Determination of regional pulmonary mechanics using a scintillation camera

Electrical circuit R-C analogue models that reflect the difference in disease state between normal and diseased subjects, and normal and diseased regions of a diseased lung, were used to evaluate distal and proximal resistances and compliances for lung regions. Experimental values of regional flows and volumes for normal and diseased human lungs were obtained from a noninvasic scintillation camera technique in which the subject breathed Xe133-seeded air. Values of resistance and compliance were obtained with the additional use of an esophageal balloon. Total volumes and flows were measured through spirometry. Regional volumes were determined and regional flows were found through numerical differentiation. In analytical modeling, values of resistances and compliances were chosen so that the computed flow and volume curves corresponded to the actual flow and volume curves. Differences in resistance were an order of magnitude higher for the diseased subjects while compliances were generally several times lower than those for the normal subjects. However, the absolute values do not correlate well with those values generally found in the literature because compliance is usually measured statically and resistance measured during tidal breathing or panting. Since the forced vital capacity maneuver used here is extremely dynamic, there is significant airway collapse which results in functionally higher resistances and lower compliances. This maneuver tends to accentuate the differences between normal and diseased subjects and a subject's normal and diseased lung regions.