Proceedings of The Physiological Society
Puerto de la Cruz, Tenerife (2003) J Physiol 548P, P167
A telemetry system for ECG acquisition from diving mammals
M. Rodríguez *, A. Ayala *, M. Díaz and J. García*
*Department of Fundamental and Experimental Physics, Electronic and Systems and Department of Animal Biology, University of La Laguna, Tenerife, Spain
One of the central physiological issues related to mammalian life in the aquatic environment is the development of cardiovascular adaptations during diving. Most of our knowledge on mammalian diving comes from studies performed in the laboratory. At present only a few reports have attempted to measure electrocardiograms (ECG) on freely diving sea mammals. The present work is focused on the design and implementation of a telemetry system prototype to allow the measurement and transmission of ECG from diving mammals, including humans. The system, also records relevant physical parameters from the diving environment, such as water temperature and hydrostatic pressure. These parameters are extremely useful for correlating ECG changes with diving and exercise activities. Measuring ECG signals on the body surface within a conductive media like seawater presents some intrinsic difficulties, such as attenuation of the signal amplitude, insulation of the associated electronics, etc. Therefore, as an initial step we needed to determine not only the levels of signal attenuation and the adequacy of different electrodes, but also the main features of real ECG from the different species. In order to obtain accurate determinations, we concentrated our studies on trained dolphins and human volunteers.
A portable acquisition system was designed consisting of a biopotential amplifier with adjustable gain and offset, A/D converter and a parallel port interface which let us to store and analyse, on a laptop computer, the ECG under real-time conditions by means of the implemented software. The system was fixed on the body surface and ECG measurement allowed us to obtain ECG waveforms, voltage levels and frequency bandwidth. These preliminary studies revealed differences between human and dolphins regarding wave amplitudes, heartbeat frequency and shape of the different ECG waves (Fig. 1) (Rodríguez et al. 2000).
These preliminary data were used to develop the autonomous telemetry system. This system is based on a microcontroller that manages the measurement instrumentation, data compression/storage, and the radio frequency (RF) output stage. In addition, a compression algorithm, based on a Max-Lloyd non-uniform quantizer (Rodríguez et al. 2002), was implemented to optimize the limited resources of the system. ECG and physical data are stored in the system memory and transmitted to a receiving station via a UHF transmitter once the system detects the specimen has contacted the water surface.
Where applicable, experiments conform with Society ethical requirements