1 Authors' version of the paper that appears in the IFMBE Proceedings book series (IFMBE, volume 65) of 2017 15th European Medical and Biological Engineering Conference Nordic-Baltic Conference on Biomedical Engineering and Medical Physics (EMBEC & NBC 2017). DOI: 10.1007/978-981-10-5122-7_168 © Springer Nature Singapore Pte Ltd. 2018. Personal use of this material is permitted. Permission from Springer Nature must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Publisher version is available in https://link.springer.com/chapter/10.1007/978-981-10-5122-7_168. Variation of Cardiac and Respiratory Waveform on Human Thorax in the Case of Inductive Coupling M. Metshein 1 , P. Annus 1 , R. Land 1 , A. Krivošei 1 , J. Ojarand 1 , A. Aabloo 2 and M. Min 1 1 Thomas Johann Seebeck Department of Electronics, Tallinn University of Technology, Tallinn, Estonia 2 Institute of Technology, University of Tartu, Tartu, Estonia Abstract— The usage of magnetic induction monitoring on human thorax for detecting the cardiorespiratory activity is shown in this paper. The utilized device for measuring the changes in equivalent parallel resonant impedance of a single coil, caused by the breathing and heart beating, is represent. The waveforms of cardiac and respiratory activity together with the waveforms of reference monitoring of ECG and breathing are depicted. The measurements were done in twelve positions on the surface of the thorax of a single volunteer by using pre- determined protocol. The respiratory activity was found to be available in all of the chosen positions. The cardiac activity was found to be recognizable in the positions on both sides and front side of the thorax. The influence of the concurrent movements was verified. The positions, suitable for monitoring the both processes of breathing and heart rate, are proposed. Keywords— Cardiac monitoring, magnetic induction sensor, respiratory monitoring, telemonitoring. I. INTRODUCTION The cardiac and respiratory processes are most often used in personal health monitors to evaluate the health condition of human. The reasons are the easiness of interpretation and the potential of calculating other interesting parameters from the gathered data – energy consumption, burnt calories etc. Historically, there have been number of methods for mon- itoring the cardiac and respiratory activity of human but not many of these are capable of gaining access into both of these processes. One of such method is electrical bioimpedance, where the gained result contains the peaks of pulse, carried by the respiratory waveform. For following the cardiac and respiratory processes in hu- man body, magnetic eddy current induction measurements can be used. The approach of using a single coil exempts from precise calibration of more than one coil in a geometric alignment [1] and allows plain estimation of the induced magnetic field. The experiments of monitoring the variation of equivalent parallel resonance impedance (Rp) of a LC resonator, caused by cardiorespiratory activity in human body, are de- scribed in current paper. In the setup of an AC resonator, a single coil, operating in predetermined resonant frequency, was used at twelve predetermined positions on thorax. The question of positioning of the sensor on the thorax ap- pears when planning the monitoring of cardiorespiratory ac- tivity. In the case of impedance pneumo- and cardiography, several results, reflecting the different shape of the gathered waveform and varying ohmic value of the result, measured at different locations of the thorax, has been reported [2]-[3]. In the case of using the magnetic eddy current induction measurements, Vedru and Solntseva have done the detection of waveforms of cardiac activity at various positions on the front side thoracic surface by using a single-turn coil. The results show the change of the shape of the waveform depending on the location of the coil [4]. Teichmann et al. have also done the experiments with inductive and capacitive sensors on the backside of the thorax and the differences in the sense of the position of the sensor can be emphasized [5]. The presented study is planned to output the comparable data of simultaneous measurements of cardiorespiratory ac- tivity by using magnetic induction measurements in synchro- nous setup of the measurements of ECG and in- and exhala- tion. The expected favor of the analyze of the gathered data is the selection of the positions on the thorax that suit the best for monitoring the cardiorespiratory activity. II. DEVICES AND PROPERTIES Three devices were used in the measuring experiments: the primary measurement device in the form of magnetic in- duction sensor and the reference signal measurement devices in the forms of ECG monitor and spirometer. A. Single Coil Magnetic Induction Sensor The cardiorespiratory activity was monitored by using the telemonitoring system of single coil magnetic induction sen- sor, described in [1]. The sensor module of this device is based on chip LDC1000, manufactured by Texas Instruments (TI), allowing the measurement of the impedance and the res-