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Biomedical subjects

H L Valenta

Publications and source records attributed to H L Valenta.

11 recordsLinked to original sources
PubMed1997

Stability analysis of a controller for a high power ultrasonic actuator.

High power ultrasonic transducers for medical surgery require closed loop regulation of operating frequency and amplitude. This is a tutorial design paper which provides a description of the fundamental component properties and the criteria which are required to drive a power ultrasonic transducer. In addition, a classical root locus system analysis of the regulator servo in conjunction with requirements for idealizing individual blocks is also provided.

Surgical Equipment↗
PubMed1996

Cutting force measurements platform for quantitative assessment of surgical cutting instruments.

This paper describes the design and development of a Cutting Force Measurement Platform (CFMP) in the R&D department at Valleylab, Inc. for quantitative assessment of surgical instruments used for cutting tissue. This system controls various parameters including cutting speed, while measuring the force required as a function of time. The cutting force measurements are acquired and analyzed by a data acquisition program. The relevance of the cutting force measurements with regards to electrosurgery are discussed.

Animals↗
PubMed1996

Dynamic simulation using a graphical programming language.

A power oscillator, suitable for energizing an ultrasonic surgical cutter was simulated using a graphical programming language. The simulation included a model of the amplitude control system as well as the ultrasonic actuator. In addition, those elements which existed in a practical oscillator and were typically obscure to the design requirements were identified, simulated and discussed.

Computer Simulation↗
PubMed1992

The next generation of students, are you ready?

School administrators across the country are under pressure from parents, community leaders and politicians to improve the public education system for the average student. As a result, several new programs are being studied, developed and implemented in grades K through 12. These programs will impact several areas at the public school building level from K through 12: 1) Goals for multicultural learning; 2) The grade structure and objectives at the elementary, middle and high school levels; 3) The use of technology in all subjects; 4) Open and direct teaching of critical thinking skills in all courses; 5) Methods of assessment which include self assessment and portfolios as well as standardized tests; and 6) The incorporation of the guaranteed high school diploma.

Curriculum↗
PubMed1991

Consideration of an activity sensor suitable for rate responsive pacing.

A three axis accelerometer and an acoustic sensor were monitored during simulated unconditioned physical activities. True RMS values of the outputs were compared with the activity, ECG rate and an impedance derived estimate of minute ventilation. Each axis of the three axis accelerometer was capable of indicating a limited range of specific activities with a quick response. For moderate activity, the acoustic sensor provided the best rejection of non-metabolic activity.

Cardiac Pacing, Artificial↗
PubMed1990

Correlation of an invasive measure of right ventricular pressure and mean arterial pressure.

Recently, cardiac pacemakers have been introduced which increase heart rate during exercise. Current rate responsive pacemakers achieve this objective by monitoring minute ventilation via a transvenous impedance measurement and provides a proportional heart rate increase with increases in minute ventilation. These devices are independent of hemodynamic parameters. Therefore, the potential exists for a sufficiently high rate which results in decreased cardiac output by virtue of Starling's Principle. An invasive measure of right ventricular (RV) pressure is compatible with the power and complexity of contemporary implantable pacemakers. In addition, mean arterial pressure is accepted as a diagnostic indicator of left ventricular hemodynamic compromise. Therefore, a correlation of right ventricular pressure and mean arterial pressure was undertaken. Twenty-six patients were studied during normal sinus rhythm and ventricular tachycardia during routine electrophysiology examination. A beat to beat measure of peak to peak RV pressure resulted in a correlation coefficient of 0.68 with mean arterial pressure.

Blood Pressure↗
PubMed1990

A Monte Carlo simulation of range for an invasive impedance respiration monitor.

One method of rate responsive pacing utilizes an analog of minute ventilation as the input to the rate control algorithm. A measure of the intravenous impedance along the pacing catheter is a convenient means of determining minute ventilation. Design of the impedance converter requires a knowledge of the range of DC and AC impedance signals. During normal and deep breathing, 116 AC measurements were taken from 34 Electrophysiology (EP) patients and 31 DC measurements were taken from 13 EP patients. The patient data produced skewed distributions with a normal AC mean of 0.45 +/- 0.40 ohms p-p, a deep AC mean of 2.0 +/- 1.6 ohms and a DC mean of 44 +/- 13 ohms. An eight variable static model was derived from prior work. Five of the physiological variables were chosen from established clinical ranges, one geometrical variable was chosen from prior work and two were selected by matching the statistics of a Monte Carlo analysis of the model with the statistics of the patient data. The blood resistivity was obtained from prior work. A simulation of 1000 measurements produced a normal breathing range of 0 to 2.24 ohms, a deep breathing range of 0 to 9.6 ohms and a DC range of 19 to 100 ohms.

Algorithms↗
PubMed1989

Comparison of ultrasound baseband signal processors for use with an implantable controller.

The measurement of blood flow is an essential feature of a chronic implantable controller for the maintenance of metabolic parameters. Since ultrasound is a reliable measure of blood flow, its feasibility for chronic use is being studied. The device would require a low power, compact and simple signal processor. A comparison of eight baseband signal processors (frequency to voltage converters) was made in conjunction with four automatic gain control (AGC) modes. Since each processor was fundamentally different, they provided unique results to complex signals. In addition, the influence of amplitude modulation provided an additional component via the AGC.

Blood Flow Velocity↗