Acute mechanical effects of lung volume changes on artificial microholes in alveolar walls.

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Abstract
A new technique was developed for making reproducible microholes in the alveolar walls of the lung without any other detectable distortion or damage by penetrating through the pleural surface of isolated, air-filled cat lung lobes with 25- to 51-[mu]-diameter tungsten microneedles sharpened to an ultrafine point. Acute mechanical effects of lung volume changes on these microholes were examined. In both dynamic and static experiments the diameter of the holes increases and decreases with lung volume according to the relation, D = k(V - V0)1/3 where D is the hole diameter, V is the fractional lung volume, V0 is the minimal lung volume at Ptp [trans pulmonary pressure] = 0, and k is a proportionality constant related, to alveolus compliance. The holes all close up at V0 regardless of their initial size or the lung volume where they are made because no tissue is lost in making the holes by this method. There is no hysteresis of hole diameter with lung volume. Alveoli and alveolar ducts seem to change size proportionally with lung volume over the range RV [Residual Volume] - TLC [Total lung capacity]. Alveolar shape does not change significantly, and alveolar surface area changes as predicted between V0 and TLC.