Figure 1: A cartoon representing a lung sound system. The on-line screen visualises lung sound and flow signals while recording. This helps identifying the area of the chest wall, which is likely to show the abnormal lung sounds. The flow signal and the sound signal are superimposed on each other in the final recording.

Vesicular (normal) lung sounds Vesicular sounds [figure 2.] is a low pitched sound caused by the friction of the air with the walls of the airways. The sound is then 'modified' through passing numerous air filled alveolar spaces and the chest wall structures.

Normal lung sounds

Figure 2: Vesicular ( normal ) lung sound. A. one respiratory cycle. This is a plot of the sound amplitude against time (time-domain). The recording is divided into segments of 100 milliseconds duration for ease of analysis. The flow is to help identifying inspiration and expiration. B. A 'Zoom on' one segment of A for more detailed analysis. C. the frequency-domain plots using fast Forrier analysis on B. the amplitude of the sound is plotted against frequency. This graph shows that the vesicular sounds are by and large of low frequency ( low pitch ) < 200 Hz.

Abnormal Lung Sounds  This can be divided into - continuous lung sounds and discontinuous lung sounds.  Abnormal continuous lung sounds Wheeze Wheeze is a continuous musical sound of >400 Hz pitch [5]. Rhonchi on the other hand is a continuous abnormal sound of < 400 Hz. Sounds between 200-400 Hz were not classified, but the author believes that clinicians perceive a sound of this frequency as wheeze. Wheeze and Rhonchi are heard in asthma, chronic bronchitis and hertz failure. Unilateral wheeze can be the result of external compression or a partial obstruction of a large airway. Tumors in adults and foreign bodies in children are the major causes of unilateral wheeze. it has been suggested that the frequency ( the pitch) of the wheeze is inversely correlated with FEV1 [6].

Wheeze

Figure 3: Monophonic wheeze (430 Hz) in a patient with severe asthma.

Stridor: this is an inspiratory and expiratory sound emanating from the larynx, the trachea or the large airways. Stridor is an alarming sound usually signifying a partial obstruction with tumors, foreign bodies or enlarging retro-sternal thyroid goitre. It is also heard in patients with narrowing trachea after prolonged intubations. Stridor in children is audible in inflammation of the glottis or the trachea.   Stridor Bronchial breathing: This sound is similar to the normal tracheal sounds. It is heard in inspiration and expiration. Bronchial breathing can be heard in thin people in the anterior chest wall just under the clavicle. This represents the sound in the two main bronchi. Pathologically it is heard over a consolidated area particularly in lobar pneumonia. Bronchial breathing is really the sound of relatively large airways transmitted to the chest wall by a non aerated segment (figure 4.). Depending on which stage of the pneumonic illness the auscultation takes place; bronchial breathing can be contaminated with or by pleural rubs, fine or coarse crackles.   Bronchial breathing

Figure 4: production of bronchial breathing. The sound originated from the relatively large airways; represented by the air bronchiogram. Unlike normal vesicular sound, which is transmitted through numerous air-filled spaces, bronchial breathing is transmitted to the microphone through the consolidated area.

Abnormal discontinuous lung sounds Coarse crackles these are low pitched explosive sounds resulting from air bubbling through secretions. In bronchiectasis destruction of bronchial walls and cartlidges can account for coarse crackles that do not disappear or change after coughing or after physiotherapy. coarse crackles can be heard over an area distant from the affected bronchi of the chest wall or by placing the stethoscope on the mouth. Coarse crackles normally disappear or reduce in number after coughing and after deep inspiration and expiration. Nath and Capel found that patients with coarse crackles have an obstructive defect of their lung function tests, which suggests an association with airway narrowing [7]. when recorded by the time expanded wave form analysis (figure 5) crackles have a wide first deflection ( also called initial deflection width) of >1.25 m.s. and two cycle duration of more than 9.32 m.s.[5]. Coarse crackles are heard in chronic bronchitis, asthma, bronchiectasis, pulmonary oedema, and in prolonged bed rest. It is also heard in terminally ill patients. Coarse crackles

Figure 5: Coarse inspiratory and expiratory crackles in a patient with bronchiectasis. In the extended time-domain graph (12 m.s.. for the crackle on the left and 10 m.s. for the right crackle). the frequency domain graph shows tat the coarse crackles are low pitched [ see the frequency domain for fine crackles for comparison]

Fine Crackles this is a high pitched discontinuous fine sound. Fine crackles is widely believed to be the result of a sudden opening of partially closed and stiff small airways and alveoli. Coarse crackles are often audible in mid to late inspiration, and they tend to be repetitive in time and place, which strongly suggests that they are due to changes in solid structures [8]. in computerised lung sound analysis crackles are narrow with an initial deflection width of < 0.92 m.s. and of a two cycle duration of, 6.02 m.s. [5]. fine crackles are heard in patients with interstitial lung disease, early stages of heart failure and in early stages of resolution of pneumonia. Nath and Capel showed that fine crackles are associated with a restrictive default of lung function [0]. in interstitial lung fibrosis the number of crackles per respiratory cycle correlates with the severity of the disease [ 10].   Fine crackles

Figure 6: two respiratory cycles showing fine mid-late inspiritory crackles in a patient with asbestosis. A. the crackles are repetitive in time and amplitude. B. the detailed graph shows that the crackles are narrow and of short duration. C. the frequency domain graph shows a large area under the curve compared with the course crackles ( figure 5).  Pleural rubs Furgacs postulated that pleural rubs are induced by contact of surfaces of the pleura roughened by fibrin. [11]. the sound is a leathery sound usually audible in mid inspiration and mid expiration. Pleural rubs are audible in pneumonia, connective tissue disease affecting the pleura and pulmonary embolism or pulmonary infarction. Bronchial rubs are often mistaken for wheeze of harsh bt=breath sounds. pleural rubs can be inconsistent and can be associated with bronchial breathing due to the underlying disease. this makes them sometimes difficult to recognise. Pleural rubs

Figure 7. Pleural rub in a patient with rheumatoid arthritis. A. There are crackle spikes with a more continuous sound in inspiration and expiration. the sound is not consistent, in that it is opt recorded in the second inspiritory cycle. B. This shows that there is a burst of short continuous signal and a peculiar crackle-like deflection with an M shaped large wave. C. Shows that pleural rub is a mixed low frequency and a high frequency sounds.     References 1. Schilling RSF, Hughes JPW, Dingwall-DeFordyce I. Disagreement between observers in an epidemiological study of respiratory disease. Br J Med 1955:1: 65. 2. Smyllie HC, Blendis LM, Armitage P. Observer disagreement in physical signs of the respiratory system. Lancet 1965;2:412. 3. Rubins EH, Rubin M. Thoracic Diseases. Philadelphia and London. WB Saunders 1961. 4. Laennec RTH. a treatise on the disease of the dnest - translated from the French. New York Publishing c. 1962, p319. 5. American thoracic Society Ad Hoc Committee on pulmonary nomenclature for membership reaction. ATS News Fall 1977; 3:5-6. 6. Braughman RP, Loudon RG. Quantification for wheezing in acute asthma. Chest 1984;86:718 7. Nath AR. Capel LH. Inspiratory crackles and mechanical events of breathing. Thorax 1994;29:695-698. 8. Al Jarad N, Davies SW, Logan Sinclair R, Rudd RM. Lung crackle characteristics in patients with asbestosis, asbestos related pleural disease and left ventricular failure using time expanded waveform analysis - a comparative study. Respiratory medicine 1994; 88:37-46. 9. Nath AR, Capel LH. inspiratory crackles, early and late. Thorax 1974; 29:223. 10. Murphy RLH, Del Bono EA, Davidson F. Validation of an automated crackles (rales) counter. Am Rev Resp Dis 1989; 140:1017-1020. 11. Fourgacs P. Lung Sounds. 1 Ed. London Bailliere Tendall 1978.

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