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RESEARCH PAPERS

J Biomech Eng. 1980;102(2):85-90. doi:10.1115/1.3138220.

A combined experimental and analytical approach was used to determine the history-dependent viscoelastic properties of normal articular cartilage in tension. Specimens along the surface split line direction, taken from the middle zone of articular cartilage were subjected to relaxation and cyclic tests. A quasi-linear viscoelastic theory proposed by Fung [31] was used in combination with the experimental results to determine the nonlinear viscoelastic properties and the elastic stress-strain relationship of normal articular cartilage.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):91-97. doi:10.1115/1.3138221.

A thermodynamic model is presented to describe the combined freezing and thawing process for living cells. Continuous changes in the cell volume are predicted according to the thermal protocol imposed on the system. Experimental verification of the model is sought by monitoring continuously the volume of cells as frozen on a cryomicroscope. The volumes of individual cells are measured from sequential photomicrographs by a computerized image analysis technique. The model and experimental data are in quite close agreement for the freezing process, but upon thawing the experimentally measured volumes consistently increased much more rapidly than predicted by the model. The model can be made to conform to the data by accounting for a substantial influx of electrolyte to the cell at subfreezing temperatures.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):98-102. doi:10.1115/1.3138222.

The effect of hypercholesterolemia on the transverse wall properties of the upper descending thoracic aorta was studied in canines. Hypothyroid animals were fed a free diet supplemented with cholesterol, propylthiouracil, and saturated fat (lard) for 11 mo. The mechanical properties of the wall showed marked changes following experimental pathology. The failure stress, failure elongation, and energy to failure decreased following hypercholesterolemia. The tensile response was bilinear in both the pathological and control tissues. In the initial region, which is controlled by elastic fibers, the response was left unchanged by the experimental pathology. In the secondary region, which is controlled by stretching of the collagen fibers, the intercept with the strain axis and the slope were decreased by the pathology. This indicates that there are changes in the strength-bearing collagen and its interaction with the amorphous matrix. However, no significant parallel histological changes were observed in the structure of collagen and elastic fibers. Although this phenomenon precedes the development of atherosclerotic plaques which are charateristic of a diagnosed human disease, the aortic wall is already “hardened” because of its reduced compliance resulting from the shift in the onset of secondary (collagenous) response.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):103-109. doi:10.1115/1.3138204.

Simulated frontal, lap-shoulder belted, barrier impact tests were performed using a Volvo sedan and General Motors Hybrid III anthropomorphic test dummy. Swedish field accident injury data for this vehicle are available from another published study. For the purpose of this program, the injuries were logically subdivided into four body regions: head, neck, thorax, and lower torso. The Hybrid III has instrumentation in each of these regions. The results of three replicated tests at barrier equivalent velocities of nominally 32 and 48 km/h are discussed in terms of the field injuries, thereby providing a basis for more intelligent interpretation of future Hybrid III test results.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):110-118. doi:10.1115/1.3138205.

Heat transfer to individual blood vessels has been investigated in three configurations: a single vessel, two vessels in counterflow, and a single vessel near the skin surface. For a single vessel the Graetz number is the controlling parameter. The arterioles, capillaries, and venules have very low Graetz numbers, Gz < 0.4, and act as perfect heat exchangers in which the blood quickly reaches the tissue temperature. The large arteries and veins with Graetz numbers over 103 have virtually no heat exchange with the tissue, and blood leaves them at near the entering temperature. Heat transfer between parallel vessels in counterflow is influenced most strongly by the relative distance of separation and by the mass transferred from the artery to the vein along the length. These two effects are of the same order of magnitude, whereas the film coefficients in the blood flow are of significant but lesser importance. The effect of a blood vessel on the temperature distribution of the skin directly above it and on the heat transfer to the environment increases with decreasing depth-to-radius ratio and decreasing Biot number based on radius. The absolute magnitude of these effects is independent of other linear effects, such as internal heat generation or a superimposed one-dimensional heat flux.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):118. doi:10.1115/1.3138206.
Abstract
Topics: Biomedicine
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):119-123. doi:10.1115/1.3138207.

Propagation of small amplitude harmonic waves through a viscous incompressible fluid contained in an initially stressed elastic cylindrical tube is considered as a model of the pulse wave propagation in arteries. The nonlinearity and orthotropy of the vascular material is taken into account. Muscular activity is introduced by means of an “active” tension in circumferential direction of the vessel. The frequency equation is obtained and it is solved numerically for the parameters of a human abdominal aorta. Conclusions concerning pressure-dependence, age-dependence, and muscular activation-dependence of the wave characteristics are drawn which are in accord with available experimental data.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):124-136. doi:10.1115/1.3138208.

The geometry of the proposed model of the parenchyma of a mammalian lung reproduces a cluster of alveoli arranged around a lowest-level air duct. The alveolar walls are assumed to be nonlinear elastic membranes, whose properties are described in terms of a strain energy function which reflects the hardening character of the stress-strain curve. The effect of the surfactant is included in terms of a variable (area-dependent) surface tension. Analyses of various mechanical processes in the parenchyma are performed with the aid of the finite element method, with the geometric and physical nonlinearities of the problem taken into account.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):137-140. doi:10.1115/1.3138209.

The relative functions of spinal elements in resisting P-A shear stress are determined from measurements of force and displacement. The response of intact, enucleate and degenerate disks are presented, as well as stress-strain characteristics of the intervertebral disk and the roles of the articular facets and the nucleus pulposus.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):141-146. doi:10.1115/1.3138210.

A flexible 0. 4-mm-dia pH probe potentially suitable for physiological use has been developed. It is based on the concept of utilizing two single plastic fiber optic strands to illuminate and remotely sense the color change of a dye indicator contained within an acutely implanted sealed cellulosic hollow fiber permeable to hydrogen ions. A supporting electronic module provides tungsten filament illumination, light sensing with a photodiode/operational amplifier, analog and digital circuitry to provide appropriate signal averaging and processing, and a mechanical assembly to enable the optical density measurements to be made both at 560 nm and, for normalization purposes, in the red. Over the physiological pH range from 7.0 to 7.4, the fiber optic probe agrees with a standard glass pH electrode to within 0.01 pH units in buffer solutions, to within 0.017 pH units in heparinized dog blood in vitro, and it has performed successfully while implanted in the jugular vein of a sheep.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):147-150. doi:10.1115/1.3138211.

The maximal extent of disk opening of the Lillehei-Kaster and Björk-Shiley aortic disk prosthetic valves was evaluated in vitro in relation to the characteristics of flow across the valve and valve orientation within the test section. The maximal opening angle of the disk of both types of prostheses was related to the mean systolic ejection rate, cardiac output, and maximal instantaneous aortic flow. Full opening of all valves occurred throughout the entire hydrodynamic range tested when the orientation of the valve was such that the disk opened in the direction of gravitational forces. However, when the valve was oriented to open against the direction of gravitational forces, less than full opening was observed at low flow rates. At such low rates of flow, the extent of opening was also dependent upon valve size. These studies indicate that full opening of the Lillehei-Kaster and Björk-Shiley disk valves appears to be affected by the orientation of the valve relative to gravitational forces. When less than full opening occurs, it is associated with abnormally low mean systolic ejection rates and low levels of cardiac output and aortic flow. Therefore, irrespective of valve orientation, less than maximal opening with normal flow may indicate a mechanical impediment to opening.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):151-154. doi:10.1115/1.3138212.

Fresh whole blood has been subjected to transient rarefactions of approximately 50 μs duration. In this loading regime blood is found to be capable of supporting propagating rarefactions of up to 3.71 MN/m2 . The character of the propagation and failure is similar to that exhibited by water.

Topics: Blood , Failure , Water
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):155-161. doi:10.1115/1.3138213.

Astronauts utilize water cooling in a liquid-cooled garment to maintain thermal comfort during extravehicular activities (EVA’s). In the Apollo and Skylab Programs, manual control of the cooling water was a necessary operation to ensure proper control of body heat storage for the EVA crewman. The development of an automatic thermal control system would be a valuable asset to the conduct of EVA, relieving the crewman of a task that can interfere with his EVA objectives. An analytical model of human thermoregulation was used to develop the equations governing the operation of such an automatic controller. A series of tests verified the feasibiliy of a controller utilizing only a measurement of the difference in coolant temperature into and out of the astronaut’s liquid-cooled garment and an estimate of environmental heat loss to maintain the proper crewman thermal balance. Three test subjects performed over a wide range of metabolic rates, and the crewman heat balance was maintained well within allowable medical limits. This study demonstrates the use of a mathematical model to generate previously unknown physiological relationships between human thermal comfort and liquid cooled garment performance. In so doing, it quantitates physiological parameters that are difficult to relate directly by experiment. Index terms: body temperature regulation, space suit cooling, temperature control, human thermoregulation.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):162-169. doi:10.1115/1.3138217.

A general, one-dimensional steady-state analysis of the thermal behavior of biological tissues is presented. The three major geometries, i.e., rectangular, cylindrical and spherical, are considered along with boundary conditions of the general type. It is shown that transport of heat inside the tissue may be dominated by conduction, convection by blood perfusion, metabolism or a combination thereof. The role of each of these mechanisms is presented by suitable dimensionless parameters expressed in terms of tissue physical properties. The order of magnitude of these parameters indicates the relative importance of the various mechanisms on the transport of heat inside the tissue. It is further shown that in areas where convection by blood perfusion is dominant, tissue temperatures are almost uniform except for narrow regions near the boundaries. The occurrence of maximum temperatures inside the tissue is also studied along with the combinations of blood perfusion and heating rates which would insure that certain predetermined values are not exceeded. This work also demonstrates that the amount of heat which may be convected into the tissue by the circulatory system depends on the heating rate and the boundary conditions, as well as the blood perfusion rate. This quantity is shown to reach a finite limit as the blood perfusion rate becomes very high.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):170-177. doi:10.1115/1.3138218.

When synthesizing the available data of vessel elasticity of mammalian lung from the literature, the lack of data in the intermediate range of vessel sizes becomes evident. In an effort to fill this gap, the distensibility of pulmonary arteries of cats, in the range of 100–1600 μm diameter was studied as a function of the perfusion pressure. The resulting percentage changes in vessel diameter (D) were expressed as polynomials of “transmural” pressure, which is taken to be the difference between the perfusion pressure and the pleural pressure, pa − pPL , in the form

D/Do = 1 + α (pa − pPL) − β (pa − pPL)2.
where Do is the value of D when pa = pPL , and α and β are constants. Our results show that for vessels whose diameters Do are in the range of 100–200 μ;m, the mean values of D/Do are represented by α = 2.02 percent per cm H2 O or 0.202 (KPa)−1 , β = 0.046 percent per (cm H2 O)2 or 0.046 (KPa)−2 . For vessels with diameter Do greater than 200 μm, the pressure-diameter relationship is linear in the ranges tested, so that β = 0. The values of the compliance constant α (slopes of the curves) for vessels in the diameter (Do ) ranges 200–300 μm, 300–400 μm, 400–600 μm, 600–1000 μm, and 1000–1600 μm are, respectively, 0.93, 0.78, 0.70, 1.10, and 2.61 percent per cm H2 O, (i.e., these numbers × 10−1 (KPa)−1 ). Thus the compliance of the pulmonary arteries appears to be the smallest in the diameter range 400–600 μm; and that the compliance of vessels in the 1000–1600 μm range is more than twice that of the smaller vessels.

Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J Biomech Eng. 1980;102(2):161. doi:10.1115/1.3138214.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):161. doi:10.1115/1.3138215.
FREE TO VIEW
Abstract
Topics: Biomaterials
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1980;102(2):161. doi:10.1115/1.3138216.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J Biomech Eng. 1980;102(2):178-180. doi:10.1115/1.3138219.

Bovine bone specimens loaded in torsion for periods of time exceeding one month exhibit pronounced time-dependent effects. The final strain exceeded the initial strain by a factor of more than four in some cases. Creep failure was observed in two cases. The effects are not attributable to prolonged immersion in Ringer’s solution.

Topics: Creep , Bone , Failure , Torsion
Commentary by Dr. Valentin Fuster

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