title: Real-time aortic pulse wave velocity measurement during exercise stress testing.
abstract: BACKGROUND
  Pulse wave velocity (PWV), a measure of arterial stiffness, has been demonstrated to be an independent predictor of adverse cardiovascular outcomes. This can be derived non-invasively using cardiovascular magnetic resonance (CMR). Changes in PWV during exercise may reveal further information on vascular pathology. However, most known CMR methods for quantifying PWV are currently unsuitable for exercise stress testing.
  
  
  METHODS
  A velocity-sensitive real-time acquisition and evaluation (RACE) pulse sequence was adapted to provide interleaved acquisition of two locations in the descending aorta (at the level of the pulmonary artery bifurcation and above the renal arteries) at 7.8 ms temporal resolution. An automated method was used to calculate the foot-to-foot transit time of the velocity pulse wave. The RACE method was validated against a standard gated phase contrast (STD) method in flexible tube phantoms using a pulsatile flow pump. The method was applied in 50 healthy volunteers (28 males) aged 22-75 years using a MR-compatible cycle ergometer to achieve moderate work rate (38 ± 22 W, with a 31 ± 12 bpm increase in heart rate) in the supine position. Central pulse pressures were estimated using a MR-compatible brachial device. Scan-rescan reproducibility was evaluated in nine volunteers.
  
  
  RESULTS
  Phantom PWV was 22 m/s (STD) vs. 26 ± 5 m/s (RACE) for a butyl rubber tube, and 5.5 vs. 6.1 ± 0.3 m/s for a latex rubber tube. In healthy volunteers PWV increased with age at both rest (R(2) = 0.31 p < 0.001) and exercise (R(2) = 0.40, p < 0.001). PWV was significantly increased at exercise relative to rest (0.71 ± 2.2 m/s, p = 0.04). Scan-rescan reproducibility at rest was -0.21 ± 0.68 m/s (n = 9).
  
  
  CONCLUSIONS
  This study demonstrates the validity of CMR in the evaluation of PWV during exercise in healthy subjects. The results support the feasibility of using this method in evaluating of patients with systemic aortic disease.
authors.affiliation: Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand. paul.roberts@auckland.ac.nz.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Roberts
authors.affiliation: Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, 85 Park Road, Auckland, 1142, New Zealand. b.cowan@auckland.ac.nz.
authors.forename: Brett R
authors.initials: BR
authors.lastname: Cowan
authors.affiliation: Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, 85 Park Road, Auckland, 1142, New Zealand. yingmin.liu@auckland.ac.nz.
authors.forename: Yingmin
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Greenlane Cardiovascular Unit, Auckland City Hospital, Auckland, New Zealand. aaronlin819@gmail.com.
authors.forename: Aaron C W
authors.initials: AC
authors.lastname: Lin
authors.affiliation: Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand. p.nielsen@auckland.ac.nz.|Department of Engineering Science, University of Auckland, Auckland, New Zealand. p.nielsen@auckland.ac.nz.
authors.forename: Poul M F
authors.initials: PM
authors.lastname: Nielsen
authors.affiliation: Auckland Bioengineering Institute, University of Auckland, Auckland, New Zealand. a.taberner@auckland.ac.nz.|Department of Engineering Science, University of Auckland, Auckland, New Zealand. a.taberner@auckland.ac.nz.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Taberner
authors.affiliation: Greenlane Cardiovascular Unit, Auckland City Hospital, Auckland, New Zealand. rstewart@adhb.govt.nz.
authors.forename: Ralph A H
authors.initials: RA
authors.lastname: Stewart
authors.affiliation: Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, 85 Park Road, Auckland, 1142, New Zealand. h.lam@auckland.ac.nz.
authors.forename: Hoi Ieng
authors.initials: HI
authors.lastname: Lam
authors.affiliation: Department of Anatomy with Radiology, Faculty of Medical and Health Sciences, University of Auckland, 85 Park Road, Auckland, 1142, New Zealand. a.young@auckland.ac.nz.
authors.forename: Alistair A
authors.initials: AA
authors.lastname: Young
mesh_terms: D000328:Adult; D000368:Aged; D001011:Aorta / Q000502:physiology*; D001331:Automation; D001642:Bicycling; D005080:Exercise Test; D005240:Feasibility Studies; D005260:Female; D064368:Healthy Volunteers; D006339:Heart Rate; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D019028:Magnetic Resonance Imaging, Cine / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D011237:Predictive Value of Tests; D063177:Pulse Wave Analysis / Q000295:instrumentation / Q000379:methods*; D015203:Reproducibility of Results; D013997:Time Factors; D059289:Vascular Stiffness; D055815:Young Adult