Longterm heartrate telemetry in small mammals: a comprehensive approach as a prerequisite for valid results

This paper describes a miniature telemetry system which is capable of precise, reliable longterm registration of heartrate (HR) in animals as small as laboratory mice. The ECG-transmitters have a weight of 0.9-1.5 g and a respective lifetime of 3-6 months depending on battery size. With suitable receiving antennas, transmitting range is sufficient for continuous reception in 200 m2 enclosures. The radio signals are demodulated in a signal processor and the ECG is converted to HR on the base of single interbeat intervals. General technical problems of telemetry like miniaturization, performance control, HR acquisition and artifact distinction are discussed. The experimental approach emphasizes the necessity of continuous registration of HR as a reference for experimental responses. Longterm shifts of HR due to social and nonsocial influences as well as experimental feedback effects are demonstrated and discussed.