title: Age dependency of intrarenal resistance index (RI) in healthy adults and patients with fatty liver disease.
abstract: BACKGROUND
  Our aim was to investigate the influence of age and gender on intrarenal resistance index (RI) measurements in 78 healthy subjects (46 males, 32 females; group 1) and 35 subjects (group 2) with fatty liver disease (28 males and 7 females).
  
  
  METHODS
  First, each subject underwent a conventional abdominal ultrasound examination. Then, intrarenal RI values were determined from three distinct interlobar and cortical arteries respectively on both kidneys. The correlation of intrarenal RI with age and gender as a variable was statistically evaluated by linear regression.
  
  
  RESULTS
  In group 1, the variables gender, kidney region and comparison of right versus left kidney had no significant effect on intrarenal RI (p>0.05). The variable age, on the other hand, showed a significant positive correlation on all four defined measuring points (p<0.01) with linear correlation coefficients of r = 0.26 (left kidney, central) to r = 0.37 (right kidney, cortical). Therefore normal RI values at ages 25, 45, 65 years could be defined as 0.59, 0.61 and 0.63, respectively. Age dependency can thus be expressed as a function with the formula y = 0.565 + 0.001.x. Patients with fatty liver disease showed age dependency on renal RI (p<0.01) as well.
  
  
  CONCLUSIONS
  In accordance with other studies, the influence of age on intrarenal RI measurement is significant in healthy subjects. Intrarenal RI values from subjects with a fatty liver disease showed age dependency as well. Therefore it is necessary to consider the age of the examined person to interpret RI values correctly.
authors.affiliation: Medizinische Klinik, Innenstadt, Klinikum der Ludwig-Maximilians-Universität München, Ziemssenstr. 1, 80336 München, Germany. christoph.kaiser@med.uni-muenchen.de
authors.forename: C
authors.initials: C
authors.lastname: Kaiser
authors.forename: M
authors.initials: M
authors.lastname: Götzberger
authors.forename: N
authors.initials: N
authors.lastname: Landauer
authors.forename: C
authors.initials: C
authors.lastname: Dieterle
authors.forename: W
authors.initials: W
authors.lastname: Heldwein
authors.forename: U
authors.initials: U
authors.lastname: Schiemann
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D005234:Fatty Liver / Q000503:physiopathology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007668:Kidney / Q000098:blood supply / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D012079:Renal Circulation / Q000502:physiology*; D012737:Sex Factors; D018608:Ultrasonography, Doppler; D014655:Vascular Resistance / Q000502:physiology*