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Biomedical subjects

J L Lewis

Publications and source records attributed to J L Lewis.

At least 253 records · Page 14Linked to original sources
PubMed1983

Ip cisplatin in patients with malignant ascites: pharmacokinetic evaluation and comparison with the iv route.

Ip chemotherapy may be useful in managing patients with malignant ascites. This approach should result in a high concentration of drug at the site of disease, while the plasma concentration and therefore systemic toxicity remain low. Six patients with malignant ascites were treated with cisplatin at a dose of 60 mg/m2. Three patients received the drug iv; one of these patients and three other patients were treated with ip cisplatin. Platinum concentrations in plasma, ascites, protein-free ultrafiltrates of plasma and ascites, and urine were assayed by flameless atomic absorption spectrophotometry. The area under the concentration x time curve for ultrafilterable platinum in ascites was 30 times greater after ip administration of cisplatin than after iv cisplatin. Ip cisplatin can be administered safely to patients with malignant ascites and may be useful in patients with minimal residual intraperitoneal disease, particularly ovarian carcinoma.

Adenocarcinoma↗
PubMed1982

The induction of mania. A natural history study with controls.

Previous reports have indicated that tricyclic antidepressants (TCAs) induce mania, but the studies suffer from lack of control groups. This study included 137 unipolar and 157 bipolar patients, all having two or more admissions to the same hospital. In many cases, the same patients were treated at one time with TCAs and at another time with no somatic therapy at all. Most patients who switched (20/23) were bipolar. Twenty-seven bipolar patients receiving no treatment had a 41% switch rate (rate/person). They had 32 admissions, and the rate of switch while receiving no treatment was 34% (rate/admission). Twenty-six patients receiving tricyclics had a 28% switch rate; for these, there were 30 admissions and the switch rate was 23%. Thus, it appears that the rate of induction of mania by TCAs is not greater than what one would expect from the natural history of the illness itself. Validity of these findings is attested to by the fact that lithium carbonate and neuroleptic treatment, as expected, significantly prevented the induction of mania.

Adult↗
PubMed1982

Mechanical properties of the fibrous tissue found at the bone-cement interface following total joint replacement.

A long-term problem associated with total joint replacements is the formation of a fibrous tissue at the bone-cement interface which may compromise the fixation of the prosthesis. In this study, harvestable amounts of interfacial fibrous tissue were generated using a prosthetic replacement of the canine stifle joint as an animal model. The collected tissues were examined histologically and by uniaxial, unconfined compression tests. The fibrous tissue had a matlike structure. The heavy collagen fibers were distributed at random in sheets and the sheets themselves were layered to form a mat. Such a structure may be able to resist compressive stresses normal to the plane of the mat but is probably not well suited to resist shearing stresses. The fibrous tissue proved to be a very compliant, deformable material and to undergo very large strains with load. The stress-strain curve for the tissue was nonlinear and was characterized by large deformations at low loads. But with increasing loads, the material became stiffer, and at high loads, the stress-strain curve became linear with a short-term tangent modulus of 1.9 MPa at a stress level of 0.5 MPa and a compressive strain level of 50%. With regard to total joint replacement systems which consist of an outer bone shell followed by a thin layer of fibrous tissue, a mantle of PMMA cement and a central core of metal or UHMW polyethylene, the fibrous tissue is substantially more yielding and deformable than the other elements of the structure and may have a significant effect on the structural behavior of the system.

Animals↗
PubMed1982

Properties and an anisotropic model of cancellous bone from the proximal tibial epiphysis.

An investigation has been made of the source and magnitude of anisotropic material properties of cancellous bone in the proximal epiphysis of the human tibia. Results are reported for stiffness measurements made in three orthogonal directions on 21 cubes of cancellous bone before testing to failure along one of the three principal axes. The structure is approximately transversely isotropic. Strength and stiffness are linear with area fraction for loading along the isotropic axis. Strength is proportional to stiffness for all directions. A finite element model is proposed, based on experimental observations, which enables one to predict the elastic constants of cylindrically structured cancellous bone in the tibia from morphological measurements in the transverse plane.

Biomechanical Phenomena↗
PubMed1982

A note on the application and evaluation of the buckle transducer for the knee ligament force measurement.

Knee ligament forces were directly measured with buckle transducers. Given a collection of buckle transducers with adequate rigidity and a variety of sizes to accommodate different ligamentous geometries, two potential problems remain when using the buckles 1) impingement of the transducers with bone, producing a false output; 2) ligament shortening due to buckle installation, potentially altering the distribution of ligament forces around the knee. This report describes our current buckle transducer designs and installation procedures, and presents data which demonstrated that the errors due to ligament shortening and bone impingement can be assessed and reduced to acceptable levels.

Humans↗
PubMed1982

In vitro growth stimulation of human ovarian cancer cells by xenogeneic peritoneal macrophages.

For improvement of the in vitro growth rate of human ovarian tumors, an irradiated xenogeneic feeder layer of adherent peritoneal cells was added to such cultures. This adherent peritoneal cell population was obtained from oil-primed adult (C57BL/6J x DBA/2J)F1 mice and contained predominantly macrophages. After irradiation of the feeder layer with 3,000 rad 137Cs, cell suspensions prepared from fresh, solid human ovarian cancers were cocultivated with the feeder cells. Two end points were used to evaluate the growth enhancement added by such a feeder layer: 1) Primary monolayer cultures of ovarian tumors were successfully grown in continuous culture through five or more serial subcultures in 25 of 64 different patient specimens studied. Control cultures without the feeder layers did not continue growing through serial subcultures. 2) With the use of the soft agar clonogenic assay, addition of the feeder layer to the petri dishes increased the number of tumor cell colonies in each of six separate experiments, compared to the number seen in control plates without the feeder layer.

Adenocarcinoma↗
PubMed1982

A comparative evaluation of tibial component designs of total knee prostheses.

UNLABELLED: Three-dimensional finite-element stress analyses were used to compare the fixation of tibial component configurations of surface-replacement-type total knee prostheses, bases on the stresses in the cancellous bone, in the polymethylmethacrylate, and at the bone cement-bone interface. The results indicate that, in general, metal components provide lower system stresses than polyethylene components, particularly in the methacrylate and the cancellous bone, and that one-piece designs give lower bone cement-bone interface stresses compared with those with separated condylar components. Of the designs considered, a single-post, metal-backed design provided the lowest system stresses over-all. CLINICAL RELEVANCE: a great and confusing variety of tibial component design exists today, with more in the process of development. Short of long term clinical trials, there are few objective methods by which these designs can be evaluated and long-term performance predicted. There is evidence from clinical results that excessively high stresses in the systems can lead to loosening of the tibial component. The finite-element method provides a method for comparing prosthetic designs using system stresses a s a design criterion. On this basis, we analyzed the stress distribution for several types of tibial components and discuss the advantages and disadvantages of their designs.

Humans↗
PubMed1982

The effect of knee-prosthesis geometry on cruciate ligament mechanics during flexion.

UNLABELLED: We used buckle transducers in conjunction with a mathematical model to investigate the mechanics of the cruciate ligaments during flexion of knees containing prostheses with differing component geometries. With normal component placement and both cruciate ligaments intact, the full range of flexion is restricted in a knee with the conforming, single radius-of-curvature geometric prosthesis because of large constraint forces in the posterior cruciate ligament. Ligament incompatibility is avoided with multicurvature designs, as represented by the kinematic prosthesis. Low conformity of components allows anterior-posterior displacements to accompany flexion, which provides for a full range of flexion and allows cruciate ligament forces to approach those of a normal knee. CLINICAL RELEVANCE: This analysis points out that special precautions must be taken to avoid ligament constraint forces (and potential loosening) if an implant with highly conforming components is used when both cruciate ligaments are intact. The information presented here, relating implant geometry to cruciate ligament mechanics, must be considered when choosing an appropriate prosthetic design to ensure ligament compatibility in the presence of one, both, or no cruciate ligaments.

Biomechanical Phenomena↗
PubMed1981

Analysis of model variables and fixation post length effects on stresses around a prosthesis in the proximal tibia.

A two-dimensional, finite element model of a single-posted, metal, tibial prosthetic component implanted with PMMA in the proximal tibia is developed. The effects upon the stresses at the PMMA-bone interface and in the cancellous bone around the component due to the inclusion in the model of the cortical shell and the heterogeneity and anisotropy of the cancellous bone, are demonstrated. Various lengths of the fixation post are considered. The cortical shell adds support and stiffness to the bone structure, and allows generation of significant stresses proximally. The heterogeneity of the cancellous bone, as assumed here, dictates the form of the stress distributions and the magnitudes and locations of the peak stress values around the post of the component. Peak stress values can occur at locations proximal to the post tip. The anisotrophy of the cancellous bone significantly alters the magnitudes of the stresses. Lower stresses along the post interface and higher stresses beneath the plate of the prosthesis are seen in the anisotropic models. Lengthening of the fixation post reduces stresses proximally, but the effects of post lengthening upon the maximum stress values around the post are highly dependent upon the assumed properties of the cancellous bone.

Analysis of Variance↗
PubMed1981

DES-related clear cell adenocarcinoma of the vagina in pregnancy.

The occurrence of diethylstilbestrol- (DES)-related clear cell adenocarcinoma of the vagina in a pregnant patient who carried the pregnancy to term is reported. The tumor, observed directly over an extended period, did not appear to be influenced by elevated plasma estrogen levels during pregnancy. Problems of diagnosis, histopathologic finding, and management are discussed.

Adenocarcinoma↗
PubMed1981

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.

Carcinoma, Squamous Cell↗