Search PubMed⌕ Search

Biomedical subjects

J R Davis

Publications and source records attributed to J R Davis.

At least 199 records · Page 11Linked to original sources
PubMed1988

Comparison of aerobic fitness and space motion sickness during the shuttle program.

Space motion sickness (SMS) is an important problem for short duration space flight and 71% of STS crewmembers develop symptoms. The search for effective countermeasures and factors that correlate with sensitivity has been extensive. Recently, several investigators have linked aerobic fitness with motion sickness sensitivity in the 1-G or high-G environment. This paper compares the aerobic fitness of 125 Shuttle crewmembers with their SMS symptom category. Aerobic fitness data were obtained from the exercise tolerance test (ETT) conducted nearest the time of launch. SMS data were derived from the medical debrief summaries. Mean VO2max for crewmembers in four SMS categories (none, mild, moderate, severe) were 44.55, 44.08, 46.5, and 44.24 ml.kg-1.min-1, respectively. Scattergrams with linear regression analysis comparing aerobic fitness and SMS symptom classification are also presented. Correlation coefficients comparing SMS categories vs. aerobic fitness for men and women reveal no definite relationship between the two factors. Due to the subjective nature of the data, further studies are suggested to corroborate these findings.

Female↗
PubMed1988

Occupational risk of prostate cancer: a cancer registry-based study.

Previous studies have suggested that certain occupational groups may be at increased risk for prostate cancer. A cancer registry-based case-control study was conducted to investigate possible associations between various occupations and the risk of prostate cancer among 1,239 case subjects and 3,717 age-matched control subjects. Elevated relative risk estimates were observed for farmers, mechanics, sheet metal workers, separating machine operators, and for men employed in several manufacturing industries. These findings are discussed in the context of previous studies, and suggestions for future research are provided.

Adult↗
PubMed1987

Mechanisms of TSH release: studies with forskolin, phorbol ester and A23187.

We have investigated the interactions of intracellular messenger systems which may regulate thyrotrophin (TSH) release in primary cultures of rat anterior pituitary cells. Calcium ionophore A23187 was used to raise intracellular free calcium, the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate (TPA) to activate protein kinase C, and forskolin to activate adenylate cyclase. Each of these agents stimulated TSH secretion in a dose-dependent manner, but the effect of forskolin was delayed for at least 6 h. The combined effects of A23187 and TPA on TSH secretion were simply additive, but forskolin synergistically enhanced the effect of A23187 and 55 mM potassium, but not that of TPA. Co-incubation of cells with 1 microM A23187 caused parallel upward shift of the TPA dose-response curve, and the further addition of 10 microM forskolin led to further upward shift. These results suggest that calcium mobilization and adenylate cyclase activation may interact synergistically to modulate TSH secretion. Raised cellular cyclic AMP content may amplify further the TSH release stimulated by the combination of protein kinase C activation and raised intracellular free calcium.

Adenylyl Cyclases↗
PubMed1987

Partial hydatidiform moles: deoxyribonucleic acid content and course.

Partial moles are either diploid (46 chromosomes) or triploid (69 chromosomes). In 35 cases ploidy was measured by flow cytometry for nuclear deoxyribonucleic acid quantitation, indicating approximate chromosome number. Six of the 35 were triploid (17%) and the balance was diploid (83%). No complications occurred in the triploid group, while five of 25 (20%) diploid cases with evaluable follow-up had nonfatal sequelae. Complications included persistent mole treated by recurettage and four cases requiring chemotherapy (human chorionic gonadotropin titer plateau, clinical metastasis, overt choriocarcinoma, and placental site trophoblastic tumor). A combined morphologic and genetic classification of partial moles is recommended for identification and risk assessment. Deoxyribonucleic acid cell cycle fractions of the diploid partial moles may be helpful in the identification of patients at high risk for complications. A proliferation index greater than 3.6 separated the cases with sequelae from most of the uncomplicated cases (sensitivity 100%, specificity 95%).

DNA, Neoplasm↗
PubMed1987

Evaluation of a sensitive chemiluminescent assay for TSH in the follow-up of treated thyrotoxicosis.

We have studied 21 patients treated for thyrotoxicosis to evaluate a highly sensitive chemiluminescent thyrotrophin (TSH) assay in the assessment of changing thyroid status. Serum TSH was generally suppressed with high serum thyroid hormone concentrations and invariably rose when free T4 and T3 fell substantially below the normal range. However TSH values in 14 of the 21 patients remained undetectable or subnormal for variable periods despite normal or even slightly subnormal free T4 and T3 values. The level of free T4 and T3 at which TSH concentrations rose was highly variable, suggesting differing degrees of hypothalamo-pituitary suppression. Sensitive TSH assays are likely to provide useful information regarding physiological regulation of TSH secretion in man, but our data indicate that in certain circumstances these assays used alone will be inadequate for biochemical assessment of thyroid status.

Adult↗
PubMed1987

Fragile sites are unrelated to reciprocal translocation breakpoints.

In 492 cases of reciprocal translocations in balanced carriers, the 984 breakpoints were studied for a possible relationship to the 45 fragile sites. Random coincidence was predicted at 14% and the observed coincidence was 14.3%, indicating that the two events are unrelated. However, chromosomes 1, 11 and 14 were exceptions and did show a statistically significant relationship.

Abortion, Spontaneous↗
PubMed1987

Interactive computer graphic image analysis for functional neurosurgery.

This study deals with the use of microcomputer graphic analysis of preoperative magnetic resonance imaging (MRI) scans in functional neurosurgical procedures. Three patients (2 treated for thalamotomy and 1 for thalamic stimulation) had preadmission MRI scans which delineated the classic internal landmarks used in functional neurosurgery. These data were then manipulated and stored using a microcomputer-based graphic analysis system. Intraoperative pattern matching of preadmission graphics with the intraoperative skull X-rays allowed determination of the planned target in the x, y and z coordinates. The accuracy of the graphics FM-PC and AC-PC points was confirmed with the use of ventriculography, stimulation, and postoperative MRI scans. This simple, inexpensive method obviates the need for ventriculography, sedation, intraoperative MRI with a scan-compatible frame, and has the accuracy necessary for functional procedures.

Aged↗
PubMed1987

Microcomputer stereotactic atlas.

A stereotactic atlas to determine thalamic target sites has been incorporated into a microcomputer. Variability studies of the thalamus with mean and standard deviations of nuclear borders are depicted graphically for overlay onto operative images. Internal landmarks traditionally used to reference target points for functional stereotaxis may be determined by conventional ventriculography or derived from magnetic resonance scans. Modeling of polyline vertices established from gray scale contour mapping and atlas reconstructions further enhance the spatial understanding of relationships to midline structures. Computer integration of anatomic reference points, graphically depicted images and stereotactic atlas data into head frame coordinates can be accomplished. This method is consistent with established stereotactic techniques and allows the visual conceptualization of imaged and graphic data for functional stereotaxis.

Brain↗
PubMed1987

Single-scan stereotactic tumor biopsy and brachytherapy.

Stereotactic tumor biopsy and brachytherapy catheter implantation can be accomplished with targets derived from computed axial tomography and magnetic resonance scans. Computer manipulation of image data allows both diagnostic and therapeutic procedures to be carried out from a single set of scan slices. This eliminates the need for repeat scanning as part of the surgical procedure. Microcomputer technology is sufficiently advanced to handle the images and graphics necessary for stereotactic neurosurgery. A system based on the IBM PC/AT designed for this purpose uses readily available graphics software and custom-designed imaging programs. Direct loading of computed axial or magnetic resonance scan images from magnetic tape can be accomplished. Determination of points, contours and volumes in three-dimensional space allows intraoperative alignment of image data and patient landmarks within the stereotactic head frame using pattern recognition overlays. Three-axis scaling for magnification correction along with rotational and linear data transformations provide the basis for single-scan stereotaxis. Interactive computer graphics integrate image, patient and frame coordinates for target determination. This method eliminates the need to design and fabricate nonmagnetic or radiolucent scanner-compatible devices.

Biopsy↗
PubMed1987

Overdrive suppression of conduction at the canine Purkinje-muscle junction.

We have shown previously that overdrive suppression of conduction in depolarized His-Purkinje tissue requires conduction asymmetry. In this study we examined whether overdrive suppression of conduction can occur at the Purkinje-muscle junction, where natural asymmetry of conduction exists. Canine Purkinje-muscle preparations were superfused with hyperkalemic Tyrode's solution (KCl 8 to 12 mM), and action potentials were recorded from Purkinje, junctional, and muscle cells. Initially, the Purkinje fiber was paced at the shortest cycle length at which 1:1 anterograde Purkinje-muscle conduction occurred. The papillary muscle then was paced for 10 to 50 beats at shorter cycle lengths during which, because of conduction asymmetry at the Purkinje-muscle junction, 1:1 retrograde muscle-Purkinje conduction also occurred. After overdrive papillary muscle pacing, Purkinje fiber pacing at the same cycle length that previously resulted in 1:1 conduction now produced transient Purkinje-muscle conduction block (overdrive suppression of conduction). The degree and duration of overdrive suppression of conduction were proportional to the rate and duration of overdrive pacing. After overdrive pacing, Purkinje cell action potential amplitude and Vmax recovered within 300 msec, yet conduction block persisted for up to 7 sec. In contrast, excitability in papillary muscle cells near the Purkinje-muscle junction increased continuously after overdrive pacing. These data suggest that rapid activation of Purkinje cells during overdrive pacing was not required for overdrive suppression of conduction and that restoration of conduction after overdrive pacing was determined primarily by recovery of excitability in papillary muscle cells. Transient Purkinje-muscle conduction block after periods of rapid ventricular rates might account for overdrive-induced conduction disturbances normally attributed to bundle branch block.

Action Potentials↗
PubMed1987

Occupation, smoking, and alcohol in the epidemiology of bladder cancer.

We conducted a case-control study to evaluate the effects of occupation, smoking, and alcohol consumption on bladder cancer risk. A total of 823 male cases and 2,469 age-matched controls were identified through the Missouri Cancer Registry. Relative risk estimates of 2.0 or greater were observed for janitors and cleaners, mechanics, miners, and printers. Current cigarette smoking was associated with a two-fold excess risk of bladder cancer, whereas alcohol consumption showed no association with bladder cancer risk.

Alcohol Drinking↗
PubMed1986

Cytogenetic and clinical features of placental moles: synopsis and update.

Abnormalities of fertilization are responsible for two types of placental moles. This synopsis of the two syndromes includes definition, relative incidence, mechanism of fertilization, and clinical course. Controversy regarding the comparative course has diminished with the recognition that partial moles can have sequelae requiring chemotherapy, although less frequently than complete moles. An important subgroup of complete moles is dispermic and heterozygous (usually 46,XY), and these have a disproportionately high rate of postmolar complications. Recommendations are made for routine cytogenetic study of moles in order to foster precision in classification and search for heterozygosity in complete moles. A technique is given for isolation and promotion of growth in vitro of molar trophoblastic cells. Additional information about the two syndromes is needed, a challenge for cytogeneticists.

Adult↗
PubMed1986

Effects of exercise-training on the thermic effect of food and body fatness of adult women.

Resting metabolic rate (RMR), thermic effect of food (TEF), aerobic capacity (VO2max), body fat, and food intake were measured in 10 healthy women before and after a 10 week graded exercise program of jogging. Pretraining TEF was a linear function of VO2max. Following exercise training, the women showed a significant increase (20%) in VO2max and loss (10.4%) of body fat; body weight did not change. Fat loss was directly related to changes in VO2max and RMR. The women showed a wide variation of changes in RMR (-21 to +2%) and TEF (-32 to +66%) from their pretraining levels. The changes in RMR and TEF were significantly positively correlated with improvements in VO2max. Analyses using multiple regression techniques, indicated that the changes in RMR and TEF accounted for 96.2% of the total variation in the changes of VO2max. Analyses of food intake indicated that diet composition (but not caloric intake) was highly related to the changes in VO2max, RMR, TEF and body fatness. Present results support further our hypothesis, that VO2max is an important physiological index of dietary thermogenesis and fat loss of individuals of normal body weight and fatness. Possible nutritional and physiological factors that may explain the wide variation in RMR and TEF of the women are discussed.

Adipose Tissue↗
PubMed1986

A comparison of the cellulose acetate electrophoretic serum lipoprotein-cholesterol profile of the adult male rat with other species.

A comparison was made of the serum lipoprotein-cholesterol profile, obtained by cellulose acetate electrophoresis coupled with an enzymatic stain for total cholesterol, of the adult male rat, mouse, rabbit, dog, monkey and human. Four cholesterol-staining lipoprotein bands were detected in rat serum, while only three cholesterol-staining lipoprotein bands were present in the other species studied. The apparently unique lipoprotein-cholesterol band in the rat was found to electrophoretically migrate in the prealbumin region of rat serum, has been named prealbumin lipoprotein-cholesterol (PAL-C) and was shown to be a high density lipoprotein (HDL). Of the species studied those more susceptible to experimentally induced atherosclerosis had higher low density lipoprotein-cholesterol to HDL-cholesterol ratios compared to those species least susceptible to experimentally induced atherosclerosis.

Adult↗
PubMed1986

Relapse prevention and smoking cessation.

A multicomponent smoking relapse prevention treatment based on Marlatt and Gordon's (1980) model of the relapse process was developed and evaluated. Behavior-analytic methods were used to develop assessment instruments, training situations, and coping responses. The prevention components were presented in the context of a basic broad-spectrum stop-smoking program, and were compared with the basic program plus discussion control, and the basic program alone. Smoking-related dependent variables generally did not differ between groups at any time from pre-treatment to 12 month follow-up. Only the subjects in the relapse prevention condition improved problem-solving and social skills needed to cope with high-risk situations. These subjects also tended to take longer to relapse and smoke fewer cigarettes at the time of relapse. Subjects above the median level of competence on measures of social skill at post-treatment remained abstinent significantly longer. Maintenance of non-smoking was found to be related to the degree of competence with which individuals deal with high-risk situations. Results are discussed in relation to models of compliance with therapeutic regimens.

Adult↗
PubMed1986

Effects of dehydroepiandrosterone acetate on metabolism, body weight and composition of male and female rats.

Twenty adult Sprague-Dawley outbred rats (10 male and 10 female) were fed a nonpurified diet without or containing dehydroepiandrosterone acetate (DHEA 6 g/kg diet) for 11 w. DHEA-treated animals weighed less than the controls after 6 wk and until the end of treatment. However, only the differences between male groups were statistically significant. Food intake of the DHEA-fed animals was not affected, but resting heat production was elevated for both sexes. Serum triglyceride levels and activity of hepatic glucose-6-phosphate dehydrogenase of the experimental groups were lower than controls. Analyses of body composition indicated DHEA-treated animals had proportionately less body fat and therefore more body water, protein and ash than controls. In most cases, differences in body composition were due primarily to effects of DHEA on the female animals. In a second experiment, DHEA treatment did not alter urinary ketone levels nor did it enhance citrate synthase activity in interscapular brown fat, skeletal muscle, heart or liver. Findings suggest that DHEA acetate treatment affected body weight, body composition and utilization of dietary energy by both impairing fat synthesis and promoting fat-free tissue deposition and resting heat production. Possible mechanisms by which DHEA may affect metabolism are discussed.

Animals↗
PubMed1986

Contour interaction in the preschool child.

Preschool children show poorer visual acuity when tested with multiple optotypes than when tested with isolated optotypes. This difference in performance could be the result of contour interaction or the greater distractions imposed by a multiple optotype display, which may be beyond a young child's ability. To differentiate between these alternatives, isolated and surrounded visual acuity were measured in children aged 2 to 7 years by pairing a Landolt C with an O. The surrounded optotypes were identical to the isolated optotypes with the exception of the flanking bars located at 2.5 times the minimum angle of resolution (MAR) of the optotype. A two-alternative forced choice interleaved paradigm was used to measure surrounded and isolated visual acuity defined as 75% correct. When the test demands were equated by measuring isolated and surrounded acuity using a single optotype, poorer visual acuity was obtained with surrounded optotypes. This suggests that preschool children, like adults, show contour interaction.

Adult↗