Pressure-volume curve of lung and lobes in kittens.

In the neonatal period, the incomplete aeration of the lung parenchyma and the presence of some pulmonary fluid could determine inequalities in the mechanical behavior of lung regions, favoring unevenness of ventilation distribution. We studied the pressure-volume (PV) curve of excised lungs of kittens in the 1st wk of life 1) by changing the volume a known amount and measuring the corresponding changes in transpulmonary pressure (PL) and 2) by ventilating them at a fixed PL at a rate of 20 cycles/min. An expiratory load equal to the value of PL at the resting volume of the respiratory system was added to avoid the collapse of the lung. A lobar bronchus was then tied, and the measurements were repeated. The difference in PV curves before and after ligature therefore represented the PV curve of the lobe. This was done for all the lobes (upper and middle right, lower right, lower left, upper left) in a random order. A total of 20 lungs and 61 lobes have been studied. Individual lobes were not different in terms of dry-to-wet weight ratio, compliance per unit weight, or per maximal volume and shape of the PV curve, indicating a similar mechanical behavior. Dynamic lung compliance averaged 76% +/- 15 SD of the static value, suggesting some degree of asynchronous behavior of lung regions or viscoelastic properties of the tissue.