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Biomedical subjects

S Chien

Publications and source records attributed to S Chien.

At least 217 records · Page 12Linked to original sources
PubMed1985

Modeling of time-variant coupling between left ventricle and aorta in cardiac cycle.

An analytical model is developed to study the interaction between the left ventricle and vascular system. Ventricular pressure is expressed as a function of the chamber volume, volumetric strain rate, and the degree of activation. A three-element Wind-kessel model is employed to represent the hydraulic properties of the vascular system. Conditions of interaction between the left ventricle and the vascular system are formulated in mathematical terms. Numerical solutions are obtained for the mechanical events occurring during a cardiac cycle as a function of time. The time variations of aortic pressure and ventricular volume predicted by the model compare well with the experimental results of Sunagawa and co-workers [Am. J. Physiol. 243 (Heart Circ. Physiol. 12): H346-H350, 1982, and Am. J. Physiol. 245 (Heart Circ. Physiol. 14): H773-H780, 1983]. Furthermore, the application of the present model to the experimental data has allowed the derivation of the intrinsic contractility parameters in these experiments. The unique features of this analytical model are that 1) it provides the time-variant pressure and volume curves of the left ventricle in relation to the aorta, 2) it generates information on the effects of heart rate on these hemodynamic parameters, and 3) it allows the derivation of intrinsic contractility parameters from experimental data.

Animals↗
PubMed1985

Rheology of fetal and maternal blood.

Rheological parameters were measured in 10 pairs of mothers and newborns. Whole blood viscosity was similar despite a higher fetal hematocrit (47.0 +/- 5.1 versus 35.5 +/- 12.0%, mean +/- SD, p less than 0.05). When the hematocrit of the suspension of red cells in plasma was adjusted to 45%, the viscosity was significantly lower in the fetal blood over a wide range of shear rates (0.52-208 S-1). The main reason for the lower viscosity in the fetal blood was the lower plasma viscosity as compared to the maternal blood (1.08 +/- 0.05 versus 1.37 +/- 0.08 centipoise, p less than 0.05); this in turn was attributable to a lower total plasma protein concentration (4.74 +/- 0.71 versus 6.47 +/- 0.64 g/dl, p less than 0.05). All protein fractions were lower in the fetal plasma. The assessment of red cell deformability by filtration through polycarbonate sieves revealed that the resistance of a fetal red cell was three times higher than that of a maternal red cell in a 2.6-micron pore, but there was no significant difference in resistance for these red cells in 6.9-micron pores. This higher filtration resistance of fetal red cells through the small pores was mainly due to their large volume (115.4 +/- 10.8 versus 93.5 +/- 5.9 fl, p less than 0.001). Measurements on membrane-free hemoglobin solutions indicated that the internal viscosity of these two types of red cells was not different.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Viscosity↗
PubMed1985

Rapid deoxygenation of red cells and hemoglobin solution using hollow capillary fibers.

A newly designed capillary deoxygenator has been constructed by using microporous polypropylene hollow fibers sealed into an airtight plexiglass housing. Oxygenated red cell suspensions and hemoglobin solutions flowing through the hollow fibers were subjected to deoxygenation with a gas mixture composed of 95 percent N2 and 5 percent CO2 passed through the housing. At a given flow rate of the oxygenated fluid, the outgoing fluid pO2 varied directly with hematocrit and inversely with the residence time. With a deoxygenator composed of 144 parallel 100-micrometers fibers with an active length of 10 cm, 2 ml of blood at 10 percent hematocrit can be converted from arterial to venous pO2 in approximately 1 min. The design of this deoxygenator provides a method for rapid deoxygenation of blood without red cell membrane damage or hemolysis.

Blood Gas Analysis↗
PubMed1985

Effects of experimental hypotension on hemodynamics and renin secretion rate.

The effects of hypotension on systemic and renal hemodynamics, plasma renin activity (PRA), and renin secretion rate (RSR) were determined in dogs anesthetized with sodium pentobarbital plus chloralose. Renal blood flow (RBF) was determined with microspheres (15 micron) and with an electromagnetic flowmeter connected to an extra-corporeal circuit from the femoral artery to the renal artery. Hypotension was induced by nitroprusside infusion, which decreased peripheral resistance, and by hemorrhage, which reduced cardiac output. RSR increased in both forms of hypotension, but the increase following hemorrhage was greater than that after nitroprusside. Thus, when the mean arterial pressure (MAP) was reduced to 75 mmHg, RSR increased from 470 +/- 26 units/min to 990 +/- 12 units/min with nitroprusside and from 415 +/- 13 units/min to 1,509 +/- 21 units/min following hemorrhage. At MAP of 50 mmHg, RSR increased to 1,541 +/- 64 units/min with nitroprusside and to 2,254 +/- 98 units/min following hemorrhage. Nitroprusside increased renin secretion not only by an increase in sympathetic beta adrenergic activity through the baroreceptor reflex, but also by its direct vasolidatory effect in the renal circulation. In hemorrhagic hypotension, the increase in renin secretion was accompanied by renal vasoconstriction. The greater increase in RSR following hemorrhage than after nitroprusside at given levels of hypotension may be explained by a stronger beta adrenergic activation, the activation of prostaglandin and kallikrein systems, a lower microvascular pressure level, and/or smaller pulse pressure and lower sodium load in the macula densa. The comparison of renin secretion at the same degree of hypotension induced by different hemodynamic alterations serves to elucidate the mechanisms of renin secretion.

Animals↗
PubMed1984

Whole blood viscosity as a determinant of cardiac hypertrophy in systemic hypertension.

The relationships among blood pressure (BP), blood viscosity and echocardiographic left ventricular (LV) muscle mass were evaluated in 24 patients with essential hypertension and in 13 normotensive control subjects. LV mass was greater in the hypertensive patients than in the control subjects (225 +/- 69 vs 170 +/- 31 g, p less than 0.02) as was blood viscosity at a shear rate of 104 sec-1 (4.7 +/- 0.1 vs 4.3 +/- 0.2 cp, p less than 0.005). Among the hypertensive patients, LV mass was most closely related to viscosity at 104 sec-1 (r = 0.80, p less than 0.001), whereas only weak correlations were found between LV mass and systolic or diastolic BP (r = 0.45, p less than 0.05 for both). The 14 hypertensive patients with normal LV mass had viscosity similar to that in control subjects (4.5 +/- 0.3 vs 4.3 +/- 0.2 cp), whereas viscosity was consistently increased (5.0 +/- 0.4 cp, p less than 0.02) in hypertensive patients with LV hypertrophy. Thus, increased blood viscosity may be a determinant of or a response to hypertensive cardiac hypertrophy.

Adult↗
PubMed1984

Determination of the partition coefficient of 133xenon between oral tissues and blood in the dog.

Ostwald solubility coefficients for 133Xe in plasma (Sp), red blood cells (Sc), and selected oral tissue homogenates (St) obtained from the dog were determined at 4, 20, 27 and 37 degrees C by counting the 133Xe activity of the air phase and the sample (liquid, red cells or tissue) in the same tube following equilibration. The partition coefficient for xenon (lambda, in ml/g) between red cells and plasma (lambda cp) and that between tissues and plasma (lambda tp) were calculated from the measured Sp, Sc and St. The tissue-blood partition coefficients (lambda tb) of oral tissues for 133Xe were then calculated using lambda cp, lambda tp and the haematocrit value. The calculated values of lambda tb at 37 degrees C and 50 per cent haematocrit were 0.650 for the pulp, 0.674 for the tongue, 0.828 for the submandibular gland and 0.881 for the gingiva of the dog. lambda cp increased and lambda tp decreased as the temperature was reduced from 37 to 4 degrees C.

Animals↗
PubMed1984

Arteriovenous distribution of hemodynamic parameters in the rat dental pulp.

A systematic investigation of the distribution of red cell velocity throughout the hierachy of the rat pulp microvascular network was performed. Luminal diameters (D) of microvessels ranging in size from 8 to 72 micron were measured in situ by an electronic video image shearing technique. Intravascular red cell velocities (Vrbc) were simultaneously measured by a variation of the "two-slit" photometric technique and intravascular volumetric flow rates (Q) were calculated. It was found that red cell velocity decreased monotonically throughout successive arteriolar divisions to attain capillary values of 1/10 those in the feeding arterioles. A slight rise in Vrbc was found in the venous confluences, however, a maximum value of Vrbc of only 1/5 large arteriolar values was evident in the large collecting venules. In contrast, the calculated volumetric flow rate distribution was found to be nearly parabolic from arterioles (40 micron) and their paired (72 micron) collecting venules. This behavior was attributed to the dominance of microvessel cross-sectional areas as a determinant of Q.

Animals↗
PubMed1984

Quantitative studies on the influence of leukocytes on the vascular resistance in a skeletal muscle preparation.

The effects of leukocytes on vascular resistance and capillary filtration coefficient (CFC) of the maximally vasodilated vascular bed of rat hindquarters were measured using servocontrolled isogravimetry . After determination of the pre- and postcapillary resistances and CFC with a cell-free perfusate, a leukocyte bolus was introduced (0.5 to 9 X 10(6) cells/100 g tissue). Experiments were performed at three flows: 0.7-0.9, 1.4-1.6, and 2.4-3.7 ml/(min X 100 g tissue). Changes in vascular resistance were calculated from continuous pressure-flow recordings during a 10-min period, followed by a CFC measurement. Leukocytes were counted in the effluent for calculation of the number of cells remaining in the vascular bed. Leukocyte infusion caused a transient increase of the precapillary resistance (Ra) by as much as 72% after infusion of 9 X 10(6) cells/100 g tissue at 0.7-0.9 ml/(min X 100 g tissue). After the initial peak the Ra usually fell to a lower, constant, level, but was still clearly elevated (maximum 23%) at the low flows of 0.7-0.9 and 1.4-1.6 ml/(min X 100 g tissue). This sustained increase of Ra was positively related to the number of cells remaining in the vasculature. At high flows of 2.4-3.7 ml/(min X 100 g tissue) the Ra increase was very small, irrespective of the number of cells infused or remaining in the vascular bed. These findings, together with the fact that CFC decreased proportionally to the sustained increase of Ra, indicate that the effect of leukocytes on Ra was due to a pressure-dependent occlusion of the microvasculature.

Animals↗
PubMed1984

Effect of colchicine on viscoelastic properties of neutrophils.

The effect of colchicine (15-60 micrograms/ml) on the viscoelastic properties of human neutrophils was studied by the micropipette technique. The small deformation of the neutrophil in response to a step aspiration pressure was analyzed by using a three-element model in which an elastic element, K1, is in parallel with a Maxwell element composed of another elastic element, K2, in series with a viscous element, mu. Colchicine treatment of neutrophils caused decreases in K2 and mu without affecting K1. The results indicate that the integrity of the microtubules plays a significant role in providing the viscoelastic resistance (as represented by the Maxwell element in the model) of neutrophils to deforming stress.

Calcium↗
PubMed1984

Constitutive equations of erythrocyte membrane incorporating evolving preferred configuration.

The erythrocyte membrane is modeled as a two-dimensional viscoelastic continuum that evolves under the application of stress. The present analysis of the erythrocyte membrane is motivated by the recent development of knowledge about its molecular structure. The constitutive equations proposed in the present analysis explain in a consistent manner the data on both the deformation and recovery phases of the micropipette experiment. The rheological equations of the present study are applied in a later section to the analysis of a plane membrane deformation that is quantitatively similar to the tank-treading motion of the erythrocytes in a shear field. The computations yield useful information on how the membrane viscosity becomes a more dominant feature in tank-treading motion. The material constants appearing in the proposed constitutive equations may be useful indications of the biochemical state of the membrane in health and disease.

Elasticity↗
PubMed1984

Estimation of viscous dissipation inside an erythrocyte during aspirational entry into a micropipette.

Viscous dissipation inside the erythrocyte during its aspirational entry into a micropipette is analyzed. The motion of the intracellular fluid is approximated by a flow into the micropipette orifice from a half space (the portion of the erythrocyte outside the micropipette). The stream function and intracellular pressure (p) in the half space are obtained as a function of radial and axial positions near the orifice. Solution of the boundary value problem for a uniform stream entering a circular hole gives p = 2 eta HQ/pi R3p, where eta H is the intracellular viscosity, Q is the total discharge, and Rp is the pipette radius. The results indicate that the moving erythrocyte membrane helps to drive the intracellular fluid into the orifice. For normal erythrocytes, p is only approximately 0.5% of the total aspiration pressure (delta P). The contribution of p to delta P, however, may become significant when there is a large increase in eta H due to a markedly elevated intracellular hemoglobin concentration or an alteration of the physical state of hemoglobin.

Animals↗
PubMed1984

Segmental and total microvascular resistances during hemorrhagic hypotension in rabbit omentum.

Single input-output microvascular modules in the rabbit omentum were studied to quantitate total modular resistance (RT) and the changes in resistance of successive serial segments (Rseg) during hemorrhagic hypotension (55 mmHg for 1 h). RT was calculated from the pressure drop between input and output vessels and the total flow through the module. Changes in Rseg were estimated from alterations in single microvessel hindrance (1/diam4) for selected microvessels within a module together with a correction for flow redistribution within each segment derived from changes in the proportion of total flow. Mean RT increased to 2.1 times control within the first 10 min of systemic hypotension and gradually declined over 1 h. Response of Rseg varied in different generations of microvessels (arterioles and venules subdivided by size). Rseg for arterioles and venules less than 30 microns, but not that for arterioles and venules greater than 30 microns, showed comparable or greater changes than RT. Calculated differences between RT and the summed Rseg of measured segments suggest that the unmeasured Rseg in capillaries and blood rheological parameters may have significantly influenced changes in RT during hemorrhagic hypotension.

Animals↗
PubMed1984

Effects of local anesthetics on pulpal blood flow in dogs.

Effects of 2% lidocaine with epinephrine (1:100,000) administered by the various local anesthetic techniques--i.e., infiltration, mandibular block, and intraseptal injection--on pulpal blood flow in dogs were determined using the 15 microns radioisotope-labeled microsphere injection method. The pulpal blood flow decreased significantly with all three techniques; however, the most drastic reduction occurred in the molar teeth with the intraseptal injection. When 2% lidocaine without epinephrine was used in the intraseptal injection, pulpal blood flow increased significantly.

Anesthesia, Dental↗
PubMed1984

Effects of arterial pressure on endothelial transport of macromolecules.

The effects of variations in transmural pressure over a range of 0 to 200 mmHg on transendothelial transport of macromolecules were studied in the canine common carotid artery. The uptake of 125I-albumin per unit artery weight increased with rising pressure. There was no significant difference in albumin permeability per unit luminal surface area between 0 and 100 mmHg, but permeability nearly doubled when pressure was raised to 200 mmHg. The contribution of an increased rate of transendothelial vesicle diffusion, as evaluated from the experimental determination of the ratio of attached-to-free vesicles and theoretical modeling, was found to be negligible. The reduction in transendothelial vesicle diffusion distance due to pressure-induced thinning of the peripheral zone contributes to a 25% increase in permeability. With the use of colloidal Ag and Au of various sizes, vesicle loading of particles with diameters greater than or equal to 15 nm was found to be severely restricted at transmural pressure less than or equal to 100 mmHg, but it was significantly enhanced at 200 mmHg, when particles as large as 25 nm became detectable in endothelial vesicles and subendothelial space. This hypertension-induced increase in macromolecular transport across the endothelium may cause an overloading of the arterial wall with low-density lipoproteins and play a significant role in atherogenesis.

Animals↗
PubMed1984

Deformation of leukocytes on a hematological blood film.

Human leukocytes in a blood film exhibit a significantly larger diameter than in the circulation. This is due to the fact that white cells are highly deformed during preparation of a blood film. Instead of having the usual spherical shape, the cells are compressed to "pancake" forms with a thickness of about 1 micron. Hematological investigation is usually performed on these compressed cells, but in the circulation they are not observed. The deformation of the cells on a blood film is due to compression by the glass edge used to spread the blood. After deformation leukocytes do not have enough time to recover since the blood film usually dries in a shorter period than is needed for cell recovery. The shape and size of the leukocyte on the blood film is not only determined by cell volume but also by the cell membrane area. This is shown for each kind of leukocyte by independent prediction of the pancake dimensions from previous measurements of cell volume and membrane area. Leukocytes which are strongly compressed during blood film preparation may exhibit mechanical damage with rupture of membranes.

Blood Specimen Collection↗
PubMed1984

Biorheological methods employing the Weissenberg rheogoniometer.

The theories and spatial concepts of Karl Weissenberg have been applied to the science of biorheology by employing the Weissenberg Rheogoniometer. Two main types of experimental methods have been used for the characterization of the bulk shear properties of biorheological fluids: (A) In continuous laminar shearing motion, the tangential and normal components of stress are measured at a series of rates of shear. From these parameters, the apparent viscosity, an elastic modulus and a recoverable strain, are calculated as functions of the rate of shear. In this continuous shear experiment, the physical structure present in the material at any given rate of shear may be quite different from the material in its rest state or at other rates of shear. (B) In harmonic oscillatory motion, the material is subjected to a harmonic laminar shear about its rest state at a number of frequencies and small strain amplitudes. From these experiments the dynamic moduli of viscosity and elasticity are calculated. Preparations of biological materials, such as whole blood and systems of blood components, both in health and disease states, have been investigated using methods A and B, together with studies of surface layers of plasma proteins at interfaces.

Blood Physiological Phenomena↗