Abstract
In a previous report on the simulation of the Velcro rale using a mathematical model we postulated that stiffening of the lung tissue was closely related to the production of the rale. In this study, the acoustic analysis of the rales heard in 6 patients with cryptogenic fibrosing alveolitis and 7 patients with pulmonary fibrosis due to collagen disease was undertaken using a sound spectrogram.
Each spike wave, components of the rale, was as certained to be composed of several resonant sounds by sound spectrogram. Therefore, a resonator theory similar to that of Helmholtz was applied to calculate each frequency of the resonant sounds in any partial lung volume of certain lung levels, and it was supposed that a wave of 1000-2000Hz, for example, was produced from the lung units of bronchiole to terminal bronchiole level. On the other hand, the so called moist rale heard in pneumonia had explosive sound acoustic characteristics, completely different from the Velcro rale.
After the calculations from postulated size in various elements of the lung, the refractory period of around 0.2-0.3 second seen at the beginning of inspiratory phase was considered to be the time required to fill the first lung unit by air until the wall of the unit reached a certain tension to produce the rale.
The meaning of the spike to spike time observed around 0.02-0.04 second was clarified by mathematical analysis. However, it was seen that inspiratory air flow was relatively related to spike to spike time and the size of spike wave.
As a result, these findings may suggest that the alveolar wall theory is supported, and that Velcro rale is heard not only in cryptogenic fibrosing alveolitis but in certain other pathologic conditions.
