Biomedical subjects

S J Simske

Publications and source records attributed to S J Simske.

39 records · Page 3Linked to original sources

PubMed1991

Effects of suspension-induced osteopenia on the mechanical behaviour of mouse long bones.

Whereas most studies of tail-suspension induced osteopenia have utilized rat femora, the present study investigated the effects of a 14 day tail-suspension on the mechanical behaviour of mice femora, tibiae and humeri. Force-deflection properties were obtained via three-point bending for long bones from suspended and control mice. Whole bone behaviour was characterized by converting the force-deflection values to stiffness, strength, ductility and energy parameters which were not normalized for specimen geometry. The effects of a systematic variation in the deflection rate over the range 0.1-10 mm min-1 were also evaluated. Statistical analysis indicated that the primary effect of the tail-suspension period was lowered bone mass which was manifested mechanically through lower values of the bone strength parameters. These effects were similar in the bones of both the fore and hind limbs. The results also demonstrated that the stiffness, ductility and energy characteristics were much less influenced by the tail-suspension. Whereas a significant dependence of the bone strength values upon deflection rate was observed for the femora and humeri, the other mechanical parameters were less sensitive. Based upon the nature of the physical and mechanical changes observed in the long bones following tail-suspension, the mouse appears to be a suitable animal model for the study of osteopenia.

Animals↗

PubMed1990

Errors due to measuring voltage on current-carrying electrodes in electric current computed tomography.

Electric current computed tomography is a process for determining the distribution of electrical conductivity inside a body based upon measurements of voltage or current made at the body's surface. Most such systems use different electrodes for the application of current and the measurement of voltage. This paper shows that when a multiplicity of electrodes are attached to a body's surface, the voltage data are most sensitive to changes in resistivity in the body's interior when voltages are measured from all electrodes, including those carrying current. This assertion is true despite the presence of significant levels of skin impedance at the electrodes. This conclusion is supported both theoretically and by experiment. Data were first taken using all electrodes for current and voltage. Then current was applied only at a pair of electrodes, with voltages measured on all other electrodes. We then constructed the second data set by calculation from the first. Targets could be detected with better signal-to-noise ratio by using the reconstructed data than by using the directly measured voltages on noncurrent-carrying electrodes. Images made from voltage data using only noncurrent-carrying electrodes had higher noise levels and were less able to accurately locate targets. We conclude that in multiple electrode systems for electric current computed tomography, current should be applied and voltage should be measured from all available electrodes.

Algorithms↗

PubMed1990

Age dependent development of osteopenia in the long bones of tail-suspended mice.

The microgravity, or weightlessness, of space causes measurable bone deterioration in humans and rats. The use of tail-suspension to simulate weightlessness in rats is well-documented. Our studies have focused on mice, as their smaller size suggests more efficient space-based experimentation. Using mice ranging from 1.3-12 months in age, the results of a 2-wk suspension were ascertained through measurement of bone mass and mechanical (3-pt bending) characteristics. Significant differences between tail-suspended (S) and control (C) mice were noted for mice less than 6 months old. Such significance was not observed for the older mice. In addition, for the 1.3 month and 1.7 month old mice, a group of mice were sacrificed (designated PC, or pre-control) with ages matching those of the S mice prior to suspension. These were assayed to determine if the effects of tail-suspension are predominantly on growth-suppression or on bone atrophy. Our results show that tail-suspension effects are best explained by growth-suppression, as both the C and S groups showed growth when compared to the PC groups. 4-wk tail-suspensions of 10 month old mice were implemented to determine if increased suspension time would produce deterioration in older mice. An indication of longer periods of suspension being effective was found, but significant differences like those obtained for younger mice were not seen in the numbers of mice used.

Aging↗