Frequency dependence of pressure-volume loops in isolated dog lobes

Eight excised dog lobes were cycled at frequencies ranging from 0.3 to 50 cycles/min. Using the retrograde catheter technique for measuring air pressure near alveoli, pressure-volume loops were recorded at several frequencies within the range. Two characteristics of these loops were examined systematically: the dynamic compliance and the hysteresis area (work loss per cycle). In the frequency range examined, all lobes showed some degree of dependence of hysteresis area on cycling frequency. About half the tracings exhibited local maxima in a work per cycle vs frequency plot. All of the eight lobes exhibited a decrease in dynamic compliance with increasing frequency. The monotonic decrease in dynamic compliance with frequency is consistent with reports of previous workers on excised and intact preparations. Our experiments demonstrate that the hysteresis area is frequency dependent and suggest that some frequency dependence should exist even in non-pathologic conditions. Possible interpretations of these results in terms of the dynamic behavior of surfactant films and lung tissue are given and the need is discussed for including such effects in continuum mechanics models of the lung.