title: Evolution of hemodialysis access resistance: a longitudinal 5-year model using functional principal components analysis.
abstract: OBJECTIVE
  Arteriovenous fistulae (AVF) and grafts (AVG) are the preferred accesses in hemodialysis (HD). By monitoring access resistance (AR) one can potentially identify problems with an established HD access, but little is known about how these changes in AR occur, or the variations between the two access types as they mature longitudinally. We postulated that AR evolves differentially between AVF and AVG, a critical aspect to further understanding of the natural history of HD accesses. To describe these changes, we applied a novel statistical methodology of functional principal component (FPC) analysis.
  
  
  METHODS
  Using ultrasound dilution flow studies, we retrospectively studied 479 functional HD accesses in which a total of 4573 assessments were made. Accounting for patient factors of age, race, gender and diabetes mellitus (DM) status, we employed a multivariate, mixed-effects model. Using the mean effects of those covariates, we then applied FPC analyses to assess the longitudinal, timedependent changes between AVFs and AVGs over a 5-year period.
  
  
  RESULTS
  Both types of upper-arm access were associated with a lower initial AR. Older age and DM were associated with a higher AR. Longitudinal AR varied significantly for both AVF and AVG, between the upper arm and lower arm. As a function of time, AVG was associated with an increasing AR. Conversely, AVF, especially upper-arm ones, demonstrated a longitudinal drop in AR.
  
  
  CONCLUSIONS
  Evolutionally, AR can be predicted not only by the type of access, but also by the location along the arm of that access and by clinical patient factors. Longitudinal change in AR does differ between AVG and AVF. Our report provides the foundation of observed changes over time and provides insight as to how these variations are affected. We endorse ongoing surveillance to screen for clinical sequelae, even years from initial placement.
authors.affiliation: Department of Internal Medicine, Division of Nephrology, University of California, Davis School of Medicine, 4150 V Street, Suite 3500, Sacramento, CA, USA. andrew.chin@ucdmc.ucdavis.edu
authors.forename: Andrew I
authors.initials: AI
authors.lastname: Chin
authors.forename: William R
authors.initials: WR
authors.lastname: Raffo
authors.forename: Xiaowei
authors.initials: X
authors.lastname: Yang
authors.forename: James R
authors.initials: JR
authors.lastname: Madison
mesh_terms: D000328:Adult; D000368:Aged; D001166:Arteriovenous Shunt, Surgical / Q000009:adverse effects; D019917:Blood Vessel Prosthesis Implantation / Q000009:adverse effects; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D025341:Principal Component Analysis; D012039:Regional Blood Flow; D006435:Renal Dialysis; D012189:Retrospective Studies; D013997:Time Factors; D034941:Upper Extremity / Q000098:blood supply*; D014655:Vascular Resistance