Electro-Thermal Bioinstrumentation Laboratory

Jonathan Valvano

Journal Papers and Conference Papers

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Areas of expertise within the Electro-Thermal Bioinstrumentation Laboratory include

• Embedded systems with mixed analog and digital circuits

• Low-power and miniature circuit design including PCB fabrication

• Development and integration of real-time operating systems into embedded systems

• Low noise data acquisition with real-time digital signal processing

• Cosimulation of software, digital signals, analog circuits, and mechanical devices

• FEM simulation of electric and thermal fields

Real-time and Low-power Measurement of Left Ventricular Volume in Humans using an Admittance Catheter (with Drs. Feldman and Pearce)  sponsored by Admittance Technologies 
              We have developed technology that can be implanted, providing real-time measurements of end diastolic volume (EDV) and stroke volume (SV). Continuous monitoring of left ventricular volume can significantly improve the effectiveness of health care for patients with chronic heart disease. Measurements of EDV can be used as an early warning of heart failure. Measurements of SV can be used decide whether or not to shock a patient during ventricular tachycardia. Measurements of SV could also be used to select timing parameters of the pacemaker.

In Vivo Measurement of Left Ventricular Volume in Laboratory Animals using a Conductance Catheter (with Drs. Feldman and Pearce)  sponsored by Scisense Inc.  
              Transgenic mice offer a valuable method to relate genes to various cardiac diseases, and pressure-volume analysis is the gold standard for assessing myocardial function. Cardiac volume can be estimated by a conductance catheter system. Experimentally a four-electrode catheter is inserted into the mouse left ventricle (LV) to generate an electric field and continuously to measure the instantaneous conductance signal. Unfortunately, both blood and myocardium are conductive, but only the blood conductance is wanted. Therefore, the parallel myocardium contribution should be removed from the total measured conductance. Research currently involves FEM numerical studies, instrumentation development, real time measurement of phase using DSP, in vitro studies and experimental verification in mice, rats, and humans.

 Chronic Measurements of Left Ventricular Volume in Laboratory Animals (with Drs. Feldman and Pearce)  sponsored by Admittance Technologies 

     Transgenic models of heart disease have been created. As a result, it has become important to accurately and thoroughly evaluate cardiac function in rodents (mice and rats). Rodent hearts are extremely sensitive to sedation and yield very different results when conscious studies are compared to those using anesthesia. Therefore, it is of paramount importance that a complete assessment of cardiac function is carried out in freely roaming, un-anaesthetized, rodents. In order to accomplish this goal we must turn to wireless devices that utilize miniature, lightweight, implants to transmit required data to a nearby base station. Left ventricular pressure-volume (LV PV) admittance catheter systems would be ideal for this type of implant, because they are more accurate than traditional conductance techniques, cheaper than MRI and 2D echocardiography, and can be implanted in conscious, ambulatory rodents to provide a complete hemodynamic profile to the academic scientist, and for drug discovery and safety studies by large pharmaceutical companies. Shown below is a demonstration of single beat elastance using our wireless admittance system, comparing it to elastance measured from caval occlusion.   

Signal processing in a hearing aid
      An audiogram tests the patient's ability to hear sounds across the audio spectrum. The sensitivity versus frequency response is used to tune the hearing aid to compensate for the specific patient's condition. The system involves a number of creative technologies. A real-time FIR filter shapes the gain versus frequency response. A nonlinear filter using auto-correlation removes background noise (shown below). Time-shifting is a novel approach that moves some high frequency sounds into lower frequencies, without making it sound like a space alien. The device is available as a miniature low-power embedded system.  

Assessment of Vulnerable Plaque using Thermal Properties 
            The overall goal of our project is to develop and evaluate an instrument that takes a “thermal X-ray” of the arterial wall. In particular, we propose to combine sophisticated thermal modeling with precision instrumentation to develop and evaluate a direct contact probe to scan the arterial wall to detect vulnerable plaque. The scan will provide the thermal properties of the arterial wall (namely thermal conductivity). The thermal property measurements will help us predict the composition of the arterial wall underneath the thermistor-based sensor. Vulnerable plaques have more lipid and less fibrous tissue as compared to stable plaques.  There is a strong correlation between the structural components of biologic tissue (fat, fiber, and calcium) and its thermal properties.   The thermal conductivity of a material is its ability to transfer heat in the steady state. The proposed technique is fundamentally different from thermography, which senses an increased temperature caused by the increased metabolic activity of the plaque. In contrast, our approach measures thermal conductivity, which in turn will help to characterize the plaque.  In particular, we believe our instrument will be able to detect the large lipid core that characterizes vulnerable plaque, and it may also help in determining the thickness of the fibrous cap.  If successful, this device will provide a low-cost tool to assess the vulnerability of plaque, as well as determine the response of the vulnerable plaque to therapy directed towards improving plaque stability.  

            The rationale of our approach is based on the fact that fatty plaques have a lower thermal conductivity as compared to thermal properties of fibrous plaques. In particular, lipid has a thermal conductivity that is 60% less than fibrous tissue.  Therefore, we hypothesize that measurements of thermal conductivity will provide information about the underlying makeup of the plaque, creating a positive predictor for vulnerable plaque.  The method involves placing a thermal transducer in direct physical contact with the endothelial surface of the artery under test, delivering a small burst of heat as well as sensing the tissue temperature response.   The low amount of heat applied for 10-second duration will not have long-term impacts on the plaque stability or vessel remodeling.

High-Performance A/D Conversion (Robin Tsang, Byung Geun Lee) 
    The overall goal of this project is to develop a high-performance ΔΣ modulator for analog-to-digital conversion. ΔΣ modulators take advantage of noise-shaping and oversampling to achieve high resolution . Noise-shaping is a collective term used to describe feedback systems that use filtering to push quantization noise out-of-band while leaving in-band signals unchanged. The main advantage of oversampling is it trades time for dynamic range. Oversampling also relaxes analog component requirements such as opamp DC gain and capacitor mismatch tolerances when compared to Nyquist rate converters. Unfortunately, the overhead of oversampling limits the maximum achievable signal bandwidth, making ΔΣ modulators attractive only in medium to low speed applications.

     The goal of this project is to develop a low-power 12-bit 80MS/s pipeline analog-to-digital converter (ADC). The proposed pipeline ADC consists of the front-end sample and hold circuit (SAH), 2.5-bit first stage, 8 1.5-bit stages followed by 2-bit flash ADC. In order to reduce power consumption, the  number of op amps will be minimized using an op amp-sharing technique. In addition, a capacitor sharing technique will be used for the SAH and the first stage to further reduce power consumption by reducing the SAH output load. The basic concept of op amp and capacitor sharing technique is explained in Fig. 2. Since the feedback capacitors of the SAH are directly used for the first stage MDAC operation, the sampling capacitors of the first stage are not needed, thus reducing SAH output load capacitance almost by 50%.