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1 Department of Radiology, Mail Code 8756, UC-San Diego Medical Center, San Diego, California, United States
2 Department of Medicine, University of California, San Diego, La Jolla, California, United States
3 Medicine, University of California, San Diego, La Jolla, California, United States
4 Department of Medicine, University of California, San Diego, La Jolla, California, United States; Department of Radiology, Mail Code 8756, UC-San Diego Medical Center, San Diego, California, United States
* To whom correspondence should be addressed. E-mail: shopkins{at}ucsd.edu.
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 underwent magnetic resonance imaging with arterial spin labeling (ASL) using a Vision 1.5T 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=standard deviation/mean, a global index of heterogeneity) of signal intensity for voxels within the right lung and by the fractal dimension (Ds). There were no significant sex differences for RD (p=0.81) or Ds (p=0.43) when age was considered as a covariate. RD increased significantly with increasing age by approximately 0.1/decade until age 50-59 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 BMI (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 (SaO2). Ds was not related to age, height, spirometry, or SaO2. The lack of relationship between age and fractal dimension 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 relative dispersion.
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