Studies in vitro of the relationship between ultrasound and laser Doppler velocimetry and applicability of the simplified Bernoulli relationship

While there has been wide general acceptance of Doppler methods that use the simplified Bernoulli relationship to estimate pressure gradients across stenotic orifices, there is still ongoing controversy related to potential sources of error in the method. In this study we tested accuracy of ultrasound Doppler measurements of flow velocity when compared with the gold standard of laser light Doppler anemometry in a pulsatile flow model of pulmonic stenosis in vitro. We tested two commercially available Doppler systems and examined steered and nonsteered, parallel, and off-axis and anglecorrected velocity determinations using continuous-wave and high-pulse repetition frequency (HPRF) methods. We also examined the potential range of error in the simplified Bernoulli method. One hundred and twenty individual flow states were examined with three stenotic valve orifices (3.0, 1.0, and 0.5 cm2 flow area) to measure velocities up to 620 cm/sec. A very high correlation coefficient was obtained for the comparison of laser Doppler anemometric and ultrasound velocity recordings by the nonsteered continuous-wave technique (r = .99, SEE = 17.9 cm/sec), but there was a tendency for underestimation of higher velocities when the transducer was positioned at 30 degrees and the ultrasound beam was steered so as to be parallel to the visualized flow jet (r = .98, SEE = 29.6 cm/sec). The HPRF ultrasound Doppler technique was also highly accurate in this optimized setting for measuring velocities (r = .99, SEE = 17 cm/sec), but also slightly underestimated the highest velocities. Our results also verified the accuracy of the simplified Bernoulli equation for converting instantaneous velocity measurements to estimated peak instantaneous gradient (r = .97, SEE = 8.4 mm Hg). Circulation 73, No. 2, 300-308, 1986. QUANTITATIVE pulsed and continuous-wave (CW) ultrasound Doppler methods have rapidly become important adjuncts to the two-dimensional echocardiographic examination because of their capabilities for estimating cardiac flows and gradients across obstructive lesions. With recent advances in Doppler technology, high velocities in the circulatory system can now be measured with the use of new steerable high-pulse repetition frequency (adaptive) (HPRF) and CW Doppler devices. However, controversies have arisen regarding the relative accuracy of these various techFrom the BioFluid Dynamic Lab, School of Chemical Engineering, Georgia Institute of Technology, Atlanta, and the Division of Pediatric Cardiology, University of California, San Diego. Supported by the American Heart Association, California Affiliate, grant No. 83-S139, American Heart Association grant-in-aid No. 84778, and by a grant from the Whitaker Foundation. Address for correspondence: Lilliam M. Valdes-Cruz, M.D., UCSD Medical Center, Division of Pediatric Cardiology, 225 Dickinson St. H814A, San Diego, CA 92103. Received April 9, 1985; revision accepted Oct. 24, 1985. 300 nologies for the measurement of blood flow velocities. Although multiple studies have been published validating various applied techniques for accomplishing these measurements in the clinical setting and in animal preparations,'12 none have reported a direct validation of the velocity readings obtained from the Doppler ultrasound instruments. The purpose of the study was to compare flow velocities measured with the different ultrasound Doppler modalities on clinically available instruments to those measured simultaneously by laser Doppler anemometry in a pulsatile flow model of isolated pulmonic valve stenosis in vitro. In addition, the accuracy of the simplified Bernoulli equation for deriving the pressure difference across a discrete obstruction was explored in this optimized and highly controlled setting. Materials and methods Pulsatile flow apparatus. The pulsatile flow apparatus used was designed to duplicate the flow and the pressure waveforms CIRCULATION by gest on N ovem er 2, 2017 http://ciajournals.org/ D ow nladed from DIAGNOSTIC METHODS-ECHOCARDIOGRAPHY PULMONARY ARTERY BIFURCATION