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Biomedical subjects

B Davis

Publications and source records attributed to B Davis.

At least 145 records · Page 8Linked to original sources
PubMed1993

Quality audit of megavoltage radiotherapy units: intercomparison of dose at a reference point using a mailed TL-dosimetry system.

A dosimetry intercomparison based on mailed TL-dosimeters and the well proven IAEA/EORTC phantom is described. Its aim is to identify discrepancies in dosimetry larger than +/- 3%. Dosimeters were mailed to all radiotherapy centres in Switzerland for irradiation with 2 Gy at a reference point in a water container, using photons and electrons. Thirty-six beams were monitored. The results show an agreement of within 2% for the majority of the beams monitored. Two electron beams were at 6% of the reference value.

Cobalt Radioisotopes↗
PubMed1993

Preliminary, dermatologic first step criteria for lupus erythematosus and second step criteria for systemic lupus erythematosus.

BACKGROUND: Comparisons of cases of systemic lupus erythematosus (SLE) with cases of rheumatoid arthritis and other rheumatologic disorders affords the basis of the 1982 revised criteria of the American Rheumatism Association (ARA) for classifying SLE cases. We address three questions: Do comparisons of LE cases with non-LE cases that have suggestive skin lesions yield criteria for use in dermatology clinics for primary classification of cases with photo distributions of skin lesions? Do comparisons of SLE with cutaneous LE cases yield the same or similar criteria to the revised ARA criteria for SLE? How should subacute cutaneous LE cases be evaluated for signs of significant systemic involvement? METHODS: Discriminant analyses on 168 cases with skin lesions suggestive of LE were performed using data based on the ARA criteria for SLE and study factors for cutaneous LE suggested by the European Academy of Dermatology and Venereology. RESULTS: These yielded two sets of criteria: (1) The 11 preliminary, dermatologic first step criteria (10 plus 1 for discoid lesions and histology) serve to classify cases as LE or non-LE. (2) The 11 preliminary, dermatologic second step criteria classify LE cases as cutaneous LE or systemic LE. Interestingly, 5 of 11 of these second step criteria differ from the 11 ARA criteria for systemic LE. These second step criteria afford a useful means of distinguishing between subacute cutaneous LE cases with or without significant systemic involvement. CONCLUSIONS: The study factors included in both the first and the second step criteria fall into three groups, notably clinical criteria, laboratory criteria, and "added study factors." The latter factors distinguish between the groups compared (LE vs. non-LE and cutaneous vs. systemic LE) but not as well as the study factors included as "criteria."

Humans↗
PubMed1993

Calibration of the Canon Autoref R-1 for continuous measurement of accommodation.

The Canon Autoref R-1 is an infrared optometer which allows free-space viewing. Pugh and Winn described hardware modifications necessary to convert the Autoref R-1 from an instrument capable of taking single static measurements of the eye's accommodative (refractive) status to an instrument capable of continuous measurement of the accommodative status of the eye. We describe two methods of calibrating the Autoref R-1 for continuous measurement of accommodation for any individual eye. The assumptions and sources of error underlying these calibration techniques are discussed. We also describe further hardware modifications to simplify signal acquisition from the Autoref R-1.

Accommodation, Ocular↗
PubMed1993

Rational behavior training effectiveness for white and nonwhite incarcerated felons.

45 incarcerated male felons in a medium-security state correctional institution participated in a Rational Behavior Training treatment outcome study. 58% of the subjects were white, 18% were African-American, 17% were Hispanic, and 7% were classified as other. Subjects were selected from an institutional group-therapy waiting list and randomly assigned to one of four group facilitators. The Novaco Provocation Inventory, Buss-Durkee Hostility Inventory, and Rational Behavior Training Concepts Test were administered before and after the 10-wk. treatment period. No differences in gain scores (pretest minus posttest) were observed although the slightly greater improvement on the concepts test by subjects of ethnic minority encourages further study.

Adult↗
PubMed1992

Impaired in vitro growth of purified (CD34+) hematopoietic progenitors in human immunodeficiency virus-1 seropositive thrombocytopenic individuals.

In this report the role played by human immunodeficiency virus type-1 (HIV-1) in the pathogenesis of HIV-1-related thrombocytopenia was investigated. CD34+ hematopoietic stem/progenitor cells were purified from the bone marrow (BM) of HIV-1(+) thrombocytopenic patients, HIV-1(+) nonthrombocytopenic individuals, HIV-1(-) patients with immune thrombocytopenic purpura, and HIV-1(-) normal donors. CD34+ cells from HIV-1(+) thrombocytopenic individuals alone showed a reduced capacity to give rise to megakaryocytic colonies (CFU-Meg) and also a progressive and significant decline in cell number when placed in liquid culture containing recombinant human interleukin-3 (rIL-3). This decline involved not only megakaryocyte but also erythroid and granulocyte/macrophage progenitors. The defects in megakaryocyte colony formation and CD34+ cell growth did not result from a productive HIV-1 infection of CD34+ cells. Moreover, HIV-1 DNA was absent from CD34+ cells in 10 of 12 thrombocytopenic patients examined. On the other hand, the decreased survival/proliferation of CD34+ cells in liquid culture, within the HIV-1(+) thrombocytopenic patients, was correlated with the presence of HIV-1 p24 antigen in BM plasma. These results demonstrate an impairment of CD34+ cells in HIV-1(+) individuals presenting thrombocytopenia as the only hematologic manifestation. Furthermore, these findings suggest that increased viral replication in the BM microenvironment may cause this impairment and possibly contributes to HIV-induced thrombocytopenia.

Acquired Immunodeficiency Syndrome↗
PubMed1992

Renin predicts diastolic blood pressure response to nonpharmacologic and pharmacologic therapy.

OBJECTIVE: Plasma renin activity was measured at baseline and 6 months in a trial of nonpharmacologic therapy of mild hypertension to determine whether plasma renin activity predicts the diastolic blood pressure (DBP) response to nonpharmacologic therapy. DESIGN, SETTING, AND PARTICIPANTS: Randomized controlled trial of volunteers from the general community with mild hypertension (DBP between 90 and 100 mm Hg), off all antihypertensive therapy at baseline, treated in special research clinics (n = 593). INTERVENTIONS: Subjects were randomly assigned to usual, weight loss, or low sodium/high potassium diet and then randomly assigned to receive placebo, chlorthalidone, or atenolol. MAIN OUTCOME MEASURES: Renin was analyzed as plasma renin activity and as a renin index (logarithm of 24-hour urinary sodium excretion times logarithm of plasma renin activity) (593 patients at baseline and 6 months) to correct for varied sodium intakes. The DBP was measured using the random zero device. RESULTS: Change in DBP at 6 months could be predicted from baseline plasma renin activity or renin index. The DBP was decreased after 6 months of therapy by 2 mm Hg for each unit increase in baseline plasma renin activity and by 0.16 mm Hg for each unit increase in baseline renin index. Patients in the highest renin index quartile had a greater DBP response to atenolol therapy, and patients in the lowest renin index quartile had a greater DBP response to chlorthalidone therapy. Weight loss diet achieved a greater reduction in DBP in patients with higher baseline renin index and had an additive effect on DBP response in both of the drug groups. Patients on a weight loss diet receiving placebo in the highest baseline renin index quartile had a reduction in DBP of 12.4 mm Hg, compared with 4.4 mm Hg in the lowest baseline renin index quartile (P = .009). A low sodium/high potassium diet had a lesser effect than a weight loss diet on pharmacologic therapy. As with the weight loss diet, patients on a low sodium/high potassium diet in the highest baseline renin index quartile had a greater reduction in DBP than patients in the lowest baseline renin index quartile. CONCLUSIONS: These data suggest a significant relationship between baseline levels of plasma renin index and the likelihood of success of nonpharmacologic treatment of hypertension.

Adult↗
PubMed1992

Development of myopia in infants with birth weights less than 1251 grams. The Cryotherapy for Retinopathy of Prematurity Cooperative Group.

The authors report on the incidence of myopia in a large group of premature infants with birth weights of less than 1251 g followed as part of the multicenter study of Cryotherapy for Retinopathy of Prematurity. None of the eyes reported here underwent cryotherapy. Eyes were refracted using cycloplegic retinoscopy at 3 months (n = 2916), 12 months (n = 2626), and 24 months (n = 961 at 5 of the 23 centers) after term. Myopia was observed in approximately 20% of the children at each test age. The percentage of high myopia (greater than or equal to 5 diopters) doubled from 2% to 4.6% between 3 and 12 months and remained stable thereafter. Lower birth weight and increasing severity of retinopathy of prematurity (ROP) were strong predictors of myopia and high myopia. In addition, anisometropia, astigmatism, and the presence of posterior pole residua from ROP also were associated with a higher incidence of myopia and high myopia.

Anisometropia↗
PubMed1992

The Trial of Antihypertensive Interventions and Management (TAIM) Study. Final results with regard to blood pressure, cardiovascular risk, and quality of life.

The Trial of Antihypertensives Interventions and Management (TAIM) was a multicenter double-blind placebo-controlled clinical trial of drug and diet combinations for the treatment of mild hypertension among 878 participants, ages 21 to 65, 110% to 160% ideal weight, and with baseline diastolic blood pressure 90 to 100 mm Hg. The drugs used were placebo, chlorthalidone (25 mg/daily) or atenolol (50 mg/daily). The diets studied were usual, weight loss, sodium reduction/potassium increase. Trial end points were 6-month diastolic blood pressure change, cardiovascular risk change, and quality of life change. Either drug combined with weight loss produced the greatest blood pressure reduction of 15 mm Hg, compared to 8 mm Hg on placebo/usual diet. Adding sodium restriction to either drug did not enhance blood pressure lowering effect. Drugs outperformed diet in terms of antihypertensive effect. However, those on placebo and assigned to weight reduction who lost more than 4.5 kg and those on sodium restriction who reduced sodium to less than 70 mEq daily lowered blood pressure to a similar extent as those on either of the two drugs alone. Cardiovascular risk at 6 months relative to baseline ranged from 0.85 in weight loss/atenolol subgroup to 1.04 in the usual diet/chlorthalidone subgroup. Blacks were more responsive to chlorthalidone plus weight loss and whites to atenolol plus weight loss. Quality of life, as measured by scales of distress and well-being, was favorably affected by weight reduction. Although there were few side effects of the drugs and most patients improved on most parameters, sexual complaints were worsened among those on chlorthalidone and usual diet compared to placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Body composition and energy metabolism in resting and exercising muslims during Ramadan fast.

Muslims abstain from food and drink from dawn to sunset during Ramadam, the ninth month of the Islamic calendar. The purpose of this study was to examine the changes that occurred in body composition and both resting and exercise metabolism during a 4 week Ramadan fast. Subjects consumed an average of 1220 kcal each day during Ramadan and lost a significant 1.92 kg body weight. The subjects also lost 2.8% fat. Fat-free mass did not change. Serum sodium, chloride, and protein increased during the first week of Ramadan and returned to the pre-fasting levels during the last week. This indicates a state of dehydratation existed during the first week of Ramadan. Consistent with this is first week 1.13 kg body weight loss with no change in percent fat. First week Ramadan tests showed a significant decrease in VO2max with a return to the pre-test levels in the last week. The lower resting afternoon VO2 suggests that during Ramadan the body's metabolism slows down during the day in order to conserve its energy stores, however, exercise economy as measured by submaximal VO2 in mk/kg/min is not affected.

Adult↗
PubMed1991

Characterization and pharmacokinetic parameters of recombinant soluble interleukin-4 receptor.

The interleukin-4 receptor (IL-4R) is expressed as a 140-Kd membrane glycoprotein that binds IL-4 with high affinity. Recently, cDNA clones for the murine IL-4R have been isolated. One clone encodes an integral membrane protein, while another encodes a protein in which translation is terminated before the transmembrane region, thus producing a soluble form of the IL-4R (sIL-4R). HeLa cell clones overexpressing sIL-4R were isolated using a novel filter-overlay and 125I-IL-4 ligand binding technique. Quantitative analysis demonstrated that the kinetics and affinity of IL-4 binding to the recombinant sIL-4R were similar to the native membrane-bound IL-4R. As low doses of sIL-4R specifically inhibited IL-4-induced proliferative responses in vitro, sIL-4R biodistribution and elimination parameters were evaluated to assess the pharmacokinetic potential of sIL-4R as a therapeutic agent. Pharmacokinetic studies demonstrated that radiolabeled sIL-4R had a distribution half-life of 9 minutes and an elimination half-life of 2.3 hours following intravenous (IV) administration. When administered by intraperitoneal or subcutaneous (SC) injection, the elimination half-lives were prolonged to 4.2 hours and 6.2 hours, respectively. Although the initial blood level of sIL-4R was reduced if administered by SC injection, the bioavailability was comparable with IV administration. The main sites of sIL-4R elimination were the liver and kidney.

Animals↗
PubMed1991

An exploratory study of environmental and medical factors potentially related to childhood cancer.

To determine whether a general-purpose epidemiologic questionnaire can be used in childhood cancer hospitals to identify associations between environmental factors and the major types of childhood cancer, we report the results of the analysis of the data obtained from such a questionnaire. On admission to St. Jude Children's Research Hospital in Memphis, Tennessee, between 1979 and 1986 a questionnaire was administered to 1,270 mothers of patients diagnosed with childhood cancer. Approximately one-half of the children had acute leukemias (n = 629); the remainder had lymphomas (n = 237) or solid tumors (n = 404). Responses to questions regarding the patients' and parents' environmental and medical histories were compared across nine diagnostic categories. Only 5 of 232 variables remained nominally statistically significant (P less than 0.05) after adjusting for confounding by patient or maternal age, year of birth or diagnosis, patient's race, and social class. The variables identified were length of time the patient was breast-fed (chi 2 = 16.1, P = 0.04); having a garden with fertilizers, herbicides, and pesticides (chi 2 = 17.2, P = 0.03); maternal use of sex hormones during the year before the patient's birth (chi 2 = 18.2, P = 0.02); maternal cigarette consumption (chi 2 = 18.0, P = 0.02); and patient contact with persons with cancer (chi 2 = 20.7, P = 0.01). Despite the large number of patients studied, we identified fewer significant variables than would be expected, on the average, under the null hypothesis. We conclude that the data obtained from a general-purpose epidemiologic questionnaire do not provide a useful overview of the association between exposure to environmental factors and several types of childhood cancer.

Breast Feeding↗