RESUMO
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.