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Biomedical subjects

J W Knutti

Publications and source records attributed to J W Knutti.

11 recordsLinked to original sources
PubMed1983

Nature of inducible ventricular tachyarrhythmias in a canine chronic myocardial infarction model.

A canine model suitable for serial conscious studies was developed to evaluate the nature of sustained ventricular tachyarrhythmias in chronic experimental myocardial infarction. Thirteen dogs underwent left anterior descending coronary artery ligation followed by complete reperfusion; 11 sham-operated dogs served as controls. In this model, ventricular tachyarrhythmias are inducible in most dogs with experimental infarction and in several dogs without this condition. The morphologic features, rate and drug response of the induced arrhythmias are unlike those of human ventricular tachycardia. Tachyarrhythmia induction is facilitated by anesthesia and thoracotomy. This canine infarct model does not adequately imitate human recurrent ventricular tachycardia, but may simulate human sudden cardiac death.

Animals↗
PubMed1983

Central body temperature as a guide to optimal heart rate.

Studies in man suggest that fixed-rate artificial pacemakers do not return hemodynamic function to normal, since the principal mechanism for the increase in cardiac output with exercise, increased heart rate, is not restored. Special pacemakers are available that can detect atrial activity and pace the ventricles in coordination, but nearly half of the patients receiving artificial pacemakers have abnormal atrial function (atrial fibrillation, sick sinus syndrome). This study examined the effects of exercise on the temperature of blood returning to the right atrium. Precision thermistors, placed in the right hearts of conscious dogs, recorded temperature increases of 1 degree C (range 0.4-1.5 degrees C) during submaximal treadmill exercise. Temperature change correlated well with work load and changes in heart rate.

Animals↗
PubMed1980

Integrated circuit implantable systems.

A series of totally implantable telemetry systems have been developed to chronically determine such parameters as blood flow, pressure, biopotentials and temperature. This instrumentation is currently used in medical research involving laboratory animals. Custom integrated circuits are used to realize the signal processing complexity needed for accurate and stable measurements within the size and power constraints of an implantable electronics system.

Animals↗
PubMed1979

Totally implantable directional Doppler flowmeters.

Two totally implantable Doppler blood flowmeters have been developed for the chronic measurement of deep-body flows; made possibly by two custom-integrated circuits. The CW and pulsed Doppler instruments are small (less than 2.5 cm3), use little power (less than 30 mW), and have excellent baseline stability. The pulsed Doppler flowmeter is applied principally when velocity-profile information or a nonencircling transducer assembly is required but where minimal restraint of the animal for inductive telemetry is permissible. Using a circumferential cuff, the CW Doppler flowmeter monitors Doppler data over a at least a 3-meter range by means of RF telemetry and produces a single velocity estimate. These instruments compliment each other and other telemetry systems by proving the researcher with alternatives for the long-term measurement of deep-body flow without percutaneous leads.

Animals↗
PubMed1979

Totally implantable dimension telemetry.

A totally implantable dimension telemetry system has been developed to instrument animals for chronic physiological research. Implantable signal processing electronics allow free-roaming animals with no percutaneous leads while retaining the long-term redproducibility of fixed implanted transducers. Two low-powered, custom-integrated circuits have been developed and assembled into an implantable package capable of measuring one dimension channel. The system has been operated in the amplitude modes of through-transmission and reflection as well as in a new Doppler-power configuration and aimed at determining interfaces between blood and surrounding structures. In a addition to single channel systems, these ICs are key elements in multimode, multidimensional implants capable of more accurate characterization of deep body structures.

Anatomy↗
PubMed1979

An integrated circuit approach to totally implantable telemetry systems.

A series of totally implantable telemetry systems has been developed to determine such key physiological parameters as blood flow, pressure, dimensions, temperature, and bioelectrical activity in chronic research animals. Custom integrated circuits provide the signal-processing complexity and performance required to sufficiently instrument the animals for an accurate prediction of human responses. Additional implant and transducer technologies are necessary to complete the instrument package. Although the costs of these technologies are high, they are more than offset by the unique information obtained and overall reduction in the expenses of medical research because fewer animals can be studied over longer periods. A number of the IC-based implants are in use in several physiology and experimental drug studies where adequate reliability and performance could not be achieved by alternate approaches.

Animals↗
PubMed1979

A general-purpose implantable multichannel telemetry system for physiological research.

The majority of physiologically significant parameters can be accurately measured with relatively simple transducers and with a minimum of sophisticated electronics; such parameters include temperature, pressure, and electrical activity and generally require less than a 200 Hz bandwidth. In most experiments, however, measurements at multiple sites are needed to characterize fully a particular response, and the use of totally implantable telemetry systems becomes attractive as the problems of percutaneous leads in conscious animals are compounded in proportion to the number of sensors. These systems have been produced in limited quantities because a large number of components and long assembly times are necessary to provide simple amplifications and signal processing in a small implantable package. A new six-channel system incorporates all signal processing on a single integrated circuit, and only one CMOS divider chain and an integrated telemetry transmitter are required for support. This high level of integration accelerates assembly time and increases reliability by minimizing the interconnections. Such advancements are essential before the full potential of implantable telemetry can be realized. This paper details the performance of this system during initial applications requiring pressure, bioelectrical, or temperature telemetry.

Animals↗
PubMed1979

Integrated power controllers and RF data transmitters for totally implantable telemetry.

Data transmitters and power/source controllers are common elements in all totally implantable instrumentation systems. Two custom-designed integrated circuits have been developed for these elements and have significant impact on the realization of compact reliable telemetry packages. The first is an elapsed-time power switch that can remotely turn on implanted battery-powered systems with a short RF burst; to prevent accidental battery drainage, it will automatically turn off after a preprogrammed time (1-5 min). The second is a precision RF transmitter capable of operation up to 125 MHz in either FM or pulse-coded format and requires only two nonintegrated inductors. These IC systems are basic building blocks for a large number of totally implantable telemetry applications.

Electric Power Supplies↗
PubMed1979

Applications of totally implantable telemetry systems to chronic medical research.

The motivation for the development of advanced totally implantable telemetry systems is to improve the quality of medical care through a more detailed understanding of basic physiological processes. Three research protocols in electrophysiology, hepatic hemodynamics, and cardiac pharmacology are described which rely on new implantable instrumentation; these devices allow chronic measurements in the conscious animal of such diverse parameters as aortic and ventricular pressures; atrial, ventricular, and bundle of HIS electrograms; aortic and coronary blood flow, and total hepatic blood flow by measuring velocity profiles in the portal vein and the hepatic artery. The compact size and high reliability now achievable with these telemetry systems provides new tools to the researcher for the study of the body in health and disease.

Animals↗