Current methods used for computerized respiratory sound analysis

Pulmonary disease is a major cause of ill-health throughout the world. In Europe, chronic obstructive pulmonary disease (COPD) and asthma have been estimated to affect between 10 and 25% of the adult population. Pulmonary infections such as acute bronchitis and pneumonia are common, and interstitial lung disease is increasing in incidence. The diagnosis of these common chest diseases is facilitated by pulmonary auscultation using a stethoscope. This device, invented in 1821 by the French Physician, Laennec, is still the commonest diagnostic tool used by doctors. Auscultation with a stethoscope has many limitations. It is a subjective process that depends on the individual's own hearing, experience and ability to differentiate between different sound patterns. It is not easy to produce quantitative measurements or make a permanent record of an examination in documentary form. Long-term monitoring or correlation of respiratory sound with other physiological signals is also difficult. Moreover, the stethoscope has a frequency response that attenuates frequency components of the lung sound signal above about 120 Hz [1], and the human ear is not very sensitive to the lower frequency band that remains. Over the last 30 yrs, computerized methods for the recording and analysis of respiratory sounds have overcome many limitations of simple auscultation. Respiratory acoustic analysis can now quantify changes in lung sounds, make permanent records of the measurements made and produce graphical representations that help with the diagnosis and management of patients suffering from chest diseases. Over recent years, the scientific activity within the field 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 it difficult to compare results from different laboratories and has hampered the commercial development of respiratory sound analysis equipment. Several efforts have been undertaken to solve these problems [2–4]. The European Community has financed a BIOMED 1 Concerted Action project entitled Computerized Respiratory Sound Analysis (CORSA). This collaboration, which was also a task force of the European Respiratory Society, involved research workers in seven European Countries (Belgium, Britain, Finland, France, Germany Italy and the Netherlands). The main objective of the participating centres was to develop guidelines for research and clinical practice in the field of respiratory sound analysis. This issue of The European Respiratory Review includes the agreed consensus of the CORSA project group. As an introduction, a survey of current clinical practice and research initiatives in Europe is presented. Because the definitions of terms including lung sound nomenclature used in the field are variable both within and between countries, a paper presenting both established and new definitions of medical and technical terms used in pulmonary acoustics is included. This paper is deliberately comprehensive in order to provide easily accessible definitions to all workers involved in this field. Another paper deals with the environmental conditions required and patient management procedures to be adopted. Further papers deal with the acquisition, pre-processing and digitization and analysis of lung sounds. Guidelines for publishing the results of research and clinical trials are given so they can be more easily related to other findings. Finally, a perspective on the future of respiratory sound analysis is given. We would like to express our cordial thanks to the whole CORSA group, which includes over 20 scientists, for their valuable and intensive work resulting in the papers in this special issue. We hope that this issue of the European Respiratory Review will facilitate the development of standardized lung sound analysis equipment and promote research into the understanding of respiratory sounds. This will inevitably lead to better and new clinical applications.