Search PubMed⌕ Search

Biomedical subjects

J A Davidson

Publications and source records attributed to J A Davidson.

At least 73 records · Page 4Linked to original sources
PubMed1989

The Georgia diabetic retinopathy screening study.

The diabetic retinopathy screening study represents a major collaborative effort of many volunteer groups interested in decreasing the risk of severe visual loss to Georgia citizens. Results of the present study have stimulated intense interest in screening more high risk persons, such as minorities, without the exclusion of whites. While age-related macular degeneration is the predominant cause of blindness in the U.S., diabetic retinopathy is a major new cause of blindness. With the continuation and completion of this study, we believe that many more of Georgia's citizens will seek ophthalmologic examinations and benefit from previous research regarding the use of laser photocoagulation and vitreoretinal surgery in preventing or reducing the risk of blindness. Since diabetic retinopathy requiring treatment can be present in patients with normal vision, such patients should obtain an annual dilated eye examination by an ophthalmologist. The value of statewide screening for undetected diabetic retinopathy, the determination of how and where to screen in order to give the most benefit to the potentially affected individuals and citizens of Georgia are only a few of the questions that may be answered when this study is completed. Moreover, to our knowledge this study is the first statewide screening for diabetic retinopathy in the United States.

Adult↗
PubMed1989

Diabetic retinopathy.

Retinal involvement from diabetes mellitus is the leading cause of new blindness in the United States. Many diabetic patients, though they have perfect vision and no ocular complaints or symptoms, harbor retinal pathology capable of leading to severe loss of vision. Therefore, all medical personnel caring for the diabetic patient must recognize the importance of dilated pupil retinal examinations by an ophthalmologist or vitreoretinal surgeon. Lack of timely diagnosis and treatment is a major factor leading to blindness from diabetic retinopathy. On a more positive note, prompt laser treatment of diabetic retinopathy can reduce severe visual loss by more than 50%.

Diabetic Retinopathy↗
PubMed1988

Heat transfer analysis of frictional heat dissipation during articulation of femoral implants.

Previous studies have shown the tendency for frictional heating to occur during articulation of total hip systems in vitro under simulated hip loading conditions. The magnitude of this heating is sufficient to accelerate wear, creep, and oxidation degradation of the UHMWPE bearing surface. It was shown that ceramic articulating systems generate less frictional heating than polished cobalt alloy against UHMWPE. This frictional heating is expected to occur primarily for younger, heavier, and more active patients. Thus, long-term performance of the articulating hip system in these patients may not be that predicted from current, body-temperature wear, creep, and degradation studies. Although the tendency to generate frictional heat has been observed only during in vitro simulated hip loading, a heat transfer analysis of this phenomenon is presented to evaluate the ability of the hip joint to dissipate such heating in vivo. Additional experiments were performed using controlled resistance heaters inside a cobalt femoral head to verify the calculated levels of frictional heat and to assess the heat dissipation under simulated in vivo conditions. The effect of blood perfusion on the effective thermal conductivity of the joint capsule is also discussed. The present study describes and analyzes the various heat dissipation mechanisms present both in vitro and in vivo during articulation of metal and ceramic hip systems. From these tests and analyses, it is concluded that frictional heating in the reconstructed hip cannot be effectively removed, and that degredative elevated temperature processes can be expected to occur in vivo to both the UHMWPE and adjacent tissue under extended periods of excessive patient activity. This is particularly true for metal cobalt alloy femoral heads articulating on UHMWPE versus ceramic heads which generate significantly lower levels of heat.

Alloys↗
PubMed1988

A study of HLA-A, B, DR and Bf bearing haplotypes derived from 304 families resident in the north west of England.

We report here haplotype frequencies for class I (HLA-A, B), class II (HLA-DR) and class III (Bf) gene products of the major histocompatibility complex (MHC) of man. As in other studies (Bertrams & Baur, 1979; Grange et al., 1981), we have chosen to document all families typed for HLA antigens and Bf phenotypes irrespective of ascertainment. We obtained 1,094 haplotypes from 304 families resident in the North West of England, of which 34.1% had been fully typed for HLA-A,B,DR and Bf polymorphisms. We have been able to find both positive and negative linkage disequilibria for two and three locus haplotypes and have listed the most commonly occurring four locus haplotypes. Our data confirms the position of the complement group between HLA-B and HLA-DR, and we have looked for evidence of segregation distortion of MHC haplotypes.

England↗
PubMed1988

Wear, creep, and frictional heating of femoral implant articulating surfaces and the effect on long-term performance--Part II, Friction, heating, and torque.

In Part I, (J.A. Davidson and G. Schwartz, "Wear, creep, and frictional heating of femoral implant articulating surfaces and the effect on long-term performance--Part I, A review," J. Biomed. Mater. Res., 21, 000-000 (1987) it was shown that lubrication of the artificial hip joint was complex and that long-term performance is governed by the combined wear, creep, and to a lesser extent, oxidation degradation of the articulating materials. Importantly, it was shown that a tendency for heating exists during articulation in the hip joint and that elevated temperatures can increase the wear, creep, and oxidation degradation rate of UHMWPE. The present study was performed to examine closely the propensity to generate heat during articulation in a hip joint simulator. The systems investigated were polished Co-Cr-Mo alloy articulating against UHMWPE, polished alumina ceramic against UHMWPE, and polished alumina against itself. Frictional torque was also evaluated for each system at various levels of applied loads. A walking load history was used in both the frictional heating and torque tests. The majority of tests were performed with 5 mL of water lubricant. However, the effect of various concentrations of hyaluronic acid was also evaluated. Results showed frictional heating to occur in all three systems, reaching an equilibrium after roughly 30 min articulation time. Ceramic systems showed reduced levels of heating compared to the cobalt alloy-UHMWPE system. The level of frictional torque for each system ranked similar to their respective tendencies to generate heat. Hyaluronic acid had little effect, while dry conditions and the presence of small quantities of bone cement powder in water lubricant significantly increased frictional torque.

Hip Prosthesis↗
PubMed1987

Wear, creep, and frictional heat of femoral implant articulating surfaces and the effect on long-term performance--Part I, A review.

Creep and wear of articulating reconstructed joints is a complex process, resulting in adverse tissue response, decreased range of motion, and eventual revision. As improvements are made in the design and surgical techniques of reconstructed joints, the long-term performance of the articulating system and materials becomes more important, particularly for younger, heavier, and more active patients. One aspect previously ignored in the long-term performance of articulating systems is the tendency for these systems to generate heat during articulation, particularly for extended periods of relatively strenuous activity. The present study reviews the various aspects of joint lubrication, friction, wear, and overall system performance. Local heating can increase the creep, wear, and oxidation degradation of UHMWPE, thus, specific attention is given to the effect that heat generation can have on long-term performance of these systems. Because of the complexity of this issue, the treatment of these various performance aspects is divided into two parts. The present part, Part I, reviews the various aspects of articulation performance. Part II presents results of friction, heating, and torque testing of various metal and ceramic hip systems. Criteria for frictional heating is also presented, along with discussion related to the various heat transfer mechanisms involved with heat dissipation.

Biomechanical Phenomena↗
PubMed1986

The effect of HIPing on the fatigue and tensile strength of a case, porous-coated Co-Cr-Mo alloy.

The process required to sinter porous Co-Cr-Mo alloys results in the formation of substrate porosity through carbide dissolution. Since hot isostatic pressing (HIPing) has been shown to eliminate casting porosity in the Co-Cr-Mo alloy, it is possible that it may be equally effective on pores that are generated from the sintering operation. The effect that HIPing a porous-coated Co-Cr-Mo material has on the fatigue and tensile properties was investigated. Fatigue testing was performed on sintered materials as well as sintered and HIPed materials, both with and without a porous coating. Further, the effect of varying coating thickness on the resulting fatigue strength of sintered and HIPed materials was studied. Light microscopy was performed in order to define the microstructural changes brought about by the various thermal cycles. Scanning electron microscopy was utilized to define the crack initiation process. The fatigue strength of uncoated "as sintered" materials was found to be reduced by 34% relative to the "as cast" condition. The same material that was HIPed revealed a fatigue strength slightly lower than the "as cast" condition. It was found that porous coatings created preferential sites for fatigue crack initiation. However, the presence of the coating did not further reduce the fatigue strength of "as sintered" materials because of the already low strength created by the sintering operation. Materials that were sintered exhibited a lowering in both tensile strength and elongation to failure relative to the "as cast" condition. The HIPing of sintered materials improved both fatigue and tensile properties relative to the "as sintered" condition.

Biocompatible Materials↗
PubMed1984

HLA antigens and risk factors for nephropathy in type 1 (insulin-dependent) diabetes mellitus.

This study of risk factors for diabetic nephropathy in juvenile Type 1 (insulin-dependent) diabetes mellitus compares two carefully characterised groups of patients, one with proteinuria (n = 23), the other a control group (n = 24) with no evidence of nephropathy despite more than 25 years of diabetic life. No significant difference was observed between the groups in any HLA-A, -B or -DR antigen of Bf allotype. DR3 was present in 87% of patients with proteinuria and 75% of the diabetic control group; DR4 was present in 48% of patients with proteinuria and 63% of diabetic controls; BfFl was present in 17% of patients with nephropathy and 9% of the diabetic control group. Compared with the control group, patients with proteinuria had significantly higher mean diabetic-clinic blood glucose concentrations before the diagnosis of microvascular disease, a significantly earlier age at diagnosis of diabetes, and had more often been treated with once-daily as opposed to twice-daily insulin regimens. Susceptibility to nephropathy in Type 1 diabetes appears to be determined by the quality of metabolic control and age of onset of diabetes; although the number of subjects studied was relatively small no evidence was found of any influence of HLA or Bf phenotype.

Adolescent↗
PubMed1984

Allotypes of properdin factor B(Bf) and lymphocytotoxic antibody production.

We have investigated the properdin factor B(Bf) polymorphism in relation to lymphocytotoxic antibody production. The Bf phenotypes of 1,113 individuals was determined; these consisted of 360 cytotoxic antibody-negative normal healthy controls, 293 HLA typing antisera, 330 sera from pregnant multiparous women, and 130 renal patients awaiting cadaveric transplantation. The allotype BfF was found to be strongly associated with cytotoxic antibody production in multiparous women.

Alleles↗
PubMed1984

Three dimensional reconstruction of the left ventricle from four anatomically defined apical two-dimensional echocardiographic views.

A method is described for three dimensional reconstruction of the left ventricle which uses four anatomically defined apical views. It is shown that the algorithms developed for reconstruction and volume estimation provide accurate results when applied to planar views with accurately defined boundaries. The linear regression equation was y = -6.32 + 1.04x, with SEE = +/- 3.4 ml, r = 0.999. For both "in vitro" and "in vivo" studies this method is found to be better than various geometrical models used to estimate volumes from two dimensional tomographic or projection views. The linear regression equation of in vitro fluid volume on volume estimate is y = 8.44 + 0.68x, with SEE = +/- 4.9 ml, r = 0.988. For pooled end diastolic and end systolic volumes (EDV and ESV) determined by three dimensional reconstruction (3-DR) and angiography the linear regression equation is y = 54.50 + 0.50x, with SEE = +/- 33.5 ml, r = 0.670. For stroke volume (SV), the regression equation is y = 21.10 + 0.40x, with SEE = +/- 12.8 ml, r = 0.750, and for ejection fraction (EF) it is y = 1.10 + 0.70x, with SEE = +/- 7.8%, r = 0.840. In patients with ischemic heart disease, the method presented is shown to be better than existing methods of volume estimation. Three dimensional perspective images can be plotted in any orientation as a visual aid to the cardiologist. In vivo studies demonstrate the feasibility of 3-DR, from anatomically defined apical views, in the clinical setting.

Cardiac Volume↗
PubMed1983

Dimensions of the anterior chamber in pigment dispersion syndrome.

A recently introduced theory of the mechanism of the pigment dispersion syndrome is that pigment granules are released by mechanical contact between the anterior surface of zonular fibrils and the posterior surface of the pigment epithelium of the iris. A photogrammetric study of the depth of the central and peripheral anterior chamber of the iris was carried out in 37 subjects with the pigment dispersion syndrome. These subjects had deeper anterior chambers, particularly in the midperiphery, than could be accounted for by their age, sex, or refractive error. Excessive depth of the anterior chamber is demonstrated to be a risk factor in the pigment dispersion syndrome. Concavity of the midperipheral iris surface was demonstrated in this group of subjects, confirming previous clinical observations and giving additional support to the mechanical theory of pigment dispersion.

Adult↗
PubMed1980

Impulsive suicidal behavior.

Previous studies have noted that a considerable proportion of suicidal behavior is impulsive. The present study aimed to ascertain the degree to which this was so and to consider whether impulsive attempters differed from non-impulsive attempters on variables such as demographic and motivational factors and circumstances that surrounded the occurrence of the act. Based on a criterion of less than 5 minutes' premeditation, 40% of two large, consecutive series were judged to have acted impulsively. While few variables differentiated between the two groups, impulsive attempters were less depressed, motivated by the desire to reduce tension, more likely to consider that they would survive, and to report that someone saw them perform the act.

Adult↗
PubMed1977

An assessment of hostility in a population of adolescents.

In the course of an epidemiological survey of adolescents, the Hostility and Direction of Hostility Questionnaire was administered to 6,709 persons aged 13 to 18 years, representing 89% of secondary school students in Hobart, Tasmania. Extrapunitiveness was found to decrease substantially between the ages of 15 and 17 years in both sexes. Intropunitiveness also decreased, although to a lesser extent. Girls were less extrapunitive and more intropunitive than boys over the whole age range. These findings are discussed in relation to their clinical relevance and to the understanding of psychiatric disorder in adolescents.

Acting Out↗
PubMed1975

Response of normal subjects to a single 2-milligram dose of glucagon administered intramuscularly.

Recently there has been increased interest in glucagon because in human radiographic and endoscopic studies it has been reported to relax the gallbladder, stomach, small bowel and colon. These results suggest it may be preferable as a diagnostic aid for these procedures. Therefore, we believed it important to assess the safety, and clinical laboratory responses after glucagon is given to normal subjects. Twenty normal subjects received 2 mg of glucagon and placebo intramuscularly at daily intervals, double-blind and crossover. After glucagon there was an increase in the WBC, bands, neutrophiles, fasting blood sugar, glucagon and insulin, and a decrease in the lymphocytes. There was no change in the pulse rate or blood pressure with minimal reports of side effects. These results tend to confirm other reports that glucagon is one of the stress hormones. Glucagon is remarkably safe and produces few, mild and transient side effects, not much greater than placebo.

Adult↗