title: Viscous energy loss in the presence of abnormal aortic flow.
abstract: OBJECTIVE
  To present a theoretical basis for noninvasively characterizing in vivo fluid-mechanical energy losses and to apply it in a pilot study of patients known to express abnormal aortic flow patterns.
  
  
  METHODS
  Four-dimensional flow MRI was used to characterize laminar viscous energy losses in the aorta of normal controls (n = 12, age = 37 ± 10 yr), patients with aortic dilation (n = 16, age = 52 ± 8 yr), and patients with aortic valve stenosis matched for age and aortic size (n = 14, age = 46 ± 15 yr), using a relationship between the three-dimensional velocity field and viscous energy dissipation.
  
  
  RESULTS
  Viscous energy loss was elevated significantly in the thoracic aorta in patients with dilated aorta (3.6 ± 1.3 mW, P = 0.024) and patients with aortic stenosis (14.3 ± 8.2 mW, P < 0.001) compared with healthy volunteers (2.3 ± 0.9 mW). The same pattern of significant differences was seen in the ascending aorta, where viscous energy losses in patients with dilated aortas (2.2 ± 1.1 mW, P = 0.021) and patients with aortic stenosis (10.9 ± 6.8 mW, P < 0.001) were elevated compared with healthy volunteers (1.2 ± 0.6 mW).
  
  
  CONCLUSIONS
  This technique provides a capability to quantify the contribution of abnormal laminar blood flow to increased ventricular afterload. In this pilot study, viscous energy loss in patient cohorts was significantly elevated and indicates that cardiac afterload is increased due to abnormal flow.
authors.affiliation: Department of Radiology, Northwestern University, Chicago, Illinois, USA.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Barker
authors.forename: Pim
authors.initials: P
authors.lastname: van Ooij
authors.forename: Krishna
authors.initials: K
authors.lastname: Bandi
authors.forename: Julio
authors.initials: J
authors.lastname: Garcia
authors.forename: Mazen
authors.initials: M
authors.lastname: Albaghdadi
authors.forename: Patrick
authors.initials: P
authors.lastname: McCarthy
authors.forename: Robert O
authors.initials: RO
authors.lastname: Bonow
authors.forename: James
authors.initials: J
authors.lastname: Carr
authors.forename: Jeremy
authors.initials: J
authors.lastname: Collins
authors.forename: S Chris
authors.initials: SC
authors.lastname: Malaisrie
authors.forename: Michael
authors.initials: M
authors.lastname: Markl
mesh_terms: D000328:Adult; D001024:Aortic Valve Stenosis / Q000503:physiopathology; D062186:Arterial Pressure; D001783:Blood Flow Velocity / Q000502:physiology*; D055424:Cardiac-Gated Imaging Techniques; D016022:Case-Control Studies; D006439:Hemodynamics / Q000502:physiology; D018056:Hemorheology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008875:Middle Aged; D010865:Pilot Projects; D014783:Viscosity
keywords: 4D flow MRI; aortic dilatation; aortic valve disease; viscous energy loss