title: How to estimate aortic characteristic impedance from magnetic resonance and applanation tonometry data?
abstract: OBJECTIVE
  Compare seven previous methods for the estimation of aortic characteristic impedance, which contributes to left ventricle pulsatile load, from phase-contrast cardiovascular magnetic resonance (CMR) and applanation tonometry data.
  
  
  METHODS
  We studied 77 healthy (43 ± 16 years) individuals and 16 hypertensive (61 ± 9 years) patients, who consecutively underwent ascending aorta CMR and carotid tonometry, resulting in flow and pressure waveforms, respectively. Characteristic impedance was semi-automatically estimated in time domain from these latter waveforms, using seven methods. The methods were based on the following: methods 1-4, magnitudes at specific times; method 5, early-systolic up-slope; method 6, time-derivatives peak; and method 7, pressure-flow loop early-systolic slope.
  
  
  RESULTS
  Aortic characteristic impedance was significantly increased in hypertensive patients when compared to elderly controls (n = 32) with a similar mean age of (59 ± 8 years) when using methods based on 95% of peak flow, up-slopes, and derivatives peaks (P < 0.05). When considering healthy individuals, impedance indices were significantly correlated to central pulse pressure for all methods (P < 0.005). Finally, characteristic impedance was correlated to the frequency-domain reference values (r > 0.65, P < 0.0001), with a slight superiority for the same three methods as above (r > 0.82, P < 0.0001).
  
  
  CONCLUSIONS
  This is the first study demonstrating phase-contrast CMR and tonometry usefulness in aortic characteristic impedance temporal estimation. Methods based on 95% of peak flow, as well as those based on derivative peaks and up-slopes, which are fast and independent of curve preprocessing, were slightly superior. They can be easily integrated in a clinical workflow and may help to understand the complementarity of this pulsatile index with other CMR aortic geometry and stiffness measures in the setting of left ventricle-aortic coupling.
authors: aSorbonne Universités, UPMC Univ Paris 06, UMR 7371, UMR_S 1146, Laboratoire d'Imagerie Biomédicale, UMR 7371 bINSERM, UMR_S 1146, Laboratoire d'Imagerie Biomédicale cCNRS, UMR 7371, Laboratoire d'Imagerie Biomédicale dUMR CNRS 7190 / UPMC, Institut Jean le Rond d'Alembert eInstitut de Cardiologie, Hôpital Pitié Salpêtrière fCardiovascular Imaging, Medical Imaging Department, Hôpital Européen Georges Pompidou, APHP gINSERM, UMR 970, PARCC, Paris, France.
authors: Emilie
authors: E
authors: Bollache
authors: Nadjia
authors: N
authors: Kachenoura
authors: Ioannis
authors: I
authors: Bargiotas
authors: Alain
authors: A
authors: Giron
authors: Alain
authors: A
authors: De Cesare
authors: Mourad
authors: M
authors: Bensalah
authors: Didier
authors: D
authors: Lucor
authors: Alban
authors: A
authors: Redheuil
authors: Elie
authors: E
authors: Mousseaux
mesh_terms: D000328:Adult; D000368:Aged; D001011:Aorta / Q000503:physiopathology*; D001794:Blood Pressure / Q000502:physiology*; D017097:Electric Impedance; D005260:Female; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008365:Manometry; D008875:Middle Aged; D013599:Systole / Q000502:physiology