title: The downward shift of the aortic bifurcation, a possible marker for vascular aging.
abstract: OBJECTIVE
  Radiographers in both clinical and research settings utilize lumbar vertebral landmarks (i.e. L5/S1) on scout films to guide imaging of the abdominal aorta. The aortic bifurcation is variably located along the anterior lower spine from L3 toL5. We sought to determine the mean distance from the aortic bifurcation to the L5-S1 disc space. We also investigated associations between cardiovascular disease (CVD) risk factors and calcified atherosclerosis to this distance.
  
  
  METHODS
  This study was a retrospective analysis of 748 participants who underwent abdominal computed tomography (CT) scans for assessment of subclinical cardiovascular disease. The CT scans were used to calculate calcium scores in six arterial beds, as well as the distance from the aortic bifurcation to the L5-S1 disc space.
  
  
  RESULTS
  Among 748 participants, the mean age was 58 ± 11 years, and 57% were male. The mean (SD) distance from the aortic bifurcation to the L5-S1 disc space was 52mm (16). There were no significant differences between males (53mm) and females (52mm). Older age was strongly associated with smaller distances, such that individuals < 50 years had bifurcations that were approximately 19mm further from the L5-S1 disc compared to those ≥ 70 years (P< 0.01). In multivariable analysis, older age, along with lower BMI and smoking were each independently associated with a smaller distance, (P <0.01). Arterial calcification was not significantly associated with this distance.
  
  
  CONCLUSIONS
  The distance from the aortic bifurcation to the L5-S1 disc is smaller in persons with advanced age, lower BMI, and a history of smoking. These associations may reflect a downward shift, which warrants consideration in studies planning to image the abdominal aorta. This downward shift may be a useful marker for vascular aging. Also, further investigations are needed to understand the mechanisms and implications of this descent.
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego, La Jolla, California.
authors.forename: Nketi I
authors.initials: NI
authors.lastname: Forbang
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego, La Jolla, California.
authors.forename: Tran
authors.initials: T
authors.lastname: Nguyen
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego, La Jolla, California ; Veterans Administration San Diego Health Caire Systems, La Jolla, California.
authors.forename: Joachim H
authors.initials: JH
authors.lastname: Ix
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego, La Jolla, California.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Criqui
authors.affiliation: Department of Family and Preventive Medicine, University of California San Diego, La Jolla, California ; Veterans Administration San Diego Health Caire Systems, La Jolla, California.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Allison
keywords: Aortic bifurcation; Atherosclerosis; Body mass index; Computed tomography scans; Lumbar vertebrae; Smoking