Biomedical subjects

D L Bader

Publications and source records attributed to D L Bader.

70 records · Page 4Linked to original sources

PubMed1989

Distraction physiolysis in the rabbit.

Axial forces across the growth plate of the upper tibia during controlled distraction were studied in 24 rabbits close to skeletal maturity. Distraction rates of 0.13, 0.26, and 0.53 mm every 24 hours were applied through a dual-frame external fixator. Strain gauges were bonded to the fixator, and axial forces were estimated prior to and following distraction. The results demonstrate two distinct patterns. In one group, forces increased to maximum values of 20-32 newtons and then suddenly decreased on subsequent distraction. This force pattern indicated fracture of the growth plate with associated hyperplasia. In the other group, lower maximum forces of 6-18 newtons were produced at the end of the distraction period, which were associated with physeal hyperplasia without fracture. These results showed that response to controlled distraction was dependent upon both the level of force acting across the growth plate and the rate of distraction; hyperplasia was achieved with lower rates of distraction up to a critical peak force above which fracture occurred.

Animals↗

PubMed1988

Changes in transcutaneous oxygen tension as a result of prolonged pressures at the sacrum.

Prolonged pressures at the patient support interface can lead to the impairment of tissue viability resulting in tissue breakdown, particularly in debilitated individuals. However there are still few clinical guidelines to indicate safe levels of pressure and time for individual tissue areas. The effects of extended loading on transcutaneous oxygen tension (tcPO2) were examined at the sacrum of twenty debilitated subjects, prone to tissue breakdown. Each load was applied for a ten minute period through an indenter incorporating a commercial oxygen electrode. Loads were incremented until the tcPO2 levels were reduced below 2.7 kPa (20 mmHg), at which time the tissue was unloaded. The interface pressure for each applied load was measured. Results are presented in terms of relating applied pressure and time to relative changes in tcPO2. When all the results are combined it is clear that there is a range of applied pressures which significantly reduce the tcPO2 levels. The applied pressures to produce, for example, 50% reduction of the unloaded resting value, ranged from 3.0 kPa (22 mmHg) to 12.2 kPa (92 mmHg). This indicated the individual nature of the tissue response, which should be determined before clinical guidelines of safe pressure levels are established.

Adult↗

PubMed1986

Pressure distribution under the ischium of normal subjects.

This paper describes the development of a system for measuring pressure distribution at the patient-support interface. The instrument uses pneumatic techniques under microcomputer control to measure pressures, with an overall accuracy of 3 per cent of full scale. The instrument has been used to investigate the pressure distribution under the ischium of four normal subjects, using a rectangular matrix. The study demonstrated a small variability in pressure distribution with a subject sitting still. Repositioning the subjects produced large variations in pressure readings, as a result of postural changes, which must be taken into account in the design of seating trials.

Adult↗

PubMed1986

Substance P facilitation of memory: effects in an appetitively motivated learning task.

Food deprived, heterogeneous strain (HS/IBG) mice were trained on two different discrimination tasks for food reinforcement. In one experiment animals were trained to make spatial discriminations in a T maze. Immediately after training they were given subcutaneous injections of either substance P (1 ng/g) or vehicle. Twenty-four hours later the animals were given reversal training in the same maze. The results showed that substance P-treated animals took significantly longer to acquire the reversal habit than did control mice. In a second experiment, animals were trained to make visual discriminations in a T maze. Immediately after reaching acquisition criterion animals were injected with either substance P (1 ng/g) or vehicle. Different groups of mice were retrained on the same task either 1, 2, 3, or 7 days after original learning. Savings scores were calculated and, at every interval, substance P-treated mice retained the task better than control animals. One interpretation of these data is that substance P-treated mice remembered the original task significantly better than vehicle-injected control animals.

Adrenocorticotropic Hormone↗

PubMed1986

Effect of externally applied skin surface forces on tissue vasculature.

The effect of surface forces on the morphologic pattern of skin capillaries was examined on the anterior surface of the forearm of healthy volunteers. A rig was designed to permit the application of uniaxial forces between two pads attached to the skin surface. A grid was printed onto the skin surface, and mechanical data are presented in terms of force intensity versus strain. During force application the skin capillaries were monitored using vital capillary microscopy. Mean values of force intensity and strain of 1.33N/mm and 10%, respectively, were sufficient to produce virtual obliteration of the blood flow to the capillaries. A simplified finite element model of the tissue was also employed to illustrate the effect of surface forces at different depths within the tissue. This study emphasizes the potentially damaging effects of surface forces on the integrity of the skin vasculature. If these forces are maintained or repeated, cell necrosis and eventual tissue damage would result.

Adolescent↗

PubMed1985

The periosteum in growth plate failure.

To investigate the periosteal contribution to the integrity of the growth plate, the authors subjected the proximal tibias of 110 male and female Sprague-Dawley rats between the ages of 25 and 65 days to axial and perpendicular forces to produce epiphysiolysis by use of a slow-loading technique and a cross-head speed of 10 mm per minute. Paired tibias of each rat were loaded under identical conditions, the only difference being the presence or absence of an intact periosteum. Mean values of body weight, tibial length, and cross-sectional areas of the growth plate after epiphysiolysis showed a linear increase with the age of the rat. No significant differences at the 5% level were observed in the tibial length and cross-sectional areas of the paired tibias. However, a consistently higher force was needed to produce epiphysiolysis with the periosteum intact. This was significant at all ages in both axial and perpendicular loading but was marked for young rats aged 45 days and under that were subjected to axial loading, where the level of significance was less than 1%. Calculated stress values showed a similar significant trend. The periosteum contributes significantly to the stiffness of the system, as shown by typical load deformation curves, and if it is divided, the gradient of the curve is clearly reduced up to epiphysiolysis. All periosteal fibers are not recruited in resisting a perpendicular force. Histologic examination of the specimens showed two patterns of failure corresponding to axial and perpendicular loading and also showed the failure path.

Animals↗

PubMed1984

A study of uniaxial tension on the superficial dermal microvasculature.

A spring-loaded apparatus was designed to apply uniaxial tension to forearm skin in 17 human subjects--10 normals, 6 psoriatics, and 1 patient with scleroderma. Simultaneously, the effects of stretching on the upper dermal vasculature were observed stereomicroscopically. Progressive changes (collapse) in the superficial microvasculature--vertical capillary loops and horizontal subpapillary plexus--with increasing tension were photographed. Force and strains were recorded at the points of disappearance of virtually all vessels. An average force of 11.9 newtons (N), accompanied by a mean strain of 10.3%, resulted in occlusion of all vessels. A much higher force (18.5 N) was necessary to occlude blood flow in the 1 patient with scleroderma. In summary, we have described a new technique for the study of mechanical forces on the blood supply of the epidermis. The data have shown that uniaxial tension has important effects on the superficial dermal microvasculature, resulting in impedance and obliteration of blood flow at relatively low magnitudes.

Adolescent↗

PubMed1983

Mechanical characteristics of skin and underlying tissues in vivo.

This paper is concerned with the mechanical characteristics of the complex composite of skin and subcutaneous tissues as they relate to the development of soft tissue replacements. Following a review of previous work and a summary of theoretical considerations, the results of a series of in vivo experiments aimed at quantifying the stiffness of skin and underlying tissues are reported. Variations in compressive properties with age, sex and body site are explained in terms of differences in anatomy and tissue structure.

Adult↗

PubMed1982

Regional hip blockade in osteoarthrosis. Effects on pain perception.

Eighteen patients with unilateral osteoarthrosis of the hip were investigated in a trial which involved the injection of nine with bupivacaine and nine with normal saline. All the patients completed daily pain analogue charts. Their pain, mobility and functional activity were assessed and gait characteristics analysed, once before the injection and then at three monthly intervals. All the patients recorded a decrease in pain level within two weeks of injection, but it subsequently rose to pre-injection levels. There were no other significant general improvements after the injection. A significant increase in the maximum force at toe-off for the good leg was recorded one month after the injection. However, no further significant differences were found in the gait performance of either group of patients throughout the study. It is concluded that the hip nerve regional blockade offers no useful relief to the pain of osteoarthrosis of the hip joint.

Aged↗

PubMed1982

Material properties of Velcro fastenings.

An assessment of the material properties of three types of touch and close fasteners (Velcro) in general orthopaedic usage is presented. The materials were tested under various loading regimes using an Instron testing machine. The force-extension curves were analyzed and values determined for both the stiffness and strength of the various attachments. Particular reference was made to the alteration in attachment strength after cyclic loading. The strength of the standard Velcro was found to be least affected after cyclic loading to simulate continuous usage. A recommendation is made on the specific application of each type of Velcro based on their material properties.

Humans↗

PubMed1981

The effects of leucocyte elastase on the mechanical properties of adult human articular cartilage in tension.

The effects of leucocyte elastase on the tensile properties of adult human articular cartilage were examined in detail in 99 specimens from hip, knee and ankle joints in the age range 16-83 years. The results showed that elastase reduced the tensile stiffness of cartilage, both at low stress and at fracture. The tensile strength of cartilage was also considerably reduced by the action of elastase. Biochemical analysis of the incubation media, and the specimens, revealed that 90%, or more, of the proteoglycan was released from the cartilage, whilst the release of collagen was negligible. Leucocyte elastase is known to degrade the non-helical terminal peptides of cartilage collagen molecules and thereby disrupt the main intermolecular cross-links in collagen fibrils. A previous study (Kempson, G.E., Tuke, M.A., Dingle, J.T., Barrett, A.J. and Horsfield, P.H. (1976) Biochim. Biophys. Acta 428, 741-760) showed the lack of effect of proteoglycan degradation alone on the tensile strength and stiffness of cartilage. The reduction in strength and stiffness recorded in the present study can, therefore, be attributed to the action of elastase on the collagen in cartilage and it emphasises the important of covalent intermolecular cross-links to the mechanical properties of collagen fibrils.

Adolescent↗

PubMedDate not supplied

Measurement of the deformation of isolated chondrocytes in agarose subjected to cyclic compression.

Mechanically induced cell deformation is one of a number of possible mechanotransduction pathways by which chondrocytes sense and respond to changes in their mechanical environment. The present study describes a system for measuring the deformation of isolated chondrocytes in agarose during both static and cyclic compression. A test rig mounted on the stage of an inverted microscope was used to apply precise levels of compressive strain to individual cell-agarose constructs bathed in culture medium. Images of the cells were recorded using a CCD video camera attached to the microscope. Cell deformation was quantified in terms of a deformation index (X/Y) representing the ratio of cell diameters measured parallel (X) and perpendicular (Y) to the axis of compression. Cyclic compression between 0 and 15% strain, at 0.3 Hz, resulted in cyclic deformation of the cells at the same frequency. However, during the unstrained phase the cells did not fully recover to their initially spherical morphology (X/Y = 1.0). During the strained phase, the level of deformation (X/Y = 0.59) was initially similar to that observed during static 15% strain. However, this level of cell deformation reduced over a 20 min period of cyclic compression (X/Y = 0.72), although during static compression the cell deformation remained constant. This system may be used to examine cellular events under a range of dynamic mechanical stimuli.

Animals↗

PubMedDate not supplied

The effect of heel pads on the treatment of Achilles tendinitis: a double blind trial.

Thirty-three subjects entered a blind-observer, random, prospective study of three forms of conservative treatment of sports-induced Achilles tendinitis, results being assessed by clinical and biomechanical parameters. Two patient groups received heel pads, ultrasound, and exercises, while the third received only ultrasound and exercises. All three groups showed some improvement at both 10 day and 2 month assessment, but the claimed benefit of viscoelastic pads widely used by athletes was not substantiated. The more striking benefit from ultrasound and exercises alone occurred in patients with a shorter history; a comparison of duration of injury in all three groups suggested this was an important factor influencing outcome. The study has highlighted the need for biomechanical outcome measures as well as for more objective clinical outcome measures in the assessment of physical therapy.

Achilles Tendon↗

PubMedDate not supplied

Biomechanical factors in wound healing following knee arthroplasty.

A significant proportion of deep infections following knee arthroplasty are consequent on a failure of primary wound healing. The management of such infections is difficult and the functional outcome is poor. It is essential to ensure that the initial biomechanical conditions are such that wound healing is encouraged. The ability of a wound to heal is dependent on factors such as the orientation of the skin incision, the wound tension and the viability of the wound edges as assessed by skin oxygen tension estimations. Consideration of these factors has led us to advocate the use of the medial parapatellar incision for knee arthroplasty. Early, excessive knee flexion following arthroplasty can lead to significant wound edge hypoxia but by modifying the rehabilitation programme and with the administration of 24% oxygen to the patient in the perioperative period, this effect can be minimized. Modification of the surgical techniques involved in knee arthroplasty can help preserve the vascular supply and hence the viability of the wound edge, and thus achieve a suitable biomechanical environment for primary wound healing.

Biomechanical Phenomena↗

PubMedDate not supplied

Instrumentation of a mobilization couch for dynamic load measurement.

Spinal mobilization or manipulation techniques are frequently used by physiotherapists in the treatment of musculoskeletal disorders. Many of these techniques involve the application of a varying force to the affected joint. Despite the routine use of these techniques, there are no objective measures to quantify their use. This paper describes the principles of the instrumentation of a mobilization couch to enable measurement of the forces applied during mobilization of the lumbar spine. The couch was linked to a personal computer with a 286 processor and data card for data collection. The system was found to be reliable and sensitive over the range of forces applied during mobilization. It has potential for use in many situations where measurements of forces applied to the patient are required.

Biomechanical Phenomena↗

PubMedDate not supplied

Intracellular mechanics and mechanotransduction associated with chondrocyte deformation during pipette aspiration.

The present study utilised pipette aspiration and simultaneous confocal microscopy to test the hypothesis that chondrocyte deformation is associated with distortion of intracellular organelles and activation of calcium signalling. Aspiration pressure was applied to isolated articular chondrocytes in increments of 2 cm of water every 60 seconds up to a maximum of 10 cm of water. At each pressure increment, confocal microscopy was used to visualise the mitochondria and nucleus labelled with JC-1 and Syto-16, respectively. To investigate intracellular calcium signalling, separate cells were labelled with Fluo 4, rapidly aspirated to 5 cm of water and then imaged for 5 minutes at a tare pressure of 0.1 cm of water. Partial cell aspiration was associated with distortion of the mitochondrial network, elongation of the nucleus and movement towards the pipette mouth. Treatment with cytochalasin D or nocodazole produced an increase in cell aspiration indicating that both the actin microfilaments and microtubules provide mechanical integrity to the cell. When the data was normalised to account for the increased cell deformation, both actin microfilaments and microtubules were shown to be necessary for strain transfer to the intracellular organelles. Mitochondria and nucleus deformation may both be involved in chondrocyte mechanotransduction as well as cellular and intracellular mechanics. In addition, pipette aspiration induced intracellular calcium signalling which may also form part of a mechanotransduction pathway. Alternatively calcium mobilisation may serve to modify actin polymerisation, thereby changing cell mechanics and membrane rigidity in order to facilitate localised cell deformation. These findings have important implications for our understanding of cell mechanics and mechanotransduction as well as interpretation and modelling of pipette aspiration data.

Animals↗