Ventilation heterogeneity does not change following pulmonary microembolism

By using the multiple-breath helium washout technique, ventilation heteroge neity (V(over dot)H) after embolic injury in the lung can be quantitatively partitioned into the conductive and acinar components. Total V(over dot)H, represented by the normalized slope of the phase III alveolar plateau, Sn- III(total), was studied for 120 min in three groups of anesthetized and par alyzed mongrel dogs. Group I (n = 3) received only normal saline and served as controls. Group 2 (n = 4) received repeated infusions of polystyrene be ads (250 mu m) into the right atrium at 10, 40, 80, and 120 min. Group 3 (n = 3) was similarly treated, except that the embolic beads used were 1,000 mu m in diameter. The data show that, despite repeated embolic injury by po lystyrene beads of different diameters, there was no significant increase i n total V(over dot)H. The acinar component of Sn-III, which represents V(ov er dot)H in the distal airways, accounts for over 90% of the total V(over d ot)H. The conductive component of Sn-III, which represents V(over dot)H bet ween larger conductive airways, remains relatively constant and a minor com ponent. We conclude that pulmonary microembolism does not result in signifi cant redistribution of ventilation.