Effects of age on pulmonary perfusion heterogeneity measured by magnetic resonance imaging

Normal aging is associated with a decline in pulmonary function and efficiency of gas exchange, although the effects on the spatial distribution of pulmonary perfusion are poorly understood: We hypothesized that spatial pulmonary perfusion heterogeneity would increase with increasing age. Fifty-six healthy, nonsmoking subjects (ages 21-76 yr) underwent magnetic resonance imaging with arterial spin labeling (ASL) using a Vision 1.5-T whole body scanner (Siemens Medical Systems, Erlangen, Germany). ASL uses a magnetically tagged bolus to generate perfusion maps where signal intensity is proportional to regional pulmonary perfusion. The spatial heterogeneity of pulmonary blood flow was quantified by the relative dispersion (RD = SD/mean, a global index of heterogeneity) of signal intensity for voxels within the right lung and by the fractal dimension (D-s). There were no significant sex differences for RD (P = 0.81) or D, (P = 0.43) when age was considered as a covariate. RD increased significantly with increasing age by similar to 0.1/decade until age 50-59 yr, and there was a significant positive relationship between RD and age (R = 0.48, P < 0.0005) and height (R = 0.39, P < 0.01), but not body mass index (R = 0.07, P = 0.67). Age and height combined in a multiple regression were significantly related to RD (R = 0.66, P < 0.0001). There was no significant relationship between RD and spirometry or arterial oxygen saturation. D-s was not related to age, height, spirometry, or arterial oxygen saturation. The lack of relationship between age and D-s argues against an intrinsic alteration in the pulmonary vascular branching with age as being responsible for the observed increase in global spatial perfusion heterogeneity measured by the RD.