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Biomedical subjects

J D Meindl

Publications and source records attributed to J D Meindl.

11 recordsLinked to original sources
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↗
PubMed1977

Direct calibration of a totally implantable pulsed Doppler ultrasonic blood flowmeter.

A totally implantable pulsed Doppler ultrasonic blood flowmeter has recently been developed to provide information on the velocity-flow profile in a vessel as well as its diameter. Volume flow can be indirectly obtained according to the formula: Q = (phi/4)(diam)2-v. In order to determine the accuracy of this estimate, in vivo direct bleedout measurements were performed on the abdominal aorta of six dogs with an overall accuracy in 77 trials of +2.0 +/- 8.7% (mean +/- 1 SD). The best-fit mean linear regression line was found to be: flowmeter output = 1.013-true flow + 5.1 ml/min. The scatter in the flowmeter's accuracy is thought to be due to small variations in the angle of the transducer. The source of the 2% overestimation in the mean accuracy could not be directly attributed to any one condition; the error is sufficiently small that in many cases it can be neglected.

Animals↗
PubMedDate not supplied

State-of-the-art in two-dimensional ultrasonic transducer array technology.

Attention is given to means of sensing ultrasonic energy distributions over an area. Under the restraints appropiate to real-time imaging of deep body organs, piezoelectric arrays offer the most promising method. Adaptation of integrated circuit techniques to array assembly permits very large arrays of small elements to be batch fabricated. Further, special semiconductor switching devices specifically designed for addressing the array have been produced and applied. These permit both the passage of weak received signals and the application of voltage and current levels sufficient for transmission without significant disturbance of the basic piezoelectric element properties. Emphasis is placed on the complete data acquisition, processing, and display flexibility that arises from an array capability. Operation becomes possible in any of the presently used A or time motion (TM), in real time B or C scan, or in novel scan patterns adapted to specific organs. Further development with acoustic and electronic focusing, taking advantage of the unique possibilities obtained with the bidirectional array structure, is discussed.

Transducers↗