J Biomech Eng. 1977;99(2):57. doi:10.1115/1.3426273.
Topics: Medical devices
Commentary by Dr. Valentin Fuster


J Biomech Eng. 1977;99(2):58-64. doi:10.1115/1.3426274.

Despite its many advantages, thermography as a medical diagnostic tool has two basic limitations: 1 its images are indirect manifestations of interior thermal structure and hence do not yield explicit spatial information; 2 it is fundamentally two-dimensional. It is shown in the present paper that the three-dimensional variations of the temperature-dependent volume heat source, often called the blood perfusion term in the bio-heat equation, can be extracted from time dependent thermographic observations. On the other hand, spatial variations of the metabolic healing term cannot be determined from a similar procedure. Numerical experiments are performed to explore the sensitivity of the technique in determining the magnitude and location of a hypothetical lesion. Limitations of the technique in terms of the thermal penetration depth and signal-to-noise ratio are also examined.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(2):65-73. doi:10.1115/1.3426275.

An ideal, hydrated, nondilute pseudo-binary solution model is presented to describe the concentration polarization of solutes within cells during osmotic experiments. This model has been applied to the case of hyman erythrocytes being cooled at subzero temperatures. The concentration polarization of solutes within the RBC intracellular solution during freezing reveals the fact that the water transport process is significantly affected not only by the permeation of water through the cell membrane, but also by the diffusion of water within the intracellular medium.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(2):74-82. doi:10.1115/1.3426276.

The effects of the number of stenoses and the distance between consecutive stenoses on the total pressure drop across a series of noncritical stenoses with 50 percent area reduction were determined experimentally. The mean flow rate was varied to correspond to a Reynolds number range of 30–280 and both in vitro and in vivo measurements of the pressure drop were carried out. Flow visualization studies also were performed. The pressure drop across a series of stenoses was found to increase linearly with the number of stenoses. Comparable results were obtained from the steady and pulsatile flow in vitro experiments as well as from the in vivo experiments. The results indicate that the total effect of a series of noncritical stenoses is approximately equal to the sum of their individual effects and that the combined effect of a series of noncritical stenoses thus can be critical.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(2):83-90. doi:10.1115/1.3426277.

An all-pneumatic driving system is presented which provides close duplication of the Starling’s cardiac regulation function to an artificial left ventricle in mock circulation. The system, built from commercially available fluid operated devices, uses atrial pressure feedback to adjust the ventricle pumping air pressure, with the aid of a hydraulic/pneumatic pressure transducer developed especially for the application. A simple linear mathematical model for the physiological circulatory system is used to compare the simulated in-vivo performance of the system with Starling’s response of the natural left heart for different systemic resistances and compliances. The model is valid for output flows from 1 to 10 l/min and atrial pressure from 1 to 8 mmHg. It shows close agreement in ventricle output, arterial and atrial pressure changes between the artificial ventricle and the natural left heart for systemic resistance changes from about 5 × 104 to 5 × 105 kN-s/m5 and for typical venous to arterial compliance ratios of 24 to 37.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(2):91-97. doi:10.1115/1.3426278.

Numerical solutions for the steady axisymmetric flow through a disk-type prosthetic heart valve were obtained for Reynolds numbers from 20 to 1300. Stream function, vorticity, and shear and normal stress plots are presented. Comparison of the length of the separated flow region downstream of the disk with experimental data shows good agreement through Reynolds number 500. The maximum value of the shear stress occurred on the upstream corner of the disk. These detailed results clearly identify regions of very high shear and normal stresses (erythrocyte deformation or damage), regions of very low or very high shear stress at walls (atheromatous lesions), and the extent of separated or reverse flow regions (thrombosis).

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(2):98-103. doi:10.1115/1.3426279.

The stress response of soft biological tissues is investigated theoretically. The treatment follows the approach of Wu and Yao [1] and is now extended for a broad class of soft tissues. The theory accounts for the anisotropy due to the presence of fibers and also allows for the stretching of fibers under load. As an application of the theory, a precise form for the strain energy function is proposed. This form is then shown to describe the mechanical behavior of annulus fibrosus satisfactorily. The constants in the strain energy function have also been approximately determined from only a uniaxial tension test.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(2):104-109. doi:10.1115/1.3426270.

A new method for collecting in-vivo bone strain data in monkeys has been developed and tested. The method includes a system which consists of a new design of implantable strain transducer and its companion telemetry package. The transducer fits into a hole drilled in a monkey tibia and is threaded for subsequent bone ingrowth. The transducers and telemetry package are biocompatible for over 503 days. The telemetry package uses Pulse Interval Ratio Modulation (PIRM) to transmit strain information to receiving equipment located outside the animal housing cage.

Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(2):110-115. doi:10.1115/1.3426271.
Topics: Prostheses
Commentary by Dr. Valentin Fuster
J Biomech Eng. 1977;99(2):116-123. doi:10.1115/1.3426272.

In an urban environment, pedestrians account for a disproportionately high percentage of traffic fatalities in comparison with the percentage of accidents in which they are involved, according to the U. S. Department of Transportation. Rural statistics are equally bad. The problem of minimizing injuries to pedestrians when struck by a vehicle involves a large number of variables, such as the type and size of the vehicle, its speed at impact, the effects of braking and vehicle pitch, the geometry and stiffness of the vehicle exterior, and the size and age of the pedestrian. Obviously, it is impractical to study the effect of all of the variables experimentally. An alternate approach is the use of a validated mathematical model to simulate this impact event. This paper deals with the comparison of the results of a three-dimensional gross motion simulator with experimental data acquired under controlled laboratory conditions.

Commentary by Dr. Valentin Fuster

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