A New Digital Stethoscope with Environmental Noise Cancellation F. BELLONI † , D. DELLA GIUSTINA † , M. RIVA † , M. MALCANGI # † Dipartimento di Fisica Università degli Studi di Milano Via Celoria 16, 20133 Milano ITALY # Dipartimento di Informatica e Comunicazione Università degli Studi di Milano Via Comelico 39, 20135 Milano ITALY federico.belloni@unimi.it, davide.dellagiustina@unimi.it, riva@unimi.it http://elettronica.fisica.unimi.it malcangi@dico.unimi.it http://dsprts.dico.unimi.it http://www.lim.dico.unimi.it Abstract: - A medical instrument for acquisition and analysis of phono-cardiac signals is described in the paper. The proposed system is based on an electronic stethoscope with enhanced performances in environmental noise reduction, achieved by means of two microphones whose signals are combined by an adaptive algorithm. A software tool able to reproduce, visualize and analyze cardiac sounds completes the system. The recorded data and the results of the analysis are stored in a database to build up clinical history of patients and to allow further consultations. A demonstrator of the tool has been realized. Experimental results show significant improvements in noise reduction, when the filtering algorithm is applied. These features make the instrument suited: i) to be employed in very noisy environment, such as ambulance, ii) to help physicians with acoustic diseases, increasing the sound level and showing the phonocardiogram, and iii) to retrieve basic information on the cardiac activity. Key-Words: - Adaptive filters, System identification, Biomedical signal analysis, Electronic stethoscope, Analysis cardiac sounds. 1 Introduction In the last century, cardiovascular illnesses are the first death cause in developed countries [1]. For this reason, many efforts have been made in order to develop sophisticated techniques for the early diagnoses of cardiac disorders. The massive diffusion of such techniques has led physicians to a progressive relinquishment of the traditional stethoscope, with a series of major consequences: • over-crowding of clinics and long waits for examinations; • increasing in the National Health Service costs; • not always justified recourse to time-consuming and expensive diagnostic procedure. This scenario was also supported by some well known disadvantages of the traditional acoustic stethoscope: • its performances are strictly linked to the audio capability of the user; • high levels of environmental noise invalidate auscultations; • analytic comparisons among delayed auscultations are impossible. Modern electronic stethoscopes [2-6], already available on the market, take advantage of modern technologies to reduce these disadvantages. They allow to adjust the volume of auscultations and to store them on a non volatile memory (f.i. on a PC). Also, top level devices are mechanically designed to reject most of the environmental noise, even though its electronic cancellation is not usually implemented. Commercial software tools [7,8] for the record, display and replay of acquired sounds are available too. This paper presents a comprehensive platform [9] which includes both hardware and software and allows to acquire, to organize and to analyze cardiac signals. Fig.1 shows a block scheme of the whole system. The core of the proposed solution is a new digital stethoscope, performing an environmental noise reduction via a distortionless electronic filter. The digital stethoscope is composed of: • a low noise signal detection system - Acquisition Board (AB) - that acquires the low level heart sound by means of two high sensitive microphones, and adapt it for the analog to digital conversion; • a processing unit - Processing Board (PB) - which combines the two signals and reduces the noise using a digital adaptive algorithm, described in the next Section. It also contains hardware resources to display and play in real-time the filtered heart sound. ADVANCES in MATHEMATICAL and COMPUTATIONAL METHODS ISSN: 1792-6114 169 ISBN: 978-960-474-243-1