title: Effects of changing blood viscosity and heart rate on vena contracta width as evaluated by color Doppler flow mapping. An in vitro study with a pulsatile flow model.
abstract: BACKGROUND
  There is only limited knowledge on how the quantification of valvular regurgitation by color Doppler is affected by changing blood viscosity. This study was designed to evaluate the effect of changing blood viscosity on the vena contracta width using an in vitro model of valvular insufficiency capable of providing ample variation in the rate and stroke volume.
  
  
  METHODS
  We constructed a pulsatile flow model filled with human blood at varying hematocrit (15%, 35%, and 55%) and corresponding blood viscosity (blood/water viscosity: 2.6, 4.8, 9.1) levels in which jets were driven through a known orifice (7 mm2) into a 110 mL compliant receiving chamber (compliance: 2.2 mL/mmHg) by a pulsatile pump. In addition, we used variable pump stroke volumes (5, 7.5, and 10 mL) and rates (40, 60, and 80 ppm). Vena contracta region was imaged using a 3.5 MHz transducer. Pressure and volume in the flow model were kept constant during each experimental condition, as well as ultrasound settings.
  
  
  RESULTS
  Blood viscosity variation in the experimental range did not induce significant changes in vena contracta dimensions. Also, vena contracta width did not change from normal to low hematocrit and viscosity levels. A very modest increase only in vena contracta dimension was observed at very high level of blood viscosity when hematocrit was set to 55% . Pump rate, in the evaluated range, did not influence vena contracta width. These results in controlled experimental settings suggest that the vena contracta is an accurate quantitative method for quantifying valvular regurgitation even when this condition is associated with anemia, a frequent finding in patients with valvular heart disease.
authors.affiliation: Division of Cardiology, Department of Internal Medicine, University Hospital, Medical School of Ribeirão Preto, University of São Paulo, Brazil. aschmidt@fmrp.usp.br
authors.forename: André
authors.initials: A
authors.lastname: Schmidt
authors.forename: Telêmaco
authors.initials: T
authors.lastname: da Silva Júnior
authors.forename: Antônio
authors.initials: A
authors.lastname: Pazin-Filho
authors.forename: Luiz
authors.initials: L
authors.lastname: Otávio Murta Júnior
authors.forename: Oswaldo
authors.initials: O
authors.lastname: César Almeida-Filho
authors.forename: Lourenço
authors.initials: L
authors.lastname: Gallo-Júnior
authors.forename: José
authors.initials: J
authors.lastname: Antonio Marin-Neto
authors.forename: Benedito
authors.initials: B
authors.lastname: Carlos Maciel
mesh_terms: D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure; D001809:Blood Viscosity; D018618:Echocardiography, Doppler, Color; D004867:Equipment Design; D006339:Heart Rate / Q000502:physiology; D006400:Hematocrit; D018056:Hemorheology; D006801:Humans; D066298:In Vitro Techniques; D008944:Mitral Valve Insufficiency / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008955:Models, Cardiovascular; D011673:Pulsatile Flow; D018709:Statistics, Nonparametric