Collagen fibril diameters increase and fibril densities decrease in skin subjected to repetitive compressive and shear stresses.

Understanding microstructural changes that occur in skin subjected to repetitive mechanical stress is crucial towards the development of therapies to enhance skin adaptation and load tolerance in patients at risk of skin breakdown (e.g. prosthesis users, wheelchair users). To determine if collagen fibril diameter, collagen fibril density, dermal thickness, epidermal thickness, basement membrane length, and dermal cell density changed in response to repetitive stress application, skin subjected to moderate cyclic compressive and shear stresses for 1h/d, 5d/week, for 4 weeks was compared with skin from an unstressed contralateral control. The lateral aspects of the hind limbs of 12 Landrace/Yorkshire pigs were used. Skin from under the stressed site and a contralateral control site was processed for electron microscopy and light microscopy analysis. Electron microscopy results demonstrated significant (p<0.01) increases in collagen fibril diameter of 15.9%, 22.4%, and 22.9% for the upper, mid, and lower layers of the dermis, respectively, for the stressed skin compared with the control skin. Collagen fibril density (fibrils/unit cross-sectional area) decreased significantly for stressed vs. control by 19.8%, 29.2%, and 31.8% for the upper, mid, and lower layers, respectively. Light microscopy results demonstrated trends of a decrease in dermal thickness and an increase in cell density for stressed vs. control samples, but the differences were not significant. Differences in epidermal thickness and basement membrane length were not significant. These results demonstrate that quantifiable changes occur in collagen fibril architecture but not in the gross tissue morphology following in vivo cyclic loading of pig skin.

Image processing techniques for quantitative analysis of skin structures.

Computer-based image processing and analysis techniques were developed for quantitative analysis of skin structures in color histological sections. Performance was compared with traditional non-image processing counting methods. Skin sections were stained with Masson's trichrome, hematoxylin and eosin, picrosirius red, or one of several elastin stains. The image processing software identified the top of the cellular epidermis and the dermal-epidermal junction and then calculated the volume of the cellular layer of the epidermis, epidermal thickness, and the ratio of the dermal-epidermal junction surface area to the in-plane surface area. It also identified cells and collagen and calculated cellular densities and collagen densities in the papillary and reticular layers of the dermis. Attempts to computationally process elastin-stained sections to determine elastin density were unsuccessful. The described techniques were used in a preliminary study to compare mechanically stressed skin with control skin. Results showed significant differences in cellular density in the papillary dermis and collagen density in the reticular dermis for skin subjected to combined shear/compression or tension compared with an unstressed control. Measurements made with the computer technique and traditional technique showed comparable results; the mean difference in measurements for epidermal features was 5.33% while for dermal features it was 2.76%. Significance testing between control and experimental groups showed similar results, though for three of the 28 comparisons the computer method identified a significant difference while the traditional method did not. The computer method took longer to conduct than the traditional method, though with recent advances in computer hardware this time difference would be eliminated.

An electromechanical testing device for assessment of hand motor function.

Instrumentation was designed and constructed to assess the strength and function of the intrinsic muscles of the index and long fingers of the hand. The device consisted of two beams instrumented with strain gages, signal conditioners, and a microprocessor-based embedded controller. A study conducted on four weak spinal cord injury (SCI), three nonweak SCI, and 21 control subjects demonstrated a trend of reduced maximum pinching force between the index and long fingers in weak SCI subjects compared with the other two groups. Weak SCI subjects also demonstrated a significantly slower rapid alternating movement speed of the index finger compared with the other two groups. The instrument has potential use as a clinical tool for quantitative evaluation of the progression of hand motor dysfunction.

Critical pedagogy in a bilingual special education classroom.

This article describes the application of critical pedagogical principles in a first- and second-grade bilingual special day class for Latino children with limited English proficiency. Recommendations for translating critical pedagogy to classroom practice are given.

Skin response to mechanical stress: adaptation rather than breakdown--a review of the literature.

The abnormal loading of skin and other surface tissues unaccustomed to bearing large mechanical forces occurs under many circumstances of chronic disease or disability. A result of abnormal loading is breakdown of the body wall tissues. An effective rehabilitation program avoids the pathological processes that result in skin trauma and breakdown and encourages load-tolerance and adaptation, changes in the body wall so that the tissues do not enter an irreversible degenerative pathological process. In the past, prevention has been the principal approach to the challenge of maintaining healthy skin and avoiding breakdown; therefore, relatively little is described in the rehabilitation literature about skin adaptation. However, adaptation has been investigated in other fields, particularly biomechanics and comparative anatomy. The purpose of this paper is to assemble the research to date to present the current understanding of skin response to mechanical stress, specifically addressing load cases applicable to rehabilitation. Factors important to tissue response are considered and their effects on adaptation and breakdown are discussed.

Silent periods after electromagnetic stimulation of the motor cortex.

Electromagnetic stimulation has been used to excite tracts in the human motor cortex, but little has been done to study inhibitory effects. In three normal subjects we have noted that an electromagnetic stimulation applied to the motor cortex during maximum voluntary contraction produces silent periods lasting up to 300 ms in the contralateral abductor pollicis brevis. Duration of the silent period is directly proportional to the intensity of the stimulus. Abductor hallucis has similar silent periods lasting 150 to 200 ms, although proximal upper and lower limb muscles have shorter silent periods. F and H waves are easily elicited during this silent period suggesting that the alpha motoneuron is still excitable. This silent period may result, at least in part, from a synchronous volley of inhibitory postsynaptic potentials induced by the electromagnetic stimulator at the cortical level. This technique may prove useful in further delineating cortical inhibitory function.

Prevention of deep vein thrombosis in neurosurgical patients: a controlled, randomized trial of external pneumatic compression boots.

A prospective, randomized clinical trial in 95 patients undergoing neurosurgical operative procedures was performed to investigate the efficacy of external pneumatic compression (EPC) of the calves as compared with results in a control group that received no specific form of prophylaxis for prevention of deep vein thrombosis (DVT). The diagnosis of DVT was established by the I125 fibrinogen scan and radiographic contrast phlebography. The data indicate that EPC provides significant protection against the development of DVT in comparison with results in the control group (p less than 0.005). There were no known pulmonary emboli in any of the EPC-treated patients. There were no complications of EPC.