Determination of Physiological Rhythms of Unrestrained Animals by Radio Telemetry

Journal/Book: Reprinted from Nature Vol. 190. No. 4770 pp. 90-91 April 1. 1961. 1961;

Abstract: Department of Physiology State University of Iowa Iowa City. THE results of 24-hr. rhythm measurements are frequently influenced by perturbations due to the presence of an observer and the measuring equipment. These perturbations can be minimized if the desired physiological data are obtained by radio telemetry 1 2. The transmitter carried by the animal should be characterized by small size long battery life and sufficient range for unrestrained movements. Several transmitters with these design goals were constructed successfully and used to relay temperature and heart-rate information to a distant observer. The transmitters contain a basic oscillator which is frequency-modulated by a voltage proportional to the phenomenon measured. For a description of the design see ref. 3. The frequency of each temperature transmitter is controlled in part by the intrinsic dependence an temperature of the transistor in the oscillator and also by a voltage derived from a thermistor half-Bridge circuit. The transmitter is built around the antenna which is a ferrite core. The life of the 75 MAH mercury cell in this circuit exceeds 200 days. The frequency of the E.K.G. transmitter is controlled by amplified potentials derived from the heart. Additional circuitry is needed for amplification ; this increases power consumption and reduces battery life to about forty days. Units with more batteries have a longer life. Both the temperature and the E.K.G. units are suitable for surgical Implantation provided a non-toxic covering is used. In these experiments temperature transmitters were hermetically sealed in cases machined from nylon rod. The temperature-sensitive elements were covered with the tip from a finger of a latex surgical glove although they could be designed to protrude into a portion of a nylon shell. Seals between the latex Finger tip and the nylon case were matte successfully by wrapping and tying with nylon suture. No toxic reactions were noted when a unit prepared in this manner was implanted in a dog. Ref. 3 describes the pretreatment required before implantation. ... ___MH

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