title: Potential role of Reynolds number in resolving Doppler- and catheter-based transvalvular gradient discrepancies in aortic stenosis.
abstract: OBJECTIVE
  Discrepancies in mean transvalvular gradient have been observed between Doppler echocardiography and catheter-based techniques in the assessment of aortic stenosis (AS). The Reynolds number (RE) has been shown to influence Doppler-derived gradients, and may be useful in resolving Doppler- and catheter-based gradient discrepancies in AS. The study aim was to assess the influence of the RE on such discrepancies.
  
  
  METHODS
  A pulsatile in-vitro heart model using a bioprosthetic aortic valve with leaflets sutured together was used to simulate AS. Simultaneous gradients were measured using Doppler echocardiography and high-fidelity catheters while the RE was varied, by testing solutions of different density and viscosity across a range of cardiac outputs.
  
  
  RESULTS
  The echocardiographic and catheter-derived mean gradient (MG) values were correlated (r = 0.89; p < 0.0001); however, significant differences in the MG were observed across hemodynamic states. A direct linear relationship was identified between RE and the absolute difference in MG measured using the two techniques (r = 0.94, p < 0.0001). Relative to catheter-based measurements, the MG was underestimated by Doppler (range: 13-16 mmHg) at low RE (median 6,999) and overestimated (7-33 mmHg) at high RE (median 34,268). However, agreement between catheter- and Doppler-derived gradients was within 5 mmHg at intermediate RE (median 17,284) (p < 0.0001).
  
  
  CONCLUSIONS
  The underestimation of Doppler-derived MGs at low RE relative to catheter-based measurements may be due to an exclusion of viscous friction from the simplified Bernoulli equation, while the overestimation of Doppler-derived MGs at high RE may be due to a pressure recovery effect. However, within an intermediate range of RE, where the effects of viscous and inertial forces are balanced, the agreement between catheter- and Doppler-derived gradients was excellent.
authors.affiliation: Division of Cardiovascular Diseases, Mayo Clinic, Scottsdale, Arizona 85259, USA.
authors.forename: Jonathon C
authors.initials: JC
authors.lastname: Adams
authors.forename: Panupong
authors.initials: P
authors.lastname: Jiamsripong
authors.forename: Marek
authors.initials: M
authors.lastname: Belohlavek
authors.forename: Eileen M
authors.initials: EM
authors.lastname: McMahon
authors.forename: Vidyasagargoud
authors.initials: V
authors.lastname: Marupakula
authors.forename: Jeff
authors.initials: J
authors.lastname: Heys
authors.forename: Hari P
authors.initials: HP
authors.lastname: Chaliki
mesh_terms: D000704:Analysis of Variance; D001021:Aortic Valve / Q000000981:diagnostic imaging* / Q000503:physiopathology* / Q000601:surgery; D001024:Aortic Valve Stenosis / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000503:physiopathology; D001705:Bioprosthesis; D006328:Cardiac Catheterization; D015150:Echocardiography, Doppler; D017276:Friction; D006350:Heart Valve Prosthesis; D006801:Humans; D016014:Linear Models; D008955:Models, Cardiovascular; D011237:Predictive Value of Tests; D011312:Pressure; D011673:Pulsatile Flow; D013536:Suture Techniques; D014783:Viscosity