title: Arterial stiffness index beta and cardio-ankle vascular index inherently depend on blood pressure but can be readily corrected.
abstract: Arterial stiffness index β and cardio-ankle vascular index (CAVI) are widely accepted to quantify the intrinsic exponent (β0) of the blood pressure (BP)-diameter relationship. CAVI and β assume an exponential relationship between pressure (P) and diameter (d). We aim to demonstrate that, under this assumption, β and CAVI as currently implemented are inherently BP-dependent and to provide corrected, BP-independent forms of CAVI and β.
  
  
  
  In P = Prefe, usually reference pressure (Pref) and reference diameter (dref) are substituted with DBP and diastolic diameter to accommodate measurements. Consequently, the resulting exponent is not equal to the pressure-independent β0. CAVI does not only suffer from this 'reference pressure' effect, but also from the linear approximation of (dP/dd). For example, assuming β0 = 7, an increase of SBP/DBP from 110/70 to 170/120 mmHg increased β by 8.1% and CAVI by 14.3%. We derived corrected forms of β and of CAVI (CAVI0) that indeed did not change with BP and represent the pressure-independent β0. To substantiate the BP effect on CAVI in a typical follow-up study, we realistically simulated patients (n = 161) before and following BP-lowering 'treatment' (assuming no follow-up change in intrinsic β0 and therefore in actual P-d relationship). Lowering BP from 160 ± 14/111 ± 11 to 120 ± 15/79 ± 11 mmHg (p < 0.001) resulted in a significant CAVI decrease (from 8.1 ± 2.0 to 7.7 ± 2.1, p = 0.008); CAVI0 did not change (9.8 ± 2.4 and 9.9 ± 2.6, p = 0.499).
  
  
  
  β and CAVI as currently implemented are inherently BP-dependent, potentially leading to erroneous conclusions in arterial stiffness trials. BP-independent forms are presented to readily overcome this problem.
authors.affiliation: aDepartment of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, Sydney, AustraliabDepartment of Biomedical Engineering, CARIM School for Cardiovascular Diseases, Maastricht University, Maastricht, The Netherlands.
authors.forename: Bart
authors.initials: B
authors.lastname: Spronck
authors.forename: Alberto P
authors.initials: AP
authors.lastname: Avolio
authors.forename: Isabella
authors.initials: I
authors.lastname: Tan
authors.forename: Mark
authors.initials: M
authors.lastname: Butlin
authors.forename: Koen D
authors.initials: KD
authors.lastname: Reesink
authors.forename: Tammo
authors.initials: T
authors.lastname: Delhaas
mesh_terms: D001794:Blood Pressure / Q000502:physiology*; D001795:Blood Pressure Determination; D003198:Computer Simulation; D003971:Diastole; D005500:Follow-Up Studies; D006801:Humans; D055641:Mathematical Concepts; D059289:Vascular Stiffness / Q000502:physiology*