Peristaltic regimes in esophageal transport

Biomechanics and Modeling in Mechanobiology - A FLIP device gives cross-sectional area along the length of the esophagus and one pressure measurement, both as a function of time. Deducing...     

Peristaltic transport of a solid bolus

An analysis of the peristaltic propulsion of a solid spherical bolus enclosed in a contractile membrane is presented. The model is based on in vitro preparations of intestinal segments, and utilizes a simplified representation of the mechanical properties of the muscular coats of the wall. The sequence of deformed configurations of the membrane and the displacement of the bolus are obtained by numerical solution of the model equations. The analysis presented in this paper could be useful for other studies in biomechanics (e.g. uterine contraction and motion of red blood cells in narrow capillaries).     

Peristaltic transport as the travelling deformation waves

Geometry approach to the theoretical and experimental investigations of peristaltic waves based on the travelling deformation waves and wave mass transfer theory (Dobrolyubov, 1991) is presented. The theory of travelling deformation waves is employed to determine uniformed expressions for mass transfer capability parameters of peristalsis. Slow (quasi-static) wave motion is considered which permits not to take into account dynamic phenomena.     

Peristaltic transport of multilayered power-law fluids with distinct viscosities: a mathematical model for intestinal flows

This paper is concerned with the theoretical study of two-dimensional peristaltic flow of power-law fluids in three layers with different viscosities. The analysis is carried out under low Reynolds number and long wavelength approximations. The shapes of the interfaces are described by a system of non-linear algebraic equations which are solved numerically as streamlines. It is found that the non-uniformity in the intermediate and peripheral layers diminishes when the viscosity of the intermediate layer is increased and that of the outermost layer is kept unaltered for both the pseudo-plastic and dilatant fluids. Similar are the observations when the viscosity of the outermost layer is increased and that of the intermediate layer is kept fixed. The flow rate increases with the viscosities of the peripheral and the intermediate layers but the viscosity of the outermost layer is more effective. However, the knowledge of the effect of the viscosity of the intermediate layer facilitates us to achieve the required flow rate without disturbing the outermost layer. An increase in the flow behaviour index too favours larger flow rates. The trapping limits increase with the viscosity of the intermediate layer but decrease with the viscosity of the outermost layer and the flow behaviour index. Thus, a medicinal intervention that creates a more viscous intermediate layer and reduces pseudo plasticity may reduce constipation.     

Peristaltic transport of a couple stress fluid in a uniform and non-uniform channels

The problem of peristaltic transport of a couple stress fluid in uniform and non-uniform two-dimensional channels has been investigated under zero Reynolds number with long wavelength approximation. Blood is represented by a couple stress fluid (a fluid which its particles size are taken into account, a special case of a non-Newtonian fluid). It is found that the pressure rise decreases as the couple stress fluid parameter gamma increases (i.e., small size fluid particle). So the pressure rise for a couple stress fluid (as a blood model) is greater than that for a Newtonian fluid. Also the pressure rise increases as the amplitude ratio phi increases for different values of gamma. Further, the pressure rise in the case of non-uniform geometry is found to be much smaller than the corresponding value in the case of uniform geometry. Finally, the maximum pressure rise when the mean flow rate over one period of the wave, Q = 0, increases as phi increases and gamma decreases.     

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.     

Peristaltic transport in a channel with a porous peripheral layer: model of a flow in gastrointestinal tract

Peristaltic transport in a two dimensional channel, filled with a porous medium in the peripheral region and a Newtonian fluid in the core region, is studied under the assumptions of long wavelength and low Reynolds number. The fluid flow is investigated in the waveframe of reference moving with the velocity of the peristaltic wave. Brinkman extended Darcy equation is utilized to model the flow in the porous layer. The interface is determined as a part of the solution using the conservation of mass in both the porous and fluid regions independently. A shear-stress jump boundary condition is used at the interface. The physical quantities of importance in peristaltic transport like pumping, trapping, reflux and axial velocity are discussed for various parameters of interest governing the flow like Darcy number, porosity, permeability, effective viscosity etc. It is observed that the peristalsis works as a pump against greater pressure in two-layered model with a porous medium compared with a viscous fluid in the peripheral layer. Increasing Darcy number Da decreases the pumping and increasing shear stress jump constant beta results in increasing the pumping. The limits on the time averaged flux Q for trapping in the core layer are obtained. The discussion on pumping, trapping and reflux may be helpful in understanding some of the fluid dynamic aspects of the transport of chyme in gastrointestinal tract.     

The role of the Womersley number in pulsatile blood flow a theoretical study of the Casson model.

The purpose of this Note is to clarify the meaning of the Womersley number alpha in pulsatile blood flow in small vessels. In particular. we explain why the use of alpha as aperturbation parameter to obtain approximate solutions of the Casson model (frequently used in the literature) is not appropriate. Using the techniques of dimensional analysis and scaling, we show that alpha is the product of the Reynolds and Strouhal numbers. Since the latter is very small for physiological flows, the result is that alpha < 1 even at relatively high values of the Reynolds number (i.e., for non-negligible inertia) and we validate our perturbation theory results by comparison with a numerical integration of the full model. Although this analysis is based on the Casson model, our method has general validity and may be applied to other models which describe more accurately the rheological properties of blood.     

Case-based learning of blood oxygen transport

A case study about carbon monoxide poisoning was used help students gain a greater understanding of the physiology of oxygen transport by the blood. A review of student answers to the case questions showed that students can use the oxygen-hemoglobin dissociation curve to make meaningful determinations of oxygen uptake and delivery. However, the fact that many students had difficulty locating the effect of carbon monoxide poisoning in the process of external respiration suggests that these students have not built a robust model of how oxygen distributes itself between the plasma and hemoglobin. This suggests that more determined emphasis on how oxygen enters the blood and how it is partitioned between hemoglobin and the plasma would help students develop more accurate mental models of how oxygen moves from the lungs to the tissues.     

Grinding Microorganisms with a Peristaltic Pump

The Randolph Co. model 610 peristaltic, ⅛-hp pump was effective for preparative purposes in disrupting baker's yeast and spores of Bacillus globigii when suspended with glass beads. Best results were obtained with use of a slurry just fluid enough to flow through tubing while stirred. Beads of 0.2 and 0.1 mm were used to best advantage for the yeast cells and spores, respectively. Yeast cells were disrupted completely within 15 min, and the spores in 10 to 30 min. Temperature and surface denaturation are readily controlled, and the system is easily modified for use with large quantities of microorganisms.     

Amiloride-sensitive sodium transport in lamprey red blood cells: evidence for two distinct transport pathways

To determine Na+/H+ exchange in lamprey erythrocyte membranes, the cells were acidified to pH(i) 6.0 using the K+/H+ ionophore nigericin. Incubation of acidified erythrocytes in a NaCl medium at pH 8.0 caused a considerable rise in 22Na+ influx and H+ efflux during the first 1 min of exposure. In addition, exposure of acidified red cells to NaCl medium was associated with rapid elevation of intracellular Na+ content. The acid-induced changes in Na+ influx and H+ efflux were almost completely inhibited by amiloride and dimethylamiloride. In native lamprey erythrocytes, amiloride-sensitive Na+ influx progressively increased as the osmolality of incubation medium was increased by addition of 100, 200, or 300 mmol/l sucrose. Unexpectedly, the hypertonic stress induced a small, yet statistically significant decrease in intracellular Na+ content in these cells. The reduction in the cellular Na+ content increased with hypertonicity of the medium. The acid- and shrinkage-induced Na+ influxes were inhibited by both amiloride and 5-(N-ethyl-N-isopropyl)-amiloride (EIPA) in a dose-dependent manner. For both blockers, the half-maximal inhibitory values (IC50) were much greater for the shrinkage-induced (44 and 15 micromol/l for amiloride and EIPA, respectively) than for the acid-induced Na+ influx (5.1 and 3.3 micromol/l, respectively). The data obtained are the first demonstration of the presence of a Na+/H+ exchanger with high activity in acidified (pH(i) 6.0) lamprey red blood cells (on average, 512 +/- 56 mmol/l cells/h, n = 13). The amiloride-sensitive Na+ influxes produced by hypertonic cell shrinkage and acid load are likely to be mediated by distinct ion transporters in these cells.     

Interaction of Peristaltic Flow with Pulsatile Couple-Stress Fluid

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Review: Ontogeny of the oxygen transport in the blood]

The biological importance of the oxygen affinity of the tetrameric haemoglobin molecule and its dependency from co-factors is described. Oxygen affinity variations during development from embryonic to adult values are discussed in respect to oxygen uptake from maternal blood via placenta, in lungs and gills as well as to oxygen delivery into tissues. Comparative aspects of the molecular mechanisms leading to affinity changes are presented.