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Results for “CAPILLARIES/physiology”

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At least 19 recordsLinked to original sources
PubMed1961

The physics of blood flow in capillaries. I. The nature of the motion.

In many capillaries erythrocytes travel singly, separated by segments of plasma (bolus flow). The peculiar flow pattern, within the plasma, has been studied visually in a model in which air bubbles separated by short columns of liquid flow through a glass tube. Injection of dye reveals an "eddy-like" motion, in that each fluid element repeatedly describes a closed circuit. The possible significance of this "mixing motion" in relation to gaseous equilibration (e.g., in pulmonary capillaries) has been studied in a thermal analogue. A copper tube passed first through a constant temperature bath which brought the fluid to a uniform temperature T(1), and then through a second smaller bath at a lower temperature T(2). From the final temperature T(3) of the fluid, which was collected in a thermally insulated flask, a calculation of the heat transfer was made (i.e., from the flow and the temperature drop (T(1)-T(3))). Bolus flow was up to twice as effective in transferring heat as Poiseuille flow (no bubbles in fluid). The theory of modelling was employed in order to apply this thermal data to gaseous equilibration, especially in pulmonary capillaries. It was concluded that gaseous equilibration may be considerably accelerated by bolus flow, though this may be more of a limiting factor in peripheral capillaries than in the pulmonary circulation. The result supports the assumption of complete mixing in plasma made by Roughton and Forster in 1957.

Capillaries↗
PubMed1962

The physics of blood flood in capillaries. II. The capillary resistance to flow.

A previous communication described the peculiar motion of the plasma trapped between erythrocytes in a capillary (bolus flow). In this paper the effect of this motion on capillary resistance to flow, as well as on dissipative effects associated directly with the cells, are described. The resistance that would be associated with plasma in bolus flow at high Reynolds numbers (relative to a capillary value of 0.01) was studied in a model, in which air bubbles, separated by short segments of water, passed along a glass tube. The resistance to flow, especially with short boluses, was at least ten times greater than that associated with Poiseuille flow. In a second series of experiments at lower Reynolds numbers, a single bolus of liquid was forced by air pressure along a glass tube. In these latter experiments, which more closely simulate biological conditions, the mean resistance to flow was only 30 per cent greater than that associated with Poiseuille flow. In the final series of experiments human blood and plasma, diluted in acid-citrate dextrose (A.C.D.) in varying degrees, were forced through glass micropipettes of capillary dimensions. The mean apparent viscosity of whole blood was found to exceed that of plasma by only about 5 per cent, thus verifying a conjecture to this effect made by Fahraeus and Lindqvist in 1931.

Biophysical Phenomena↗
PubMed1962

The physics of blood flow in capillaries. III. The pressure required to deform erythrocytes in acid-citrate-dextrose.

Two previous communications dealt with the nature of the motion and the resistance to flow in capillary blood flow. In this final paper measurements are reported of the pressure required to force mammalian erythrocytes through pores having a diameter less than the cells. The cells, from fresh human or dog blood, were resuspended in acid citrate dextrose solutions. The final suspensions (about 1,000 times more dilute than whole blood) were immediately emptied into a millipore filter apparatus and the rate of filtration was measured. Filters having pore diameters of 5.0 and 3.0 microns were employed. The cellular concentration of samples of the original suspensions and of the filtrate was determined. It was observed that the rate of filtration decreased rapidly initially and then became constant. In the ;steady state' the cellular concentration of samples of the filtrate was found to be approximately equal to that of the original suspension. A simple theory is presented which adequately describes the flow of a suspension through such filters. It is concluded that mammalian erythrocytes, particularly human and dog cells, will pass steadily, without hemolysis, through pores 5.0 or 3.0 microns in diameter under pressures of 4 cm of water or less.

Animals↗