A simulation study of diffusion-convection interaction and its effect on multiple breath washout indices

Abstract Experimental studies of acinar ventilation heterogeneity (S acin ) derived from the multiple breath washout have shown the potential of S acin to pick up structural change in lung disease. Recent S acin data suggest that even when intra-acinar structure is unaltered, the combination of convection, diffusion and number of acini fed by patent terminal bronchioles can modify S acin . We show here how S acin is affected by structural features such as the secondary alveolar septa, intra-acinar ramification and number of ventilated acini. The simulations also predict relationships between respective alterations in S acin and washout indices such as lung clearance index (LCI) and alveolar mixing efficiency (AME). This was verified experimentally, with highly significant correlations between S acin and LCI (r = +0.85;p  acin and AME (r = − 0.92; p