title: Magnitude and return time of the reflected wave:  the effects of large artery stiffness and aortic geometry.
abstract: BACKGROUND
  Increased large artery stiffness is a major determinant of systolic pressure and indicator of cardiovascular events. The reflected wave, its arrival time (return time) and magnitude, contributes to systolic pressure, and is a supposed indicator of aortic stiffness. With aortic stiffening, the return time is assumed to decrease inversely with PWV as 2L/PWV, where L is the aortic length. However, several studies reported that the inflection point of aortic pressure, a surrogate of return time, varies little with aortic stiffness.
  
  
  METHODS
  We studied the effects of aortic stiffness on wave reflection in an anatomically accurate arterial model. Return time is time difference of forward, Pf, and backward, Pb, pressure. Return time, inflection and shoulder points, augmentation index, and reflection magnitude (Pb/Pf) were calculated by standard rules.
  
  
  RESULTS
  Peripheral resistance does not affect reflection directly, but only through pressure (stiffness) changes. Magnitude of reflected waves depend about equally on aortic geometry (taper, branches) and distal aortic reflection. Therefore, relations of augmentation index and reflection magnitude with stiffness are nonlinear and complex; augmentation index is most sensitive to stiffness. Between PWV 6 and 12  m/s, representing ages of 20-80 years, return time and inflection and shoulder points change differently with stiffness and PWV cannot be derived from them. Pulse pressure is strongly dependent on aortic stiffness. Taper changes return time by a factor 2, but has little effect on reflection magnitude, augmentation index, and inflection point.
  
  
  CONCLUSIONS
  Accurate quantitative information on arterial stiffness cannot be obtained from reflection parameters. The augmentation index is most sensitive to stiffness changes.
authors.affiliation: BMEYE, Academic Medical Center Amsterdam, The Netherlands. n.westerhof@vumc.nl
authors.forename: Berend E
authors.initials: BE
authors.lastname: Westerhof
authors.forename: Nico
authors.initials: N
authors.lastname: Westerhof
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001011:Aorta / Q000033:anatomy & histology*; D001158:Arteries / Q000033:anatomy & histology*; D001783:Blood Flow Velocity; D001794:Blood Pressure / Q000187:drug effects; D001795:Blood Pressure Determination; D002309:Cardiology / Q000379:methods; D003198:Computer Simulation; D055119:Elastic Modulus; D006801:Humans; D008875:Middle Aged; D008955:Models, Cardiovascular; D015203:Reproducibility of Results; D013997:Time Factors; D014655:Vascular Resistance; D059289:Vascular Stiffness