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PubMed1988

Flow measurements in an atherosclerotic curved, tapered femoral artery model of man.

Flow visualization and pressure measurements were made for physiological conditions in a model derived from a femoral angiogram of a patient with lesion localization on the inner curvature wall and with vessel taper. Effects of curvature and taper were evaluated separately in other curved, tapered, smooth and straight, tapered, smooth models. Double helical secondary flow patterns were modified by plaque on the inner wall, and flow separations were observed between plaques at higher flow rates and Reynolds numbers. Pressure drop data for the plaque simulation model were similar in trend with Reynolds number as for the smooth model, but flow resistances were 25 to 40 percent higher. Significant pressure drops were measured due to the mild taper which could be estimated from momentum considerations, and smaller increased pressure drops were found due to curvature effects at the higher Dean numbers. Flow resistances for in vivo pulsatile flow simulation were about 10 percent higher than for steady flow for the plaque model, whereas no differences were observed for the smooth model.

Arteriosclerosis↗
PubMed2001

Intraoperative measurement of arterial blood flow using a transit time flowmeter: monitoring of hemodynamic changes during cerebrovascular surgery.

BACKGROUND: The purpose of this study was to examine the utility and reliability of arterial flow measurements made with a transit time ultrasonic flowmeter for monitoring blood flow changes during intracranial and carotid surgery. METHOD: A total of 25 patients underwent intra-operative arterial blood flow measurements. The pulsatile flow curve and mean flow values were obtained using 1- to 6-mm transit time probes with a dual channel flowmeter. Four cases underwent aneurysm clipping, 11 cases superficial temporal artery (STA)--middle cerebral artery (MCA) bypass, 2 cases external carotid artery (ECA)--radial artery--MCA bypass for aneurysm trapping, and 8 cases carotid endarterectomy. In aneurysm clipping, blood flow in the branches distal to the aneurysm was measured before and after clipping. Blood flow in the STA was measured before and after STA-MCA anastomosis, and blood flow in the internal carotid artery (ICA) cervical portion was measured during carotid endarterectomy. Blood flow in the MCA and STA was monitored during radial artery grafting. FINDINGS: Blood flow in the STA was elevated after STA-MCA anastomosis. However, post-operative hyperperfusion syndrome was found in some cases whose flow elevation was over 50 ml/min. Also in one case of carotid stenosis, of which blood flow of ICA was elevated to 400 ml/min after carotid endarterectomy, hyperperfusion syndrome was found after surgery. In the cases of MCA aneurysm clipping, decreasing of M2 flow was detected when clipping caused bifurcation stenosis. INTERPRETATION: We found transit time flow measurement useful for management of cerebrovascular surgery: the technique was simple to use and provided stable, reliable results. The method was able to reveal distal branch flow diminution in aneurysm clipping, or residual flow during temporary clipping in aneurysm surgery, and has the potential to predict post-operative complications such as hyperperfusion by signalling over-elevation of donor artery flow in bypass surgery or ICA flow in carotid surgery.

Adolescent↗
PubMed1999

Impaired coronary blood flow in nonculprit arteries in the setting of acute myocardial infarction. The TIMI Study Group. Thrombolysis in myocardial infarction.

OBJECTIVES AND BACKGROUND: While attention has focused on coronary blood flow in the culprit artery in acute myocardia infarction (MI), flow in the nonculprit artery has not been studied widely, in part because it has been assumed to be normal. We hypothesized that slower flow in culprit arteries, larger territories infarcted and hemodynamic perturbations may be associated with slow flow in nonculprit arteries. METHODS: The number of frames for dye to first reach distal landmarks (corrected TIMI [Thrombolysis in Acute Myocardial Infarction] frame count [CTFC]) were counted in 1,817 nonculprit arteries from the TIMI 4, 10A, 10B and 14 thrombolytic trials. RESULTS: Nonculprit artery flow was slowed to 30.9 +/- 15.0 frames at 90 min after thrombolytic administration, which is 45% slower than normal flow in the absence of acute MI (21 +/- 3.1, p < 0.0001). Patients with TIMI grade 3 flow in the culprit artery had faster nonculprit artery CTFCs than those patients with TIMI grades 0, 1 or 2 flow (29.1 +/- 13.7, n = 1,050 vs. 33.3 +/- 16.1, n = 752, p < 0.0001). The nonculprit artery CTFC improved between 60 and 90 min (3.3 +/- 17.9 frames, n = 432, p = 0.0001), and improvements were related to improved culprit artery flow (p = 0.0005). Correlates of slower nonculprit artery flow included a pulsatile flow pattern (i.e., systolic flow reversal) in the nonculprit artery (p < 0.0001) and in the culprit artery (p = 0.01), a left anterior descending artery culprit artery location (p < 0.0001), a decreased systolic blood pressure (p = 0.01), a decreased ventriculographic cardiac output (p = 0.02), a decreased double product (p = 0.0002), a greater percent diameter stenosis of the nonculprit artery (p = 0.01) and a greater percent of the culprit artery bed lying distal to the stenosis (p = 0.04). Adjunctive percutaneous transluminal coronary angioplasty (PTCA) of the culprit artery restored a culprit artery CTFC (30.4 +/- 22.2) that was similar to that in the nonculprit artery at 90 min (30.2 +/- 13.5), but both were slower than normal CTFCs (21 +/- 3.1, p < 0.0005 for both). If flow in the nonculprit artery was abnormal (CTFC > or = 28 frames) then the CTFC after PTCA in the culprit artery was 17% slower (p = 0.01). Patients who died had slower global CTFCs (mean CTFC for the three arteries) than patients who survived (46.8 +/- 21.3, n = 47 vs. 39.4 +/- 16.7, n = 1,055, p = 0.02). CONCLUSIONS: Acute MI slows flow globally, and slower global flow is associated with adverse outcomes. Relief of the culprit artery stenosis by PTCA restored culprit artery flow to that in the nonculprit artery, but both were 45% slower than normal flow.

Adult↗
PubMed1996

Demonstration of fetal coronary blood flow by color-coded and pulsed wave Doppler sonography: a possible indicator of severe compromise and impending demise in intrauterine growth retardation.

We report four cases of uteroplacental insufficiency with severe intrauterine growth retardation in which coronary blood flow was demonstrated by means of color-coded and pulsed wave Doppler sonography. Intrauterine fetal compromise was indicated by pathological uterine and umbilical flow indices and decreased impedance in the cerebral vasculature. Later, this was followed by normalization of middle cerebral artery Doppler indices in one case. The latter change was associated with abnormal atrial systolic reverse blood flow initially in the inferior vena cava, then in the ductus venosus and finally resulting in pulsatile flow in the umbilical vein. In the late stage of fetal deterioration pulsatile flow in the umbilical vein was replaced by a biphasic flow pattern. In two cases coronary flow was visualized preceding intrauterine fetal death. In the two other cases a severely growth retarded newborn was delivered by Cesarean section. The postnatal course was complicated by a prolonged period of circulatory insufficiency and renal failure and in one case by a persistent ductus arteriosus. Visualization of fetal coronary blood flow in severe uteroplacental insufficiency could be a preterminal event when urgent delivery may be warranted.

Adult↗
PubMed2000

[3D-spectrogram of the doppler signal in real time].

AIM: Doppler signals are normally displayed as an x/y-graph. The frequency is plotted in the y-direction, and the intensity is represented by the brightness. This represents less information than is contained in the acoustic signal: often one can hear more one can see. We are investigating the question as to whether it is feasible to render the complete information visible without the use of expensive additional equipment. METHOD: The sound card (SB16 P&P value edition) in a Pentium-PC (200 MHz 32 MB RAM) was used as a 16 bit dual channel a/d converter and connected to the ultrasound system Sonoline Elegra (Siemens, Erlangen, Germany). We used a standard 32 bit dual channel real-time FFT-software (SpectraPro, Sound Technology, California) to display a 3D-spectrogram on the PC-screen in real-time mode. This system was first tested on a flow model both with laminar steady flow and with pulsatile flow. Following this, measurements were made of the arteries and veins in healthy volunteers. RESULTS: In the 3D-Spectrogram the character of the flow can easily be seen. The quantitative parameters of velocity (Doppler frequency), direction and intensity of flow can be readily determined. Additional information about quality of flow, erythrocyte clusters and changes occurring in areas of slight stenoses can be used for diagnostic evaluation. The orthograde and retrograde flow are displayed separately using the dual channel technique. The arterial and venous flow in small and closely neighbouring vessels, such as the central retinal artery and vein, can easily be differentiated. The venous flow in particular is more turbulent in the 3D-spectrogram than would be expected from the normal display mode. CONCLUSION: The 3D-spectrogram provides much additional information in comparison with the normal Doppler spectrogram of the ultrasound system. This 3D-spectrogram can be easily obtained using inexpensive standard hard- and software.

Arteries↗
PubMed2001

Limits of time-of-flight magnetic resonance angiography.

Many of the limits to current time-of-flight (TOF) magnetic resonance (MR) angiographic methods, including flow voids from turbulent flow, flow artifacts from pulsatile flow, and oblique flow displacement, are not inherent to the TOF enhancement mechanism and will be eliminated with technological advancements. Slowly flowing blood and physiological motion will remain an obstacle to these methods, although technological advancements will improve on current methods. Future TOF MR angiographic methods will prove to be a cost-effective competitor to MR angiographic methods requiring contrast agents in many applications.

Artifacts↗
PubMed1992

Hemodynamic foundation of umbilical arterial Doppler waveform analysis.

This paper reviews various in vitro and in vivo studies which have been conducted to investigate the influence of central and peripheral circulatory factors on the Doppler indices. These studies indicate that the Doppler indices are affected by both central and peripheral hemodynamics. Of the central factors, the heart rate influences the indices predominantly through the variations during the diastolic phase of the cardiac cycle. This was confirmatory of the clinical findings. Of the other central factors, cardiac contractility may not affect the rising slope of the Doppler waveform. Regarding the peripheral hemodynamics, both in vitro and in vivo studies confirm that the indices reflect the changes in the peripheral resistance; however, opposition to flow in a pulsatile flow can be adequately described only by impedance. Initial in vivo and in vitro studies demonstrate that the indices correlate well with the impedance parameters. However, this is true only when the central circulation remains stable.

Animals↗
PubMed1984

Transcutaneous Doppler ultrasound in paediatric cardiology.

Recent developments in transcutaneous ultrasound, encompassing M-mode and two-dimensional echocardiography as well as continuous wave and pulsed Doppler techniques, have provided substantial contributions in facilitating noninvasive cardiac assessment. With Doppler systems diagnostic information is obtained through analysis of changes in the velocity and direction of blood flow, pulsatile character and flow pattern (laminar or turbulent) in the arteries, veins and cardiac chambers. Using Doppler, measurements of peripheral blood pressure correlate well with invasive recordings; coarctation of the aorta can be localized and the pressure gradient determined; stenotic valvular lesions can be diagnosed and pressure gradients estimated; and, based on blood flow patterns, the orifice area of stenotic mitral valves can be calculated. Regurgitant valvular lesions are detected readily and their severity can be graduated semiquantitatively. Septal defects can be identified and the pulmonary to systemic flow ratio estimated. The flow characteristics associated with patent ductus arteriosus are adequately specific to enable its detection even in the presence of other complex anomalies and, similarly, the diagnosis of total anomalous pulmonary venous drainage can be established. Doppler ultrasound is useful in evaluating conduit blood flow after surgery for cyanotic congenital heart disease and enables anatomical and functional assessment after the Mustard or Senning procedure for transposition of the great arteries. Transcutaneous aortovelography has been used to monitor cardiac output, phasic blood flow velocities, changes in stroke volume, aortic systolic ejection times and other parameters considered indicative of myocardial performance. Combined application of Doppler and two-dimensional ultrasound enables calculation of cardiac output and stroke volume. Thus, Doppler ultrasound techniques will play an increasingly-valuable role in noninvasive outpatient screening and post-surgical follow-up.

Aortic Coarctation↗
PubMed1993

Hemodynamics of a side-to-end proximal arterial anastomosis model.

PURPOSE: The purpose of this article was to analyze the fluid mechanical effects of a side-to-end proximal anastomosis and to compare the results with those from our earlier study on the end-to-side distal anastomosis. METHODS: The photochromic tracer technique was used to determine the instantaneous wall shear stress and to visualize the overall flow field under pulsatile flow conditions. The flow consisted of a sinusoid plus a steady component with mean and modulation Reynolds numbers of 355 and 565, respectively, and a Womersley number of 7.9. RESULTS: At the toe and heel of the junction, very high and positive wall shear stresses were seen together with substantial nonperiodic fluctuations. The peak wall shear stress was about four times higher at the toe and about seven times higher at the heel than the maximum values observed at about four tube diameters upstream from the junction. On the bed of the host vessel, nonperiodic fluctuations were also observed, but the shear stresses were mainly negative with magnitudes comparable to those seen upstream. With leakages of 11% and 28% of the mean flow through the blocked end of the host vessel, the shear stress pattern seemed to be significantly affected only at the toe for the higher leakage. Further, when the mean Reynolds number was reduced to 320, the magnitudes of the variations in the wall shear stress were reduced proportionately, except at the heel, where the reduction was much larger than expected. CONCLUSIONS: It appears that the preferential development of intimal hyperplasia at the distal end-to-side anastomosis may be promoted by low wall shear stress at the toe and heel, and probably by high shear stresses or shear stress gradients on the bed.

Anastomosis, Surgical↗
PubMedDate not supplied

Establishing a protocol to quantify leaflet fibroblast responses to physiologic flow through a viable heart valve.

Mechanical stresses are thought to affect the metabolism of a variety of cell types. Little quantitative data exist regarding heart valve leaflet fibroblast activity after dynamic loading. The goal of this study was to examine leaflet fibroblast function and differentiation in response to flow through an intact valve. This requires the development of a flow system capable of reproducing the valve's native environment, as well as assay protocols to analyze cellular viability and protein and collagen synthesis. As a tool to expose viable tissue valves to physiologic flow, a sterilizable pulsatile flow system has been developed to recreate the dynamic flow environment of the aortic valve while preventing contamination from room air. Physiologic flow conditions [frequency 70 bpm, aortic pressure 129/82 mmHg (systolic/diastolic), cardiac output 2.3 L/min] were sustained for 71 hr without microbiologic contamination. Analytic tools for assessment of fibroblast function include a viability assay, which demonstrated that leaflet viability decreases after prolonged exposure to antibiotics. Proline incorporation studies revealed that 11 times more protein is retained by leaflet tissue than is released into the medium, and 27% of this protein is collagen. Polyacrylamide gel electrophoresis clearly resolved collagen Types I and III from both prepared standards as well as leaflet extracts. In ongoing work, the sterile flow loop will be used to expose fresh porcine aortic valves to defined flow conditions, and the viability and protein/collagen biosynthetic activity of leaflet fibroblasts in response to flow will be quantified. These experiments will provide a baseline by which to design and evaluate future tissue engineered substitutes.

Animals↗
PubMed2006

Cardiopulmonary bypass and renal injury.

Renal dysfunction following cardiopulmonary bypass (CPB) is well recognized. The extent of perioperative renal impairment ranges from subclinical injury to established renal failure requiring dialysis. Its incidence varies considerably, depending on the definition and criteria used in the different studies. Acute renal failure (ARF) affects 1-5% of patients and remains a major cause of morbidity and mortality. Co-morbidities, including diabetes mellitus, impaired left ventricular function and advanced age, are recognized predisposing factors. The pathophysiology is multifactorial and is thought related to the systemic inflammatory response and renal hypoperfusion secondary to extracorporeal circulation. Non-pulsatile flow during CPB is thought to be an important aetiological factor, resulting in renal vasoconstriction and ischaemic renal injury. A theoretical reduction in the incidence and severity of postoperative renal impairment has been proposed by advocating the use of pulsatile flow during CPB, or eliminating CPB, especially in high-risk patients. The current evidence, however, is conflicting. Several large observational studies, including a large proportion of high-risk patients, have demonstrated a significant reduction in the frequency of renal failure in patients undergoing off-pump surgery. As older, sicker patients increasingly constitute the cardiac surgical population, the incidence of postoperative renal injury is likely to increase. Further studies addressing various renoprotective strategies in higher-risk patients are awaited.

Cardiopulmonary Bypass↗
PubMed2005

Cardiopulmonary bypass in pregnancy: possible new role for the intra-aortic balloon pump.

Cardiopulmonary bypass (CPB) during pregnancy is associated with a maternal mortality similar to the nonpregnant population; however, fetal morbidity and mortality are high. Various strategies to improve fetal survival have been advocated. Alteration in uterine artery flow velocity has been reported during nonpulsatile CPB; however, roller pump-generated pulsatile flow for CPB remains controversial. We report use of the intra-aortic balloon pump (IABP) in two cases of pregnancy. In the first, the IABP was inserted after termination of a long bypass, specifically in an attempt to improve uterine perfusion and thereby relieve a profound fetal bradycardia. In the second, the IABP was used electively to provide pulsatile flow during the bypass period primarily to benefit fetal hemodynamics.

Adult↗
PubMed2002

Real-time rectilinear volumetric imaging using a periodic array.

Current real-time phased array volumetric scanners use a 2-D array to scan a pyramidal volume comprised of many sector scans stacked in the elevation direction. This scan format is primarily useful for cardiac imaging to avoid interference from the ribs. However, a real-time rectilinear volumetric scan with a wider field-of-view (FOV) close to the transducer could prove more useful for abdominal, breast or vascular imaging. In our previous work, a 94 x 94 Mills cross array operating at 5 MHz was fabricated, and the first real-time rectilinear volumetric images were made using a 2-D array and the Duke real-time 3-D scanner. The FOV for the Mills cross was 30 x 8 x 60 mm. Despite reasonable success with the Mills cross array, the array had limitations of poor off-axis sensitivity and a smaller FOV in one direction. To overcome these limitations, a new rectilinear array containing over 65,500 elements was developed with a periodic geometry to increase the FOV to 30 mm x 30 mm x 60 mm and improve the off-axis sensitivity. Images of tissue-mimicking phantoms and the carotid artery in vivo were obtained. In addition, spectral and color flow Doppler results from a pulsatile flow phantom were obtained.

Cardiac Volume↗
PubMed2006

Biomechanical regulation of hedgehog signaling in vascular smooth muscle cells in vitro and in vivo.

Hedgehog (Hh) signaling has recently been shown to be both responsive to mechanical loading in vitro and to control vascular development in vivo. We investigated the role of cyclic strain and pulsatile flow in modulating Hh signaling and growth of adult rat vascular smooth muscle cells (SMC) in culture. Exposure of SMC to defined equibiaxial cyclic strain (0% and 10% stretch, 60 cycles/min, for 24 h) significantly decreased sonic hedgehog (Shh) and patched 1 (Ptc1) expression while concurrently inhibiting Gli(2)-dependent promoter activity and mRNA expression, respectively. Cyclic strain significantly decreased SMC proliferation (cell counts and proliferating cell nuclear antigen expression) concomitant with a marked increase in SMC apoptosis (fluorescence-activated cell sorter analysis, acridine orange staining of apoptotic nuclei and Bax/Bcl-x(L) ratio). These strain-induced changes in proliferation and apoptosis were significantly attenuated following addition of either recombinant Shh (3.5 microg/ml) or overexpression of the Notch 3 intracellular domain (Notch IC). Further studies using a perfused transcapillary culture system demonstrated a significant decrease in Hh signaling in SMC following exposure of cells to increased pulsatile flow concomitant with a decrease in proliferation and an increase in apoptosis. Finally, the pulsatile flow-induced decreases in Hh signaling were validated in vivo following flow-induced rat carotid arterial remodeling after 28 days. These data suggest that Hh expression is diminished by biomechanical stimulation in vitro and in vivo and thus may play a fundamental role in arterial remodeling and atherogenesis in vivo.

Animals↗
PubMed1998

Flow visualization and 1- and 3-D laser-Doppler-anemometer measurements in models of human carotid arteries.

Pulsatile flow, wall distensibility, non-Newtonian flow characteristics of blood in flow separation regions, and high/low blood pressure were studied in elastic silicon rubber models having a compliance similar to human vessels and the same surface structure as the biological intima models of (1) a healthy carotid artery model, (2) a 90% stenosis in the ICA, and (3) 80% stenosis in both the internal and external carotid arteries. Flow was visualized for steady flow and pulsatile studies to localize flow separation regions and reattachment points. Local velocity was measured with a 1-, 2-, or 3-D laser-Doppler-anemometer (LDA). Flow in the unstenosed model was Re = 250. In the stenosed models, the Re number decreased to Re = 180 and 213 under the same experimental conditions. High velocity fluctuations with vortices were found in the stenosed models. The jet flow in the stenosis increased up to 4 m/s. With an increasing bifurcation angle, the separation regions in the ECA and ICA increased. Increased flow (Re = 350) led to an increase in flow separation and high velocity shear gradients. The highest shear stresses were nearly 20 times higher than normal. The 90% stenosis created high velocity shear gradients and velocity fluctuations. Downstream of the stenoses, eddies were found over the whole cross-section. In the healthy model a slight flow separation region was observed in the ICA at the branching cross-section whereas in the stenosed models, the flow separation regions extended far into the ICA. We conclude that a detailed understanding of flow is necessary before vascular surgery is performed especially before artificial grafts or patches are implanted.

Blood Flow Velocity↗
PubMed1999

The effect of hemodynamics, vessel wall compliance and hematocrit on ultrasonic Doppler power: an in vitro study.

Previous in vitro studies in rigid tubes under pulsatile flow conditions have reported a lack of a cyclic variation in blood echogenicity that contradicts in vivo results. To investigate whether or not these variations can be attributed to the compliance of the vessel wall, a series of in vitro experiments with compliant tubes, under pulsatile flow conditions, was performed. Two important factors that may affect the Doppler power were investigated: 1. the dependence on hematocrit and 2. the effect of the vessel wall elasticity. In the present study, it is shown that, at the low beat rates, the peak of the mean Doppler power within the flow cycle depends on the vessel wall compliance. When the vessel becomes more compliant, the peak is shifted from the early to the late systole. Additionally, there is a correlation between the power peak and hematocrit that is more evident in compliant vessels. At a higher pulsation rate of 37 beats/min, a different variation is observed. A drop in the power occurs near peak systole in compliant tube experiments and is more pronounced as the vessel becomes more constricted. The observed power drop agrees with previously reported in vivo results, but is not seen in rigid tube experiments. The results of this study suggest that proper interpretation of cyclic variations in Doppler power requires a knowledge of hemodynamic parameters, such as the modulus of elasticity of the vessel wall, propagation velocity or, possibly, the phase angle of input impedance.

Animals↗
PubMed1996

A computer controlled pulsatile pump: preliminary study.

A Stepper Motor Driven Reciprocating Pump (SDRP) can replace roller pumps and rotary pumps for cardio pulmonary bypass, hemodialysis and regional perfusion. The blood pumping ventricles are basically the same as ventricles used for air driven artificial hearts and ventricular assist devices. The electric stepper motor uses a flexible linkage belt to produce a reciprocating movement, which pushes a hard sphere into the diaphragm of the blood ventricles. The SDRP generates pulsatile flow and has a small priming volume. The preset power level of the motor driver limits the maximum potential outflow pressure, so the driver acts as a safety device. A double pump can be made by connecting two fluid pumping chambers to opposing sides of the motor base. Each pump generates pulsatile flow. Pressure and flow studies with water were undertaken. Preliminary blood studies showed low hemolysis, even when circulating a small amount of blood up to 16 hours.

Animals↗