modulus of more than 50 GPa and a flexural strength of at least 800 MPa. On the basis of these criteria, a heart valve consisting of a TiA15Fe2,5 ring and occluders made partially stabilized zirconia is introduced.

Biomechanical Phenomena↗