Discontinuous lung sounds and hysteresis in control and Tween 20-rinsed excised rat lungs

In the past, the relationship between pulmonary hysteresis and a model of t he recruitment-derecruitment of lung units has been explored (Cheng, W., De Long, D.S., Franz, G.N., Petsonk, E.L., Frazer, D.G., 1995, Resp. Physiol. 103, 205-215. The recruitment process is characterized by a sequence of eve nts which represents discrete configurational changes in lung structure. It is assumed that energy released during the opening of lung units is associ ated with the formation of discontinuous lung sounds. The goal of this stud y was to record tracheal sounds for lungs inflated from different end-expir atory pressures and to relate the sound power to the normalized hysteresis of individual pressure-volume (PL-VL) loops. PL-VL curves and lung sounds w ere recorded for control lungs and lungs rinsed with Tween 20 in order to e stimate the role of alveolar surfactant on the recruitment-derecruitment pr ocess. Results indicate that there may be two populations of lung units, on e which is altered by Tween 20 and another which is not. The population not affected by Tween 20 appeals to be responsible for producing discrete lung sounds and may represent the opening of larger conducting airways. The sec ond population, possibly within the respiratory zone, is affected by altera tions in surface tension and contributes to pulmonary hysteresis, but, appa rently, does not contribute significantly to lung sound power measured at t he trachea. (C) 1999 Elsevier Science B.V. All rights reserved.