Non contact monitoring of the respiration act electromagnetic sensing. Lorenzo Scalise Dipartimento di Meccanica Università Politecnica delle Marche Ancona, ITALY l.scalise@univpm.it Alfredo De Leo, Valter Mariani Primiani, Paola Russo, Desar Shahu, Graziano Cerri Dipartimento di Ingegneria Biomedica, Elettronica e Telecomunicazioni Università Politecnica delle Marche Ancona, ITALY g.cerri@univpm.it Abstract—The aim of this paper is to present a novel measurement method for the detection of the respiratory activity (respiration rate and respiration period) based on the use of a continuous wave (6 GHz) microwave radar reflectometry technique. The paper aims, in particular, to explore the effect on the signal quality of distance D between the sensing apparatus and the patient. The measurement method proposed is based on the measurement of the phase variation of the reflection coefficient (S 11 ) signal measured by a vectorial network analyzer connected to a double ridge horn antenna. The S 11 signal has been compared with the synchronous acquisition made by means of a laser Doppler vibrometer (LDVi), measuring the thorax oscillations caused by the respiratory activity. Both signals have been filtered in order to eliminate the effect of high frequency disturbances (heartbeat) and noise. Results show an high correlation between respiration peaks measured with the proposed system and with LDVi; a reduction of the amplitude of the S 11 signal phase (as well as the SNR) is reported in correspondence to an increasing of the distance D (-0.11 dB/cm). Tests have been repeated for standing as well as for sitting condition of the subject confirming a better signal quality for the later. Despite the fact that S 11 phase variation and SNR are reduced by the distance D, in our experiments, it is still possible to correctly measure the respiration period up to 2.5 m. Data measured show that the reflectometeric approach can be used to monitor at distance with sufficient high SNR (18 dB at 2.5 m) the respiration activity of a subject without the need of a direct contact with the subject skin by means of electrods of sensing belts. Keywords: Respiration rate monitoring, microwave reflectormetry, laser doppler vibrometry I. I NTRODUCTION A multitude of daily clinical activities requires the monitoring of the physiological activities of the human body, frequently named as vital signs. From standard, daily patient observation to intensive care monitoring the instantaneous values of heart rate, heart electrical activity, respiration rate, arterial pressure, oxygen saturation, temperature are a part of the many vital signs typically measured and reported on the patient monitor. To be accessed, each of these quantities requires one or more transducers, electrodes and cables to be connected to the patient. Such quantity of devices and limit his movements and can cause movement artifac fake alarms requiring the intervention of the medical pers for an accurate check of the situation and the eventual replacing of the sensor or electrodes. Moreover the appli of electrodes can be difficult (this is the case of burned pa infants, post-surgery patient monitoring, etc.) and always associated to a certain degree of biological or electric risk therefore of interest to explore the possibility to mea vital signs without physical contact with any part of his bo and possibly at a sufficient distance from the patient and the other instrumentation. In the past, many techniques, avoiding patientcontact, have been proposed for the monitoring of the heart rate such as: Sismocardiography balistocardiography [4] and kinetocardiography [5-7] have been proposed, but up to now, they have not found application. In the 90’s the seismocardiography has been presented as a novel non-invasive technique (although requires the contact of an accelerometer with the pa recording and analysing cardiac vibratory activity [1-3]. M recently, Augousti et al. [8] developed a fiber optic plethysmographer for cardiacmonitoring. These papers demonstrate the interest of the research community development of novel non-invasive methods for cardiac monitoring and heart rate assessment, alternative to ECG recently, a non-contact, opticalheartactivitymonitoring measurement procedure – named vibrocardiography (V was proposed. In [9] it was firstly successfully demon and in [10-13] its ability to assess heart rate and its varia with the same precision as the gold standard technique (E is reported; while the cardiac function evaluation retrievi filling time similarly to digital phonocardiography (PC reported in [14]. At the moment arterial pressure and o saturation are still measureable only with contact, even if indirect measurement of these quantities are possible direct contact with patient blood [15-17]. For what c respiration monitoring, the scientific literature [18-21] and market solutions propose under-the-mattress transducers individuation of apnea events in infants or chest belt applied around the patient thorax. These devices are used for monitoring and sleep disorders diagnosis. The us 978-1-4244-9338-8/11/$26.00 ©2011 IEEE