In situ measurements of Doppler power vs. flow turbulence intensity in red cell suspensions

Blood flow of the acral finger arterioles in patients with type 2 diabetes by quality Doppler profiles

Patients with diabetes mellitus exhibit peripheral arterioles lesions that is associated with reduced blood flow. Here, we intended to assess the acral arterioles lesion in patients with type 2 diabetes based on the rate of blood flow by multigate spectral Doppler ultrasonography. Fifty-two patients with type 2 DM were divided into two groups. Group 1 included 13 men and 12 women with an average age of 60.60 ± 14.03 years and a duration of type 2 diabetes for 2.44 ± 1.50 years. Group 2 included 17 men and 11 women with an average age of 64.25 ± 10.84 years and type 2 diabetes for 12.57 ± 6.26 years. Age-matched control subjects (n = 52) were recruited (30 men and 22 woman, mean age of 61.19 ± 10.38 years). A multigate spectral Doppler algorithm was applied to the acral finger of the thumb of the right hand to test the arteriole diameter and hemodynamic parameters, including diameter of the acral finger arterioles (D), area of the blood flow profile of the acral finger arterioles (A_max) and hemodynamic parameters. Patients with diabetes exhibited a significant reduction in the arteriole diameter (1.63 ± 0.18 and 1.57 ± 0.22 mm, respectively, P < 0.001 for both) compared to control subjects (2.09 ± 0.17 mm). A_max were significantly reduced in patients with diabetes (61.35 ± 10.66 mm²/s for group 1 and 46.50 ± 6.59 mm²/s for group 2, P < 0.001 for both) compared to that in control subjects (77.93 ± 12.37 mm²/s). Furthermore, a significant difference in Amax was found between group 1 and group 2 (P < 0.001). The vascular resistance index (RI) was significantly higher in both patient groups 0.58 ± 0.06 for group 1 (P < 0.001) and 0.64 ± 0.07 for group 2 (P < 0.001) than that in control subjects (0.48 ± 0.04). The RI value of the acral finger arterioles differed significantly between group 1 and group 2 (P < 0.01). Diabetic patients exhibited a weak blood flow in the acral finger arterioles. The multigate spectral Doppler technology can be used to test blood flow in the acral finger arterioles and provide hemodynamic data for systematic analyses of the peripheral arteriole lesions in diabetes.

Correlation functions and power spectra of Doppler response signals in ultrasonic medical applications

Ultrasound Doppler methods are widely used in clinical practice as prospective investigational tool to study the vascular system and soft biological tissues. Meanwhile, the most general relationship between the power Doppler spectra, spectral characteristics of the scattering fluctuations and the probing ultrasound field parameters for some clinical implementations are still unexplored. Based upon the continuum model of scattering inhomogeneities, a set of the closed-form expressions for the correlation functions and the spectra of Doppler response of soft tissues and blood have been derived. The influence of the correlation among inhomogeneities and the diffusion processes on the Doppler power spectra formed by stationary flows have been examined. Computer simulations of Doppler spectra were performed for different values of correlation radius and diffusion coefficient. With simulation results the effects of the correlation among inhomogeneities and the diffusion processes on the spectral width and mean frequency are established and discussed in respect to turbulent flows. Closed-form expressions for correlation functions and Doppler spectra for the vibrational sonoelastography technique for visualizing malignant tumors in tissues have been derived. Based on the peculiarities of the obtained Doppler spectra, it is shown that the differentiation of soft tissues with respect to the amplitude value of constrained oscillations is feasible. The expressions were derived for the cases of non-stationary accelerated blood movement. It has been found that the frequency dependence reveals solely at a finite time of observation and depends on the initial phase of the accelerated movement.

Use of an ultrasound blood-mimicking fluid for Doppler investigations of turbulence in vitro

Turbulence is an important factor in the assessment of stenotic disease and a possible causative mechanism for thromboembolism. Previous Doppler studies of turbulence have typically used whole-blood preparations or suspensions of erythrocytes. Recently, a water-glycerol based blood-mimicking fluid (BMF) has been developed for use in Doppler ultrasound studies. This fluid has desirable ultrasound properties but it has not previously been described during in vitro investigations of turbulence intensity. We report on investigations of grid-generated and constrained-jet turbulence in an in vitro test system. The BMF was found to generate significant levels of turbulence during steady flow at physiological flow rates, producing turbulent patterns in the distal region that were consistent with previous studies. Turbulence intensity increased significantly with flow rate (p < 0.005) for both the constrained jet and the constrained grid. Based on our observations, we conclude that a water-glycerol based BMF provides a suitable working fluid during in vitro investigations of turbulence using Doppler ultrasound.

The Cumulative and Sublethal Effects of Turbulence on Erythrocytes in a Stirred-Tank Model

Mechanical forces generated by prosthetic heart devices (artificial valves, artificial hearts, ventricular assist devices) have been known to cause damage and destruction of erythrocytes. Turbulent flow within such devices generates shear stresses and can induce cell damage. Current models of cell damage rate utilize only the power input per unit mass as a modeling parameter. A stirred-tank reactor provides for a more extensive characterization of turbulence through eddy scale calculations. Through a simplified model, turbulence can be characterized by evaluating the Kolmogorov microscale. Our analysis of erythrocyte rupture in a stirred tank reactor suggests that parameters such as eddy wavelength and eddy velocity may better characterize and model the turbulent damage. Further, hemolysis of red blood cells by turbulent effects has been shown to have a fixed rate for constant levels of power input. Damage inflicted on the remaining, intact erythrocytes (sublethal damage) was evaluated by exposure to turbulence followed by osmotic fragility (OF) testing. Logistic models were fit to the OF data indicating a significant osmotic sensitivity in the sublethal damaged population between control and turbulence-exposed cells (chi(2) test; p < 0.001). This susceptibility indicates a significant cell population more susceptible to destruction as a result of turbulent exposure. This work has therefore helped identify optimization parameters for evaluating cell damage potential when engineering cardiovascular prosthetic devices.

Noninvasive quantitation of blood flow turbulence in patients with aortic valve disease using online digital computer analysis of Doppler velocity data

Previous experimental studies have demonstrated that aortic valve disease is associated with significant downstream turbulence (T). In this study, we developed a noninvasive method on the basis of Doppler velocity recording for quantitating aortic blood flow T in patients with aortic valve disease. The instantaneous blood velocity at a point in the aorta is equal to the sum of a mean periodic velocity component with a random or turbulent velocity component. According to the ensemble average method, time mean absolute T intensity is the root-mean-square value of turbulent velocity averaged over time and T is better quantitated by the relative T intensity (TIr), which is the ratio of absolute T intensity to the ensemble average velocity averaged over time. We computed TIr in 18 patients with mild to severe aortic stenosis and in 13 healthy volunteers from instantaneous modal velocities of 70 cycle length-matched heart beats recorded in the proximal part of the descending aorta by pulsed Doppler using an ultrasound system with an output port for online digital data transfer into a microcomputer. TIr was greater in patients with aortic valve disease (18.4 +/- 5.1%, range 11.2%-28.9%) than in control patients (7.9 +/- 1.9%, range 4.8%-9.8%; P =.0001). In patients with aortic valve disease, TIr was better linearly related to the ratio of postvalvular aorta to valvular orifice cross-sectional areas (r = 0.89, P =.0001) than to other parameters of valve restriction: transvalvular pressure gradient (r = 0.78, P =.0001); valve area (r = -0.56, P =.01); and valve resistance (r = 0.72, P =.0002). Thus, T that can be computed noninvasively from direct digital transfer of Doppler velocity data appears to be linearly related to indices of aortic valve restriction. Our data support the concept of the postvalvular aorta to valvular orifice cross-sectional areas ratio as a new important hemodynamic parameter in patients with aortic valve disease.

In vivo measurements of ultrasonic backscattering in blood

Ultrasonic backscattering in blood including its dependence on the hematocrit, plasma proteins, shear rate, and flow disturbance, has been studied extensively theoretically and experimentally in vitro. However, much of the result has never been validated in vivo. To do so, backscattering measurements were made on pigs using a 10-MHz non-focused intravascular transducer in direct contact with blood. The probe was placed in either the abdominal aorta or the inferior vena cava. The backscattering coefficient (BSC) of blood flowing in these vessels as well as downstream from a stenosis was measured using an approach that was originally developed for measurements with focused transducers. With this approach, 6% porcine red cell saline suspensions prepared immediately after each in vivo measurement were used as the reference medium. Result from seven pigs at hematocrits ranging from 29 to 36% (31.9 +/- 2.5%) demonstrated that BSC of blood in the vena cava, (4.62 +/- 2.06) x 10(-5) cm-sr-1, is consistently higher than that in the aorta, (2.65 +/- 1.22) x 10(-5) cm-sr-1. The difference has been attributed to the lower shear rate and the formation of red cell aggregation in venous blood. These in vivo results are in agreement with those obtained in vitro. In response to stenoses created by ligating the aorta, backscattering of the blood measured downstream from the stenosis showed that the closer the site of measurement relative to the stenosis, the higher the backscatter, presumably resulting from the higher degree of flow disturbance. In vitro backscattering results on porcine whole blood were also acquired at 20 MHz with a Diasonics intravascular scanner.