Fractal nature of regional ventilation distribution

High-resolution measurements of pulmonary perfusion reveal substantial spat ial heterogeneity that is fractally distributed. This observation led to th e hypothesis that the vascular tree is the principal determinant of regiona l blood flow. Recent studies using aerosol deposition show similar ventilat ion heterogeneity that is closely correlated with perfusion. We hypothesize that ventilation has fractal characteristics similar to blood flow We meas ured regional ventilation and perfusion with aerosolized and injected fluor escent microspheres in six anesthetized, mechanically ventilated pigs in bo th prone and supine postures. Adjacent regions were clustered into progress ively larger groups. Coefficients of variation were calculated for each clu ster size to determine fractal dimensions. At the smallest size lung piece, local ventilation and perfusion are highly correlated, with no significant difference between ventilation and perfusion heterogeneity. On average, th e fractal dimension of ventilation is 1.16 in the prone posture and 1.09 in the supine posture. Ventilation has fractal properties similar to perfusio n. Efficient gas exchange is preserved, despite ventilation and perfusion h eterogeneity, through close correlation. One potential explanation is the s imilar geometry of bronchial and vascular structures.