Slow Blood Flow Research Articles

Velocity Profiles of Slow Blood Flow in a Narrow Tube**The project supported by the National Basic Research Project “Nonlinear Science”, National Natural Science Foundation of China and the State Education Commission through the Foundation of Doctoral Training

A fractal model is introduced into the slow blood motion. When blood flows slowly in a narrow tube, red cell aggregation results in the formation of an approximately cylindrical core of red cells. By introducing the fractal model and using the power law relation between area fraction and distance from tube axis , rigorous velocity profiles of the fluid in and outside the aggregated core and of the core itself are obtained analytically for different fractal dimensions. It shows a blunted velocity distribution for a relatively large fractal dimension , which can be observed in normal blood; a pathological velocity profile for moderate dimension , which is similar to the Segre–Silberberg effect; and a parabolic profile for negligible red cell concentration , which likes in the Poiseuille flow.

Amplitude Doppler US: slow blood flow detection tested with a flow phantom.

To evaluate the in vitro sensitivity for the detection of slow blood flow in tiny tubes with an amplitude Doppler ultrasound (US) technique at different angles and pulse repetition frequencies. Human blood treated with heparin was pumped through silicone tubes (flow phantoms made by the author) with lumina of 3.00 mm, 0.30 mm, and 0.05 mm. Slow flow was imaged by using amplitude and color Doppler US techniques with two US devices at different pulse repetition frequencies and angles and in different sound propagation media. Under ideal conditions, the lowest detectable velocity was 0.04-0.06 cm/sec in the 3.00-mm tube. Detection was about three to four times less sensitive in the 0.30-mm and 0.05-mm tubes. Amplitude Doppler US sensitivity is only slightly dependent on the angle of incidence and propagation medium. The fractional volume flow determined the sensitivity of the amplitude Doppler technique for detecting low flow. Amplitude Doppler US is nearly angle independent; thus, it is superior to color Doppler US. Amplitude Doppler US is three to four times more sensitive when tube have very tiny lumina and when probes of a lower frequency are used.

Early Life Stage Toxicity of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in Zebrafish (Danio rerio)

Toxicity and histopathology of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in zebrafish (Danio rerio) early life stages was characterized from 12 to 240 hr postfertilization (hpf) following waterborne exposure of newly fertilized eggs. TCDD did not increase egg mortality (0–48 hpf), nor did it affect time to hatching (48–96 hpf). Egg doses of 1.5 ng [3H]TCDD/g or greater elicited toxic responses in zebrafish larvae. Pericardial edema and craniofacial malformations were first observed at 72 hpf, followed by the onset of yolk sac edema (96 hpf) and mortality (132 hpf). At 240 hpf the ED50s for pericardial edema, yolk sac edema, and craniofacial malformations were 2.2, 2.1, and 1.9 ng [3H]TCDD/g egg, respectively. The LD50, determined at 240 hpf, was 2.5 ng [3H]TCDD/g egg. Severe hemodynamic changes, observed as slowed blood flow in vascular beds of the trunk, head, and gills and slowed heart rate, occurred in TCDD-treated zebrafish prior to or coincident with the onset of gross signs of toxicity. Histological examination of TCDD-treated zebrafish revealed a variety of epithelial tissue lesions including arrested gill development and ballooning degeneration and/or necrosis of the renal tubules, hepatocytes, pancreas, and all major brain regions. Mesenchymal tissue lesions included subcutaneous edema in the head, trunk, and yolk sac, edema of the pericardium and skeletal muscle, and underdevelopment of the swim bladder. This demonstration of zebrafish responsiveness to TCDD early life stage toxicity coupled with the considerable information on developmental biology and genetics of zebrafish provides a foundation for future investigations into the mechanism of TCDD developmental toxicity.

Effect of gadolinium on phase-contrast MR angiography of the renal arteries.

Our aim was to evaluate the effect of gadolinium chelates on image quality in phase-contrast MR angiography of renal arteries in patients suspected of having renal artery stenosis. In 24 patients, axial three-dimensional phase-contrast MR angiography of the renal arteries was obtained on a 1.5-T MR imaging system before and after administration of gadolinium contrast agent. The improvement in distal renal artery signal-to-noise ratio after enhancement was measured and correlated with patient age, serum creatinine level, clinical estimation of renal artery flow, and the imaging parameter flip angle. On average, the distal renal artery signal-to-noise ratio increased 2.2-fold after gadolinium administration (p < .001). The increase was greatest in patients more than 60 years old (3.1-fold; p < .001) and in patients with serum creatinine levels greater than 3.0 mg/dl (4.3-fold; p < .01). After enhancement, we found an apparent increase in renal artery diameter (3.5 +/- 1.1 mm before enhancement versus 4.8 +/- 1.4 mm after enhancement [mean +/- SD; p < .001]). We believe this increase reflects improved visualization of slow blood flow along the artery wall. Although the visualization of renal arteries was better in most patients after enhancement, two patients had poorer image quality after enhancement because of increased venous signal obscuring the arteries. Gadolinium administration significantly increases distal renal artery signal-to-noise ratio on three-dimensional phase-contrast MR angiography in most patients. The signal-to-noise ratio improvement is greatest in older patients and in patients with impaired renal function. However, in some cases, increased venous signal may obscure arteries.

Blood flow characteristics of vessels in the ligamentum teres fissure at color Doppler sonography: findings in healthy volunteers and in patients with portal hypertension.

The purpose of our study was to assess flow characteristics of vessels in the ligamentum teres fissure with color Doppler sonography in subjects without and with portal hypertension. Color Doppler sonography of the ligamentum teres fissure was performed with either a 5.0- or a 7.5-MHz linear transducer in 55 consecutive thin healthy volunteers. Retrospective review was performed of sonograms of 21 consecutive patients with portal hypertension in whom blood flow in a paraumbilical vein was shown with 2.0- to 5.0-MHz sector/curved array transducers. Nine (16%) of the 55 healthy subjects had venous flow in the ligamentum teres fissure, which was hepatofugal in five and hepatopetal in four. Hepatofugal venous flow velocity in the ligamentum teres fissure did not exceed 5 cm/sec (mean, 3.2 cm/sec; SD, 1.0 cm/sec; range, 2-5 cm/sec), and flow extending anterior to the liver's surface was not noted with color Doppler sonography in the healthy subjects. In the 21 patients with portal hypertension, venous flow in the ligamentum teres fissure was always 7 cm/sec or greater (mean, 16 cm/sec; SD, 7.1 cm/sec; range, 7-33 cm/sec) and was shown by color Doppler sonography to continue beyond the anterior surface of the liver in 12 patients (57%). Slow (< or = 5 cm/sec) hepatofugal venous blood flow may be detected in the ligamentum teres fissure in healthy subjects and by itself does not necessarily indicate portal hypertension. Hepatofugal venous flow in the ligamentum teres fissure with a velocity greater than 5 cm/sec or visualized with color Doppler sonography continuing anterior to the liver's surface is highly specific (100% in this series) for the presence of portal hypertension.

Cerebral Arteriovenous Malformation

Figure 1. Magnetic resonance imaging and angiography of the brain revealed a left parietal arteriovenous malformation measuring 2.5 cm in diameter in a 32-year-old woman who presented with severe headache. Panel A, a coronal T1-weighted magnetic resonance image, and Panel B, an axial T2-weighted magnetic resonance image, demonstrate a tangle of abnormal vascular channels. Rapid blood flow causes a lack of signal intensity within the larger vessels of the arteriovenous malformation. Interspersed areas of higher signal intensity within the nidus of the arteriovenous malformation may represent regions of slow blood flow or hemorrhage (arrow, Panel A). . . .

S17.6. Models for slow blood flow in narrow tubes; Effects of aggregation and sedimentation of flow resistance

S17.6. Models for slow blood flow in narrow tubes; Effects of aggregation and sedimentation of flow resistance

Apogeotrophic type of direction-changing positional nystagmus related to slow vertebrobasilar blood flow.

We examined the incidence of slow blood flow (SBF) in the vertebrobasilar system by magnetic resonance imaging (MRI) in 35 patients showing direction-changing positional nystagmus (DCPN). The subjects consisted of 20 patients with apogeotrophic type (group A) and 15 with geotrophic type (group B) of DCPN. Fifty-seven age-matched subjects without vestibular symptoms were examined as a control group (group C). SBF was detected in 11 (55%), 3 (20%) and 6 (11%) patients in groups A, B and C, respectively. Lacunae of the brainstem were found in 7 (35%) patients in group A and 1 (7%) in group B. The higher incidence of SBF in group A suggested a possible relationship between SBF and apogeotrophic type of DCPN. Apogeotrophic type of DCPN associated with SBF was considered to be caused by ischemia in the posterior circulation, though it was unclear whether the vestibular labyrinth or the hindbrain was mainly involved.

Magnetic resonance angiographic findings in vertiginous patients with slow vertebrobasilar blood flow.

To investigate arterial lesions underlying slow vertebrobasilar blood flow (SBF) which appears as a high intravascular signal on proton-density images, we examined 35 vertiginous patients, 15 with SBF and 20 without, using magnetic resonance angiography. Vertebrobasilar dolichoectasia, segmental stenosis with elongation and diffuse narrowing of the vertebrobasilar arteries (VBA) were found in 4, 4 and 2 patients with SBF, respectively. In one patient with SBF, the thrombi that induced SBF seemed to have embolized to distal arteries. These abnormalities were not detected in patients without SBF, although 2 patients demonstrated aneurysm in the VBA. Because SBF is frequently associated with atherosclerotic arterial lesions, patients with SBF should be treated to prevent more severe ischemic brain disease.

Maturational changes in arterial impedance of the normal testis in boys: Doppler sonographic study.

The use of color Doppler sonography to diagnose scrotal disorders in children has been hampered by the small size of the vessels and the slow blood flow compared with those in adults. Spectral analysis is the best means available of confirming the vascular origin of questionable color-flow signals arising from testes of small volume. The range of normal and abnormal Doppler sonographic arterial waveforms arising from the testis in boys, as distinct from those in adults, has never been described. The purpose of our study was to establish the normal range of testicular arterial impedance, measured as resistive index (RI), in both prepubertal and pubertal/post pubertal boys. Bilateral scrotal color Doppler sonography was performed in 33 healthy boys aged 3 days to 17.5 years. The mean RI in the parenchymal artery was measured in 44 testes and plotted against testicular volume. Chi-square statistics were used to test differences in mean RI, testicular volume, and age between testes with volumes of 4 cm3 or less and testes with volumes greater than 4 cm3. In testes with volumes of 4 cm3 or less, the mean RI ranged from 0.39 to 1.00 (mean, 0.87), and in testes with volumes greater than 4 cm3, the RI ranged from 0.43 to 0.75 (mean, 0.57). In 20 of 30 testes with volumes of 4 cm3 or less, the RI of parenchymal arteries was equal to 1.00 (i.e., diastolic flow was undetectable). Mean RI, testicular volume, and age were significantly different between testes with volumes of 4 cm3 or less and testes with volumes greater than 4 cm3 (p < .001 for all variables). Mean testicular RI in our samples of pubertal and postpubertal boys is decreased compared with the mean RI in prepubertal boys. Diastolic arterial flow may not be detectable in normal testes with volumes of 4 cm3 or less. Despite the existence of a statistically significant difference in mean RI between prepubertal and pubertal/postpubertal testes, substantial variability exists within each group, particularly among the prepubertal testes. Norms of testicular flow previously established for adults are therefore not routinely applicable to prepubertal boys with testicular volumes less than 4 cm3. However, RI values in normal pubertal and postpubertal boys where testicular volumes exceed 4 cm3 are comparable to those previously described in adults.

Transthoracic echo/Doppler in the identification of patients with chronic non-valvular atrial fibrillation at risk for thromboembolic events

Left atrial spontaneous echo contrast, detected by transoesophageal echocardiography in patients with non-valvular atrial fibrillation reflects slow blood flow and is associated with an increased risk of cardio-embolism. The purpose of this study was to find echo/Doppler predictors of left atrial spontaneous echo contrast by transthoracic examination. In a retrospective case control study, 17 patients with chronic non-valvular atrial fibrillation who had suffered a recent cerebral ischaemic event (group A) and 17 patients with chronic non-valvular atrial fibrillation who had not suffered such an event (group B) were studied. Both groups were matched for age and sex. All patients underwent standard transthoracic echocardiography with transmitral Doppler as well as transoesophageal echocardiography. Left atrial spontaneous echo contrast was demonstrated by transoesophageal echocardiography in nine group A patients and in two group B patients (P = 0.028); left atrial spontaneous echo contrast was not detected by transthoracic echocardiography in these patients. All patients with left atrial spontaneous echo contrast (11 patients) had a left atrial size, corrected for base index, exceeding 24 mm and a transmitral time velocity integral < 10 cm (sensitivity 100%). Left atrial spontaneous echo contrast was absent in six patients with both characteristics (specificity 74%). transthoracic echo/Doppler aids in the prediction of the presence of left atrial spontaneous echo contrast and the identification of patients with non-valvular atrial fibrillation with increased cardioembolic risk, thus avoiding transoesophageal echocardiography.

Red blood cell aggregability in patients with a history of leg vein thrombosis: influence of post‐thrombotic treatment

Reversible aggregation of red blood cells (RBC) plays an important role in determining blood flow properties, and it is this aggregation which increases blood viscosity at low shear rates. The structure and sites of venous thrombi, as well as the fact that stasis is a major predisposing factor in venous thrombosis, suggest a strong association between vein thrombosis, slow blood flow and increased blood viscosity. RBC aggregation and disaggregation were measured (SEFAM erythroaggregameter, France) in 54 patients with a history of unexplained leg vein thrombosis. Results were compared to those of controls classified according to age. Increased RBC aggregability was observed in 41% of the patients, and the mean values indicated a significant elevation of RBC aggregability in patients when compared with controls (P < 0.05). Subgroups were compared to study the influence of thrombus recurrence and thrombosis type (deep versus superficial vein thrombosis) on the aggregation parameters. No significant difference was found between these subgroups. The use of compression stockings and veinotropic drugs tended to reduce the abnormalities in RBC aggregability (P < 0.05). An increase in RBC aggregability and in the shear resistance of RBC aggregates, by predisposing to circulatory stasis, is likely to contribute to the evolution and complications of leg vein thrombosis.

A Model for Motion and Sedimentation of Cylindrical Red-Cell Aggregates During Slow Blood Flow in Narrow Horizontal Tubes

When blood flows slowly in a narrow tube, red-cell aggregation results in formation of an approximately cylindrical "core" of red cells, which moves as a rigid body. The core is denser than the surrounding fluid, and sedimentation is observed in horizontal tubes. To model this, the Stokes flow of a fluid surrounding a long solid cylinder (the core) contained in a long hollow cylinder (the tube) is considered. The cylinder axes are parallel but not coincident. An exact analytic expression for the resistance coefficient for motion perpendicular to the axes is given. This coefficient increases rapidly with the ratio of core radius to tube radius, and core eccentricity. The predicted rate of sedimentation is comparable to that observed experimentally. The apparent viscosity of a two-phase medium consisting of a core of aggregated particles and surrounding pure fluid is calculated. For a core radius corresponding to experimental conditions, the apparent viscosity increases rapidly with increasing eccentricity of the core.

Hepatic arterial chemotherapy for metastatic colorectal carcinoma.

In this review, the rationale of regional chemotherapy for treatment of hepatic metastases in advanced colorectal carcinoma is discussed. Pharmacokinetic principles and early clinical experience of hepatic arterial drug administration are summarised. The regional advantage of fluoropyrimidine compounds in this setting is well established, and recent evidence suggests that 5-fluorouracil (5-FU) is more efficacious than the analogue 5-fluoro-2'-deoxyuridine (FUDR). However, while significantly higher clinical response rates can be achieved with hepatic arterial infusion (HAI) chemotherapy compared with conventional intravenous drug administration, patient survival benefit is not significantly different. Several novel approaches to overcome the limitations of HAI therapy are currently being explored. These include concomitant use of biodegradable microspheres, which both slow tumour blood flow and enhance tumour drug uptake, and use of vasoactive agents to redistribute arterial blood flow towards tumours. In addition, novel chemotherapeutic agents which exploit unique biological characteristics of hepatic tumours are entering clinical trial.

The Blood Circulation of Malignant and Benign Tumours of the Genital Interior as a Diagnostic Tool

<i>Background</i>: Malignant tumours usually display a blood circulation different from that of benign ones. This fact can be used in sonographic dignity diagnostics. A prerequisite is a technology capable of detecting this difference which becomes evident in the smallest blood vessels, where flow is extremely slow. <i>Patients and Method</i>: The Sonolayer SSH 140A (Toshiba) and the Quantum 2000 (Siemens) devices were used. These systems are in a position to detect slow blood flow in the tissue tested. We examined the very small vessels in the tumour which cannot be identified by black and white ultrasound image but only with the colour Doppler. The colour pixels which we found in or around the tumour in the colour mode were examined with the pulsed Doppler in order to quantify the blood flow. The resistance index (RI) was calculated from systole and diastole. The lowest RI was used for the evaluation. 51 female patients with ovarian tumours (29 malignant, 22 benign), 41 patients with transmutations of the endometrium (25 malignant, 16 benign), 3 patients with sarcoma, 12 patients with myoma and 39 patients with transmutations of the cervix (24 malignant, 15 benign) were preoperatively examined and the result was correlated with the dignity. None of the patients was treated with hormones. <i>Results</i>: The following RI values were measured: ovarian tumours: malignant 41%, benign 77% (premenopause: 45%); endometrial findings: malignant 49%, benign 66% (premenopause: 51%); sarcoma/myoma uteri: sarcoma 33%, myoma 35% (premenopause: 34%); cervical findings: malignant 51%, benign 78% (premenopause: 52%). According to these results the division into premenopause and postmenopause is decisive. As our results demonstrate, differentiation before the menopause is barely possible due to the blood circulation pattern present at this stage, whilst in the postmenopausal status the distinction between benign and malignant tumours becomes highly significant. <i>Conclusion</i>: The organs of the genital interior have physiologically a high circulation of blood in the premenopause. Therefore, the difference between benign and malignant transmutations is low. Thus we can see a significant difference between the blood flow in benign and malignant tumours of the uterus and ovary in the postmenopausal women but no significant difference in the premenopausal woman. The colour Doppler examination is able to improve the dignity diagnostics in postmenopausal women. We could not verify a differentiation between sarcoma and myoma by Doppler examination. If all the restrictions listed are taken into consideration, the blood circulation diagnostics of transmutations of the genital interior in the postmenopause will be able to make an important contribution to dignity diagnostics.

Sudden sensorineural hearing loss associated with slow blood flow of the vertebrobasilar system.

To determine the characteristics of sudden deafness associated with slow blood flow (SBF) within the vertebrobasilar arteries, we evaluated 57 patients with sudden deafness using magnetic resonance imaging (MRI). We detected SBF in 12 (21%) patients, predominantly men over 50 years of age. A second MRI performed in 5 patients 2 months after the onset of symptoms showed recovery of blood flow. All 12 patients complained of vertigo. Audiological and neurotologic tests suggested that hearing loss mainly involved the inner ear. Our findings suggest that unless central lesions are detected, headache, hypoesthesia of the external ear canal, and electronystagmographic abnormalities are signs of SBF. Because sudden deafness may recur in patients who have SBF, they should be monitored and treated to prevent recurrence.

Die Durchblutung maligner und benigner Tumoren des inneren Genitale

Malignant tumours differ mostly from benign lesions in their blood supply. This fact can be used in the sonographic diagnosis of the tumour status. This, however, depends on the availability of ultrasound equipment, capable of demonstrating this difference, which can only be detected in smallest blood vessels, in which the blood flow is extremely slow. We employed the Sonolayer SSH 140A (Toshiba, Japan) and the Quantum 2000 (Siemens, Germany) for diagnosis of lesions of the female inner genital tract. Both instruments could visualize the slow blood flow velocities in the tissues examined. Diagnosis of blood circulation in tumours of the inner genital tract thus seems less dependent on the technology employed as is the case in examining the breasts. 41 patients with ovarian tumours, 31 with endometrial pathology, and 33 with cervical lesions were examined preoperatively. Findings were correlated to histology. The lowest resistance index (RI) measured was evaluated. The following RI values were found: Ovarian tumours: malignant 46%, benign 78% (49%). Tumours of the corpus uteri: malignant 54%, benign 65% (55%). Cervical lesions: malignant 55%, benign 79% (58%). Results in premenopausal women with non-malignant lesions are specified in brackets. Pre- and postmenopausal status proved essential. When compared to breast findings, the difference between benign and malignant tumours of the inner genital tract is less pronounced due to the fact, that, physiologically, these tissues are characterised by a higher blood supply. Differentiation was thus almost impossible in premenopausal women. However, in menopausal patients, a highly significant difference between benign and malignant tumours was found, which could serve as basis for tumour status prognosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiopulmonary vascular imaging.

Magnetic resonance angiography (MRA) effectively maximizes the flow sensitivity of MR imaging (MRI) to display the body's vasculature. Although MRA has proven quite effective in imaging the intracranial and extracranial vessels, cardiopulmonary MRA faces several additional inherent challenges. Cardiorespiratory motion, vessel pulsatility, and irregular flow patterns all degrade image quality and necessitate appropriate compensation schemes. Although preliminary cardiopulmonary MRA methods appear promising, near instantaneous scan times may be necessary to fully maximize the potential of this technique. Multislice spin-echo and gradient-echo techniques have also proven effective. These methods may compensate for cardiac motion through either ECG-gating or referencing, and may maximize the signal characteristics from the intrinsic slow blood flow of the pulmonary vasculature. Phase velocity mapping techniques, which have proven capable of quantifying blood flow in the body, appear equally promising in preliminary studies in evaluating the cardiopulmonary vascular system. Because of the nature of blood flow dynamics in the cardiopulmonary vascular system, spin-echo (SE), gradient refocussed echo (GRE), and possibly phase mapping technique appear well suited for evaluating these regions.

Pathogenesis of Venous Thrombosis

This brief review attempts to describe the present understanding of the pathogenesis of venous thrombosis in general with special reference to venous thromboembolism in spinal cord injury patients with paralysis. The component parts of Virchow's triad are examined. Most venous thrombi seem to originate in regions of slow blood flow, ie, the large venous sinuses of the calf and thigh or in valve cusp pockets. Decreased blood flow or even stasis due to lack of the pumping action of the large muscle packages in paralyzed patients is undoubtedly one of the major factors. As blood pools, activation products of the coagulation system accumulate locally leading potentially to local hypercoagulability. Activation products of clotting and fibrinolysis can induce endothelial damage which in turn leads to further activation of the hemostasis system. Endothelial damage may also result from distension of the vessel walls by the pooling blood. Blood flow is further decreased by hyperviscosity due to elevated fibrinogen levels and dehydration. Some spinal cord injury patients may sustain direct trauma to the legs; others may encounter vessel wall damage by the immobilized limbs. Shortly after injury, certain changes develop in the clotting system, especially increases in components of the von Willebrand factor macromolecular complex and increased platelet aggregability which could further contribute to hypercoagulability. Recently, an inhibition of the fibrinolytic system was suggested which also could add to a prothrombotic state. All of these interrelated processes clearly explain the high risk of venous thromboembolism in spinal cord injury patients with paralysis which has been clearly demonstrated by many investigators. It is hoped that intense thrombosis prophylaxis will reduce the incidence of this potentially devastating complication.

Transcranial Doppler Sonography in the Early Phase of Alzheimer's Disease

Transcranial Doppler sonography examination of 23 patients with Alzheimer''s disease (AD) showed significantly slower blood flow velocities, bilaterally, in the middle cerebral arteries (MCAs) than in 10 healthy controls. The asymmetries of velocities in MCA were positively correlated with asymmetries of cognitive impairment, but not with global severity or duration of disease. Patients with prevalent left hemispheric neuropsychological dysfunction showed significantly slower blood flow in the left MCA, while the opposite pattern was observed in patients with prevalent right hemisphere dysfunction. The possibility that these findings are an expression of the reduction of cerebral blood flow and metabolism shown in AD by emission tomography studies is discussed.