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An electromechanical servo-controlled device has been developed. This device can be used to test the mechanical behavior of a wide variety of biological soft tissues. Control and execution of material testing procedures such as stress-strain, vibration, relaxation, creep etc. can be performed by manual operation of the device or by interfacing it with a laboratory type minicomputer. Experiments on excitable tissues such as muscle can also be executed. The design details and system performance are discussed.

A theoretical analysis provides a means to estimate the blood flow into a branch from a measurement of the pressure drop from the main stream into the branch, and the ratio of the width of the branch to that of the main vessel. It shows that in the ordinary circumstance in which the diameter of the branch is one-half that of the trunk or smaller, a large drop of pressure from the main stream to the branch is expected. Such a pressure drop would be particularly accentuated if there is a local narrowing in the branch such as a sphincter.

The analysis of G. I. Taylor on the dispersion of solutes in a circular cylindrical tube is extended to the case of flow in a channel bounded by porous layers. Creeping flow in the channel and the porous layers stimulates the blood flow in the alveolar sheets of the lung. Overall perturbation on the longitudinal dispersion due to the porous layers is evaluated. It is shown that the mean coefficient of apparent diffusivity is smaller in a channel bounded by porous layers than that in a channel with impermeable walls for the case that the channel walls are permeable to solvent but not to tracer. For the case that channel walls are permeable to both solvent and tracer, the mean coefficient of apparent diffusivity is nearly the same as that of a channel with impermeable walls.

The tracer (indicator-dilution) technique is often used to measure the volume of interstitial water in the lung tissue. The basic hypotheses required for the validity of the formula: volume = flow × (mean transit time) are reviewed. One of the conditions is that, at a steady state, the average concentration of the tracer over the entire system be equal to the concentration at the sampling site. It is shown that if a tracer (such as THO) is permeable through the membrane that separates the blood from the tissue space, which in turn is limited by an impermeable wall, then, at a steady state, the concentration of that tracer is uniform in both compartments. If a tracer is confined to the vascular space by a semipermeable membrane, then its concentration is nonuniform, but the average value meets the requirement of the tracer-volume formula.

To determine the shear force acting on a white blood cell sticking to the endothelium of a blood vessel, the flow field about a single white blood cell in a venule was determined by hign-speed motion picture photomicrography. The force acting on the white blood cell was then calculated according to the principles of fluid mechanics. In this paper, the calculation was made using an experimentally determined dimensionless shear force coefficient obtained from a kinematically and dynamically similar model. The large physical model of the hemodynamic system could be easily instrumented, and the shear force acting on the model cell and the flow field around it were measured. The data were then used to calculate a shear force coefficient. On the basis of dynamic similarity, this shear force coefficient was applied to the white blood cell in the venule. The shear force coefficient was strongly influenced by the hematocrit, so in vivo hematocrits were measured from electron micrographs. It was found that in the venules of the rabbit omentum a white blood cell sticking to the endothelial wall was subjected to a shear force in the range of 4 times 10--5 dynes to 234 times 10--5 dynes; the exact value depended on the size and motion of the white blood cell, the size of the blood vessel, the velocity of the blood flow, and the local hematocrit, which varied between 20% and 40% in venules of about 40 mum in diameter. The contact area between the white blood cell and the endothelial cell was estimated, and the shear stress was found to range between 50 dynes/cm-2 and 1060 dynes/cm-2. The normal stress of interaction between the white blood cell and the endothelium had a maximum value that was of the same order of magnitude as the shear stress. The accumulated relative error of the experimental procedure was about 49%. The instantaneous shear force was a random function of time because of random fluctuations of the hematocrit.

The stress-strain relationship of the lung parenchymal tissue depends on the alveolar geometry, the elastic property of the alveolar walls (sheets, septa) and the surface tension characteristics. This nonlinear relationship is derived in the present paper.

The smallest microscopic blood vessels in the human lung are organized into sheet-like networks. These sheets form the walls of the 300 million alveoli in which air flows due to breathing. Each sheet may be idealized into a channel bounded by two thin layers of porous media. This paper is concerned with the blood flow in the channel and water movement in the porous wall. The Reynolds number in the lung alveolar sheets is very low, so creeping flow is assumed. Analytical and numerical results on the velocity and pressure distribution in the porous layers are presented.

A formulation of the finite-element method for both two-dimensional and axisymmetric slow viscous flow is presented. Its application to flow of large particles in a channel or a circular cylindrical tube is discussed. The particles are assumed to be disk-shaped and are disposed axisymmetrically in the tube. The velocity profiles, the pressure gradient, and the shear stress on the wall are determined as functions of kinematic parameters. The conditions are selected to represent an idealization of the motion of red blood cells and plasma in capillary blood vessels.

With an objective to understand arteriosclerosis, the blood flow in a circular cylindrical tube with a local constriction is analyzed. Numerical results are presented for the streamlines and the distributions of velocity, pressure, vorticity, and shear stress in the Reynolds number range 0–25. These results have applications to other fluid-mechanical problems such as gauges for velocity measurements, etc.

The major political purge taking place in Communist China has now encompassed several top leaders within the Party and military hierarchy. Initiated within the context of a struggle against "bourgeois ideology" and "revisionism," the purge is essentially a fierce power rivalry among the potential heirs of Mao Tse-tung. Although the tide of struggle is still rising, available data indicates that with the removal of Mayor Peng Chen as First Secretary of the Peking City Party Committee, the ouster of Chief of Staff Lo Jui-ch'ing and the mountains eminence of Marshal Lin Piao, the power structure of the highest echelons in Peking has already undergone a dramatic reorganization. The outcome is decisive to the issues of Mao's succession, but may have little effect on foreign policy. The Historical Background In the 17 years it has controlled the Mainland, the ruling group within the Chinese Communist Party (CCP) has ostensibly displayed a high degree of stability at its inner core. In fact, however, factional strife has been a continuing undercurrent of Party life. A major purge, resulting in the removal of one or two powerful leaders within the Party hierarchy, has occurred on the average of once every six years. The first power struggle in the post-1949 period broke out in early 1954. Kao Kang, the influential Party Secretary in the Manchurian region and Jao Shu-shih, an ambitious leader in the East China Region, were the chief contenders against the established leadership. Although the full story of their challenge to Mao's authority remains undisclosed, scattered data and official documents indicate that their main opponents were Liu Shao-ch'i, Chou En-lai and Teng Hsiao-ping. Mao himself appears to have played a "balancing" role between the two factions.1 In 1930, Kao and another veteran Communist leader, Liu Chih-tan, established the first Communist government in Northwest China, and led guerrilla operations in the Shensi-Kansu-Ninghsia Border region during Chiang Kai-shek's "bandit suppression campaigns." This region became Mao's base at the end of the "Long March" from South China in the mid1930's. In 1948, Kao Kang, together with Lin Piao and Peng Chen, two other major figures in the current jostle, led the Red Army into Manchuria.

The so-called Maxwell and Voigt models of muscles are shown to be equivalent, so that one is convertible into the other, if the series elasticity is not assumed to be absolutely independent of the muscle length. Different types of muscle-elasticity-modulus-versus-tension data are interpreted as yielding information about the dependence of the series elasticity on muscle length.

The micromechanics of fiber composite columns under compression is investigated theoretically. The model is based on the assumption that the fiber buckles inside the matrix. In the postbuckling range the fiber is considered as a beam on elastic foundation. The value of the foundation constant is evaluated for a cylindrical fiber. It is shown that prebuckling separation between fiber and matrix affects the critical buckling load and the postbuckling behavior of the fiber.Computations show that in the linear elastic range of common materials the buckling of the fiber does not affect significantly the overall mechanical behavior of the composite.

The features of the dynamics of capillary blood flow are analyzed and compared with those of the large blood vessels. The physical causes of the constantly varying unsteady flow are attributed to the random statistical distribution of red blood cell sizes, blood vessel geometry, and the multiloop system. The influence of the capillary system topology and compliance are discussed. Among other things, it is shown theoretically that (1), at a branching point of a capillary blood vessel the branch with a faster stream gets most of the red blood cells, thus explaining the extreme nonuniformity in hematocrit distribution in the capillaries, and (2), in a contracting muscle bundle in which capillaries are parallel to the muscle fibers, the percentage reduction of resistance to blood flow is three times the percentage reduction in length of the muscle bundle if active control by sphincter is absent.

A 10–20-fold improvement of resolution of optical microscopic dimensional determination of the red blood cell (RBC) over the current method is demonstrated. Results on cell diameter, maximum and minimum thickness, surface area, volume, index of refraction, as well as the cross-sectional shape of the red cells from one healthy person are reported as functions of the tonicity of the environmental solutions.

Explicit results concerning blood flow, alveolar blood volume, regional differences, and transit time distribution are derived from the sheet-flow theory and compared with experimental evidence available in the literature. A general consistency is indicated. The theory exhibits in a simple form the effects on flow of the arterial, alveolar, and venous pressures, the alveolar area, the mean path length between arterioles and venules, and the tension in the alveolar membrane, both elastic and surface tension; thus the theory provides a quantitative understanding of a large number of factors.

Methods of direct moment distribution applied to the rigid frame bridges with inclined legs are introduced in this paper. Formulas are derived for the anti-symmetric loading conditions. By using these formulas with the aid of the tables that are provided, a simplified method for influence line analysis is introduced.

The viscoelastic behaviour of the heart muscle (papillary muscle) in the passive unstimulated) state is studied by such methods as stress relaxation, creep, vibration and stress-strain testing. The tests are conducted on a newly developed electromechanical muscle testing device which is suitable for conducting active and passive tests on biological materials.

The machine-building industry is one of the newest branches of modern industry in China. Even as late as 1949, machinery accounted for only 2·7 per cent. of the nation's gross industrial output value. Since 1952, however, the industry has been given a high priority in development plans; in official statements, it is often referred to as “the basis for technological transformation of the national economy” and “the pillar of national defence.” By 1966 the relative share of machinery production in total gross industrial output value had increased to 12 per cent., making it one of the most dynamic branches of Chinese industry. A study of this industry not only serves as a gauge of China's potential economic and military strength but also illustrates the role of machine-building in the development of an under-developed economy.

The motion of a fluid created by the peristalsis is a problem of importance for a better understanding of some physiological transport phenomena. As a mathematical model of a rather unusual type of peristalsis involved in small intestines, the low Reynolds number flow of a Newtonian fluid in a circular cylindrical tube involving a series of traveling nodal constrictions, which is axisymmetric and infinitely sharp, is studied. The solution is posed in a series form. Two fundamental solutions are (1) a peristaltic carrying in which the motion of the fluid is created by the peristalsis without a net pressure gradient and (2) a peristaltic compression without net transport of the fluid. A general solution is obtained by a linear combination of these two fundamental solutions. Numerical calculation is carried out for a set of combinations of internode distances and depth of nodal constrictions. The distribution of the fluid velocity and the effectiveness of the peristaltic carrying and compression is discussed. The physiological significance of carrying, mixing and compression, accompanied by peristalsis is discussed.

An analysis of experimental data on the pulmonary alveolar sheet of the cat shows: (1) As far as elasticity in the plane of the sheet is concerned, the alveolar sheet may be regarded as uniform; the compliance of the posts is the same as that of the membranes. (2) Within a physiological range of positive transmural pressure, the mean thickness of the sheet varies linearly with the pressure. Also, the stress distribution in the alveolar-capillary membrane is nonuniform and nonisotropic. A theoretical sheet thickness-pressure relationship is derived in which the effect of stress resultants (sum of elastic stress and surface tension) is explicitly linked to the compliance of the sheet thickness. The sheet-flow theory then shows that average flow is very sensitive to the arteriole pressure. The flow per alveolar sheet is (1/ C ) ( h a 4 -- h v 4 ). Here h a and h v are equal to alveolar sheet thickness at the arteriole and venule, respectively. When art > alv , h a = h 0 + α( art - alv ), where art is the blood pressure in the sheet at the arteriole, alv is the gas pressure in the alveolus, α is the compliance constant for the sheet thickness, and h 0 is the thickness at Δ = 0. The constant C = 4µf Lα/ (SA), where µ is the coefficient of viscosity of blood, f is a friction parameter (on the order of 4, depending on the post geometry), L is the average length of the streamlines in the sheet, S is the vascular space-tissue ratio (on the order of 0.9), and A is the sheet area. Comparison of this formula with the experimental results of Roos et al., using h 0 and α values from Glazier et al., shows reasonable agreement.

The purpose of this study was to describe quantitatively the geometric organization of the pulmonary alveolar capillary bed. Conventional representation of these vessels as a tight network of circular cylindrical tubes (tube-flow model) was contrasted with a suggested alternative of a continuous sheet bounded on two sides by endothelium held apart by connective tissue and cellular posts (sheet-flow model). A vascular space-tissue ratio, VSTR, is defined as the ratio of vascular lumen volume to the circumscribing tissue volume. The VSTR was obtained by planimetric measurements. Formulas were developed to relate VSTR to the geometric models. Cat lungs were perfused in situ with liquid silicone elastomer at 25 mm Hg, and the liquid elastomer was allowed to catalyze at 15 or 25 mm Hg static pressure while the airway pressure was maintained at 10 cm H 2 O. After the silicone became solid, the lungs were fixed with formalin-steam, and morphometric analysis was carried out on photographs of frozen sections. The mean values of VSTR of each cat (six lobes) were 0.91 to 0.92, irrespective of intracapillary pressure. These data are consistent with a sheet-flow model. Sheet thickness then becomes a significant variable.

Heart muscle has been subjected to many experiments in many laboratories, and many reports are conflicting with each other. To unify the picture, resolve the conflicts, and describe the complex phenomenon in a compact set of equations, a mathematical formulation of the mechanical properties of the heart muscle is presented on the basis of the sliding-element theory and Hill's model. It is proposed that the tensile stress in the parallel and series elements. P and S respectively, can be represented in the form P=(P ∗ + β )e α (L−L ∗ ) − β S=(S ∗ +β)e α (η−η ∗ ) −β in which L is the muscle length, η is the extension of the series elastic element, α, α , β, β , P ∗ , L ∗ , S ∗ , η ∗ are physiological constants. The total tensile stress τ is the sum of tensile stresses in the parallel and series elements τ=P+S The length is related to the lengths of myosin M, actin C, the ‘insertion’ of actin and myosin Δ, and the series elastic element extension η by the relation L=(M+2C)−Δ+η The contractile element velocity seems best represented by the equation d Δ d t = b(L)sgn S 0 λ sin Π 2 t+t 0 t m −S n a(L)+S in which a(L), b(L) are functions of L, S0 is the peak tensile stress arrived in an isometric contraction at length L, n is an exponent whose value lies between 0 and 1·0, λ sin π (t 0 + t) 2t m is a function describing the active state of the contractile element, t is the time after stimulation, t0 is a phase shift related to the initiation of active state at stimulation, tm is the half-time to peak activity, λ is an amplitude factor, sgn stands for the ± sign of the quantity S 0 λ sin [π. (t + t 0 ) 2t m ] − S . If the time to reach the peak isometric tension is tip, and if the level of activity at that instant is arbitrarily set as 1, then 1 λ = sin π 2 t ip +t 0 t m . If experiments are done in the neighborhood of maximum active state, then our equation reduces to the modified Hill's equation υ= d Δ d t = b[S 0 −S] n γS 0 +S The meaning and justification of these formulas are discussed in the paper. Isotonic and isometric processes, the active state and the relaxation law are analyzed. Necessary corrections to the procedures for measuring the elasticity of series element are discussed; and methods for determining the dependence of series elasticity on the length of the muscle are described.

To determine the degree to which the capillary blood vessels in vivo are supported by the elasticity of the surrounding tissue, a study was made of the elastic properties of the mesentery of the rabbit. A torsion test was made on a circular membrane of the avascular region of the mesentery, by applying a graded static torque and measuring the resulting deformation. The mesentery was found to have a modulus of rigidity in the same category as that of larger arteries and veins. It has a nonlinear stress-strain relationship with a tendency to harden at larger strains. In torsion experiments, the shear modulus G can be reduced to the following form G = µ+c 2 |τ| Where c 2 is a constant and |τ| is the absolute value of the shear stress. The constant µ depends on the initial tension in the membrane. For the mesentery specimens, µ ranges from 215 to 1900 gm/cm 2 , whereas the nondimensional constant c 2 has an average value of 8.23 with a standard deviation of 2.1. The hypothesis is advanced that the medium in which the capillaries of the mesentery are embedded is a gel and the capillary in effect is a tunnel in this gel. Such a hypothesis could explain the apparent rigidity of the blood capillaries.

Peristaltic pumping in a circular cylindrical tube is analyzed. The problem is a viscous fluid flow induced by an axisymmetric traveling sinusoidal wave of moderate amplitude imposed on the wall of a flexible tube. A perturbation method of solution is sought. The amplitude ratio (wave amplitude/tube radius) is chosen as a parameter. The nonlinear convective acceleration terms in the Navier-Stokes equation is retained. The governing equations are developed up to the second order in the amplitude ratio. The zeroth-order terms yield the classical Poiseuille flow, the first-order terms yield the Sommerfeld-Orr equation. If there is no pressure gradient in the absence of wall motion, the mean flow and mean pressure gradient (averaged over time) are both shown to be proportional to the square of the amplitude ratio. Numerical results are obtained for this simple case by approximating a complicated group of products of Bessel functions by a polynomial. The results show that the mean axial velocity is dominated by two terms. One term corresponds to a parabolic profile which is due to the mean pressure gradient set up by the wall motion. The other term arises from satisfying the no-slip boundary condition at the wavy wall rather than at the mean position of the wall. In addition, there are perturbations arising from the convective acceleration. If the mean pressure gradient set up by the wall motion itself reaches a certain positive critical value, the velocity becomes zero on the axis. Values of the mean pressure gradient larger than the critical value will induce backward flow in the fluid. Values of the critical pressure gradient for several cases are presented.

In the past, macroscopic models of microcirculation have used either gas or liquid droplets or rigid particles to simulate red cells. These models cannot simulate the boundary conditions correctly at the cell wall. In the present paper we used flexible, thin-walled rubber models which were liquid-filled and geometrically similar to the human red blood cells. These cells were made to flow in a silicone fluid into circular cylindrical tubes with diameters comparable to that of the cell model. The Reynolds number based on the mean flow velocity and tube diameter was in the range of 4 × 10 −4 −4 × 10 −2 similar to the range encountered in microcirculation. Measurements were made of the entry condition, the entry length, the deformation pattern of the cells, the cell velocity and the mean flow velocity, the local pressure difference on the tube wall across the red cell, and the loss of pressure head due to a single red cell. All these quantities are functions of the ratio of the cell diameter D c to the tube diameter D T . A dimensional analysis yields functional forms with which experimental data are organized. The entry length is less than a cell diameter in all cases. The cells are severely deformed if D c D T > 0.98 . For larger D c D T , large buckling occurs at the trailing end of the cell at higher velocities of flow; the buckled cell shape resembles the familiar pattern seen in vivo . The cell velocity V c is related to the mean flow velocity V M by the relation V c = k ( V M − α ); the value of k increases as D c D T decreases. The disturbance to the pressure field due to a red cell is rather localized. Data on the resistance (pressure drop) to cell motion when D c D T = 1.36, 1.13, and 0.98 are presented as a function of the cell velocity.

Data on the nonlinear and inelastic mechanical properties of the canine aorta are presented. Major differences in the properties of the aorta from those of the mesentery, the skin, the muscle, etc, are pointed out. Mathematical representations of the experimental results are given. The relaxation spectrum is analyzed.