Influence of pulmonary embolism on absorption of inhaled iodide-125

To evaluate the influence of embolus size on the absorption of ¹²⁵I^- deposited on the bronchoalveolar surface, we exposed isolated perfused rabbit lungs to an aerosol containing ¹²⁵I^- for 5 min. We monitored the blood radioactivity for the subsequent 2 h. Several groups of lungs were studied, including those in which blood flow was varied and those in which enough glass beads ranging in size from 58 to 548 μm were injected into the pulmonary artery to approximately double the vascular resistance. The results indicated that under control conditions ~94% of the ¹²⁵I^- deposited on the intrapulmonary bronchoalveolar surface was able to reach the pulmonary circulation during the 2-h perfusion period, and the bronchoalveolar surface was sufficiently perfused so that absorption was limited by the rate of diffusion into the blood rather than the rate of blood flow. In the absence of embolization, the initial absorption rate was ~10.4%/min regardless of the total flow rate. The 58-μm beads reduced the rate to ~7.5%/min, whereas the beads ≥194 μm in diameter reduced the rate to ~4.5%/min. Thus the effect of the embolization on the absorption rate was directly related to the bead diameter, even though the number of beads injected was adjusted to produce about the same increase in vascular resistance.