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Dr. TR Hudrlik - InventionShare. Blaine, MN, US

Dr. TR Hudrlik

CSO | InventionShare


Dr. TR Hudrlik has been a Biomedical/Biophysics Research Scientist and Inventor for over 35 years.


Dr. TR Hudrlik studied under Dr. Otto H. Schmitt, the Schmitt Trigger, as a graduate student. He developed techniques to control the electrocautery’s ability to produce action coagulation and fulgeration by dynamically adjusting the effective output impedance under dynamic microprocessor control, an 8085. He was Co-Author of an NIH grant as a graduate student titled Automated Impedance Bioassay Measurement Technique for Cystic Fibrosis.

He moved to industry with CPI where he designed the sensing and the rate responsive analog computer and did the clinicals on the RS4 pacemaker the world’s first chronically implanted rate responsive pacemaker. He moved to Dahlberg a large hearing aid company where he endeavored to develop techniques that would alter the hearing curves of response gradually to help recipients train their brain to the prosthetics hearing augmentation.

At Medtronic he managed a large team of software and hardware engineers that developed a computer based office practice system that would collect and coordinate real time telemetered pacemaker data and other aspects of the patient data. He moved to the Pacemaker Division as a Research Scientist later to become a Sr. Research Scientist. In Research he developed an in Vitro technique to calibrate and prove the function of an implantable pressure sensor proximal to the leads distal pacing tip. He then developed a new sensing technique that had a signal to noise ratio over 40db better than that of the present sensing techniques used. This technique was able to reliably detect the evoked response from a successful paced beat. This technique was also shown to be capable of tracking the presence and progress of Congestive Heart Failure as well as proving its ability to monitor and track the impact of ion channel impacting cardio-active drugs. He has produced over a dozen patents demonstrating these new sensing and stimulation techniques.

He went back to the University of Minnesota at 52 to finish an earlier started PhD program to detail the Electromagnetic Field theoretical basis of the new sensing technique called the Field Density Clamp. The title of the thesis is Sensing with Macro Electrodes. The technique details how to break from the traditional high input impedance sense amplifiers by widening the approach to use variable input impedance including shorting the electrodes and measuring the short circuit current that then flows between the two shorted electrodes.

Areas of Expertise (9)

Electrode Electrolyte Interface

Advanced Mathematics


Cardiac Pacemakers

Cardiac Sensing

Sensing Techniques

Complementary Current Field Effect Transistor (CiFET)


Electrical Engineering and Electrochemistry

Education (4)

University of Minnesota: BSEE, Electrical Engineering 1975

University of Minnesota: M.S. Biophysics, Biophysics 1980

University of Minnesota: MSEE, Electrical Engineering 1984

University of Minnesota: Ph.D., Bioengineering 2004

Affiliations (1)

  • IEEE Senior member since 1986

Patents (14)

Low noise sensor amplifiers and trans-impedance amplifiers using complementary pair of current injection field-effect transistor devices



This invention relates to low noise sensor amplifiers and trans-impedance amplifiers using a complementary pair of current injection field effect transistor (iFET) devices (CiFET). CiFET includes a N-type current field-effect transistor (NiFET) and a P-type current field-effect transistor (PiFET), each of the NiFET and PiFET has a source, a drain, a gate, and a diffusion (current injection) terminal (iPort). Each iFET also has a source channel with a width and a length between the source and diffusion terminal, and drain channel with a width and a length between the drain and the diffusion terminal. A trans-impedance of the CiFET device is adjusted by a ratio of width / length of source channel over width / length of drain channel of the iFET and supply power voltage. In one configuration, the gate terminals of the NiFET and PiFET are connected together to form a common gate. In another configuration that common gate is configured as a voltage input for a high input impedance mode. Output voltage swings around a common mode voltage.

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Signal processing circuit for pyro/piezo transducer



An adapter for interfacing a pyro/piezo sensor to a polysomnograph machine comprises a differential input amplifier coupled to receive the raw transducer signals from a PVDF film transducer to provide a requisite gain while rejecting common mode noise. The resulting amplified signal is filtered to separate the pyro signal from the piezo signal and the piezo signal is further applied to half-wave rectifier stages that function to remove baseline noise from the piezo signal before its being applied to a microphone channel of an existing PSG machine.

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Bi-atrial and/or bi-ventricular sequential cardiac pacing systems



A multi-chamber cardiac pacing systems for providing synchronous pacing to at least the two upper heart chambers or the two lower heart chambers or to three heart chambers or to all four heart chambers employing one or more field density clamp (FDC) sense amplifiers for accurately sensing and timing cardiac depolarizations of the right and left heart chambers is disclosed. The synchronous pacing of one of the right and left heart chambers is provided on demand following expiration of programmable pace CDW and sense CDW that are started by both a paced event and a sensed event first occurring in the other of the right and left heart chambers. The delivery of the pacing pulse is inhibited by a sensed event detected in the other of the right and left heart chambers before the expiration of the corresponding CDW. In a four channel atrial and ventricular pacing system, the right and left atrial chambers are sensed and paced as necessary upon at the end of a V-A escape interval and right and left, pace and sense, AV delays are commenced for sensing ventricular depolarizations in the right and left ventricles. The four channel system is programmable to pace and sense in three selected heart chambers. Each FDC sense amplifier allows the timing of a short CDW from a paced event or a sensed event. Preferably, a pacing output stage is coupled with the FDC sense amplifiers to deliver pacing pulses to each heart chamber.

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Implantable medical device system with method for determining lead condition



In an implantable medical device system such as a pacemaker system, there is provided a system and method for measuring lead impedance so as to obtain reliable data concerning any indication of the need to replace the lead. A relatively short duration low current AC burst is delivered after a standard pacing pulse, at a time to coincide with the heart's refractory period. The pulse is long enough in duration, e.g., 50-125 ms and preferably around 100 ms, to achieve the benefit of substantially steady state measurement, but short enough to substantially avoid the possibility of inducing any cardiac arrhythmia. The current level of the burst is limited to about 30 microamps, providing a further factor of safety against inducing an unwanted arrhythmia. The PPAC technique is adaptable for automatic measurement within an implantable device, or for implementation involving an external programmer which triggers the test.

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Rate-responsive heart pacemaker



A rate-responsive pacemaker pulse generator and lead system that allows the rate at which the pacemaker delivers electrical stimulation pulses to the heart to be adjusted as needed in order to satisfy the body's physiological needs. The pulse generator and lead system include first and second electrodes coupled to a virtual load and monitoring circuit for monitoring the electrical energy provided through the virtual load in order to detect the magnitude of cardiac depolarization signals. The impedance of the virtual load is intentionally mismatched to the source impedance of the cardiac tissue in order to increase the peak-to-peak variation of the cardiac depolarization signals as a function of modulation of the tissue source by respiratory activity. The peak to peak modulation of the cardiac signals is processed to provide a pacing rate control signal.

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Waveform discriminator for cardiac stimulation devices



An apparatus for producing signals indicative of power levels of depolarizations of heart tissue, particularly adapted for use in an implantable antiarrhythmia device or an implantable pacemaker. The device distinguishes between the power level of sensed depolarization signals in order to distinguish between different types of depolarization waveforms. In particular, the measured power level of the sensed depolarizations may be employed to distinguish between normally conducted and ectopic beats, for use in controlling the operation of an implantable antiarrhythmia device such as an implantable pacemaker/cardioverter/defibrillator or for use in controlling the operation of a bradycardia pacemaker.

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Medical stimulator with multiple operational amplifier output stimulation circuits



A cardiac pacemaker or other tissue stimulator including first and second stimulation electrodes mounted adjacent to one another and adjacent the tissue to be stimulated, such as a chamber of a heart, a return electrode and a pulse generator which independently generates two or more stimulation pulses. The pulses are applied between the first stimulation electrode and the return electrode and between the second electrode and the return electrode in an overlapping fashion. By controlling the relative timing and polarity of the pulses, the potential gradient between the electrodes and the rate of change of the potential gradient may be varied.

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Multiple frequency impedance measurement system



A physiological monitoring system for monitoring the condition of a patient's body tissue. The device includes electrodes for contacting the tissue to be monitored, circuitry for generating electrical signals at at least two frequencies for application to the tissue and circuitry for monitoring the impedance of the tissue, at the frequencies applied. The device includes in addition apparatus for detecting changes in the relationship of the measured impedances at the frequencies applied, and for processing the detected changes in impedance relationship to provide an indication of the condition of the tissue. The monitoring apparatus may be practiced in the context of an implantable stimulator, such as a cardiac pacemaker, in which the pulse frequency is varied as a function of the detected condition of the tissue.

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Electronic capture detection for a pacer



A pacemaker sense amplifier which includes active circuitry which establishes and attempts to maintain a constant field density between two electrodes, effectively clamping them together at substantially fixed relative electrical potentials. The amount of current or power provided to the electrodes monitored and forms the basis of detection of the passing cardiac depolarization wavefront. A timer is sued to define a detection window after the generation of a pacing pulse. The occurrence of a detected depolarization within the detection window is indicates that the pacing pulse has captured the heart.

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Ring-to-ring cardiac electrogram pacemaker



A pacemaker having two bipolar leads, one atrial, one ventricular, each with TIP and RING electrodes, configured as for conventional bipolar pacing/sensing in both chambers. Switching circuitry in the pacemaker is operable to select from among various possible sensing configurations, including one configuration in which sensing is performed between the ring electrodes of the respective pacing/sensing leads. Pacing is preferably performed in a conventional unipolar configuration in each chamber, from the respective tip electrodes. The "ring-to-ring" EGM signal is applied to filtering and EGM amplifier circuitry, and then provided to a telemetry system for transmission to an external receiver. The ring-to-ring EGM signal possesses the high resolution properties of conventional intracardiac signals, and is relatively unaffected by the after-potentials and tissue polarization effects that arise when the same lead is used for pacing and sensing. Additionally, the ring-to-ring EGM signal is a composite of atrial and ventricular electrical signals, and thus has an appearance similar to that of surface ECGs.

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Myocardial conduction velocity rate responsive pacemaker



A system for detecting changes in the myocardial conduction velocity and deriving control signals therefrom for controlling the delivery of electrical or other therapy to the heart or for monitoring or diagnostic purposes. The system comprises two spaced electrodes coupled to amplifiers which detect the relative arrival times of the depolarization wavefront at the electrodes, measurement circuitry for measuring the difference in arrival times to determine conduction velocity circuitry for deriving control signals for controlling operation of an implantable medical device as a function of measured conduction velocity. The particular embodiment disclosed is a cardiac pacer in which the measured conduction velocity is used to control pacing rate.

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Cardiac pacemaker with operational amplifier output circuit



A medical electrical stimulator employing an operational amplifier output circuit for producing an electrical stimulating pulse for application to body tissue and for sensing electrical activity in the body tissue. A first input to the operational amplifier is coupled through a virtual load to a probe electrode in close proximity to the body tissue. The second input is coupled to a second electrode which may be remote from the tissue to be stimulated. A defined voltage signal may be provided to the second input to the amplifier, and the amplifier correspondingly delivers current through the virtual load to the probe electrode as the amplifier maintains equal voltage levels at its two inputs. The current delivered to the probe electrode functions to stimulate the body tissue. By varying the defined voltage signals provided to the second input of the amplifier, arbitrary stimulation pulse waveforms may be generated. After termination of the defined voltage signal, the amplifier functions to restore the electrode/tissue system to its previous electrical equilibrium condition and to sense induced or spontaneous electrical activity in the tissue. The circuit may be employed in cardiac pacemakers, with the probe electrode located on or in the heart, or in other electrical medical stimulators.

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Sensor for detecting cardiac depolarizations particularly adapted for use in a cardiac pacemaker



A pacemaker sense amplifier which includes active circuitry which establishes and maintains a constant field density between two electrode poles, effectively clamping them together at a substantially fixed potential difference. The amount of current or power required to maintain this condition in the steady state is monitored and forms the basis of detection of the passing depolarization wavefront.

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Atrial rate sensitive cardiac pacer circuit



An electrical pacer device which responds to cardiac demand so as to alter the cardiac output in a fashion to satisfy that demand. Changes in the fundamental period of the atrial electrical cycle are detected and averaged over a predetermined time interval and the resulting control signal is used to raise and lower the ventricular heart rate to increase and decrease the aforesaid cardiac output. At the same time, means are provided for continuously driving the ventricular rate toward a predetermined lower rate (the at rest rate) on a time cycle which is significantly longer than the above-mentioned predetermined time interval.

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Selected Articles (3)

Automated Impedance: A Case Study in Microprocessor Programming

Computers in Biology and Medicine 11(3):153, 1981

Tucker, R.D., Hudrlik, T.R., Silvis, S.E., and Ackerman, E.

An automated system for measuring biological impedances is described. A microcomputer system is utilized for experimental control, data acquisition, and data reduction. The developed software uses high-level languages and the ability to mix subroutines written in different languages, which are available for microcomputer systems. The software control of analog-to-digital and digital-to-analog conversions is also discussed. The pitfalls, as well as the advantages, of employing a microcomputer system in a task-dedicated laboratory system are presented.

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The Effect of Serum from Patients with Pancreatic Disease on the Short Circuit Current of Rat Jejunum

IEEE Transactions on Biomedical Engineering ( Volume: BME-26 , Issue: 11 , Nov. 1979

Tucker, R.D., Hudrlik, T.R., Gibbs, G.E., and Christensen, M.

The short circuit current rat jejunum bioassay, first employed in an attempt to discern the cystic fibrosis (CF) serum "factor," was evaluated using sera from patients with pancreatic disease. The data suggest other pancreatic diseases, specifically genetic diabetes and alcoholic pancreatitis, also present with a serum "factor" (or "factors") which reduce the short circuit current of rat jejunum, an effect very similar to that of the CF serum "factor." A large number of sera from presumed normal subjects also exhibited a significant reduction in short circuit current; these (false positives) represent a yet to be defined mechanism, however, they do decrease the likelihood that the observed effect is merely due to pancreatic destruction. Detailed procedure and equipment specifications for the bioassay system are included.

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Electrocautery by Programmable Dynamic Microcomputer Control.

31st ACEMB, Marriot Hotel, Atlanta, Georgia, 21-25 October 1978.

T.R. Hudrlik, O.H. Schmitt, S.E. Silvis and J.A. Vennes.