Computational simulation of blood flow in human systemic circulation incorporating an external force field

A quasi-one-dimensional non-linear mathematical model for the computation of the blood flow in the human systemic circulation is constructed. The morphology and physical modelling of the whole system (arteries, capillaries and veins) are completed by different methods for the different vessel generations. A hybrid method is used to solve the problem numerically, based on the governing equation (continuity, momentum and state equations), the input boundary conditions and the predetermined initial conditions. The two-step Lax-Wendroff finite-difference method is used to compute variables for each individual vessel, and the characteristic method is employed for the computation of internal boundary conditions of the vessel connection and the input and output system boundary conditions. Using this approach, blood flow, transmural pressure and blood velocity are computed at all vessel sites and for each time step. The pressure and flow waveforms obtained show reasonable agreement with clinical data and results reported in the literature. When an external conservative force field is applied to the system, the results computed from the model are intuitively correct. The term representing the external pressure added to the system by the muscle, which represents active control on the cardiovascular system, is also embodied in this model.     

The Morton-Keele pump—a hydraulically activated pulsatile pump for use in extracorporeal circulation

A new pulsatile pump is described, and the results of bench tests and animal experiments are presented. The arterial blood pressure and flow waveforms generated by the pump resemble those produced by the canine heart. The present pump is satisfactory for dog perfusions, and should, with minor modifications, be suitable for use in human surgery.     

Endotoxinemia in the portal and the systemic circulation in obstructive jaundice

Abstract. Endotoxinemia in patients with obstructive jaundice is linked to acute renal failure and sepsis and remains a major cause of complications during postoperative treatment. The current study examines the mechanisms of endotoxinemia in the portal and the systemic circulation in obstructive jaundice. As an experimental model of the disease we used rabbits subjected to sham operation. Serum total bilirubin aminotransferases and endotoxin concentrations were determined at 2, 5, 8, and 13 days after operation. Endotoxin concentrations were estimated by the limulus lysate endotoxin test. A high frequency of portal or systemic endotoxinemia is observed in obstructive jaundice, but no difference between endotoxinemia levels in the portal and systemic circulation was observed.     

Autoregulation of portal circulation: A correlative study of circulation and vascular morphology

To Investigate the mechanism of portal circulation and the genesis of portal hypertension, an in vivo model was made to Increase portal venous flow (PVF) by forming a bypass shunt between the femoral artery to the spienic venous branch in pigs and dogs via a regulatable pump. Using this model, an autoregulatory hemodynamics of the portal circulation and corresponding morphological changes of the intrahepatic vascular system were determined. Immediately after blood flow increase (100 mL/min) to the portal vein, PVF increased to the baseline level plus bypass shunt flow. But, PVF returned to the baseline level within 1 h for both animals. Portal venous resistance (PVR) at 1 h was significantly higher than the baseline level (R0.05). By histometric analysis of the cross-sectional area of the portal and hepatic venous branches (CSA-PV, CSA-HV) using the biopslzed liver, CSA-HV at 1 h was 27.6% of the CSA-HV of the baseline level in dog, which showed narrowing and contractive changes of the hepatic venous branches, and CSA-PV at 1 h was 36.4% of the CSA-PV of the baseline level In pig. which showed narrowing and contractive changes of the portal venous branches. It Is suggested that a tone of the intrahepatic vascular system has an important role In the portal autoregulatory hemodynamics.     

Path-Dependent Hemodynamics of the Stenosed Carotid Bifurcation

Previous work using computational simulations and experimental flow visualizations has demonstrated marked differences in local flow patterns between stenosed carotid bifurcation models having the same stenosis severity but different stenosis geometries. Since local blood flow patterns are known to influence thrombosis and atherosclerotic plaque development and rupture, such differences may in turn reflect differences in thromboembolic and atherosclerotic potential, and hence risk of ischemic stroke. Towards testing this hypothesis, we tracked point particles, representing uniformly distributed blood elements, through concentrically and eccentrically stenosed carotid bifurcation models, and computed and compared various path-dependent hemodynamic parameters between the models. Our results suggest that residence time alone is not sensitive to stenosis geometry; however, notable differences between the stenosis models were observed with residence time indicators that incorporate shear-related phenomena, such as the transit times and levels of activation of platelets that exceed a given shear threshold. Specifically, these and other indicators, including the magnitude of platelet shear exposure and the size and density of local platelet and monocyte deposition, were found to be higher in the eccentric model. Experimental work is now required to assess the significance of these differences. © 2003 Biomedical Engineering Society. PAC2003: 8719Uv     

Computer simulation of the mechanically-assisted failing canine circulation

A model of the cardiovascular system is presented. The model includes representations of the left and right ventricles, a nonlinear multielement model of the aorta and its main branches, and lumped models of the systemic veins and the pulmonary circulation. A simulation of the intra-aortic balloon pump and representations of physiological compensatory mechanisms are also incorporated in the model. Parameters of the left ventricular model were set to simulate either the normal or failing canine circulation. Pressure and flow waveforms throughout the circulation as well as ventricular pressure and volume were calculated for the normal, failing, and assisted failing circulation. Cardiac oxygen supply and consumption were calculated from the model. They were used as direct indices of cardiac energy supply and utilization to assess the effects of cardiac assistance. This work was supported in part by Grant No. EET-8620120 from the National Science Foundation.     

Involvement of the human splanchnic circulation in pressor response induced by handgrip contraction

We have analysed the adjustment of blood flow and vascular conductance in the abundantly supplied splanchnic circulation to a generally released pressor reaction. Pressor responses were induced by 2-min periods of standardized, sustained handgrip in seven healthy students. The effects of handgrip tests were followed both in the fasting state and after the consumption of a substantial, mixed meal. In the first of the two sessions, changes in superior mesenteric artery blood flow were recorded and concomitant changes in local vascular conductance derived. In the other session, pressor released cardiac output changes were recorded and changes in total peripheral vascular conductance derived. Both types of flow changes were recorded using ultrasound Doppler technique. Typically, blood flow in the superior mesenteric artery increased two- to threefold after a meal. Handgrip contractions induced an initial rapid increase in heart rate, cardiac output and total peripheral conductance, followed by a gradual decline in total peripheral conductance and stroke volume and a gradual increase in heart rate and mean arterial pressure for the rest of the period. At the end of 2-min pressor periods, total peripheral conductance was only about 10% below the pre-handgrip level, whereas vascular conductance locally in the area of the superior mesenteric artery decreased by some 30%. Thus, it appears that the splanchnic vascular bed contributes markedly to the compound pressor response. Handgrips caused significantly less reduction in local vascular conductance in the post-prandial than in the pre-prandial state, indicating that blood flow to the digesting gastrointestinal tract retains a relatively high priority also in a pressor situation.     

Effect of ornid on regulation of the cerebral circulation

An investigation by radioisotope, electromagnetic, and resistographic methods showed that Ornid reduces the cerebral blood flow. At the same time it completely inhibits constrictor reactions of the cerebral vessels to stimulation of sympathetic and somatic nerves. Ornid also has a protective action against experimental disturbances of the cerebral circulation of adrenergic nature.Laboratory of Pharmacology of the Nervous System, Institute of Pharmacology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 87, No. 5, pp. 427–429, May 1979.     

Multivariate autoregressive modelling combined with transcephalic electrical impedance: method to relate neonatal systemic circulation and respiration to cerebral circulation

We studied the pulsatile component of cerebral circulation with transcephalic electrical impedance (ΔZ) in six preterm newborns, three of whom had severe cerebral bleeding, peri-intraventricular haemorrhage (PIVH). The transcephalic electrical impedance ΔZ signal, ECG, arterial blood pressure, (aBP) and respirogram were recorded on analogue magnetic tape for 30 min. Artefact-free stationary segments (lasting for 2 min) of the four signals were digitised. A digital multivariate autoregressive (MAR) model was used to study frequency-specific variability in the signals and to quantify interrelations between the variabilities of ΔZ, HR, aBP and respiratory signals. MAR modelling describes a system where all the signals simultaneously explain each other. The inherent variability of ΔZ was lower and the influences of respiration and aBP on ΔZ significantly greater in infants with severe PIVH than in controls. These changes were observed at high frequencies corresponding to respiration and heart rate. This may be interpreted as a marker of pressure passivism in the cerebral circulation following PIVH. We conclude that in preterm babies the application of MAR modelling, together with transcephalic impedance, may be a new, helpful and quantitative method for the study of simultaneous interrelations between variables of cerebral and systemic circulations and respiration.     

运动对动脉内皮功能的调控及血流剪切力的介导作用

<正>常的动脉内皮功能在调节血管通透性、维持正常的凝血功能以及免疫、炎症反应中起重要作用,受损的内皮功能则可引起血管的重构以及血栓、动脉粥样硬化等疾病的发生和发展。合理的运动训练能够通过促进一氧化氮(nitric oxide,NO)、前列环素(prostacyclin,PGI2)等物质的分泌来维持和改善动脉内皮功能,并预防动脉粥样硬化的发生。而高强度运动训练则会导致氧化应激的发生并降低NO的生物活性,从而造成内皮功能障碍及心血管疾病的发生。大量研究表明,运动引起的血流剪切力幅度及形式的变化在上述血管生物学响应中起重要的介导作用。本文综述了运动训练对动脉内皮功能的调控作用、血流剪切力的介导作用以及相关分子生物学机制等方面的研究进展,为进一步深入研究运动调控内皮功能的血流动力学机制特别是血流剪切力的重要介导作用提供参考,同时也为通过监控血流剪切力等血流动力学参数以选择最佳运动方式提供一定的科学依据。     

ACTH inhibits development of primary decompensation of the systemic and portal circulation in rats with acute blood loss

Institute of General Pathology and Pathological Physiology, Russian Academy of Medical Sciences, Moscow. (Presented by Academician of the Russian Academy of Medical Sciences G. N. Kryzhanovskii.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 114, No. 8, pp. 128–130, August, 1992.     

脉动流实验装置研究

为了进一步研究脉动流的压力和流量分布规律,本文设计了一套可以产生脉动流,并可进行弹性管道内流体压力和流量测量的实验装置。首先参照工业用液压系统的原理,利用单片机89S51控制电磁阀的开关频率,得到入口流脉动频率;再利用LabVIEW编写采集程序,得到管道内流体压力及流量的测量数据。通过初步测试及数据结果分析得出压力与流量的不同分布特征,即入口流脉动频率增加时,流量增加,管壁受到的压力也增大;对于相同的入口脉动频率,随着与动力源距离的增加,压力减小,流量没有显著变化。本文测试结果将为进一步的临床实验提供有效实验依据。     

Heart and brain circulation and CO2 in healthy men

Aim: To compare blood flow response to arterial carbon dioxide tension change in the heart and brain of normal elderly men. Methods: Thirteen healthy elderly male volunteers were studied. Hypercapnea was induced by carbon dioxide inhalation and hypocapnea was induced by hyperventilation. Myocardial blood flow [mL min^?1 × (100 g of perfusable tissue)^?1] and cerebral blood flow [mL min^?1 × (100 g of perfusable tissue)^?1] were measured simultaneously at rest, under carbon dioxide gas inhalation and hyperventilation using the combination of two positron emission tomography scanners. Results: Arterial carbon dioxide tension increased significantly during carbon dioxide inhalation (43.1 ± 2.7 mmHg, P < 0.05) and decreased significantly during hyperventilation (29.2 ± 3.4 mmHg, P < 0.01) from baseline (40.2 ± 2.4 mmHg). Myocardial blood flow increased significantly during hypercapnea (88.7 ± 22.4, P < 0.01) from baseline (78.2 ± 12.6), as did the cerebral blood flow (baseline: 39.8 ± 5.3 vs. hypercapnea: 48.4 ± 10.4, P < 0.05). During hypocapnea cerebral blood flow decreased significantly (27.0 ± 6.3, P < 0.01) from baseline as did the myocardial blood flow (55.1 ± 14.6, P < 0.01). However, normalized myocardial blood flow by cardiac workload [100 mL mmHg^?1 × (heart beat)^?1 × (gram of perfusable tissue)^?1] was not changed from baseline (93.4 ± 16.6) during hypercapnea (90.5 ± 14.3) but decreased significantly from baseline during hypocapnea (64.5 ± 18.3, P < 0.01). Conclusion: In normal elderly men, hypocapnea produces similar vasoconstriction both in the heart and brain. Mild hypercapnea increased cerebral blood flow but did not have an additional effect to dilate coronary arteries beyond the expected range in response to an increase in cardiac workload.     

Effect of sodium hydroxybutyrate on the cerebral circulation and regional vasomotor reflexes

Experiments on cats in which electromagnetic and resistographic methods were used showed that sodium hydroxybutyrate (100 mg/kg) considerably increases the cerebral circulation. It also increases the blood flow into the brain during the period of formation of pressor blood pressure reflexes. An increase in blood flow also is observed in the system of the femoral arteries, whereas in the intestinal artery, on the other hand, the increase in the blood flow is reduced during vasomotor reflexes. Reflex changes in the resistance of the regional vessels also differ in character: depression of pressor reflexes in the cerebral vessels accompanied by facilitation in the intestinal and femoral arteries and potentiation of the dilator phase of the reflex in the limb vessels. These differences are evidently based on differences in the sensitivity of sympathetic formations in the central components of the different regional vasomotor reflexes to hydroxybutyrate.Laboratory of Pharmacology of the Nervous System, Institute of Pharmacology, Academy of Medical Sciences of the USSR, Moscow. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 11, pp. 555–557, November, 1979.     

New versatile physical model fitting the systemic circulation accurately

A physical model is developed for the simulation of the left heart and systemic circulation. The simulator includes a transparent and compliant ventricle pumping into an arterial model. The ability of the system to reproduce thein vivo conditions accurately is demonstrated by quantitative comjcarisons with physiological pressure and flow waveforms. As an example of application, flow patterns within the ventricle obtained by visualisation techniques and ultrasonic Doppler velocimetry are presented. Its versatility makes the system an essential tool in cardiovascular flow dynamics.