Heart rate, multiple body temperature, long-range and long-life telemetry system for free-ranging animals.

A long-range and long-life telemetry system for heart rate and multiple body temperatures from free-ranging animals is described. This system includes an implantable transmitter, external receiver-retransmitter collar, and a signal conditioner interface circuit to assist in demodulation of receiver tone outputs before data processing. The size of the implant is suitable for animals with body weights of a few kilograms or more; further size reduction of the implant is possible. The ECG is sensed by electrodes designed for internal telemetry and to reduce movement artifacts. The R-wave characteristics are then specifically selected to trigger a short radio frequency pulse. Temperatures are sensed at desired locations by thermistors and then, based on a heart-beat counter, transmitted intermittently via pulse interval modulation. This modulation scheme includes first and last calibration intervals for a reference by ratios with the temperature intervals for as much as a range of 0-50 degrees C with a resolution of 0.1 degrees C. Pulse duration and pulse sequencing are used to discriminate between heart rate and temperature pulses as well as radio frequency interference. The implanted transmitter might be used alone for experiments on animals that frequent particular locations within a large territory, on animals in virtually any laboratory situation, or on animals in moderate-sized enclosures, such as those in a zoological garden. The implanted transmitter is otherwise interfaced with the receiver-retransmitter collar that employs commercial tracking equipment to achieve the long-range transmission. The objective of the design was to achieve a high degree of experimental flexibility and overall high quality in performance. The system was tested in prototype form on a dog.

Epidural measurement of intracranial pressure.

Although the measurement of intracranial pressure (ICP) is gaining widespread acceptance, the most desirable method of measurement is disputed. Subdural fluid-coupled techniques are associated with an increased risk of infection, and epidural techniques are associated with decreased accuracy. We investigated epidural measurement techniques and suggest that the necessary and sufficient criteria for accurate epidural measurement of ICP are adequate transducer size and stiffness, transducer-dura coplanarity, transducer-guard ring coplanarity, complete dural contact, and rigid fixation. An epidural transducer design was developed and prototypes were constructed using these principles. The transducer requires no percutaneous connections, fluid coupling, or batteries. Transducer accuracy was +/- 2.2 torr in bench stability studies lasting up to 198 days, +/- 3.0 torr in acute animal studies of less than 24 hours, and +/- 7.9 torr in chronic animal studies lasting up to 112 days. Error bounds are expressed such that 95% of individual measurements are expected to have error less than the bound; average error is one-third of the bound. Average transducer drift was 0.1 torr per day; our reported accuracy in chronic studies used drift correction from preimplantation data. We conclude that accurate measurement of ICP using an epidural transducer is feasible.

An inductively powered telemetry system for temperature, EKG, and activity monitoring.

An implant telemetry system for the simultaneous monitoring of temperature, activity, and EKG from small animals, such as rats, has recently been designed with the novel feature that instead of a battery the system is energized by an inductive field. A 250 kHz resonant coil surrounds the cage (30 X 30 X 20 cm) and provides the approximately 100 muW of power required to operate the implant transmitter while allowing the animal unrestrained movement in the cage. The implant can also be battery operated if desired RF transmission is in the 8-10 MHz band, which allows the use of a simple, essentially single IC chip, receiver.

Telemetry of intracranial pressure.

In the care of patients with abnormal intracranial pressure, it is important to continuously and accurately measure the intracranial pressure so that treatment can be instituted. Strain gage pressure cells have successfully replaced the open-end manometer for chronic use but have lacked the stability for accurate long-term measurements. The system described uses a capacitive pressure transducer with excellent long-term stability. The transducer, electronics, and transmitter package can be implanted to telemeter the pressure transcutaneously, reducing the danger of infection by the elimination of transcutaneous leads. The pressure modulates the frequency of an oscillator in the 8-10 MHz region and provides an easily telemetered signal. To eliminate the problems of periodic battery replacement, the system is energized inductively by a coil placed externally over the implant device, so that the operating life is virtually unlimited.

The use of hybrid integrated circuit techniques in biotelemetry applications.

A review is presented of some features of hybrid integrated circuits that make their use advantageous in miniature biotelemetry applications. The various techniques for fabricating resistors, capacitors and interconnections by both thin film and thick film technology are discussed. The use of chip capacitors, resistors, and especially standard IC chips on substrates with fired-on interconnection patterns is emphasized. The review is designed primarily to acquaint biotelemetry users and designers with an overview of this fabrication technique so that they can better communicate their needs with an understanding of its limitations and advantages to facilities specializing in hybrid construction.

A multichannel implantable telemetry system for flow, pressure, and ECG measurements.

The design of telemetry systems for chronic implantation within the body have progressed from simple single-channel devices to complex multichannel systems over the last 15 yr. Although chronic measurements of temperature, ECG, and pressure have been reported with good results, measurements such as dimension and blood flow have been difficult because of heavy power requirements. The design to be described is a multiplex system that will measure up to eight individual parameters simultaneously, including blood flow. Flow is measured using an electromagnetic transducer, and by special design, the normal high power requirements of the electromagnetic technique have been reduced to a few hundred milliwatts. The system is powered by two NiCad, rechargeable batteries which are periodically recharged through the intact skin by induction at 250 kHz to an implanted pickup coil. The presently constructed units have been configured to measure ECG, two pressures, temperature and ascending aortic flow.

A multichannel EEG telemetry system utilizing a PCM subcarrier.

A multichannel personal type telemetry system is described that utilizes PCM encoding for the most effective range with minimum RF bandwidth and noise interference. Recent IC developments (COS MOS) make it possible to implement a sophisticated encoding system (PCM) within the low power and size constraints necessary for a personal biotelemetry system. This system includes low level, high impedance preamplifiers to make the system suitable for EEG recording.