Reduced blood flow in abdominal viscera measured by Doppler ultrasound during one-legged knee extension

The redistributionof blood flow (BF) in the abdominal viscera during right-legged kneeextension-flexion exercise at very low intensity [peak heart rate(HR), 76 beats/min] was examined by using Doppler ultrasound.While sitting, subjects performed a right-legged knee extension-flexionexercise every 6 s for 20 min. BF was measured in the upper abdominalaorta (Ao), right common femoral artery (RCFA), and left common femoralartery (LCFA). Visceral BF(BF_Vis) was determined by theequation [BF_Ao  (BF_RCFA + BF_LCFA)]. A comparisonwith the change in BF (BF) preexercise showed a greater increase inBF_RCFA than inBF_Ao during exercise. Thisresulted in a reduction of BF_Visto 56% of its preexercise value or a decrease in flow by 1,147 ± 293 (±SE) ml/min at the peak workload. Oxygen consumptioncorrelated positively withBF_Ao, BF_RCFA, andBF_LCFA but inversely withBF_Vis during exercise andrecovery. Furthermore, BF_Vis (% of preexercise value) correlated inversely with both an increase in HR(r = 0.89), and percent peakoxygen consumption (r = 0.99).This study demonstrated that, even during very-low-intensity exercise(HR <90 beats/min), there was a significant shift in BF from theviscera to the exercising muscles.     

Changes in mammary blood flow during the lactation period in goats measured by the ultrasound Doppler principle

1. Mammary blood flow was measured during the lactation period in two low- and two high-yielding dairy goats (peak milk yields approx. 1.5 and 3.6 kg/day respectively), using the ultrasound Doppler principle for determination of blood velocity in both milk veins (subcutaneous abdominal veins) of the animals, and ultrasound scanning for measurement of cross-sectional area of the veins. 2. Milk vein cross-sectional area ranged from 0.11 to 0.38 cm2 in the four goats, with a close to significant (P = 0.06) difference between the veins in the two sides of the animals. Cross-sectional area remained constant during the lactation period. Changes in mammary blood flow was therefore caused by changes in blood velocity. 3. Milk vein blood velocities ranged from 4.4 to 34.7 cm/sec independently of the time of the day, and were of the same magnitude in the two sides of the animals. Except in one goat (P = 0.1), blood velocity decreased significantly (P less than 0.01) with progressing lactation, during which period also milk yield was declining. 4. In the two low-yielding goats, a positive linear relationship (R2 = 0.20) was found between milk yield and milk vein blood velocity, whereas a diminishing exponential relationship (R2 = 0.97) was found in the two high-yielding goats. At a given milk vein blood velocity, high-yielding goats obtained a higher milk yield and also responded to changes in blood velocity (up to approx. 15 cm/sec) with greater increases in milk yield than low-yielding goats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Some characteristics of laminar flow velocity spectra detected by a 20 MHz pulsed ultrasound Doppler

For the purpose of improving accuracy of noninvasive flow measurements in small (1–2 mm diameter) blood vessels, an existing 20 MHz pulsed ultrasound Doppler velocimeter (PUDVM) has been augmented to allow fast Fourier transformation (FFT) of its Doppler shift signal. The modified instrument was used to collect velocity spectra for a benchtop test section delivering precise Poiseuille flows at velocities in the range of physiological interest. The velocity spectra demonstrated a substantial degree of broadening, much of which was attributable to the geometry of the finite sample volume size. Several spectral indices were studied as a function of flow field variables. Results showed that the intensity-weighted mean Doppler shift frequency, when converted to its corresponding velocity v_M, agreed very closely with the theoretically predicted local fluid velocity. Measurement linearity and repeatability were evaluated for a number of system variables, indicating that FFT performance was essentially unaffected by several parameters capable of causing major degradation of (phasic) Doppler shift signals produced by conventional zero-crossing-counter circuitry. As presently configured, the augmented PUDVM instrument is fully capable of detailed flow field mapping in small subcutaneous vessels such as human digital arteries.     

Comparison of blood flow parameters measured by Doppler ultrasound and radionuclide techniques in the baboon (Papio ursinus)

Ascending aortic blood velocity was measured in the baboon (Papio ursinus) by using continuous wave Doppler ultrasound. The blood flow parameters thus obtained were compared to those by the standardized radionuclide technique. It appears that, due to the anatomical position of the ascending aorta and brachiocephalic trunks in relation to the ultrasound beam, Doppler ultrasound does not provide an accurate method of measuring aortic blood velocity in the baboon, which could be the reason for the poor correlation of the results from the two techniques.     

The resolution of the ultrasound pulsed Doppler for blood velocity measurements

Pulsed ultrasound Doppler velocity meters (PUDVM) permit noninvasive blood velocity measurements. The emitted ultrasound beam characteristics primarily determine the resolution of the instrument when recording velocity profiles. The sample volume, the small region over which velocity information data are detected, was found to be > 2·3 mm³ depending on the transducer disk dia., distance in front of the disk, sampling time increment, and pulse length. The shape of the sample volume approximates a cylinder in the near field and a frustrum of a cone in the far field. The end surfaces of the sample volume were affected by the emitted pulse shape. Ultrasonic beam cross-sections were found to be smaller than predicted by theory due to the finite threshold levels of the PUDVM. The variation of the sample volume with range was illustrated by steady laminar flow velocity profile measurements in rigid tubes. The accuracy of velocity measurements was within 5 per cent with slightly larger deviations occurring near the walls due to the finite sample volume.     

Fetal growth as measured by ultrasound

Until the last decade, investigation of fetal growth has been based on data from premature births and abortuses. Advances in ultrasound scanning have expanded the precision and uses of this technology in studies of fetal growth. Most ultrasound studies of fetal growth are based on clinical populations and are reported in clinical journals. The present paper reviews features of ultrasound technology relating to fetal measurement. The most commonly measured dimensions and their associated measurement errors, distributions and uses are detailed. Ultrasound studies of intrauterine growth retardation and in utero fetal weight estimation are critically reviewed. Finally, a comparison between the fetal growth curve based on ultrasound measurement and on data from preterm or aborted fetuses is compared. Critical comments on sample design and statistical treatment of the data from ultrasound studies is included in each of the areas discussed.     

Neural correlates of blood flow measured by ultrasound

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Measuring stroke volume of the ascending aorta with an extravascular Doppler ultrasound probe in comparison with aortic thermodilution]

Currently, no reliable minimally invasive method of measuring cardiac output continuously in neonates and children undergoing cardiac surgery is available. An extravascular Doppler probe was used to measure cardiac output in 15 New Zealand White rabbits (average weight 3.5 kg, range 2.5-4.5 kg). The results obtained were compared with cardiac outputs determined using the aortic thermodilution principle. The mean cardiac outputs measured with the extravascular Doppler probe was 0.37 +/- 0.01 l/min as compared with 0.39 +/- 0.01 l/min with aortic thermodilution. Regression analysis revealed a close correlation (r = 0.973) between the two techniques. The extravascular Doppler techniques is an option for continuous and reliable cardiac output measurement in small animals used in surgical experiments (open chest models) and in neonates or children during surgical repair of complicated congenital heart conditions.     

Color Doppler ultrasound evaluation of testicular blood flow in stallions

The objectives of this study were to evaluate the potential use of color Doppler ultrasound to characterize blood flow to the stallion testis, and to establish reference values for Doppler measures of blood flow in the testicular artery of the stallion. Both testes from each of 52 horses were examined using a pulsed-wave color Doppler ultrasound with a sector array 5/7.5 MHz transducer with a 1mm gate setting. Peak systolic velocity (PSV), end diastolic velocity (EDV), resistive index (RI), and pulsatility index (PI) of the testicular artery were measured in each of two locations, the convoluted aspect (spermatic cord) and the marginal aspect of the artery (on the epididymal edge of testis). We found that: (1) all measures were obtainable; (2) except for EDV, the majority of the measures were higher at the cord location than at the marginal aspect of the artery (P < 0.05); and (3) measures for left and right testes were similar (P > 0.10). Resulting measures from 41 of these stallions (82 testes) that appeared free of testicular pathology provide useful reference values for clinical evaluation. Evaluation of 11 cases with testicular pathology suggested further investigation of possible effects of these various conditions on testicular blood flow and testicular function.     

Characterisation of vortex shedding in vascular anastomosis models using pulsed Doppler ultrasound.

Vortex shedding at vascular anastomoses were investigated in vitro using a 20 MHz pulsed-wave Doppler velocimeter. Centreline velocity measurements were made at various axial distances in simplified polyurethane models of proximal and distal end-to-side anastomoses of angles 15, 30, 45, 60 and 80 degrees using pulsatile flow waveforms similar to those in femoropopliteal bypass grafts. The in-phase and quadrature Doppler signals were recorded and the maximum frequency waveform, averaged over 64 cycles, was obtained using short-time Fourier transform. A fourth-order Butterworth low-pass filter was employed to separate the vortex velocity signal from the convective velocity. The vortex signal envelope was calculated using a Hilbert transform method and the vortex amplitude was taken as the maximum of this envelope. The results show that higher vortex amplitude were found in the proximal anastomoses and under resting flow conditions. Although the vortex amplitudes generally increased with angles of anastomosis, they were found to be higher in the 60 degrees than in the 80 degrees proximal anastomosis. The vortex structures were investigated using spectrograms and these show prominent features at 40-50 Hz indicative of the short-duration oscillatory signals during the decelerative phase of systole expected from the passage of vortices. The study indicates that flow disturbances due to vortex shedding may be a common feature in femoropopliteal bypass grafts.     

Automated computation of relative flow resistance using a pulsed Doppler flowmeter

Use of a pulsed Doppler flowmeter to assess changes in blood flow resistance often requires a laborious series of calculations, and full characterization of resistance changes frequently necessitates replotting of calculated data. To facilitate the interpretation of pulsed Doppler flowmetry data, a simple, inexpensive device was constructed that computes the signal ratio of mean arterial pressure (MAP) to directional pulsed Doppler outputs. With this device, relative flow resistance can be recorded and quantitatively assessed at a glance in three vascular beds in real time. This computer-like device was designed around the Burr-Brown DIV100HP integrated circuit. C741G OpAmps provide input buffering, zeroing, and ranging adjustments enabling the user to accurately follow resistance over a very broad range of changes without exceeding the device's operating limits. A LM339 quad comparator monitors the input of each DIV100 and indicates when operating limits are exceeded via a channel-specific LED indicator and an audible alarm. No significant attenuation of the input signals occurs over the range of direct current to 50 kHz, and the output is without significant phase shift. Comparisons with calculated changes in resistance derived from the MAP and pulsed Doppler flowmetry in unanesthetized, unrestrained rats confirmed that resistance changes can be measured with precision and accuracy.     

The muscular blood flow in rats in ontogenesis as measured by the needle probe laser Doppler flowmeter "LAKK-01"

In anesthetized Wistar rats of the age of 4, 13, 30 and 90 days, blood flow in m. gracilis was measured with the aid of laser-Doppler flowmeter "LAKK-01" with a needle probe. The sharpest postnatal falling of a muscular blood flow was revealed in the first month of life. Features of measurement of the blood flow and biological background by a needle probe in skeletal muscles of rats of various age described.     

Evaluation of mammary blood flow measurements in lactating goats using the ultrasound Doppler principle

1. Non-invasive methods were developed for measuring mammary blood flow in lactating goats. 2. A Doppler principle ultrasound device was equipped with an external detector measuring maximal blood velocity (Vmax) and average blood velocity (Vav) was calculated as Vmax/2. Volume flow then depended on determination of the angle of insonation and the cross-sectional area of the milk vein (the caudal superficial epigastric or subcutaneous abdominal vein). 3. Blood velocities were measured on the milk vein of either side of the animal while clamping the pudendal veins manually. Blood velocities ranged from 7-34 cm/sec. 4. The milk vein diameter was measured by means of a slide gauge which, for clearly protruding veins, gave similar results to that measured by ultrasound scanning. In protruding veins the cross-section was circular. In non-protruding veins the cross-section was elliptical and the slide gauge significantly (P less than 0.01) overestimated the cross-sectional area. The milk vein diameter of either side measured in 10 lactating goats was 8.8 +/- 1.1 mm (means +/- SD). 5. Blood flow ranged from 90-675 ml/min in a dry and a high-yielding (3.4 l milk daily) goat, respectively. The reproducibility of the blood flow measurements was 12-16%. 6. It is concluded that the present method may be used for quantitative measurements of mammary blood flow in goats.     

A three-dimensional computational simulation of some sources of measurement artifact in microvascular pulsed ultrasound Doppler velocimetry

Recent applications of 20 MHz pulsed ultrasound Doppler velocimetry (PUDVM) in microsurgical research have necessarily employed piezoelectric crystals whose diameter is not negligible compared to the lumen size (1-2 mm) of many vessels of interest. A three-dimensional numerical model was developed to explore relationships between actual and detected flow field parameters, for (steady) Poiseuille flow, when appreciable velocity gradients exist within the PUDVM sample volume. Validation studies showed that highly accurate velocity profiles could be obtained in the limiting case of a very small sample volume (0.1 mm radius), but that for currently employed crystals (approximately equal to 0.5 mm radius) there was appreciable underestimation of the centersteam velocity, and appreciable overestimation of the flow stream diameter. Errors in perceived velocity and flow rate were found to be relatively insensitive to perturbations in the sample volume thickness, in the size of the sampling range increment, or in the angle of insonation beam divergence. By contrast, these apparent flow parameters were found to be very sensitive to perturbations of sample volume diameter or of the Doppler angle. Small variations in the degree of partial sample volume overlap of the flowstream periphery were shown to be capable of causing large fluctuations in apparent flow stream diameter.