Effects of blood viscosity on proximal flow convergence calculations of regurgitant flow rate and jet dimensions as evaluated by color Doppler flow mapping: An in vitro study

There are limited data on the potential influence of blood viscosity on the quantification of valvular regurgitation by color Doppler in the clinical setting. This study was designed to evaluate the effects of blood viscosity on jet dimensions and the proximal flow convergence (proximal isovelocity surface area, PISA) method of estimating valvular insufficiency severity. W e used an in vitro flow model filled with human blood at varying hematocrit s (15%, 35%, and 55%) and blood viscosity (blood/water viscosity: 2.6, 4.8, 9.1) in which jets were driven through a known orifice (16 mm(2)) into a 1 10-mL, compliant receiving chamber (compliance: 2.2 mL/mm Hg) by a power in jection pump. Blood injections (2 and 4 mL) at flow rates of 4, 6, 8, 10, a nd 12 mL/s were performed. Proximal now convergence and spatial distributio n of jets were imaged by a 3.5-MHz transducer. Pressure and volume in the n ow model were kept constant before each injection. Ultrasound settings were the same for all experiments. Jet area decreased significantly with increa sing blood viscosity, but the difference in jet dimensions was much larger for lower than for higher flow rates and for highest blood viscosity. Estim ation of now rate by the PISA method was not significantly influenced by bl ood viscosity. Blood viscosity has a major influence in jet area, especiall y for lower flow rates, but did not change significantly the grading of reg urgitation by the PISA method. Thus this factor should be considered for de termining the method of choice when quantification of valvular regurgitatio n is performed in patients with anemia or polycythemia.