Computer-assisted three-dimensional volumetry of the human pulmonary acini

Computer-aided three-dimensional (3-D) volumetry of human pulmonary acini was undertaken using the left upper lobe of a 51-year-old female operated for small lung cancer. A normal part of this lobe, fixed by intrabronchial infusion with a mixture of polyethylene glycol and formalin, was subjected to serial sectioning, using a special slicer, into 48 serial slices of 0.5 mm in thickness. A soft x-ray radiograph was prepared from each slice at x 12, and the contours of airways and acinar boundaries contained in it were input by digitization into a microcomputer for 3-D reconstruction and volumetry. The estimated volumes of 130 acini were unexpectedly uniform, showing a normal type distribution with a mean of 172.7 +/- 37.9 mm3. No significant correlation proved to exist between the volume of acini and the number of branching generation of the terminal bronchioles (TBs) they received. Furthermore, there was no significant difference in volume among the acini facing the costal surface, those facing the mediastinal surface and those not facing any pleural surface. However, the generation number of TBs was shown to differ significantly with the location of acini. These results suggest that the tree of conductive airways is designed so as to meet the requirement of constant acinar volume.