OF BREATH SOUNDS. of sounds generated from the

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1 OF BREATH OUND of sounds generated from the ense value to the clistethoscope. The present project was motivated by the resurgent interest in pulmonary disord the necessity for teaching physical ex- ( clinical chest disease to medical students. The current availability of suitable instrumentation permits a rapid and simple amplification of respiratory acoustic data and their recording and play-back with visual sequence as didactic devices. This approach permits a more objective definition of respiratory transients and is appl ;r.tble for research, reachor for bcdtside identification of present preliminary report is concerned only with the instrumentation and clinical spectrum of lung sounds, Further discussions of the origins of respiratory sounds and the effect of pulmonary ventilation on sound intensity are available 1-5 The following system -was adopted for accurate reproduction of breath sound frequencies up to 2,000 cycle per sec. When desired, actual stethoscopic conditions were use of active filters. For transformation o sound vibrations at the chest wall, it was found that a piezoelectric, crystal microphone predominant frequency Yes 100 cycle per sec, and minor attenuation sharp roll-off over 2,000 cycle per sec was optimal,6 This unit has an aluminum bell, 60 mm in diameter, with a relatively airtight, rubber contact edge to minimize ambient and surface noise, Because such units are very sensitive, surface movement should be minimal, particularly if the unit is hand-held. This signal was preamplified (linear) and then fed with a ate impedance matching and equalizatio low level input of a stan recorder. Excluding the tape deck, a flat freick, V. A., Jenkins, j. T., and Webb, T. N. : Amer, 2 LeBlanc, P., ',. D. : Amer. Rev. Resp. Dis., 1970, 102, Forgacs, P. : Lancet, 196, 4 Pottenger, F. M, : Ann, ntern. Med., 1949, 30, Fahr, G. : Arch. ntern. Med. (Chicago), 1927, 39, Model , Cambridge nstruments, Brookline, Massachusetts. quency response between 20 and 20,000 cycle per me (A 2 db), a signal to mw;c ratio better than 80 db and harmonic (isioitiwi typically less than 0.05 per cent at rated output ensured minimal signal distortion from pick-up to tape recording. With commercial low noise, high output recording tape (TDK-D150) and a recording speed of 7.5 inch per sec, a final frequency response of 40 to 15,000 cycle per sec (:t 2 db) and a theoretic signal to noise ratio of 55 db was thus projected.. n actual practice, however, signal to noise ratios were of the order of 10 to 15 db for highly attenuated breath sounds. tandardization of the actual recordin achieved by a predetermined 2-mv, A directly to the recor ensity of -20 db below ecording levels, body posiisovolume conditions were controlled tion, and patient. imultaneous airflow and volrecording was also possible. A flow-depenphotoelectric impellar system was used linear from 0.2 liter per sec to 8.0 liter a square wave signal was directly proportional to the frequency conversion pneumoeath sound signal can be fore or during the actual recordg by earphones or conventional speakers or both, or it can he displayed on a standard oscilloscope to ensure suitable recording levels. imilarly, this taped data can be retrieved for audio-visual inspection at any further time. n this study, a Tektronix-560 series, p ode ray oscilloscope coupled with a Polaroid camera was used for the figures presented. Finally, a nose reduction unit based on the Dolby roduced to minimize tape this Visual examples of typical recorded data in normal subjects and patients with a variety of diseases are displayed in the figures. Calibrated temporal and intensity features were easily visualized in a continuous pattern, parallel to the back of the original audio signal. n inary observations, lung volume and flows were not necessarily controlled nor analyzed. 72 mpellaways, Fibre Optics ndustrie Milton, Massachusetts. AMERCAN REVEW OF REPRATORY DEAE, VOLUME 105,

2 Fig. 1. Bronchial breathing (trachea). Expiration is louder, higher pitched (from audio recording), and longer than inspiration. n this and other figures intensity is displayed on the y-axis and time on the x-axis. Fig. 2. Bronchovesicularsounds. (middle lobe). ntensity of expiration is markedly reduced with a duration equal to inspirat Fig. 3. Vesicular sounds (base). nspiration is louder, of greater duration, and higher pitched, Fig. 4. Acute asthmatic attack (right base). ounds are bronchial with prolonged, loud, expiratory wheezing. Note the reversal of the normal end-expiratory pause. nspiration is held with only a minor pause after expiration. Wheezing was also present during inspiration. Fig, 5. ame patient as in figure 4, 30 minutes after bronchodilator, nspira are now sequenced in a more normal pattern with bronchovesicular tones. nspiration is higher pitched and more prolonged whereas expiration is less intense but absolutely o greater duration than the acute attack. Fig. 6. Clinically asymptomatic asthmatic (middle lobe), Minor inspiratory wheezing and slight prolongation of expiration. Fig. 7. Rhonchi in chronic bronchitis (lower lobe). Note the "outspikes," or deflections from the basic diamond-shape, breath sound configuration present in both inspiration and expiration. These are coarse and of variable intensity and duration. (Contrast with fibrotic rales.) Fig. 8. Fibrotic rales (right base) (visual sequence magnified lox). Ratio of inspiratory time to expiratory time is 1.0, with bronchovesicular characteristics. The "outspike" rales are fine, regular, and equally distributed throughout inspiration.

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