INERT-GAS SINGLE-BREATH WASHOUT AFTER HEART-LUNG TRANSPLANTATION

We prospectively studied the distribution of ventilation in 22 heart-l ung transplant (HLT) recipients. At entry into study, the patients had undergone surgery an average of 6.7 mo earlier, and were followed for a mean period of 16 mo. Vital-capacity (VC) single-breath washouts as well as single-breath washouts using a 1-L inspiration from FRC were performed on a total of 395 occasions. The inhaled gas mixture consist ed of 5% He, 5% 5F(6), and 90% O-2, and the expired N-2, He, and SF6 c oncentrations were analyzed. Six patients showed normal standard pulmo nary-function tests and indexes of ventilation distribution throughout the study. five patients gradually developed an irreversible airflow obstruction, presumably due to obliterative bronchiolitis (OB). They s howed increases in the slopes of the N-2, SF6, and He alveolar plateau s (S-N2 S-SF6, S-He), but because S-He increased more than S-SF6, the slope difference (S-SF6 - S-He) invariably decreased and became negati ve in four of five patients. Thirteen patients developed 16 episodes o f reversible airflow obstruction as a result of acute infection or rej ection of the lung allograft, The alterations in ventilation distribut ion were qualitatively similar to those seen in patients with OB. We c onclude that: (1) ventilation distribution in the lung periphery is no rmal in HLT recipients with adequate allograft function; (2) the airfl ow obstruction elicited by OB and acute episodes of lung infection or rejection is accompanied by increases in S-N2, S-SF6, and S-He and dec reases in S-SF6 - S-He. This alteration, which seems to be unique to H LT recipients, can best be explained by the development of cross-secti onal inequalities at branch point nt subtending membranous or terminal bronchioles. The alteration of S-N2, S-SF6, S-He, and S-SF6 - S-He ma y be more sensitive than standard pulmonary-function tests to lung-all ograft dysfunction.