Prediction of ulcer formation on the skin.

The study reported in this paper investigates the feasibility of developing criteria for predicting the formation of ulcers on the human skin. Published data on the effect of pressure, friction, shear, oxygen tension, temperature, and exposure time on ulcer formation are analyzed, combined, and incorporated in developing the criteria. The results illustrate the relative contributions of the different parameters to the formation of ulcers. The developed relationships can provide guidelines for more rigorous clinical studies which would take into consideration the effect of age, sex, and physical conditions on the formation of ulcers at different sites of the body.

A generalized procedure for predicting bone mass regulation by mechanical strain.

Understanding of the mechanisms that control the modifications of the bone weight-bearing attitude in response to external load conditions attracted considerable attention from researchers in the biological, medical, and radiological fields. This study presents a general approach for predicting the reaction of the bone tissue to cyclic loads with different intensity and temporal distribution. Empirical relationships are generated that incorporate the wealth of published experimental data, obtained from in vivo, ex vivo, and in vitro studies, into an integrated analysis. The developed procedure was guided by and is in close agreement with the published experimental data. The approach provides a general framework for predicting the effect of mechanical strain deviation from the physiological strain environment only, without consideration of the influence of any other changes in the biochemical, physiological, or psychological mechanisms controlling bone growth and damage. Further clinical investigations with controlled exercise and systematic bone scanning are necessary to check the applicability of the coefficients generated in the proposed method for general use on human subjects.

The influence of mediolateral deformity, tibial torsion, and foot position on femorotibial load. Prediction of a musculoskeletal computer model.

The influence of mediolateral deformity, tibial torsion, and different centers of foot support was studied with a three-dimensional computer model that incorporates the significant muscles of the lower extremities needed for quasi-static walking. This theoretical method avoids the variability in gait pattern from the pain and discomfort associated with deformity in patients. The study illustrates the possible importance of the muscle force on the load across the knee and ankle. High strains in the medial gastrocnemius and the medial hamstring created particularly high loads in the medial compartment of the knee. Internal torsion and varus deformity were associated with the highest loads in the medial compartment of the knee, although the peak load for each deformity occurred in different phases of the gait cycle. Both external torsion and valgus deformity generally decreased the load in the medial compartment, but early in the gait cycle external torsion increased the loads on the medial side. In addition, when the center of support of the body was in the forefoot, the loads through the knee were lower than when foot support was at the heel. As expected, if the center of support was on the lateral foot line, the lateral compartment was subjected to more load and, conversely, when the center of support was on the medial part of the foot the medial compartment of the knee was more loaded. Although the predicted forces agree well with those found with other methods, we think that the model is best used to measure the direction of influence of specific factors.

Pathogenesis of canine aural hematomas.

Morphologic examination of 3 ears from 2 dogs with aural hematomas revealed that the hematomas had developed within the pinnal cartilage. The cartilage had fractured from perichondrium to perichondrium and in some areas clefts had formed within the cartilage. Cartilage fracture could have resulted from wave motions set up in the pinna during head shaking. An explosive burst of head shaking exceeding a critical head velocity or a more gentle but sustained head shaking establishing a sinusoidal wave motion within the ear could have caused cartilage fracture.

Single-tissue modeling of decompression schedules.

This paper deals with the development of a single-tissue model that simulates the uptake and elimination of inert gases by the body of a diver. The model utilizes an effective single tissue with different uptake and elimination time constants to account for the asymmetrical behavior of multiple-tissue human body models. The parameters of this effective tissue are selected according to an optimal strategy that minimizes safe deviation from the decompression requirements recommended by safe practice. The developed strategy is general in nature and can be readily applied to select the optimal parameters for a single-tissue model suitable for any dive regimen on air or mixed gas. As an illustration, the procedure is used to select the optimal tissue that best fits the Standard Air Decompression Tables recommended by the U.S. Navy. The results obtained are in close and safe agreement with the requirements of the U.S. Navy, and consistently fall in the range between the U.S. Navy and the Royal Navy tables.

A feasibility study for the use of a silastic gage as an in vivo muscle force transducer.

This study investigates the feasibility of utilizing silastic gages for in vivo dynamic muscle force measurement. The gastrocnemius muscle of a fifty-one pound black short hair dog was selected for the test. The study shows that such measurements can be reliably performed in vivo for short durations without interfering with the natural movement of the animal. The durability of the gage appears to be primarily limited by the biological rejection process at the gage site.

Distribution of spinal disc pressures in the seated posture subjected to impact.

A musculoskeletal model for the human spine developed by the authors is used for this study. The model takes into account the equilibrium of the vertebral bodies, the intervertebral discs and segments of the upper extremities under the influence of all major muscle and joint forces. Linear programming techniques are used to obtain the muscle load sharing and the disc pressures, based on a preselected linear criterion. The criterion is formulated as a combination of all muscles forces (F), joint forces and ligament action (R,M) with suitable weighting factors, and a minimization is sought of U = F + k1R + k2M. The model is used to study the effect of sudden forward or backward acceleration forces, such as during the impact situation, on the distribution of disc pressures in the spinal column in the unsupported seated posture.

Effect of load, speed, and activity history on the EMG signals from the intact human muscle.

A specially instrumented bicycle ergometer is utilized in this investigation to induce reproducable loading conditions on the muscles of the lower extremity at different speeds. Various tehcniques for evaluating the electromyographic signals from the vastas medialis muscle are investigated for different load and speed conditions and shown to be essentially equivalent. The RMS signal power computed by means of a real time spectral analyzer is shown to be a convenient means of quantification of the dynamic EMG signals. The electromyographic signals are shown to be stable under repeated static or dynamic conditions but not under sustained isometric static loading.

Nitrogen elimination in man during decompression.

The effect of ambient pressure on inert gas elimination during decompression was investigated using human subjects breathing air in a dry hyperbaric chamber. This was done by measuring nitrogen recovery during three different decompression schedules following identical simulated dives. Five subjects were used, each with normal pulmonary function. In each case the simulated dives consisted of exposure for 40 min to air at 4 ATA corresponding to a depth of about 100 fsw and 28 degrees C. Following these exposures each subject was decompressed in different experiments to 50 fsw (2.515 ATA) and to 10 fsw (1.303 ATA) while breathing a mixture of 80:20 helium-oxygen. In addition, two of these subjects were denitrogenated isobarically, at 100 fsw, breathing 80:20 helium-oxygen. Significant differences in nitrogen-elimination rate were observed, with nitrogen removed most effectively at 50 fsw and least at 100 fsw. To explained these unexpected results it is tentatively suggested asymptomatic bubble formation occurred at both 10 and 50 fsw.

Normal postural stability and steadiness: quantitative assessment.

A force platform was utilized to provide a new and sensitive means to measure postural steadiness and stability. Normal standards are presented for the center of pressure of the vertical supportive force during standing and sustained weight-shifting of normal men in three age groups. Two distinguishing characteristics were seen for normal upright posture: (1) a large area of stability over which weight can be safely shifted and maintained, and (2) steadiness such that the center of pressure fluctuates incessantly, traversing large total excursions, while remaining remarkably close to the mean point. The youngest age group showed the greatest steadiness and stability and the oldest group showed the least.