Effects of experimental recurrent microembolization on pulmonary function and distribution of labeled macroaggregates of sulfur

The effects of repeated microembolization using polystyrene beads were studied in twelve dogs. Hemodynamic changes included transient pulmonary hypertension with return to control values associated with increased cardiac output. In five long-term survivors the lack of development of persistent pulmonary hypertension correlated with evidence of increased arteriovenous shunting. Measurements of alveolar-arterial oxygen gradient showed an increase of 94 per cent mean at seven to eight weeks after initiation of embolization. Increased uptake of radioisotope by the liver was observed when lung scintiphotography was performed with technetium 99m macroaggregates of sulfur colloid. Passage of these 10 to 50 μ particles into the systemic circulation provided further evidence of increased pulmonary arteriovenous shunting and correlated quantitatively with changes in the A-aO₂ gradient. These changes were not observed in seven control dogs. Lung scintiphotography also showed decreased peripheral perfusion and focal perfusion defects. The most pronounced ventilatory change was an increase in ventilatory dead space of 55 per cent at the three to four week restudy period and V_D subsequently remained significantly elevated. V_T increased proportionately with the increase in V_n so that the V_D V_T ratio did not change. These radioisotope studies combined with determinations of A-aO₂ gradient and ventilatory dead space are important diagnostic tools in documenting and quantitating recurrent or chronic pulmonary microembolization.