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TECHNICAL PAPERS

High Capacity Implantable Data Recorders: System Design and Experience in Canines and Denning Black Bears

[+] Author and Article Information

Departments of Surgery and Physiology, University of Minnesota, Minneapolis, MN 55432 and Medtronic Inc., Minneapolis, MN 55455

Henry J. Harlow

Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071

Jon C. Werder, Mark T. Marshall

Medtronic Inc., Minneapolis, MN 55432

Paul A. Iaizzo1

Departments of Surgery and Physiology, University of Minnesota, Minneapolis, MN 55455

1

To whom correspondence should be addressed.

J Biomech Eng 127(6), 964-971 (Jul 29, 2005) (8 pages) doi:10.1115/1.2049340 History: Received April 01, 2005; Revised July 29, 2005

Abstract

Background: Implantable medical devices have increasingly large capacities for storing patient data as a diagnostic aid and to allow patient monitoring. Although these devices can store a significant amount of data, an increased ability for data storage was required for chronic monitoring in recent physiological studies. Method of Approach: Novel high capacity implantable data recorders were designed for use in advanced physiological studies of canines and free-ranging black bears. These hermitically sealed titanium encased recorders were chronically implanted and programmed to record intrabody broadband electrical activity to monitor electrocardiograms and electromyograms, and single-axis acceleration to document relative activities. Results: Changes in cardiac T-wave morphology were characterized in the canines over a $6month$ period, providing new physiological data for the design of algorithms and filtering schemes that could be employed to avoid inappropriate implantable defibrillator shocks. Unique characteristics of bear hibernation physiology were successfully identified in the black bears, including: heart rate, respiratory rate, gross body movement, and shiver. An unanticipated high rejection rate of these devices occurred in the bears, with five of six being externalized during the overwintering period, including two devices implanted in the peritoneal cavity. Conclusions: High capacity implantable data recorders were designed and utilized for the collection of long-term physiological data in both laboratory and extreme field environments. The devices described were programmable to accommodate the diverse research protocols. Additionally, we have described substantial differences in the response of two species to a common device. Variations in the foreign body response of different mammals must be identified and taken into consideration when choosing tissue-contacting materials in the application of biomedical technology to physiologic research.

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Figures

Figure 1

The system and implant configuration used in the bear studies. The implantable data recorders were programmed and the data quality was assessed in each animal at the den sites prior to final system implantation.

Figure 2

Exploded view of the implantable data recorder detailing the internal componentry. Within the outer titanium-alloy canister halves the following main components were contained: (1) compact-flash memory card (SanDisk® 96Mbyte CompactFlash™), (2) microcontroller circuit board with a microcontroller (PIC16F877, Microchip Technology Inc., Chandler, AZ) and an accelerometer, (3) batteries (nominal 3.6V, two AA tadiran lithium TL-5903, 2.4 AH), (4) a magnetic switch, and (5) a polyurethane connector block.

Figure 3

Photos of the internal components of the data recorders. The circuit board and memory card are shown in (A) and in (B). The posterior surface of the board is shown with the microprocessor in place (B). The system was packaged within a titanium-alloy housing and hermetically sealed using laser welding. The componentry is shown prior to welding in (C) and (D).

Figure 4

Circuit diagram of the implantable data recorders

Figure 5

Shown is the interface page employed for programming the bear implantable data recorders in the field. This program, written using LabView™ software, allows the user to set the desired data collection parameters of each implanted system in the field setting (e.g., in the case of the bears, in remote regions of the Rocky Mountains of Colorado and Wyoming). The specific start delay noted on this initial screen was shown at 15days, but in most cases was reprogrammed to 21, 30, or 60days.

Figure 6

Implant configuration used in the canine study. IDR=implanted data recorder; ICD=implantable cardioverter defibrillator.

Figure 7

Shown here are sample electrograms from the canine testing. The signals were collected from leads placed in the right ventricular apex. An electrogram from week 1 (left) is shown during a period of low activity (above) and high activity (below). Note that the morphology of the T-wave is similar in both cases. Additional electrograms are shown for week 26 (right) for periods of low activity (above) and high activity (below). In this case, the T-wave is both inverted (reversed polarity) and has a substantial increase in amplitude. The x axis is time (seconds).

Figure 8

Photos of recovered data recorders from two different implants: bear B03 shown in panel (A), and bear B01 shown in panel (B). In both cases these bears bit onto these titanium canisters with such force as to leave tooth impression on both the anterior (left) and posterior surfaces (right).

Figure 9

Subcutaneous electrical data for a 30s period recorded while an American black bear (Ursus Americanus) was overwintering in a den. The wideband signal is shown in the upper panel and a filtered signal in the lower panel (third order Butterworth bandpass filter with cutoff frequency of 5–50Hz). A pronounced respiratory sinus arrhythmia is apparent in this recording, which is a transient decrease in vagal tone following inspiration that results in a temporary increase in heart rate. The amplitude of the QRS complex is modulated by the change in chest impedance due to inspiration and expiration. One respiratory cycle is shown, with the higher heart rates occurring following inspiration.

Figure 10

Shown here is a single cardiac cycle recorded from a subcutaneous site while an American black bear (Ursus Americanus) was overwintering in a den. The wideband signal is shown in the upper panel and a filtered signal in the lower panel (third order Butterworth bandpass filter with cutoff frequency of 5–50Hz). One second of data is shown. Following an isopotential period, a QRS cardiac wave form can be seen (cardiac depolarization) followed by a T-wave (cardiac repolarization).

Figure 11

Shown here is an example of the recorded broadband electrical activity and the corresponding acceleration from a system implanted in the peritoneal cavity of an American black bear

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