title: Influence of age on intrarenal resistive index measurement in normal subjects.
abstract: BACKGROUND
  We investigated the influence of age on intrarenal arterial resistive index (RI) measurement in 135 normal subjects (71 male, 64 female; age range = 17-68 years, median age = 37 years).
  
  
  METHODS
  Each subject underwent color Doppler measurement of the intrarenal RI from three distinct interlobar arteries in the superior, middle, and inferior parts of both kidneys. The mean of six RI values obtained from both kidneys was used for analysis. The correlation of RI with different variables was investigated by linear regression and stepwise multiple linear regression. Variables analyzed were age, systolic blood pressure, diastolic blood pressure, mean blood pressure, pulse pressure, and pulse rate.
  
  
  RESULTS
  The results of linear regression showed that age had a significantly positive correlation ( r = 0.276, p = 0.0012) and diastolic blood pressure had a significantly negative correlation ( r = -0.186, p = 0.0311) with the RI. The results of stepwise multiple linear regression showed that the combination of age and diastolic blood pressure could explain approximately 15% of the RI changes ( r(2) = 0.1535).
  
  
  CONCLUSIONS
  Although there is a statistically significant positive correlation between intrarenal RI and age, the correlation is weak. This suggests that the influence of age on RI measurement is small and may be of no clinical importance.
authors.affiliation: Department of Internal Medicine, Kaohsiung Medical University Hospital, No.100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan, Republic of China.
authors.forename: Z Y
authors.initials: ZY
authors.lastname: Lin
authors.forename: L Y
authors.initials: LY
authors.lastname: Wang
authors.forename: M L
authors.initials: ML
authors.lastname: Yu
authors.forename: C Y
authors.initials: CY
authors.lastname: Dai
authors.forename: S C
authors.initials: SC
authors.lastname: Chen
authors.forename: W L
authors.initials: WL
authors.lastname: Chuang
authors.forename: M-Y
authors.initials: MY
authors.lastname: Hsieh
authors.forename: J-F
authors.initials: JF
authors.lastname: Tsai
authors.forename: W-Y
authors.initials: WY
authors.lastname: Chang
mesh_terms: D000328:Adult; D000367:Age Factors; D001794:Blood Pressure; D005215:Fasting; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D011187:Posture; D011446:Prospective Studies; D012077:Renal Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D018615:Ultrasonography, Doppler, Color; D014655:Vascular Resistance