Bulging of Rubber through Apertures

1. When rubber bulges through an aperture, the bulge height varies linearly with applied pressure. It also varies linearly with radius or width of the aperture when the dimensions of the rubber block are much larger than the aperture, in good agreement with linear elasticity theory. When the block is not much larger than the radius or width of the aperture, a simple empirical factor provides a satisfactory correction. 2. FEM results were in good agreement with experiment in all cases and confirmed the empirical correction for relatively large apertures. 3. Bulge profiles were calculated to be elliptical in all cases. 4. Results for an elastic solid are wholly consistent with Roscoe's results for a viscous liquid. 5. Changing slip conditions at the interface had a surprisingly small effect. The exact theory, Equations (5) and (7), is based upon a nonslip condition. When a fully lubricated condition was employed instead, so that free sliding was allowed at the interface, the maximum bulge heights predicted by FEM were only about 5% higher than before for a circular aperture and about 12% higher for a slit. Experimental observations of bulge heights with dry and lubricated interfaces were in good agreement with these predictions. 6. Bulge heights through small apertures provide a simple means of measuring pressure at contact surfaces.

Cellular immunity in species with variable rejection of vascularized grafts

We studied the in vitro and in vivo cellular response in three distinctly different xenograft models, using C57BL/6 mice as responders and Lewis rats (LR), Golden Syrian hamsters (GSH), and Strain 2 guinea pigs (GP) as stimulators. Previous work has shown that cardiac grafts from rats, hamsters, and guinea pigs are rejected by C57BL/6 mice in 7 days, 4 days, and 10 min., respectively. In xenogeneic mixed lymphocyte culture, response was in general greatest to GSH splenocytes: stimulation index (S.I.) = 11.4 +/- 3.6 followed by the response to LR cells, S.I. = 3.5 +/- .09, which was less than that of an allogeneic control C57BL/6 anti-DBA, S.I. = 8.4 +/- 1.7. GP stimulator splenocytes produced inhibition of response (S.I. = 0.23 +/- .07) with all counts being below baseline and remaining low despite addition of IL-1, IL-2, or both. In fact, these cells were inhibitory to other allo or xeno mixed lymphocyte cultures in a dose-dependent manner. Cytotoxicity studies revealed maximal killing of ConA blasts in the allogeneic control followed by killing of GSH blasts and LR blasts and no killing of GP blasts. There was also a moderate degree of nonspecific killing between allo and xeno systems. In vivo analysis of cell-mediated cytotoxicity was done using a sponge matrix allograft model. The sponge was injected with donor cells and implanted into C57BL/6 mice. The response to donor cells was tested using cells accumulating in the sponge. There was maximal response to GSH cells greater than DBA greater than LR greater than GP.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic hypertension and left ventricular hypertrophy facilitate induction of sustained ventricular tachycardia in dogs 3 hours after left circumflex coronary artery occlusion

The purpose of this study was to investigate the electrophysiology of acute ischemia in hypertrophic as compared with nonhypertrophic myocardium. Left circumflex coronary artery occlusion was produced in anesthetized open chest dogs. Of 40 dogs studied, 22 were normotensive and 18 had chronic hypertension produced by a single kidney renal clamp procedure. Recordings of electrograms and extrastimulus testing were performed in endocardial and epicardial sites in both normal and ischemically damaged zones documented by triphenyltetrazolium chloride. In the hypertrophy group, there was greater endocardial to epicardial conduction delay in ischemic zones, mean +/- SEM 57 +/- 4 ms versus 31 +/- 2 ms in the normotensive group (p less than 0.05). Also, sustained monomorphic ventricular tachycardia was inducible in seven of eight dogs with hypertrophy and in none of eight normotensive dogs surviving to 3 h. Entrainment and several observations during induction were consistent with reentrant ventricular tachycardia. To exclude hypertension alone as an etiology of tachycardia, five normotensive dogs without inducible monomorphic tachycardia remained unchanged during hypertension produced with low doses of phenylephrine or descending aortic occlusion. Thus, the electrophysiologic response to ischemia is altered in hypertrophied myocardium, which predisposes to rapid sustained monomorphic ventricular tachycardia.

Pulmonary arteriovenous malformations: techniques and long-term outcome of embolotherapy

Over a 10-year period, 276 pulmonary arteriovenous malformations (PAVMs) were occluded with balloon embolotherapy in 76 patients, 67 (88%) of whom had hereditary hemorrhagic telangiectasia. Eleven patients (14%) were discovered by means of family screening with measurement of arterial blood gases and chest radiography. Epistaxis, dyspnea, hemoptysis, and hemothorax occurred in 79%, 71%, 13%, and 9% of patients, respectively. Clinical histories of strokes and transient ischemic attacks were present in 18% and 37% of patients, respectively. Computed tomographic scans of 59 patients showed stroke in 36%. Sixty-five percent of PAVMs were located in the lower lobes, which correlated with the finding of more pronounced hypoxemia in the upright position. After embolotherapy, symptomatic hypoxemia was corrected, and serial values have remained constant for 5 years. Complications were minimal, and no patient required surgery. Balloon embolotherapy is effective long-term therapy for PAVMs, and family screening should be pursued because of the possibility of a higher frequency of paradoxical embolization (stroke) than previously recognized.

Quantification of thermal asymmetry. Part 2: Application in low-back pain and sciatica

Temperature differences between the lower extremities were measured using a computerized thermometric scanning system in order to compare the degree of thermal asymmetry in 144 patients with low-back pain. The patients displayed highly significant thermal asymmetries, with the involved limb being cooler (p less than 0.001). When asymmetries exceeded 1 standard deviation from the mean temperature of homologous regions measured in 90 normal control subjects, the positive predictive value of thermometry in detecting root impingement was 94.7% and the specificity was 87.5%. These values indicate that calculation of temperature asymmetry is particularly effective in evaluating reported pain in psychosocially affected patient populations in whom the chance of positive myelography or impaired root function is low. In this group of patients, thermometric study provides physicians with important information for proper decision making. The test can be performed to avoid more invasive and probably less revealing diagnostic or exploratory surgical procedures.

Treatment of primary osteoarthritis of the hip. A comparison of total joint and surface replacement arthroplasty

Of 285 total hip arthroplasties (260 patients) performed for primary osteoarthritis during a six-year period, 135 were resurfaced using a Tharies prosthesis (total hip articular replacement with internal eccentric shells) and 150 were treated with the Trapezoidal-28 total hip replacement. From each of these two groups 100 hips (ninety-one patients in the Tharies group and eighty-six in the Trapezoidal-28 group) that had been followed for two to seven years were evaluated at the time of follow-up in accordance with a predetermined protocol. The patients were younger in the Tharies than in the Trapezoidal-28 group (average ages, fifty-eight and sixty-six years), included more men (sixty compared with thirty-five), and were more active postoperatively. The average follow-up was forty-seven months for the total joint-replacement group and thirty-eight months for the surface replacement group. At follow-up the ratings for pain, walking, and function according to the University of California at Los Angeles 10-point scale and the clinical results were identical in the two groups. Heterotopic ossification (Brooker grade III or IV) developed after thirteen Trapezoidal-28 and twenty-two Tharies arthroplasties. Radiographs made at six and twelve months and at final follow-up showed that the incidence of radiolucencies about the acetabular component was higher in the resurfacing group: fifty-seven with complete radiolucent lines after an average follow-up of thirty-eight months compared with thirty-six with complete lines after an average follow-up of forty-seven months. There were three failures in the joint-replacement group: a hematogenous staphylococcal deep infection that required a Girdlestone procedure, a femoral stem fracture that required revision, and loosening of an acetabular component for which revision was performed. There was also one dislocation, successfully treated by closed reduction. Similarly, in the resurfacing group there were three failures: two loose acetabular components, revised successfully, and one loose femoral component that necessitated total joint arthroplasty. Multivariate stepwise regression analysis showed that the factors that affected the final extent and width of the acetabular radiolucencies adversely after resurfacing were: any radiolucent lines that were visible at six months, a high level of physical activity after arthroplasty, and a thin superior cement mantle.(ABSTRACT TRUNCATED AT 400 WORDS)

Bony ingrowth fixation of newly designed acetabular components in a canine model

Implantation of a newly designed acetabular component with a porous coating has resulted in superior fixation when compared with acrylic cementation in the short term. Experiments in dogs demonstrate rapid ingrowth within the porous layers, resulting in rigid fixation of the acetabular components despite defects in the prepared bony bed. Acute infection prevents bony ingrowth and causes loosening. The absence of any foreign-body response to the titanium fiber mesh components suggests that this is a biocompatible metal. The fixation has been excellent; progressive or delayed loosening is not encountered once successful ingrowth is achieved. Progressive radiolucent zones generally do not appear in the short term but when visible soon after surgery, may consolidate and disappear. Ingrowth fixation of acetabular components appears to offer an attractive alternative to the use of acrylic cement and may even be feasible in patients with periarticular bony abnormalities.

Prosthetic replacement in osteonecrosis of the hip

The young patient with avascular necrosis of the hip presents one of the unsolved problems in orthopaedics today. Many of these patients are active and have expectations of continuing activities that may be far in excess of reality, considering the results achieved in these patients with replacement arthroplasty. In contrast to this group of patients, the patient with systemic disease has a built-in "brake" and appears to do well with conventional arthroplasty. New fixation techniques are yielding more promising results, and continued research into new modes of fixation such as porous ingrowth may well cast a new light on the problem. At this time, however, the clinician is called on to evaluate not only the disease process but the anticipated continuing activity of the patient. Thus there is no one procedure appropriate for this disease but rather several alternatives, each having its own indication at a specific stage in the disease process.

Hypercalcemia associated with epidermoid carcinoma in ovarian cystic teratoma

A case of metastatic epidermoid carcinoma arising in benign cystic teratoma of the ovary is reported. The clinical course was complicated by severe hypercalcemia and respiratory distress due to associated diffuse calcification of the lungs. Presumptive evidence is presented to show that prostaglandin E found in the tumor was the cause of the hypercalcemia.

Therapeutic embolization with detachable balloons. Physical factors influencing permanent occlusion

Twenty-one detachable Silastic 3 balloon embolizations were performed in 12 swine. Late balloon rupture was associated in vivo with increased size and decreased radiopacity of the balloons. Variables affecting the permanency of occlusion by the Silastic balloons were the osmolarity of the contrast medium and the size of the balloon relative to its uninflated size.