Uneven Distribution Of Blood Flow Research Articles

Comparison of hemodynamic features and thrombosis risk of membrane oxygenators with different structures: A numerical study

PurposeThe geometric structure of the membrane oxygenator can exert an impact on its hemodynamic features, which contribute to the development of thrombosis, thereby affecting the clinical efficacy of ECMO treatment. The purpose of this study is to investigate the impact of varying geometric structures on hemodynamic features and thrombosis risk of membrane oxygenators with different designs. MethodsFive oxygenator models with different structures, including different number and location of blood inlet and outlet, as well as variations in blood flow path, were established for investigation. These models are referred to as Model 1 (Quadrox-i Adult Oxygenator), Model 2 (HLS Module Advanced 7.0 Oxygenator), Model 3 (Nautilus ECMO Oxygenator), Model 4 (OxiaACF Oxygenator) and Model 5 (New design oxygenator). The hemodynamic features of these models were numerically analyzed using the Euler method combined with computational fluid dynamics (CFD). The accumulated residence time (ART) and coagulation factor concentrations (C[i], where i represents different coagulation factors) were calculated by solving the convection diffusion equation. The resulting relationships between these factors and the development of thrombosis in the oxygenator were then investigated. ResultsOur results show that the geometric structure of the membrane oxygenator, including the location of the blood inlet and outlet as well as the design of the flow path, has a significant impact on the hemodynamic surroundings within the oxygenator. In comparison to Model 4, which had the inlet and outlet located in the center position, Model 1 and Model 3, which had the inlet and outlet at the edge of the blood flow field, exhibited a more uneven distribution of blood flow within the oxygenator, particularly in areas distant from the inlet and outlet, which was accompanied with lower flow velocity and higher values of ART and C[i], leading to the formation of flow dead zones and an elevated risk of thrombosis. The oxygenator of Model 5 is designed with a structure that features multiple inlets and outlets, which greatly improves the hemodynamic environment inside the oxygenator. This results in a more even distribution of blood flow within the oxygenator, reducing areas with high values of ART and C[i], and ultimately lowering the risk of thrombosis. The oxygenator of Model 3 with circular flow path section shows better hemodynamic performance compared to the oxygenator of Model 1 with square circular flow path. The overall ranking of hemodynamic performance for all five oxygenators is as follows: Model 5 > Model 4 > Model 2 > Model 3 > Model 1, indicating that Model 1 has the highest thrombosis risk while Model 5 has the lowest. ConclusionThe study reveals that the different structures can affect the hemodynamic characteristics inside membrane oxygenators. The design of multiple inlets and outlets can improve the hemodynamic performance and reduce the thrombosis risk in membrane oxygenators. These findings of this study can be used to guide the optimization design of membrane oxygenators for improving hemodynamic surroundings and reducing thrombosis risk.

Diagnostic Value of Superb Microvascular Imaging in Parotid Tumors

BackgroundThe aim of this study was to evaluate the clinical diagnostic value of superb microvascular imaging (SMI) in assessing vascular distribution, vascularity, and vessel morphology of parotid tumors (PTs).Material/MethodsPT patients confirmed by postoperative histopathological detection and who underwent color Doppler flow imaging (CDFI), microvascular imaging (MVI), and SMI examination were recruited. PTs were classified into 3 groups: pleomorphic adenoma (PA), Warthin tumor (WT), and malignant PT (MT). The tumor vascular distribution, vascularity, and vessel morphology recorded by CDFI, MVI, and SMI were compared among PA, WT, and MT group. PT diagnosis was performed using histopathological detection. Fisher’s exact test was used to compare the diagnostic sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV), and accuracy between SMI and MVI examination in PTs.ResultsWe enrolled 198 PTs consisting of 114 PAs, 56 WTs, and 28 MTs into our study. CDFI examination found no significant differences in vascular distribution and vascularity among the PA, WT, and WT groups. SMI examination found significant differences in vascular distribution and vascularity among the 3 groups. MVI found significant differences in vessel morphology, including uneven distribution of blood flow, arborization, and irregular blood flow among the PA, WT, and MT groups. SMI found significant differences in arborization and irregular blood flow, but none of the differences in uneven distribution of blood flow among the 3 groups were significant. The diagnostic sensitivity, specificity, and accuracy of SMI and MVI in PTs showed no significant differences.ConclusionsSMI more accurately evaluated the vascular distribution and vascularity of PTs than CDFI. SMI might be a potential non-invasive diagnostic method for PTs in clinical practice.

Some Unanticipated Consequences of Early Cardiac Catheterization. Insights into Pulmonary Pathophysiology.

One of the most interesting unanticipated findings by André Cournand and Dickinson Richards in their groundbreaking studies of cardiac catheterization was the very low pressure in the normal pulmonary circulation. At the time, in the 1940s, the significance of this was not appreciated. For example, in their speeches at the Nobel Prize ceremony, neither of these laureates referred to the low pressure, although they did discuss other features of the pulmonary circulation. It was up to the cardiologist, William Dock, to point out that these low pressures implied a very uneven distribution of blood flow in the lung, and in particular that in the normal upright lung, the blood flow to the apex would be extremely small. Dock went on to argue that this low blood flow at the top of the lung was responsible for the characteristic apical distribution of adult pulmonary tuberculosis. Since that time, it has been recognized that the low pressures in the pulmonary circulation have many implications in pulmonary pathophysiology. For example, if the vascular pressure is further reduced, such as in hemorrhagic shock, gas exchange is seriously affected because of the development of a large alveolar dead space. Furthermore, if humans are subjected to increased acceleration, such as in a high-performance aircraft, the distribution of blood flow becomes extremely abnormal, with much of the lung being completely unperfused. There are also diseases where distribution in the lung is affected by the uneven distribution of blood flow. These include alpha-1 antitrypsin deficiency and metastatic calcification of the lung.

Haemodynamics determined by a genetic programme govern asymmetric development of the aortic arch

Laterality of the internal organs of vertebrates is determined by asymmetric Nodal signalling in the lateral plate mesoderm. A deficiency of such signalling results in heterotaxia syndrome, characterized by anomalous laterality of visceral organs and complex congenital heart conditions. Pitx2, the transcription factor induced by the Nodal signal, regulates left-right asymmetric morphogenesis. The cellular and molecular bases of asymmetric morphogenesis remain largely unknown, however. Here we show that ablation of unilateral Pitx2 expression in mice impairs asymmetric remodelling of the branchial arch artery (BAA) system, resulting in randomized laterality of the aortic arch. Pitx2-positive cells were found not to contribute to asymmetrically remodelled arteries. Instead, Pitx2 functions in the secondary heart field and induces a dynamic morphological change in the outflow tract of the heart, which results in the provision of an asymmetric blood supply to the sixth BAA. This uneven distribution of blood flow results in differential signalling by both the platelet-derived growth factor receptor and vascular endothelial growth factor receptor 2. The consequent stabilization of the left sixth BAA and regression of its right counterpart underlie left-sided formation of the aortic arch. Our results therefore indicate that haemodynamics, generated by a Pitx2-induced morphological change in the outflow tract, is responsible for the asymmetric remodelling of the great arteries.

Circumferential skin blood flow measurements in the ischaemic limb.

Skin blood flow (SBF) values were estimated on the posterior, medial and lateral aspects of the lower leg in 47 patients presenting for assessment of amputation level. Measurement was made using a radioisotope (iodoantipyrine) clearance technique. Medial SBF was 9.0 +/- 5.2 ml 100 g-1 min-1; posterior SBF was 8.3 +/- 5.0 ml 100 g-1 min-1 and lateral SBF was 6.5 +/- 4.1 ml 100 g-1 min-1. The results gave significantly higher SBFs on the medial and posterior aspects of the ischaemic leg. The finding of an uneven distribution of blood flow at the below knee amputation level has important implications in the planning of amputation flaps.

Blood and Dialysate Flow Distributions in Hollow-Fiber Hemodialyzers Analyzed by Computerized Helical Scanning Technique

ABSTRACT. The efficiency of a hemodialyzer is largely dependent on its ability to facilitate diffusion between blood and dialysis solution. The diffusion process can be impaired if there is a mismatch between blood and dialysate flow distribution in the dialyzer. This article describes the distribution of the blood and dialysate flows in hollow-fiber hemodialyzers analyzed with a computerized scanning technique. Blood flow distribution was studied in vitro by dye injection in the blood compartment during experimental extracorporeal circulation using human blood with hematocrit (Hct) adjusted at 25 and 40%. Sequential images were obtained with a helical scanner in a 1-cm-thick fixed longitudinal section of the dialyzer. Average and regional blood flow velocity and wall shear rates were measured by using the reconstructed imaging sequence. The method allowed the calculation of single-fiber blood flow and single-fiber wall shear rate (SF wSh) in different regions of the hemodialyzer. In 38 patients on chronic hemodialysis, creatinine and phosphate clearance displayed a significantly negative correlation with Hct (P < 0.05), but this correlation was not found for urea, although a trend toward reduction could be observed. The suggested explanation of this phenomenon is the significant reduction in effective plasma water flow across the hemodialyzer in presence of a progressive rise in Hct. The second explanation for this phenomenon may be found in the nonhomogeneous distribution of blood flow within the fibers observed at the sequential imaging. This, in fact, could also explain the negative trend observed for urea. At higher Hct levels, single-fiber blood flow velocity and SF wSh were significantly lower in the fibers situated at the periphery of the bundle. At the same time, SF wSh tended to decrease in peripheral fibers, showing a value near half of that observed in the central fibers of the bundle (165 versus 301 s−1). A similar technique was used to study the flow distribution in the dialysate compartment in three different types of hemodialyzers with characteristic dialysate compartment design: (A) standard configuration; (B) space yarns (spacing filaments preventing contact between fibers); and (C) Moiré structure (wave-shaped fibers to prevent contact between adjacent fibers). Clinical sessions of hemodialysis were also carried out to measure blood- and dialysate-side urea clearances in the different hemodialyzers. Macroscopic and densitometric analysis revealed that flow distribution was most homogeneous in the dialyzer with Moiré structure (type C) and least homogeneous in the standard dialyzer (type A). Space yarns (type B) gave an intermediate dialysate flow distribution. Urea clearance (P < 0.001) increased significantly with types B and C, compared with the standard dialyzer. Type C had the highest clearances, although they were not significantly greater than type B. In conclusion, a significant blood-to-dialysate flow mismatch may occur in hollow-fiber hemodialyzers due to either uneven blood flow distribution or a dialysate channeling phenomenon external to the fiber bundle. Improvement in dialyzer design may overcome these problems, at least in part.

Pulmonary thromboembolism in cats: 29 cases (1987–1997)

Objective To determine clinical signs, clinicopathologic abnormalities, radiographic findings, histologic abnormalities, and predisposing factors or diseases in cats with pulmonary thromboembolism (PTE). Design Retrospective study. Animals 29 cats in which PTE was confirmed at necropsy. Procedure Information on signalment, body weight, history, results of physical examination, results of CBC and serum biochemical analyses, whether PTE was suspected prior to death, type of indwelling venous catheter and duration of venous catheterization, results of thoracic radiography, and whether cats had any concurrent diseases was obtained from medical records. Results PTE was identified in cats of various ages (median, 8.7 years), weights (median, 4.1 kg [9 lb]), and breeds. The most common owner-reported problems included lethargy (17 cats), anorexia (14), weight loss (10), and difficulty breathing (8); physical abnormalities included lethargy (21), tachypnea or dyspnea (16), and dehydration (13). Clinicopathologic abnormalities reflected concurrent or underlying diseases. Common radiographic abnormalities included pulmonary vessel abnormalities (11), pleural effusion (8), and peripheral noncircumscribed consolidations (6). Underlying or predisposing conditions, including cardiac disease (12), neoplasia (10), corticosteroid administration (8), disseminated intravascular coagulation (5), protein-losing nephropathy (4) or enteropathy (4), immune-mediated hemolytic anemia (2), and sepsis (2) were identified in all cats. Conclusions and Clinical Relevance Results suggest that PTE can develop in cats of any age, sex, or breed. Because PTE is a serious, potentially life-threatening disease, it should be suspected in cats with thoracic radiographic changes suggestive of uneven distribution of blood flow between lung lobes, especially in cats that have predisposing factors or diseases. (J Am Vet Med Assoc 1999;215:1650–1654)

Evaluation of Laser Doppler Flowmetry in the Assessment of Intestinal Blood Flow in Cat

Laser Doppler flowmetry with a differential detector system has been used in the assessment of blood flow in the feline small intestine. Simultaneous mucosal and serosal laser Doppler flowmeter recordings were compared with total blood flow of a bowel segment measured by an optical drop-recorder unit in 6 cats. Blood flow through the muscularis layer was estimated using the 85Kr washout technique. A correlation coefficient of r = 0.96 (mucosal recordings = 90, serosal recordings = 80, p less than 0.001) was obtained between laser Doppler flowmeter output signals and total blood flow at different levels of vascular tone, regardless of whether the flowmeter recordings were made from the mucosal or the serosal side of the bowel wall. At intense vasodilation, the flowmeters showed a tendency to underestimate blood flow. The flowmeter signals were at variance with the muscularis blood flow but were clearly correlated to the calculated mucosal-submucosal blood flow. The uneven blood flow distribution in the intestinal wall did not affect the ability of the flowmeters to reflect total blood flow from either side of the bowel wall. A calibration curve could be constructed for approximate interpretation of the laser Doppler signals in absolute flow units. However, further experiments in humans and further development of the technique must be performed to elucidate clinical applications of the method.

Effect of prostaglandin E1 on fractional distribution of cardiac output and organ blood flow in man: a simultaneous and non-invasive determination using double dose thallium-201 scintigraphy.

Taking advantage of the fact that the distribution of Thallium-201 in an organ almost parallels the blood flow to the organ, we devised a non-invasive method of simultaneously determining blood flow and its distribution in human organs. With this method, we investigated the effect of exogenous prostaglandin E1 (PGE1) on the central and peripheral circulation. Scintigraphy was performed after two injections of 201Tl chloride, one at rest and one after the administration of PGE1 or saline. In eight subjects given PGE1 (0.2 microgram X kg-1 X min-1, iv), blood pressure fell, whereas both heart rate and cardiac output rose. The fractional distribution was increased in the heart (+13.3 +/- 2.98%, mean +/- SD), but decreased in the liver (-10.2 +/- 1.95%) and gastro-intestinal tract (-7.09 +/- 2.65%). No significant change was observed in the kidneys or leg. The blood flow in all these organs was increased. In the six control subjects given saline, there was no change in these central and peripheral haemodynamics. Thus, the intravenous infusion of PGE1 in man causes uneven blood flow distribution in heart, liver, kidney, gastro-intestinal organs and leg muscles, despite increased blood flow to all these organs. The method used in this study is relatively non-invasive and useful in evaluating organ blood flow in man, and seems to be widely applicable to physiological and pharmacologic research.

Idiopathic sclerosing cholangitis: Pathophysiologic observations

Selective hepatic arteriography and umbilical portography in a patient with idiopathic sclerosing cholangitis revealed uneven distribution of blood flow through the liver, the majority of the contrast media being demonstrated in the central portions of the liver. Mild portal hypertension was present. The stenotic biliary tree offered no unusual resistance to the passage of dye from the main biliary radicals into the duodenum. T tube drainage dramatically relieved pruritis, but clinical improvement with weight gain, disappearance of jaundice, and reduction of portal pressure did not occur until after the administration of steroids. After one year of steroid therapy, liver biopsy showed a reduction in the periportal inflammatory reaction and lessening of the diffuse stenosis of the biliary tree. The relationship of these findings to current pathophysiologic hypotheses concerning sclerosing cholangitis is discussed.

Uneven distribution of maternal and fetal placental blood flow, as demonstrated using macroaggregates, and its response to hypoxia.

A technique is described for studying the distribution of blood flow to the maternal and fetal placental vessels in sheep and dogs with radioactive labeled macroaggregates of albumin. When the maternal animal breathed room air the distribution of maternal placental blood flow was uneven among the cotyledons as well as within a given cotyledon. Fetal blood flow was also distributed nonuniformly among and within the cotyledons. The relation of maternal to fetal placental blood flow was also markedly uneven (coefficient of correlation, tau = 0.066). After the animal was made hypoxic by breathing 10-12% O(2) the distribution of maternal, fetal, and maternal/fetal placental flows became more uniform. The coefficient of correlation of maternal to fetal flow was high (tau = 0.53, P < 0.01). While the maternal animal breathed room air, after ligation of a major branch of the umbilical artery the distribution of maternal, fetal, and maternal/fetal flows in the remaining two-thirds to three-fourths of the placenta became more uniform. The correlation coefficient for maternal to fetal flow was high (tau = 0.35, P < 0.01).It appears that under normal circumstances with uneven distribution of blood flows there is a considerable portion of the placenta that does not receive blood flow in optimum quantities to promote efficient O(2) exchange. Failure to consider the influence of nonuniform maternal flow/fetal flow will result in overestimation of mean maternal-fetal oxygen tension gradients, and thus underestimation of the placental diffusing capacity for oxygen. In response to maternal hypoxia or compromise of the fetal placental circulation the distribution of maternal, fetal, and maternal/fetal flows becomes more uniform, thereby increasing the efficiency of placental O(2) exchange.

Influence of hydrostatic pressure on the pulmonary circulation.

The uneven topographical distribution of blood flow in the lung is an inevitable consequence of the intimate apposition of blood and air which results in large pressure differences across the pulmonary vessels at different levels in the lung. The resulting imbalance of blood flow and ventilation causes large regional differences in gas exchange but interference with overall gas transfer is negligible unless the normal pulmonary arterial pressure is reduced or alveolar pressure is increased when an alveolar dead space may develop. The uneven distribution of blood flow results in peculiar overall pressure-blood flow relations in that the pulmonary vascular resistance falls considerably when either the pulmonary arterial or venous pressures are raised. These characteristics are advantageous to the lung, the one organ of the body which receives the whole cardiac output during a variety of physiological states.In general, the patterns of distribution of blood flow observed in health and disease can apparently be explained by the interactions between the pulmonary arterial, venous and alveolar pressures. However patients with an increased pulmonary venous pressure as in mitral stenosis or left ventricular failure may show a reduction of blood flow in the lower zones and a similar pattern has been found in the isolated lung where it is caused by interstitial oedema. The mechanism is postulated to be an interference with the normal expanding action of the inflated lung parenchyma on the extra-alveolar blood vessels.

Effects of changes in topographical distribution of lung blood flow on gas exchange.

The left lung of a dog was suspended in a Lucite box, ventilated with negative pressure, and perfused with venous blood from another dog at 37 C. By varying the pulmonary artery pressure, it was possible to perfuse all the lung or leave increasing proportions of the upper and middle lobes unperfused. The mean Pco2 difference between end-tidal gas and pulmonary venous blood was 1.7 mm Hg (se mean 0.6) when all the lung was perfused, but steadily increased up to 17 mm Hg as more and more of the lung was unperfused. Alveolar dead space/alveolar tidal volume increased linearly with the proportion of lung unperfused. By contrast, the venous admixture component remained small as increasing amounts of lung were unperfused. The results were compared with calculations made on a theoretical model of the lung and it was concluded that the uneven distribution of blood flow caused by hydrostatic pressure differences down the lung may seriously interfere with CO2 exchange when the pulmonary artery pressure is low, but that this type of uneven distribution affects O2 exchange much less. isolated lung; hydrostatic effect; alveolar-arterial differences; physiologic dead space; alveolar dead space; shunt effect; venous admixture; increased acceleration; hypoxemia; hemorrhage; positive-pressure breathing Submitted on September 10, 1964