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S M Swartz

Publications and source records attributed to S M Swartz.

8 recordsLinked to original sources
PubMed1993

The technique of patch testing: role of the office staff.

Patch testing is a very useful office diagnostic tool to help clarify the cause of allergic contact dermatitis. The dermatology nursing staff can help the physician with some of the time-consuming steps in using this technique, which can be very valuable to patient outcome.

Dermatitis, Contact↗
PubMed1992

Wing bone stresses in free flying bats and the evolution of skeletal design for flight.

The primary mechanical functions of limb bones are to resist deformation, and hence provide stiff levers against which muscles can act, and to be sufficiently strong to prevent breaking under static or dynamic loads which arise from normal and accidental activities. If bones perform these functions with a minimum amount of material, the energetic costs associated with building, maintaining and transporting the skeleton will be minimized. Appropriate skeletal architecture for minimizing mass while maximizing strength depends on forces imposed on structural elements. In the evolutionary acquisition of flight in the bat lineage, the forelimb skeleton must have come to experience locomotor-forces that differed from those engendered by the terrestrial locomotion of non-flying bat relatives. Here we successfully measure in vivo strain on the wing bones of flying mammals. Our data demonstrate that torsion and shear are unique and crucial features of skeletal biomechanics during flight, and suggest that the evolution of skeletal design in bats and other flying vertebrates may be driven by the need to resist these loads.

Animals↗
PubMed1992

Sutural complexity in artificially deformed human (Homo sapiens) crania.

The pattern of complexity of cranial sutures is highly variable both among and within species. Intentional cranial vault deformation in human populations provides a controlled natural experiment by which we were able to quantify aspects of sutural complexity and examine the relationship between sutural patterns and mechanical loading. Measures of sutural complexity (interdigitation, number, and size of sutural bones) were quantified from digitized tracings of 13 sutures and compared among three groups of crania (n = 70) from pre-European contact Peru. These groups represent sample populations deformed in 1) anteroposterior (AP) and 2) circumferential (C) directions and 3) an undeformed population. Intergroup comparisons show few differences in degree or asymmetry of sutural interdigitation. In the few comparisons which show differences, the C group is always more interdigitated than the other two while the AP group has more sutural bones. The sutures surrounding the temporal bone (sphenotemporal, occipitotemporal, and temporoparietal) most frequently show significant differences among groups. These differences are related to the more extreme binding of C type deformation and are consistent with hypothesized increases in tension at coronally oriented sutures in this group. The larger number of sutural bones in the AP group is consistent with the general broadening of the cranium in this group and with experimental evidence indicating the development of ossicles in areas of tension. We suggest that so few changes in sutural complexity occurred either because the magnitude of the growth vectors, unlike their direction, is not substantially altered or because mechanisms other than sutural growth modification are responsible for producing the altered vault shapes. In addition, the presence of fontanelles in the infant skulls during binding and the static nature of the binding may have contributed to the similarity in complexity among groups.

Adult↗
PubMed1989

Telemetered in vivo strain analysis of locomotor mechanics of brachiating gibbons.

The slender elongated form that is characteristic of the forelimb long bones of gibbons (Hylobates) has long been attributed to their functional adaptation to habitual armswinging locomotion, although potential selective advantages of this morphology for brachiation have yet to be demonstrated. If the forces exerted on the limb skeleton during brachiation indeed differ greatly from those of other locomotor modes, then the changes in skeletal loading accompanying a shift in locomotor behaviour could favour alterations in skeletal morphology in brachiating lineages. In vivo skeletal strain patterns recorded by using radiotelemetry during brachiation indicate that the forelimb bones of the gibbon are loaded in substantial tension and show reduced bending and compression in comparison with those of other mammals. We suggest that this unique loading regime could have contributed to the evolution of the distinctive morphology of hylobatid limbs.

Animals↗
PubMed1986

Bone modeling during growth: dynamic strain equilibrium in the chick tibiotarsus.

Bone loading was quantified, using in vivo strain recordings, in the tibiotarsus of growing chicks at 4, 8, 12, and 17 weeks of age. The animals were exercised on a treadmill at 35% of their maximum running speed for 15 minutes/day. In vivo bone strains were recorded at six sites on the tibiotarsus. Percentages of the bone's length and a percentage of top running speed were used to define functionally equivalent sites on the bone, and a consistent exercise level over the period of growth was studied. The pattern of bone strain defined in terms of strain magnitude, sign, and orientation remained unchanged from 4-17 weeks of age, a period when bone mass and length increased 10-fold and threefold, respectively. Our findings support the hypothesis that bones model (and remodel) during growth to achieve and maintain a similar distribution of dynamic strains at functionally equivalent sites. Because strain magnitude and sign (tensile versus compressive) differed among recording sites, these data also suggest that cellular responses to strain-mediated stimuli differ from site to site within a bone.

Animals↗