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RESEARCH PAPERS

J Biomech Eng. 1978;100(2):57-66. doi:10.1115/1.3426193.

We put forward an efficient method for computing the input impedance of complex asymmetrically branching duct networks, and apply this method to simulation of the dynamic response of the lungs of normal adult humans in the frequency range extending to 10,000 Hz. The results indicate that the response of comparable symmetric and asymmetric branching networks differ at high frequency (> 2 kHz in air), and that the airway wall response is an important factor in determining system damping and resonant frequencies.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1978;100(2):67-71. doi:10.1115/1.3426194.

We describe a transient forced oscillation method for measurement of the input impedance of excised canine lungs. The technique employs a single uncalibrated data channel to record short duration pressure transients incident upon and reflected from the airway opening, from which the input impedance up to 10,000 Hz is computed using lossy transmission line theory. Data acquisition time is less than 10 ms. The lung responses exhibit numerous resonances and anti-resonances below 10,000 Hz, and exhibit lung volume dependence. The branching structure of the airways and response of the airway walls appear to be important factors in the lung response.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1978;100(2):72-78. doi:10.1115/1.3426195.

The individual muscle forces in the leg during human walking are unknown, because of a greater number of muscles when compared to degrees of freedom at the joints. The muscle force-joint torque equations can be solved, however, using optimization techniques. A linear programming solution of these equations applied at discrete, time-independent steps in the walking cycle using dynamic joint torque data is presented. The use of this technique, although capable of providing unique solutions, gives questionable muscle force histories when compared to electromyographic data. The reasons for the lack of confidence in the solution are found in the inherent limitations imposed by the linear programming algorithm and in the simplistic treatment of the muscles as tensile force sources rather than complex mechanochemical transducers. The definition of a physiologically rationalized optimal criterion requires both a global optimization approach and more complete modelling of the system.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1978;100(2):79-87. doi:10.1115/1.3426196.

This paper investigates the deformations and stresses in the buttocks of a person when he sits on a cushion. The study is motivated by the need for a better understanding of the design of wheelchair cushions and the prevention of decubitus ulcers. The finite element method is used on an axisymmetric model. Surface pressure distribution, surface friction, hydrostatic pressures and von Mises stresses are obtained. The finite element model reveals the three-dimensional state of stress at all internal locations for a typical human body. Thus the study complements the experimental measurements performed by many physicians and bioengineers.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1978;100(2):88-92. doi:10.1115/1.3426197.

Optimization solutions to the indeterminate distribution problem of determining muscle forces are discussed. A method of predicting muscle force during joint function is presented which encourages the prediction of synergistic muscle action with physiologically reasonable individual muscle forces. The method uses limits on muscle strength that are a set portion of the lowest muscle strength that will permit a solution at the particular joint moment. The method is shown to correlate well with recorded EMG activity.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1978;100(2):93-98. doi:10.1115/1.3426198.

Growth of the human face occurs in unequal amounts at various areas. This results in relative motion of the upper and lower jaws. Relative motion creates changes in facial appearance and dental occlusion. Orthodontic treatment seeks to therapeutically use or alter this relative motion. Most existing orthodontic analyses have interpreted facial growth as translatory in nature. The analysis introduced in this paper is based on applying kinematic fundamentals—that is, poles of rotation and fixed and moving centrodes—as a tool for more accurately analyzing jaw motion. Reliable data is utilized and computer graphics routines are employed to help visualize output data. Several alternative approaches for analyzing relative motion due to jaw growth are presented here indicating the development of this research.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1978;100(2):99-104. doi:10.1115/1.3426199.

The amount of local tissue deformation at the equatorial region of the left ventricle is quantitated by the ratio of the instantaneous cross-sectional area of a tissue element to the cross-sectional area at end-diastole. The area ratio, AR, was computed for the circumferential and longitudinal, apex to base, direction throughout the cardiac cycle from catheterization and cineangiographic data on 36 patients. The patients were divided into four groups: normal left ventricualr function—15, compensated volume overload—6, decompensated volume overload—9, and congestive cardiomyopathy—6. The peak longitudinal area ratio was elevated in the compensated group (P <0.001) and not statistically significant from normal in the decompensated group. A larger fraction of the cardiac cycle was required to reach the peak longitudinal (p <0.01) and circumferential (p <0.05) area ratio in the compensated group. The volume overload compensatory process apparently involves a change in the relative magnitude and timing of tissue deformation. The hypo-contractile ventricle was characterized by a reduction in the sum of the logitudinal and circumferential area ratios, which for all six patients in the congestive cardiomyopathy group, had a value less than any of the other thirty patients.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

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