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Comparison of lung sounds and gas trapping in the study of airway mechanics.

Frazer-DG; Smith-LD; Brancazio-LR; Weber-KC
Environ Health Perspect 1986 Apr; 66:25-30
A study was performed to correlate lung sounds measured in isolated lungs from male Long-Evans-hooded-rats with past gas trapping experiments in isolated rat lungs. Such a correlation would allow measurement of lung sounds in animals and humans exposed to cotton dust and provide a valid prediction of peripheral airway function changes. Following administration of anesthetic, the heart and lungs were removed en-bloc and placed in a liquid filled plethysmograph. A microphone acoustically coupled to the tracheal cannula was used to record lung sounds. Discontinuous lung sounds in the form of crackles occurred during lung inflation simultaneously with gas trapping. During deflation, sound energy was only generated when low transpulmonary pressures were reached. Past studies have demonstrated that the rate of inflation greatly affects the amount of trapped gas in a lung while the deflation rate is far less important. Past studies have also shown that gas diffuses through a liquid barrier such as a meniscus to enter the trapped gas space. The present study indicated that airway closure was related to two separately occurring events as the lungs were deflated: the formation of a meniscus across the airway at positive transpulmonary pressures, followed by a mechanical buckling of the airway wall at negative values of the end expiratory pressure. The total sound energy level resulting from the summation of all the discontinuous lung sounds increased as the end expiratory pressure decreased. During lung deflation very little acoustical energy was detected at the trachea. The authors conclude that the usefulness of noninvasive measures of tracheal lung sounds to predict alterations occurring in the periphery of the lung brought about by disease will enable studies to be made on live animals and humans. Of particular interest will be studies of tracheal lung sounds in animals exposed to cotton dust in the study of small airway obstruction during the onset of byssinosis.
NIOSH-Author; In-vitro-studies; Pulmonary-system-disorders; Pulmonary-function-tests; Laboratory-animals; Analytical-methods; Acoustical-measurements
David G. Frazer, Division of Respiratory Disease Studies, National Institute for Occupational Safety and Health, Morgantown, WV 26505
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Environmental Health Perspectives