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Biomedical subjects

D R Davis

Publications and source records attributed to D R Davis.

At least 19 recordsLinked to original sources
PubMed1992

AIDS/HIV risk behavior among the chronic mentally ill.

OBJECTIVE: There is growing concern that chronic mentally ill adults living in the community have a high risk for HIV infection. The purpose of this study was to identify risk knowledge, high-risk behaviors, and risk-related encounters of chronic psychiatric outpatients. METHOD: Detailed information on high-risk behaviors and risk-related situations during the past 12 months was collected from 60 outpatients appearing for regular visits at inner-city community mental health clinics. RESULTS: Of the 60 outpatients, 37 (62%) had been sexually active during the past year, and 42% of the men and 19% of the women reported multiple sexual contacts and infrequent use of condoms during intercourse. Assessments of the patients' knowledge of AIDS risks revealed substantial deficits in their practical understanding of AIDS and risk reduction measures. Although use of intravenous drugs was uncommon in this group, many subjects reported histories of 1) trading sex for money, drugs, or a place to stay, 2) coercion to engage in unwanted sex, 3) causal sexual encounters, and 4) sexual activity after use of drugs or intoxicants. Twenty percent of the subjects had met their sexual partners on the streets, in parks, or in other public places. One-third had been treated for sexually transmitted diseases other than AIDS. CONCLUSIONS: These findings underscore the need for AIDS risk assessment, counseling, and prevention programs for the chronic mentally ill.

Acquired Immunodeficiency Syndrome↗
PubMed1991

1H-15N NMR studies of Escherichia coli tRNA(Phe) from hisT mutants: a structural role for pseudouridine.

Escherichia coli tRNA(Phe)U39 was isolated from a specially constructed bacterial strain (DD1003/pRK3) carrying mutations in the hisT gene (the structural gene for tRNA pseudouridine synthase I) and in the pyrB gene (uracil auxotrophy). The pheU gene for tRNA(Phe) under control of the native tRNA promoter was on a multicopy plasmid and gave up to 40-fold overproduction of tRNA(Phe)U39. The double mutant permitted efficient incorporation of [3-15N]uracil, resulting in greater than 95% 15N enrichment of uracil-derived bases. 1H and 1H-15N NMR experiments were used to assign the low-field proton resonances to specific hydrogen-bonding interactions. 1H NMR assignments indicate that tRNA(Phe)U39 has a structure similar to that of native tRNA(Phe) except in the anticodon region where replacement of pseudouridine (psi) at position 39 with uridine (U) destabilizes hydrogen-bonding interactions at the base of the anticodon stem. We propose that U----psi modifications further stabilize interactions normally available to U by providing an additional locus for hydrogen bonding to the pyrimidine ring.

Base Sequence↗
PubMed1991

Central and peripheral nervous system demyelination after infection with Mycoplasma pneumonia: evidence of an autoimmune process.

We have reported a unique case of multiple central and peripheral nervous system abnormalities after a serologically documented infection due to Mycoplasma pneumoniae. The evidence suggests that this organism is capable of causing demyelination, probably through an autoimmune process. This case may help to provide further insight into the pathogenetic mechanisms involved in other demyelinating diseases in which the triggering exogenous agent is unknown. Certainly this case demonstrated that both central and peripheral nervous system demyelination can occur and that patients with M pneumoniae infections should be observed closely for possible development of neurologic symptoms.

Adult↗
PubMed1991

Significance of circumsporozoite-specific antibody in the natural transmission of Plasmodium falciparum, Plasmodium vivax, and Plasmodium malariae in an aboriginal (Orang Asli) population of central peninsula Malaysia.

Two hundred and seventy-five Orang Asli volunteers living in nine villages in the Pos Legap Valley of Perak State, peninsular Malaysia, participated in a prospective study designed to characterize the epidemiological, parasitological, and entomological characteristics of Plasmodium falciparum, P. vivax, and P. malariae malaria transmission. Prevalence rates for the three plasmodial species at initiation of the study ranged from 56% in the 0-4-year-old age group to 0% in individuals over the age of 40. Entomological surveys were conducted, enabling us to determine mosquito salivary gland-positive rates and entomological inoculation rates of 1.2 infectious mosquito bites per person per month for P. falciparum, 2.4 for P. vivax, and 0.3 for P. malariae. Cumulative incidence rates over the 16 weeks of the study, following radical cure of all volunteers, were 22.5% for P. falciparum, 12.7% for P. vivax, and 1.5% for P. malariae. The median baseline antibody titer against the immunodominant repetitive B cell epitope of P. falciparum or P. vivax circumsporozoite protein was significantly higher for volunteers who did not become parasitemic. Volunteers were selected for further study if they had evidence of being challenged with P. falciparum sporozoites during the study, based on a two-fold or greater increase in antibody titer against the immunodominant repetitive B cell epitope of the circumsporozoite protein. Resistance to infection was seen in six of 10 individuals who had high (greater than 25 OD units) baseline ELISA titers, compared with only three of 24 individuals who had low baseline ELISA titers (chi 2 P less than 0.02). A similar analysis for P. vivax did not show a significant correlation.

Adolescent↗
PubMed1991

A report on dementia in South Carolina, 1988-1990.

With the over age 65 population growing at a faster rate than the under 65 population, and with the strong effect of age on the incidence and prevalence of dementia, South Carolina faces a major health problem among its elderly residents by the year 2010. This report summarizes data on the 4,283 persons identified by the Statewide Alzheimer's Disease and Related Disorders Registry during the period 1988 to 1990. Sixty-one percent of these cases had a diagnosis of Alzheimer's disease or senile dementia and 62 percent of these were currently institutionalized. The demographic distribution of the AD cases did not change over the three-year period. Compared to community cases, those in institutions were generally older, and more likely to be women, unmarried, and white. The average time from onset of symptoms to diagnosis of AD was about five years.

Aged↗
PubMed1990

Xeroradiographic determination of effective setting expansion of a cristobalite investment.

Previous studies of setting expansion of gypsum-bonded investments have not examined how wax patterns expand with time. The purpose of this study was to provide a method of measuring wax patterns during the setting reaction. Ten MOD inlay wax patterns were invested individually in plastic casting rings and imaged at specific intervals on a stage on which both the rings and xeroradiographic cassettes were fixed. Distances between the axiogingival proximal walls, axiopulpal proximal walls, and axial walls were measured at each interval. Reproducibility of measurements of xeroradiographic images was about 0.3%. After setting, the wax was burned out, and the rings were cooled to room temperature and cast in a Bi-Sn alloy that did not shrink upon solidification. The castings were measured and the means compared with the means of xeroradiographic measurements. There was no significant difference between the expansion means of the axiogingival or axiopulpal dimensions measured by casting or xeroradiographically (p greater than 0.05, two-tailed t test). Significant differences (p less than 0.05) were seen between means of the axial expansion measured by castings and xeroradiographically, suggesting the formation of a void at the proviral walls of the wax patterns. All horizontal expansion occurred between two and 22 min from the start of mix.

Dental Casting Investment↗
PubMed1990

Effect of ring length and diameter on effective radial setting expansion.

It was previously demonstrated that flaring of MOD inlay castings was inversely proportional to the diameters of casting rings. The purpose of this study was (1) to determine if radial setting expansion of investment was primarily responsible for the inverse proportion and (2) to characterize further the fluid mechanics of setting expansion by determination of setting expansion in casting rings of different lengths and diameters. Eight sets of ten MOD inlay wax patterns with radiopaque markers at the axiogingival and axiopulpal junctions were individually invested in plastic casting rings in two groups: (A) 28 mm diameter and 30 mm, 32 mm, 34 mm, and 42 mm long; and (B) 28 mm, 40 mm, 51 mm, and 60 mm diameter and 34 mm long. All specimens were imaged (by xeroradiography) at specific intervals during the setting reaction; dimensions were measured on the images at each interval. In casting rings of different lengths, no significant differences (p greater than 0.05) were found in total effective setting expansion. Because setting expansion in the 28-mm-diameter rings was from 1.3% to 1.5% and diminished proportionately in rings of increasing diameter, setting expansion of investment appears to be the primary determinant of mold expansion. In casting rings of different diameters, significant differences (p less than 0.001) were found in total expansion in an apparent inverse proportion (p less than 0.001). Changes in dimension at intervals were strongly associated with time, and with time combined with diameter (p less than 0.001).

Dental Casting Investment↗
PubMed1990

Patterns of non-response to a mail survey.

This paper describes a basic investigation of possible non-response bias in a mail survey. We compare characteristics of responders and non-responders to a mail survey of health outcomes among participants of a longitudinal study of physical activity, physical fitness, and health. Results indicate that, at the first clinic visit, the responders were essentially the same as the non-responders on personal health history and laboratory measurements, while reporting significantly more family history of specific chronic diseases (cardiovascular disease, hypertension, stroke). The male responders were younger and reported more positive health behaviors as well as better weight and treadmill times at the first clinic visit. These results suggest that both response groups were equally healthy at entry, and that individuals who had family members with certain chronic conditions and who had positive health behaviors were more likely to respond (participate) in this health-related survey. Differences of this type could affect interpretation of future analyses. This work illustrates the importance of incorporating methods to examine non-response into any epidemiologic study.

Bias↗
PubMed1989

Plasmodium vivax resistance to chloroquine?

Two soldiers continued weekly prophylaxis with 300 mg chloroquine base on their return to Australia from Papua New Guinea but were not protected against Plasmodium vivax malaria. Both had symptoms and parasitaemia although plasma concentrations of chloroquine were considerably higher than those regarded as adequate for suppression of vivax malaria. Parasitaemia did not clear after one of the patients was treated with 600 mg chloroquine base. The results suggest the emergence of strains of P vivax with a reduced susceptibility to chloroquine.

Acute Disease↗
PubMed1989

Void formation by axial expansion of a gypsum-bonded investment.

The lengths of castings have been found to be dependent, in part, on the length of the ring lining material relative to the length of the casting ring. Five MOD inlay wax patterns were invested individually in open metal, in closed metal, and in plastic casting rings 35 mm or 42 mm long and 28 mm in diameter. The gingival walls of the wax patterns were placed either 8 mm or 15 mm from the uppermost ends of the rings. Specimens were broken in a mesiodistal direction, and the voids at the gingival walls were measured. The largest voids (139 microns) occurred in 42-mm-long plastic rings with the gingival walls 8 mm from the uppermost ends of the rings. The smallest voids (20 microns) occurred in the 35-mm-long closed metal rings. The boundaries between the investment and the voids were curved rather than accurately reflecting the straight gingival walls of the wax patterns.

Calcium Sulfate↗
PubMed1989

Effect of investment mass on distortion of MOD wax patterns.

Flaring of proximal walls of years, but not examined. In this experiment, the mass of investment peripheral to the wax patterns was varied by use of casting rings of the same lengths but of different diameters. Thirty castings were made individually, ten from each ring of 28 mm, 48 mm, and 60 mm diameter. The castings were cemented to their parent dies, sectioned mesiodistally, and the cement spaces at specific sites measured. Flaring angles were calculated for the proximal walls and were found to be inversely proportional to the diameters of the casting rings, and, thus, to the peripheral mass of investment. Further studies to detail the fluid mechanics of investments and to predict wax pattern behavior are warranted.

Dental Casting Investment↗
PubMed1989

Antimalarial drug susceptibility of Plasmodium falciparum isolates from forest fringe dwelling aborigines (Orang Asli) of Peninsular Malaysia.

The drug susceptibility of 70 isolates of Plasmodium falciparum to standard and experimental antimalarials was evaluated using a radioisotope microdilution method. All isolates were from forest fringe dwelling Orang Asli, the aborigines of Peninsular Malaysia. The geometric mean IC50 values were: chloroquine, 10 ng/ml; amodiaquine, 4.7 ng/ml; mefloquine, 2.8 ng/ml; quinine, 40.5 ng/ml; halofantrine, 1.5 ng/ml; enpiroline, 3 ng/ml; and pyrimethamine, 21 ng/ml. Four isolates exhibited decreased susceptibility to chloroquine (IC50 greater than 60 ng/ml), and one exhibited decreased susceptibility to quinine (IC50 = 161 ng/ml). Three isolates showed decreased susceptibility to mefloquine (IC50 = 10-11 ng/ml). The lack of drug pressure may account for the high prevalence of P. falciparum isolates susceptible to chloroquine.

Animals↗
PubMed1979

Impaired fertility in the jaundiced female (Gunn) rat.

The hyperbilirubinemic female Gunn rat has been reported to have impaired fertility. A total of 267 jaundiced (j/j) and 91 nonjaundiced (+/j) female Gunn rats were used in a series of experiments to characterize the nature of this reduced fertility. Sixteen percent of the jaundiced females mated and delivered litters which were characteristically small in number (4.5 pups). A comparison of the gross observations at necropsy of jaundiced and nonjaundiced pregnant rats indicated that the number of implantation sites and live fetuses were significantly lower in the jaundiced females. The number of fetal resorptions in these rats were significantly higher; whereas, the number of corpra lutea was similar for both genotypes. The significantly lower plasma bilirubin levels in the pregnant jaundiced rats compared to the nonpregnant suggested that the observed effect on fertility was related to the concentration of plasma bilirubin.

Animals↗