Dean C. Jeutter

Cochlear implant employing frequency-division multiplexing and frequency modulation

A cochlear prosthesis composed of a transmitter part which is to be carried exterior to the users body and a receiver part which is to be implanted in the user, the transmitter and receiver parts being coupled by a radio link provided by implanted receiver coils and external transmitter coils free of any percutaneous connections. In the transmitter part, sound signals are obtained in plurality of channels, and these channels are frequency multiplexed into a composite signal with the aid of a plurality of surface acoustic wave filters, each having a respective passband. In the implanted receiver, the received composite signal is frequency demultiplexed by means of a similar plurality of surface acoustic wave filters each having a respective passband. A further signal is transmitted from the transmitter part to the receiver part via the radio link in order to supply operating power for the circuits in the receiver part, where the further signal is rectified to produce d.c. operating voltages.

Computer-Automated Impedance-Derived Cardiac Indexes

In this study, an automated signal processing technique, ensemble averaging, provided artifact-free impedance data which permitted analysis during quiet breathing and exercise in normal young male subjects. Moreover, impedance-derived stroke volumes and other cardiac indexes calculated by ensemble-averaging showed close correlation with those calculated by conventional hand digitization methods. The results indicate that ensemble averaging can considerably increase the potential applicability of impedance cardiography.

Flow-Induced Responses in Piglet Isolated Cerebral Arteries

Although cerebral hemorrhage is a widely occurring neurologic disorder thought to be caused by fluctuating blood flow, the response to flow in the neonatal cerebrovasculature has not been characterized. In the present study, we examined the effect of changing flow on middle cerebral artery diameter and pathways by which flow modulates cerebrovascular tone. Arteries from 2-14-d-old piglets were mounted on cannulas and bathed in and perfused with physiologic saline solution. An electronic system controlled pressure and a syringe pump provided constant flow. The transmural pressure was held constant at 20 mm Hg, and changes in vessel diameter were measured as flow was increased in steps from 0 to 1.60 mL/min (flow/diameter curves). Increasing flow at constant pressure resulted in constriction at flows from 0.077 to 0.152 mL/min and dilation at flows from 0.212 to 1.60 mL/min. The flow/diameter curves were repeated in arteries bathed in Na+-reduced or Ca2+-free physiologic saline solution; denervated with 6-hydroxydopamine; or treated with indomethacin, N-nitro-L-arginine methyl ester, Nω-nitro-L-arginine (NLA), and L-arginine), ryanodine, or glutaraldehyde. In Na+-reduced and in Ca2+-free physiologic saline solution, flow constriction was eliminated. Neither indomethacin nor 6-hydroxydopamine affected the biphasic response. N-Nitro-L-argininel, NLA, and ryanodine blocked dilation, whereas L-arginine restored dilation in NLA-treated arteries. These data suggest that neither prostaglandins nor adrenergic nerve endings participate in flow-induced responses in piglet cerebral arteries. Elimination of flow-constriction by Na+ reduction or Ca2+ removal is consistent with findings in other artery types. The elimination of dilation byN-nitro-L-arginine methyl ester, NLA, and ryanodine suggests that dilation is mediated by nitric oxide and intracellular Ca2+. Whereas the contractile and dilatory responses to agonists remained intact after glutaraldehyde perfusion, both flow-induced constriction and dilation were eliminated, indicating that both types of flow responses result from endothelial cell deformation.

A Linear Permanent Magnet Generator for Powering Implanted Electronic Devices

Permanent magnet (PM) machines provide high efficiency, compact size, robustness, lightweight, and low noise. These features qualify them as the best suitable machine for medical applications. The system presented in this paper is a self-contained, small size, and reliable device that can continuously provide power. The core of the system is a linear generator that consists of two layers of PMs and one layer of coils. It generates power from multidirectional body movements. The movement of the device causes the coil layer to move. The relative movement of the coils versus PMs, on two sides, creates a varying flux in the windings. This change in flux produces voltage in the winding and can be converted into electrical power if a load is connected. The best place to implement this device to produce continuous power is on a muscle inside the body that is linked to the respiratory system. Design, simulation, implementation, and testing of the generator are presented in this paper. The testing results reveal that the generator can produce up to 1 mW of power in the body.

Design of a radio-linked implantable cochlear prosthesis using surface acoustic wave devices

Cochlear prosthesis systems for postlingually deaf individuals (those who have become deaf due to disease or injury after having developed mature speech capability) are considered. These systems require the surgical implantation of an array of electrodes within the cochlea and are driven by processed sound signals from outside the body. A system that uses an analog signal approach for transcutaneous transfer of six processed speech data channels using frequency multiplexing is described. The system utilizes a filterbank of six narrowband surface acoustic wave (SAW) filters in the range 72-78 MHz with a 1.2-MHz channel spacing to multiplex the six carrier signals, frequency modulated, by the processed speech signals, onto a composite signal. The same SAW filters are used in the receiver filterbank for signal separation, but are housed in a miniaturized package. The system includes a portable transmitter and a receiver package which is to be implanted in the patient. The implanted circuits are supplied exclusively from power transferred from outside the body via a separate 10-MHz transcutaneous link.<<ETX>>

Identification algorithm for systemic arterial parameters with application to total artificial heart control

A new algorithm for estimating systemic arterial parameters from systolic pressure and flow measurements at the root of the aorta is developed and tested through a systems identification approach. The resulting procedure has direct application to a total artificial heart (TAH) control system currently under development. Identification models, representing the systemic arterial system, are developed from existing work in the area of cardiovascular modeling. The resistive and compliance components of these models are physically significant, representing overall hydraulic properties of the systemic arterial system. A unique method of parameterizing the identification models is designed which operates on the basis of aortic pressure and flow measurements taken exclusively during systole. The estimator is a modified recursive least squares algorithm which utilizes covariance modification to track time-varying parameters and a dead-zone to improve the robustness. Performance of the estimation algorithm was tested on data generated by a higher-order distributed model of the systemic arterial bed using normal canine parameters. Results from model-to-model experiments verify the consistency of the estimates and the ability of the estimator to converge quickly and track dynamically varying parameters.

Design of a portable guided SH-SAW chemical sensor system for liquid environments

Following successful application in gas sensing, acoustic wave liquid sensors attracted considerable attention due to the need for real-time, rapid and direct detection where the device is in direct contact with the solution. More importantly, there is a need for field measurement capability with portable devices. Challenges include a physical layout of the RF circuitry to minimize parasitic and spurious noise, continuous and realtime measurements capability, and obtaining vector network analyzer (VNA) performance in a portable RF unit, especially since the sensor signal noise dictates the limit of detection (LOD). Polymer-guided shear horizontal surface acoustic wave (SH-SAW) sensor platforms operating around 105 MHz on 36deg rotated Y-cut LiTaO 3 are investigated as portable detectors in liquid environments. The described system is self-contained including RF signal source, sensor input/output signal conditioning, and sensor signal amplitude and phase measuring capabilities. Amplitude and phase signals from the sensor are differentially compared with concomitant signals available directly from the RF signal source. The two primary outputs from the system are voltages related to the detected amplitude and phase changes that are caused by the sensors response to analyte sorption by the coated device. Several devices, coated with chemically sensitive polymers, are investigated in the detection of low concentrations (10-60 ppm) of ethylbenzene and xylenes in water using the RF portable unit. The units were tested for both reproducibility and repeatability, and the results matched very well with VNA measurements

Silicon Force Transducer for Extraluminal Measurement of Oviduct Contractile Activity

A miniature, implantable force transducer has been developed for the extraluminal measurement of segmental smooth muscle contractility and has been applied to the oviduct in the Macaca mulatta. The force transducer makes use of a commercially available piezoresistive silicon strain sensor bonded to a flexible metal strip. The device is housed in a tissue compatible, gas sterilizable tubule upon which are placed sutures for subsequent extraluminal attachment to an organ.

Estimation of system arterial parameters for control of an electrically actuated total artificial heart

A novel method for estimating the parameters of a model of the systemic arterial system for control of an electrically actuated total artificial heart (TAH) has been developed and tested. The parameters have physical meaning, and are estimated on the basis of noninvasive measurement of aortic flow and pressure during systole. Performance of the estimation algorithm was tested on data generated by a model of the systemic arterial bed using normal canine parameters. Results demonstrate the ability of the estimator to converge quickly and track time-varying parameters.<<ETX>>

Understanding the importance of natural neuromotor strategy in upper extremity neuroprosthetic control

A key challenge in upper extremity neuroprosthetics is variable levels of skill and inconsistent functional recovery. We examine the feasibility and benefits of using natural neuromotor strategies through the design and development of a proof-of-concept model for a feed-forward upper extremity neuroprosthetic controller. Developed using Artificial Neural Networks, the model is able to extract and classify neural correlates of movement intention from multiple brain regions that correspond to functional movements. This is unique compared to contemporary controllers that record from limited physiological sources or require learning of new strategies. Functional MRI (fMRI) data from healthy subjects (N = 13) were used to develop the model, and a separate group (N = 4) of subjects were used for validation. Results indicate that the model is able to accurately (81%) predict hand movement strictly from the neural correlates of movement intention. Information from this study is applicable to the development of upper extremity technology aided interventions.