原田 昌彦

Masahiko HARADA

東邦大学医学部第三内科

The 3rd Department of Internal Medicine, Toho University School of Medicine

キーワード : Turbulent free jet, Phantom experiment, Quantitative assessment, Aortic regurgitation, Doppler echocardiography

The purpose of this study is to quantify aortic regurgitation by combining continuous wave Doppler (CWD) and Doppler color flow mapping (CFM).
[experimental study]
A phantom experiment for quantifying the jet flow volume was carried out by using a flow circuit filled with a saline solution, in which nylon corpuscles were suspended to enhance the Doppler effect. A turbulent jet flow (Reynolds numbers: 2000-5000) simulating valvular regurgitation was produced in a water bath through a circular orifice of 2, 3, and 4 mm in diameter. This was driven by a constant flow pump. The flow rate varied from 5 to 46 ml/sec and was calibrated by an electromagnetic flowmeter (EM).
The cross-sectional area (A_C) of the color jet signal was measured at a point 3 cm distant from the orifice with a 2.5 MHz transducer. The velocity (V) of the jet flow at the same point was measured by CWD. The Doppler estimated flow rate (Q) was calculated as product of the Ac and V, which was compared to the actual flow rate (Q_EM) was calibrated by the EM.
The color jet area in the long axis view (AL) was linearly related to the actual flow rate at each orifice, but the higher flow rate was required maintaining the same jet area at the larger orifice.
The estimated flow rate (Q=Ac×V) correlated well (r=0.86) with the actual flow rate irrespective of the orifice diameter, although Q was overestimated as compared with Q_EM.
This overestimation may be the result of the following factors.
(1). The data obtained by CWD may display the maximum velocity at the center of the jet rather than the mean velocity derived from taking a parabolic velocity profile. (2). The jet of turbulent fluid emerging from a circular orifice mixes with some of the miscible stationary fluid and expands.
[clinical study]
Doppler echocardiography was performed in 13 patients with chronic aortic regurgitation to quantify regurgitant volume. No mitral regurgitation, diagnosed by CFM, was present in any of the patients.
The short-axis area (A_CS) of the regurgitant jet at mitral valve level was obtained by taking a planimetric measurement and the velocity of the regurgitant jet at the same level was measured by CWD in an apical long-axis view.
On the basis of this experimental study, an index of aortic regurgitant volume (Q_AR) was determined as the product of A_CS and the time-velocity integral of the aortic regurgitant jet at the level of mitral valve orifice.
For reference, the regurgitant volume (PD_AR) and regurgitant fraction (PD_RF) were calculated from pulsed Doppler measurements of left ventricular outflow (LV_OUT) and mitral inflow (LV_IN) volumes; PD_AR ml/beat=LV_OUT-LV_IN, PD_RF%=PD_AR/LV_OUT×100. Q_AR correlated well with the PD_AR (r=0.75, p[Conclusion]
This study would be useful in the quantitative assessment of aortic regurgitation. The aortic regurgitant volume can be accurately quantitated noninvasively by combining CFM and CWD and by using a regression curve when applying the same equipment and transducer.