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Biomedical subjects

P Chaturani

Publications and source records attributed to P Chaturani.

At least 19 recordsLinked to original sources
PubMed1990

Casson fluid model for pulsatile flow of blood under periodic body acceleration.

Pulsatile flow of a Casson fluid under the influence of a periodic body acceleration has been studied in this paper. An implicit finite difference numerical procedure has been used to analyze the flow. Applicability of this method has been checked by comparing the obtained results with the analytical solution for Newtonian flow and explicit scheme solution. The agreement between the implicit and explicit scheme solutions and the analytical solution is good (error less than 1%). Flow variables have been computed at three locations in cardiovascular system (wide (femoral) and narrow (arteriole and coronary) tubes). Effects of yield stress, tube radius and pressure gradient combined, body acceleration amplitude and frequency etc., on flow have been studied. The following observations have been made: (i) Initial transient time It changes with yield stress in narrow tubes are insignificant, whereas in wide tubes It decreases with yield stress; (ii) The axial velocity and fluid acceleration variations with yield stress are uniform (changes only quantitatively, profiles shape remain same) in narrow tubes, whereas in wide tubes these variations are non-uniform (profiles change qualitatively as well as quantitatively); (iii) Yield stress effects on wall shear amplitude are insignificant in narrow tubes (congruent to 0.3% in arteriole and congruent to 6% in femoral); and (iv) For Newtonian fluid, mean flow rate does not change with body acceleration amplitude a0 and frequency fb but it increases (decreases) with a0(fb) for Casson fluid.

Acceleration↗
PubMed1990

Pulsatile flow of power-law fluid model for blood flow under periodic body acceleration.

A mathematical model has been proposed to study the pulsatile flow of a power-law fluid through rigid circular tubes under the influence of a periodic body acceleration. Numerical solutions have been obtained by using finite difference method. The accuracy of the numerical procedure has been checked by comparing the obtained numerical results with other numerical and analytical solutions. It is found that the agreement between them is quite good. Interaction of non-Newtonian nature of fluid with the body acceleration has been investigated by using the physiological data for two particular cases (coronary and femoral arteries). The axial velocity, fluid acceleration, wall shear stress and instantaneous volume flow rate have been computed and their variations with different parameters have been analyzed. The following important observations have been made: (i) The velocity and acceleration profiles can have more than one maxima, this is in contrast with usual parabolic profiles where they have only one maximum at the axis. As n increases, the maxima shift towards the axis; (ii) For the flow with no body acceleration, the amplitude of both, wall shear and flow rate, increases with n, whereas for the flow with body acceleration, the amplitude of wall shear (flow rate) increases (decreases) as n increases; (iii) In the absence of body acceleration, pseudoplastic (dilatant) fluids, with low frequency pulsations, have higher (lower) value of maximum flow rate Qmax than Newtonian fluids, whereas for high frequencies, opposite behavior has been observed; for flow with body acceleration pulsations gives higher (lower) value of Qmax for pseudoplastic (dilatant) fluids than Newtonian fluids.

Acceleration↗
PubMed1989

Microcontinuum model for pulsatile blood flow through a stenosed tube.

The effects of polar nature of blood and pulsatility on flow through a stenosed tube have been analysed by assuming blood as a micropolar fluid. Linearized solutions of basic equations are obtained through consecutive applications of finite Hankel and Laplace transforms. The analytical expressions for axial and particle angular velocities, wall shear stress, resistance to flow and apparent viscosity have been obtained. The axial velocity profiles for Newtonian and micropolar fluids have been compared. The interesting observation of this analysis is velocity, in certain parts of cycle, for micropolar fluid is higher than Newtonain fluid. Variation of apparent viscosity eta a with tube radius shows both inverse Fahraeus-Lindqvist and Fahraeus-Lindqvist effects. Finally, the resistance to flow and wall shear stress for normal and diseased blood have been computed and compared.

Arterial Occlusive Diseases↗
PubMed1988

Theory for flow of Casson and Herschel-Bulkley fluids in cone-plate viscometers.

Mathematical models for blood flow in cone-plate viscometer have been considered, by assuming blood as a Casson/Herschel-Bulkley fluid. Three different cases have been analyzed (i) when there is no shearing, (ii) partial shearing and (iii) full shearing. The relationships between the angular velocity and torque have been obtained for the above three cases. By assuming total shearing, the analytical expression for apparent viscosity has been obtained. Variation of apparent viscosity with yield stress, angular velocity, Casson co-efficient of viscosity, consistency index and flow behaviour index has been computed. It is observed that as the angular velocity increases, the apparent viscosity decreases for both fluids. Further, it is found that as the cone angle increases, the apparent viscosity increases. This behaviour of apparent viscosity in cone-plate viscometer is interesting and unexpected and is being reported first time.

Animals↗
PubMed1986

Pulsatile flow of Casson's fluid through stenosed arteries with applications to blood flow.

The effects of non-Newtonian nature of blood and pulsatility on flow through a stenosed tube have been investigated. A perturbation method is used to analyse the flow. It is of interest to note that the thickness of the viscous flow region is non-uniform (changing with axial distance). An analytic relation between viscous flow region thickness and red cell concentration has been obtained. It is important to mention that some researchers have obtained an approximate solution for the flow rate-pressure gradient equation (assuming the ratio between the yield stress and the wall shear to be very small in comparison to unity); in the present analysis, we have obtained an exact solution for this non-linear equation without making that assumption. The approximate and exact solutions compare well with one of the exact solutions. Another important result is that the mean and steady flow rates decrease as the yield stress theta increases. For the low values of the yield stress, the mean flow rate is higher than the steady flow rate, but for high values of the yield stress, the mean flow rate behaviour is of opposite nature. The critical value of the yield stress at which the flow rate behaviour changes from one type to another has been determined. Further, it seems that there exists a value of the yield stress at which flow stops for both the flows (steady and pulsatile). It is observed that the flow stop yield value for pulsatile flow is lower than the steady flow. The most notable result of pulsatility is the phase lag between the pressure gradient and flow rate, which is further influenced by the yield stress and stenosis. Another important result of pulsatility is the mean resistance to flow is greater than its steady flow value, whereas the mean value of the wall shear for pulsatile flow is equal to steady wall shear. Many standard results regarding Casson and Newtonian fluids flow, uniform tube flow and steady flow can be obtained as the special cases of the present analysis. Finally, some applications of this theoretical analysis have been cited.

Arterial Occlusive Diseases↗
PubMed1985

Blood flow in tapered tubes with biorheological applications.

A steady laminar flow of blood in a uniform tapered tube has been examined. Blood rheology is assumed to be described by a polar fluid. The analytical expressions for velocities (both axial and radial), total angular velocity, wall shear and pressure drop have been obtained. In literature, the parameters N (coupling number) and L (length ratio) have been chosen independently. But, in the present analysis, it is found that they are interrelated. Variation of the flow variables with suspension concentration and tapered angle have been investigated. Some of the theoretical models for the flow through tapered tubes have been critically examined. The pressure-flow relationship has been studied numerically over the flow rate range 0.01-0.1 cc/sec and compared with experimental results. It has been shown that the existing experimental results are for the tapered tubes of larger diameter which correspond to the flow under Newtonian conditions. Finally, some biological implications and future developments of this theory have been indicated.

Blood↗
PubMed1985

A study of non-Newtonian aspects of blood flow through stenosed arteries and its applications in arterial diseases.

Blood flow through a stenosed artery has been investigated in this paper. Blood has been represented by a non-Newtonian fluid obeying Herschel-Bulkley equation. This model has been used to study the influence of the fluid behaviour index n, shear-dependent nonlinear viscosity K and the yield stress tau H in blood flow through stenosed arteries. The variation of the wall shear stress and the flow resistance with n, K and tau H has been shown graphically. It is observed that the wall shear stress and the flow resistance increase in Herschel-Bulkley fluid in comparison with corresponding Newtonian fluid. It is of interest to note that, in the present model, the thickness of the plug core varies with the axial distance z in the stenotic region. Finally, some biological implications of the present model for some arterial diseases have been briefly discussed.

Arterial Occlusive Diseases↗
PubMed1983

Three-layered Couette flow of polar fluid with non-zero particle spin boundary condition at the interfaces with applications to blood flow.

In this paper, Couette flow of blood is modelled as a three-layered flow. The model basically consists of a core (red-cell suspension) and plasma (a Newtonian fluid) in the top (near the moving plate) and bottom (near the stationary plate) layers. Flow is assumed to be steady and laminar and fluids are incompressible. A spin boundary condition at the interfaces is used by introducing two parameters. Analytic expressions for velocity, total angular velocity and effective viscosity have been obtained and their variations with spin parameters S and s, layer thickness, coupling number N and characteristic length ratio L are computed and shown graphically. One of the important observations of the analysis is the permissible values of the coupling number N is between 0 and 1/square root2 (in the existing literature, the range of N is 0 to 1). The present model includes Couette flow of one and three-layered Newtonian fluids and one-layered polar fluid models as its special cases. Applications of the proposed model to blood flow have been briefly discussed.

Blood Flow Velocity↗
PubMed1982

Poiseuille flow of micropolar fluid with non-zero couple stress at boundary with applications to blood flow.

Poiseuille flow of a micropolar fluid has been reexamined from the point of view of its applications to blood flow. Couple stresses are assumed to be non-zero at the boundary, and a method has been proposed to determine such boundary conditions for a given suspension. Velocity profiles (both axial and rotational) as well as apparent viscosity have been computed for various values of s (a boundary condition and concentration parameter). The results obtained have been compared with experimental values (for blood flow). It is found that they are in a reasonably good agreement. Some of the earlier workers have used solvent viscosity for the classical shear viscosity of the suspension and obtained infinite relative viscosity for a suspension concentration of 40% which, according to experimental results, is not feasible. An appropriate expression for the classical shear viscosity has been used in the present analysis which removes the apparent viscosity anomaly, i.e., apparent viscosity tends to infinity as the concentration approaches 40%, from the micropolar fluid theory. Finally, some biological applications of this theory have been discussed.

Blood Flow Velocity↗
PubMed1981

A theoretical model for pulsatile blood flow with applications to cerebrovascular diseases.

A solution for fully developed pulsatile flow of a couple stress fluid through a circular, rigid tube of infinite length has been obtained in the form of a Bessel-Fourier series. The velocity profiles and flow rates for different values of flow parameters have been shown graphically. It has been observed that velocity and flow rate are almost in phase with pressure gradient for low values of pulsatile Reynolds number alpha (alpha 2 = 0.1). For higher values of alpha(= 2) a phase difference of approximately 30 degrees between the velocity profile and pressure gradient has been observed. The obtained results are in good agreement with other theoretical and experimental results. The present analysis is valid for both values of alpha , i.e., alpha greater than or equal to 1 and alpha less than 1, whereas the existing analysis for pulsatile flow of couple stress fluid is valid for only alpha less than 1. The first, second, and third approximate solutions have been obtained and it is found that the convergence of the solutions is quite fast and the series could be terminated after the second term. This theoretical work could be useful in the measurement of blood flow rates, its apparent viscosity, and peripheral resistance of the circulatory system which, at present, are thought to be some of the main causes of many cerebrovascular diseases and stroke problems.U

Cerebrovascular Circulation↗