Copyright ©ERS Journals Ltd 2000 Eur Respir Rev 2000; 10: 77, 585 European Respiratory Review Printed in UK - all rights reserved ISSN 0905 - 9180 Standardization of computerized respiratory sound analysis A.R.A. Sovijärvi, J. Vanderschoot, J.E. Earis Pulmonary disease is a major cause of ill-health thro- was also a task force of the European Respiratory Society, ughout the world. In Europe, chronic obstructive pulmo- involved research workers in seven European Countries nary disease (COPD) and asthma have been estimated to (Belgium, Britain, Finland, France, Germany Italy and the affect between 10 and 25% of the adult population. Pul- Netherlands). The main objective of the participating cen- monary infections such as acute bronchitis and pneumonia tres was to develop guidelines for research and clinical prac- are common, and interstitial lung disease is increasing in tice in the field of respiratory sound analysis. This issue of incidence. The diagnosis of these common chest diseases The European Respiratory Review includes the agreed con- is facilitated by pulmonary auscultation using a stetho- sensus of the CORSA project group. As an introduction, a scope. This device, invented in 1821 by the French Physi- survey of current clinical practice and research initiatives cian, Laennec, is still the commonest diagnostic tool used in Europe is presented. Because the definitions of terms by doctors. including lung sound nomenclature used in the field are Auscultation with a stethoscope has many limitations. It variable both within and between countries, a paper pre- is a subjective process that depends on the individual's senting both established and new definitions of medical own hearing, experience and ability to differentiate between and technical terms used in pulmonary acoustics is in- different sound patterns. It is not easy to produce quantita- cluded. This paper is deliberately comprehensive in order tive measurements or make a permanent record of an to provide easily accessible definitions to all workers involv- examination in documentary form. Long-term monitoring ed in this field. Another paper deals with the environmen- or correlation of respiratory sound with other physiologi- tal conditions required and patient management procedures cal signals is also difficult. Moreover, the stethoscope has to be adopted. Further papers deal with the acquisition, a frequency response that attenuates frequency compo- pre-processing and digitization and analysis of lung sounds. nents of the lung sound signal above about 120 Hz [1], Guidelines for publishing the results of research and clini- and the human ear is not very sensitive to the lower fre- cal trials are given so they can be more easily related to quency band that remains. other findings. Finally, a perspective on the future of respi- Over the last 30 yrs, computerized methods for the ratory sound analysis is given. recording and analysis of respiratory sounds have over- We would like to express our cordial thanks to the whole come many limitations of simple auscultation. Respiratory CORSA group, which includes over 20 scientists, for their acoustic analysis can now quantify changes in lung so- valuable and intensive work resulting in the papers in this unds, make permanent records of the measurements made special issue. We hope that this issue of the European Res- and produce graphical representations that help with the piratory Review will facilitate the development of standard- diagnosis and management of patients suffering from chest ized lung sound analysis equipment and promote research diseases. into the understanding of respiratory sounds. This will Over recent years, the scientific activity within the field inevitably lead to better and new clinical applications. of respiratory acoustics has increased markedly. However, a lack of guidelines for data acquisition, storage, signal processing and analysis of the lung sound signal has made References it difficult to compare results from different laboratories and has hampered the commercial development of respira- 1. Abella M, Formolo J, Penny DG. Comparison of acoustic tory sound analysis equipment. Several efforts have been properties of six popular stethoscopes. J Acoust Soc Am undertaken to solve these problems [2–4]. 1992; 91: 2224–2228. The European Community has financed a BIOMED 1 2. Mussel MJ. The need for standards in recording and ana- lysing respiratory sounds. Med Biol Eng Comput 1992; Concerted Action project entitled Computerized Respira- 30: 129–139. tory Sound Analysis (CORSA). This collaboration, which 3. Gavriely N. Breath Sounds Methodology. Boca Raton, FL, CRC Press 1995. Correspondence: A.R.A. Sovijärvi, Dept of Clinical Physiology and 4. Pasterkamp H, Kraman SS, Wodicka GR. Respiratory Nuclear Medicine, Helsinki University Hospital, P.O. Box 340, FIN- sounds. Advances beyond the stethoscope. Am J Respir 00029 HUS, Finland. Fax: 358 947174592. Crit Care Med 1997; 156: 974–987. Copyright ©ERS Journals Ltd 2000 Eur Respir Rev 2000; 10: 77, 586–590 European Respiratory Review Printed in UK - all rights reserved ISSN 0905 - 9180 Current methods used for computerized respiratory sound analysis J.E. Earis*, B.M.G. Cheetham** Current methods used for computerized respiratory sound analysis J.E. Earis, B.M.G. *Aintree Chest Centre, University Hospi- Cheetham. ©ERS Journals Ltd 2000. tal, Aintree, Liverpool, UK. **School of ABSTRACT: The study of respiratory sounds by computer has a considerable his- Engineering, University of Manchester, tory, which spans a time of rapidly evolving technology and changing perceptions of Manchester, UK. analogue and digital signal processing. Much of the knowledge gained in recent years Correspondence: J.E. Earis has resulted from the use of a wide variety of data acquisition, processing and analy- Aintree Chest Centre sis techniques. Details of the techniques used in published research emanating from University Hospital European and other world wide centres over the past 10 yrs are surveyed in this Aintree paper. The survey reveals the range of clinical conditions studied, the type of analysis Longmoor Lane equipment used and the extent to which the engineering parameters of the various Liverpool L9 7AL equipment used were similar and/or different. It is clear that, in addition to the well- UK established analysis of adventitious sounds, there is increasing interest in the analysis of breath sounds as a measure of regional physiology. In addition, over 60% of pub- Keywords: Computer analysis respiratory sounds lished studies over the 10 yrs involve upper airway sounds. Although marked similar- ities in the basic methodology were found, there was considerable variation in the way This study was supported by the EU that sound was processed and analysed. It is concluded that there is a need for the BIOMED 1 programme (contract BMH1- development of guidelines for the recording, processing and analysis of respiratory CT94-0928) and by the European Respira- sounds in order to facilitate the easy exchange of data and to enable a meaningful tory Society (ERS task force). comparison of results between research centres. Eur Respir Rev 2000: 10: 77, 586–590. This paper forms part of the publications of the CORSA project. With the use of modern digital signal processing tech- Medicus and the ILSA (International Lung Sounds Asso- niques, the analysis of wave forms by computer has ciation) bibliography (http://www.ilsa.cc/referenc.htm) as become an established research technique for the investi- current in January 1996. The 1,672 papers referring to gation of respiratory sounds [1, 2]. As research in this area upper and lower respiratory sounds published world-wide has developed, many different types of equipment and were analysed. Among these, 163 papers were identified techniques have been used. The aims of this paper are to that used some form of electronic wave-form analysis analyse the activities, in this field, in European and other techniques (12.6% of the total number of papers). The main world-wide centres, to assess the degree to which ILSA bibliography includes all papers that use form of equipment is standardized and to identify the techniques electronic analysis published since 1970. The analysis used to analyse respiratory sounds. To enable comparisons techniques used in each of the main European, North Amer- to be made between the various types of equipment and ican and Israeli centres were identified and catalogued techniques used currently, and recently, for the computer- according to the criteria presented in table 1. A detailed ized analysis of respiratory sounds, the authors have analysis of all papers in the survey originating in Europe undertaken a survey of this area of research. between 1991 and 1996 was undertaken in order to pro- vide a detailed catalogue of the equipment and techniques used. Methods The survey was carried out in the main European and Survey of respiratory sounds research world centres by addressing the published literature, making site visits and holding meetings with workers active in the The survey revealed that within Europe, the most active field. The study was undertaken as part of the concerted contributors were from the CORSA groups in Finland, action project, CORSA (Computerized Respiratory Sound England, France, Italy and The Netherlands who were Analysis), included in the BIOMED 1 programme of the responsible for about 25% of the total published world- European Union. wide papers on respiratory sounds. Table 2, produced A study of the world