Effects of couple stresses on the blood flow through an artery with mild stenosis

An analysis of the effects of couple stresses on the blood flow through thin artery in the presence of very mild stenosis has been carried out with the help of two nondimensional parameters, alpha (the length ratio parameter) and eta (the parameter characterizing the antisymmetric property of the couple stress tensor). It is shown that an increase in the couple stress (small value of alpha and eta), increases the resistance to the flow and the wall shear stress. These characteristics are further enhanced by the presence of the stenosis.     

Effects of stenosis on non-newtonian flow of the blood in an artery

It has been shown that the resistance of flow and the wall shear increase with the size of the stenosis but these increases are comparatively small due to non-Newtonian behaviour of the blood indicating the usefulness of its rheological character in the functioning of the diseased arterial circulation.     

Effects of peripheral layer viscosity on blood flow through the artery with mild stenosis

The effects of peripheral layer viscosity on physiological characteristics of blood flow through the artery with mild stenosis have been studied. It has been shown that the resistance to flow and the wall shear decrease as the peripheral layer viscosity decreases.     

A note on "effects of couple stresses on the blood flow through an artery with mild stenosis"

Some errors have been observed in the analytical expression for the resistance to flow (lambda R), and in the computation of shear stress distribution (tau R) in the analysis of Prawal Sinha and Chandan Singh (1). These errors have been rectified in the present analysis. Also, better values have been suggested for the couple stress parameter alpha for getting better results for lambda R and tau R.     

Pulsatile spiral blood flow through arterial stenosis

Pulsatile spiral blood flow in a modelled three-dimensional arterial stenosis, with a 75% cross-sectional area reduction, is investigated by using numerical fluid dynamics. Two-equation k-ω model is used for the simulation of the transitional flow with Reynolds numbers 500 and 1000. It is found that the spiral component increases the static pressure in the vessel during the deceleration phase of the flow pulse. In addition, the spiral component reduces the turbulence intensity and wall shear stress found in the post-stenosis region of the vessel in the early stages of the flow pulse. Hence, the findings agree with the results of Stonebridge et al. (2004). In addition, the results of the effects of a spiral component on time-varying flow are presented and discussed along with the relevant pathological issues.     

An evaluation of a micropolar model for blood flow through an idealized stenosis

In this paper, the behavior of a viscous fluid described by Newtonian constitutive theory is compared with that predicted by a model based on micropolar continuum theory. The geometry chosen for this comparative analysis is a stenosis in which gradient effects should be pronounced. A range of boundary conditions for fluid microspin are considered. Although velocities and streamlines are found to be similar for the two continuum models, striking differences in shear stresses are revealed. These differences may be as high as 50% for vanishing microspin boundary conditions. Such significant discrepancies highlight the need for further study of higher order modeling of blood flow.     

Effects of compliance mismatch on blood flow in an artery with endovascular prosthesis

The objective of this paper is to study the mechanical effects caused by the local stiffening of an artery (due to the vascular prosthesis, for instance). At the junction of the host artery and the more rigid implantant, the abrupt change in compliance creates an abnormal stress concentration that initiates an adaptive response in the vascular tissue. The roles of both fluid and solid mechanical phenomena must be considered in the prosthesis design optimization. In this context, even the simple models could provide helpful tools for designing process. We present here a model of blood flow in compliant vessel. The artery is supposed to be an orthotropical thin elastic shell. We obtain the solution by matched asymptotic expansions. The results prove the high flexure concentration close to the compliance jump. It is shown that the use of orthotropical graft may reduce the peak value of these shear forces to a remarkable extent. Waves reflected from the suture and pressure increase in the prosthesis are discussed. Compliance mismatch is shown to reduce the peak value of maximal wall shear stress.     

Homocysteine decreases blood flow to the brain due to vascular resistance in carotid artery

An elevated level of Homocysteine (Hcy) is a risk factor for vascular dementia and stroke. Cysthathionine β Synthase (CBS) gene is involved in the clearance of Hcy. Homozygous individuals for (CBS−/−) die early, but heterozygous for (CBS−/+) survive with high levels of Hcy. The γ-Amino Butyric Acid (GABA) presents in the central nervous system (CNS) and functions as an inhibitory neurotransmitter. Hcy competes with GABA at the GABA_A receptor and affects the CNS function. We hypothesize that Hcy causes a decrease in blood flow to the brain due to increase in vascular resistance (VR) because of arterial remodeling in the carotid artery (CA). Blood pressure and blood flow in CA of wild type (WT), CBS−/+, CBS−/+ GABA_A−/− double knockout, and GABA_A−/− were measured. CA was stained with trichrome, and the brain permeability was measured. Matrix Metalloproteinases (MMP-2 and MMP-9), tissue inhibitor of metalloproteinase (TIMP-3, TIMP-4), elastin, and collagen-III expression were measured by real-time polymerase chain reaction (RT-PCR). Results showed an increase in VR in CBS−/+/GABA_A−/−double knockout > CBS−/+/ > GABA_A−/− compared to WT mice. Increased MMP-2, MMP-9, collagen-III and TIMP-3 mRNA levels were found in GABA_A−/−, CBS−/+, CBS−/+/GABA_A double knockout compared to WT. The levels of TIMP-4 and elastin were decreased, whereas the levels of MMP-2, MMP-9 and TIMP-3 increased, which indirectly reflected the arterial resistance. These results suggested that Hcy caused arterial remodeling in part, by increase in collagen/elastin ratio thereby increasing VR leading to the decrease in CA blood flow.     

Homocysteine decreases blood flow to the brain due to vascular resistance in carotid artery

An elevated level of Homocysteine (Hcy) is a risk factor for vascular dementia and stroke. Cysthathionine β Synthase (CBS) gene is involved in the clearance of Hcy. Homozygous individuals for (CBS−/−) die early, but heterozygous for (CBS−/+) survive with high levels of Hcy. The γ-Amino Butyric Acid (GABA) presents in the central nervous system (CNS) and functions as an inhibitory neurotransmitter. Hcy competes with GABA at the GABA_A receptor and affects the CNS function. We hypothesize that Hcy causes a decrease in blood flow to the brain due to increase in vascular resistance (VR) because of arterial remodeling in the carotid artery (CA). Blood pressure and blood flow in CA of wild type (WT), CBS−/+, CBS−/+ GABA_A−/− double knockout, and GABA_A−/− were measured. CA was stained with trichrome, and the brain permeability was measured. Matrix Metalloproteinases (MMP-2 and MMP-9), tissue inhibitor of metalloproteinase (TIMP-3, TIMP-4), elastin, and collagen-III expression were measured by real-time polymerase chain reaction (RT-PCR). Results showed an increase in VR in CBS−/+/GABA_A−/−double knockout > CBS−/+/ > GABA_A−/− compared to WT mice. Increased MMP-2, MMP-9, collagen-III and TIMP-3 mRNA levels were found in GABA_A−/−, CBS−/+, CBS−/+/GABA_A double knockout compared to WT. The levels of TIMP-4 and elastin were decreased, whereas the levels of MMP-2, MMP-9 and TIMP-3 increased, which indirectly reflected the arterial resistance. These results suggested that Hcy caused arterial remodeling in part, by increase in collagen/elastin ratio thereby increasing VR leading to the decrease in CA blood flow.     

Numerical study on the flow of a non-Newtonian fluid through an axisymmetric stenosis

The laminar steady flow of non-Newtonian fluid (biviscosity fluid) through an axisymmetric stenosis is calculated using the finite element methods. The flow pattern, the separation and reattachment points, and the distributions of pressure and shear stress at the wall are obtained. Then, the axial force acting on the stenosis is evaluated. It is suggested by the authors that this force can become one of the causes of post-stenotic dilatation. Calculated results show that the non-Newtonian property of blood weakens the distortion of flow pattern, pressure and shear stress at the wall associated with the stenosis and that the non-Newtonian property of blood decreases the axial force acting on the stenosis.     

Numerical technique of blood flow through catheterized arteries with overlapping stenosis

This study is concerned with the surgical technique for the injection of a catheter through arteries with overlapping stenosis in the presence of externally applied magnetic field and Hall currents influences. The nature of blood is analyzed mathematically by considering it as a micropolar fluid. The analysis is carried out for an artery with a mild stenosis. The governing equations with the corresponding boundary conditions solved numerically using Crank–Nicolson implicit finite difference scheme. The numerical technique give excellent agreement for axial velocity of the fluid, the circumferential microrotation, the wall shear stress distribution and the contour plots of stream lines. The obtained results show that the value of axial velocity is higher for a Newtonian fluid than that for a micropolar fluid model, the effect of suitable moving magnetic field (Hall currents influences) accelerates the speed of blood, the size of trapped bolus for the stream lines decrease if the spinning movement of the fluid molecules have considerable value regardless of small or large size of the fluid molecules and the flow of fluid is better with increasing the Hall current effect and the size of trapping bolus increase clearly by increasing the maximum height of stenosis where the fluid moves as a bulk.     

Mathematical modelling of flow through an irregular arterial stenosis.

A mathematical model of flow through an irregular arterial stenosis is developed. The model is two-dimensional and axi-symmetric with the stenosis outline obtained from a three-dimensional casting of a mildly stenosed artery. Agreement between modelled and experimental pressure drops (obtained from an axi-symmetric machined stenosis with the same profile) is excellent. Results are also obtained for a smooth stenosis model, similar to that used for most mathematical modelling studies. This model overestimates the pressure drop across the stenosis, as well as the wall shear stress and separation Reynolds number. Also, the smooth model predicts one instead of three recirculation zones present in the irregular model. The original stenosis is modified to increase the severity from 48 and 87% areal occlusion, while maintaining the same general shape. This has the effect of increasing the pressure drop by an order of magnitude and decreasing the number of recirculation zones to one, with a lower separation Reynolds number.     

On the effect of the concentration profile of red cells on blood flow in the artery with stenosis

The effects of the viscosity-concentration dependence and of the concentration profile on blood flow through a vessel with stenosis have been studied. The flow resistance and the wall shear stress have been found to be smaller than in the two-fluid model with constant viscosities.     

Effects of histamine on bronchial artery blood flow and bronchomotor tone

The effects of aerosolized 5% histamine (10 breaths) on bronchial artery blood flow (Qbr), airflow resistance (RL), and pulmonary and systemic hemodynamics were studied in mechanically ventilated sheep anesthetized with pentobarbital sodium. Histamine increased mean Qbr and RL to 252 +/- 45 and 337 +/- 53% of base line, respectively. This effect was significantly different from base line for 30 min after challenge. The histamine-induced increase in RL was blocked by pretreatment with the histamine H1 receptor antagonist, chlorpheniramine, whereas the histamine-induced elevation in Qbr was prevented by the H2 antagonist, metiamide. Both responses were blocked only when both antagonists were present. Changes in Qbr were not directly associated with alterations in systemic and pulmonary hemodynamics or arterial blood gas composition. In vitro histamine caused a dose-dependent contraction of ovine bronchial artery strips that was prevented by H1 antagonist. The H2 agonist, impromidine, caused relaxation of precontracted arterial strips and was more potent and efficacious than histamine, whereas H1 agonists failed to elicit a relaxant response. Thus these findings indicate that histamine aerosol induces a vasodilation in the bronchial vascular bed; histamine has a direct effect on Qbr that is independent of alterations in RL, systemic and pulmonary hemodynamics, or arterial blood gas composition; and, histamine-induced bronchoconstriction is mediated predominantly by H1-receptors, whereas increased Qbr is controlled predominantly by H2-receptors, probably located in resistance vessels. This local effect of histamine on Qbr may have important implications in the pathophysiology of bronchial asthma and pulmonary edema.     

Effects of cyclooxygenase inhibition on canine coronary artery blood flow and thrombosis

This study was designed to determine the effect of inhibitors of cyclooxygenase (COX)-1, COX-2, and the nonselective COX inhibitor naproxen on coronary vasoactivity and thrombogenicity under baseline and lipopolysaccharide (LPS)-induced inflammatory conditions. We hypothesize that endothelial COX-1 is the primary COX isoform in the canine normal coronary artery, which mediates arachidonic acid (AA)-induced vasodilatation. However, COX-2 can be induced and overexpressed by inflammatory mediators and becomes the major local COX isoform responsible for the production of antithrombotic prostaglandins during systemic inflammation. The interventions included the selective COX-1 inhibitor SC-560 (0.3 mg/kg iv), the selective COX-2 inhibitor nimesulide (5 mg/kg iv), or the nonselective COX inhibitor naproxen (3 mg/kg iv). The selective prostacyclin (IP) receptor antagonist RO-3244794 (RO) was used as an investigational tool to delineate the role of prostacyclin (PGI(2)) in modulating vascular reactivity. AA-induced vasodilatation of the left circumflex coronary artery was suppressed to a similar extent by each of the COX inhibitors and RO. The data suggest that AA-induced vasodilatation in the normal coronary artery is mediated by a single COX isoform, the constitutive endothelial COX-1, which is reported to be susceptible to COX-2 inhibitors. The effect of the COX inhibitors on thrombus formation was evaluated in a model of carotid artery thrombosis secondary to electrolytic-induced vessel wall injury. Pretreatment with LPS (0.5 mg/kg iv) induced a systemic inflammatory response and prolonged the time-to-occlusive thrombus formation, which was reduced in the LPS-treated animals by the administration of nimesulide. In contrast, neither SC-560 nor naproxen influenced the time to thrombosis in the animals pretreated with LPS. The data are of significance in view of reported adverse cardiovascular events observed in clinical trials involving the use of selective COX-2 inhibitors, thereby suggesting that the endothelial constitutive COX-1 and the inducible vascular COX-2 serve important functions in maintaining vascular homeostasis.     

Adrenal-renal portal circulation contributes to decrease in renal blood flow after renal artery stenosis in rats.

The aim of the present study was to investigate a role of adrenal-renal portal circulation (ARPC) in a decrease in renal blood flow due to acute stenosis of the renal artery in rats. Animals were divided into three groups. In the control group (I), in order to eliminate the ARPC tissue between the adrenal gland and the ipsilateral kidney was cut. In the second and the third group (II) (III), left renal artery was stenosed by a silver clip (ID 0.40 mm). Then, in the group II, ARPC was surgically eliminated. In the group II, prior to the elimination of ARPC, alpha-adrenergic receptors blockade was produced by phentolamine administration. In the control group, ARPC elimination did not influence either renal blood flow (RBF) or renal vascular resistance (RVR). In the group II, elimination of ARPC caused increase in RBF and decrease in RVR In the group III elimination of ARPC influenced neither RBF nor renal vascular resistance (RVR). Results of the present study provide the functional evidence that catecholamines reaching the kidney through ARPC, contribute to the decrease in RBF and increase in RVR during acute renal artery stenosis in the rat.     

Relation between regional function and coronary blood flow reserve in multivessel coronary artery stenosis

In the setting of chronic coronary stenoses, percent wall thickening (%WT) both at rest and during catecholamine stimulation can be abnormal despite normal resting myocardial blood flow (MBF). We hypothesized that this phenomenon is related to abnormal MBF reserve. Accordingly, 15 dogs were studied between 7 and 10 days after placement of Ameroid constrictors around the proximal coronary arteries and their major branches, at a time when collateral development had not yet occurred. %WT and MBF were measured at rest, after 0.56 mg/kg of dipyridamole, and at incremental doses of dobutamine (5-40 microgram. kg(-1). min(-1)). Resting %WT and MBF were normal in all four sham dogs. Resting transmural MBF was normal in all segments in the 11 study dogs, despite reduced (-2 SD of normal) %WT (<30%) in 40 of 82 segments. MBF reserve was reduced (<3) in segments with reduced %WT, and a close coupling was noted between resting %WT and MBF reserve. All segments showed an increase in %WT with dobutamine up to a dose of 20 microgram. kg(-1). min(-1), above which those with abnormal endocardial MBF reserve showed a "biphasic" response. It is concluded that, in the presence of chronic coronary stenoses, abnormalities in resting %WT as well as inducible reduction in %WT during pharmacological stress are related to the degree of abnormal MBF reserve.     

Blood flow through a stenosis in microcirculation

A theoretical and experimental study concerning two-component fluid pulsating flow through cylindrical ducts having a slight constriction is presented. The model corresponds to blood flows through small diameter vessels (smaller than 400 micron) affected by a singular stenosis. The theoretical approach is based on a asymptotical expansion of the stream function. The physical hypotheses used were based on findings from simultaneous visualization methods. The influence of geometrical, hydrodynamical and structural parameters is systematically examined and related to velocity profiles, hydrostatic pressure, surface stresses.