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Biomedical subjects

D Thompson

Publications and source records attributed to D Thompson.

At least 343 records · Page 19Linked to original sources
PubMed1989

Adolescent third-trimester enrollment in prenatal care.

This study reports the demographic and reproductive characteristics of 87 adolescents (11-19 years of age) who entered prenatal care during the third trimester of pregnancy at a publicly funded program during a 6-month period of 1987-1988, as well as their self-reported reasons for delayed prenatal care. The findings suggest that concealment of the pregnancy was the primary reason for younger adolescents (11-17 years), while poor motivation to attend prenatal care was often cited by the older adolescents (18-19 years). Older adolescents appeared to be particularly at risk for poor pregnancy outcome: 63% were mothers; the identified pregnancy was the third child for 20%; 42% smoked during pregnancy; and 22% entered care during the period from 36 to 41 weeks of gestation. The apparently poor motivation to attend prenatal care and the closely spaced pregnancies of this age group suggest that the second and third children of adolescent mothers may be a particularly vulnerable pediatric population.

Adolescent↗
PubMed1989

Machine vision system for diagnostic histopathology.

In a machine vision system for the diagnostic assessment of histopathologic sections, human diagnostic knowledge and human ability to recognize components in a complex image need to be emulated. This is attempted by three integrated expert systems, supported by a multiprocessor computer with data-driven, dynamically reconfigurable architecture.

Adenocarcinoma↗
PubMed1989

Exercise performance following intense, short-term ventilatory work.

Evidence exists to indicate that prolonged ventilatory work fatigues respiratory muscles and may limit exercise tolerance. However, the effects of short-duration, high-intensity ventilatory work on subsequent exercise remains in question. We tested the hypothesis that intense short-term volitional hyperpnea would result in respiratory muscle fatigue and would therefore hinder subsequent exercise tolerance. Pulmonary function was determined in ten healthy, male subjects before and after two constant load exercise tests to exhaustion on a cycle ergometer. Test 1 was a preliminary test to determine VO2max, peak exercise VE, and peak exercise power output. Test 2 was a constant load (85% peak power output) exercise test to exhaustion. Test 3 was identical to test 2 but was preceded by 10 min of volitional, isocapnic hyperpnea (85% of peak exercise V.E) at a controlled frequency and tidal volume. Pulmonary function measures (FVC, FEV1, FEV1/FVC, and peak flow) were not significantly (P less than 0.05) altered by the volitional hyperpnea. Ventilation and gas exchange variables (VO2, VE, f, end-tidal PO2 and PCO2, VE/VO2, VE/VCO2, %SaO2) during exercise and time to exhaustion were not significantly (P less than 0.05) different between treatments. These experiments failed to show any effect of short-term ventilatory work on pulmonary function or subsequent exercise performance.

Adult↗
PubMed1989

Reach distance and safety standards.

The reach of British males of 99th percentile stature over different height barriers was determined to establish reach distances for a proposed Comité Europeen de Normalisation (CEN) standard. The distances recorded are considerably in excess of those given in the draft West German standard DIN 31001 1984, and those given in the recently published British standard code of practice for safety of machinery BS.5304. Data are included from earlier experiments which show that the safety distances would also be inadequate for the 95th percentile stature British male. It is suggested that reasons for the discrepancies arise mainly from the differences in the way that the reach measurements were obtained.

Adult↗
PubMed1989

Genetic analysis of the N transcription antitermination system of phage lambda.

Regulation of coliphage lambda gene expression occurs, in part, by a process of termination and antitermination of transcription. The N gene product, one of two lambda encoded antitermination proteins, acts with host encoded proteins, Nus, at sites, nut, located downstream of the early promoters to render the transcribing RNA polymerase resistant to many downstream termination signals. We discuss the nature of some of the proteins and sites involved in this process.

Amino Acid Sequence↗
PubMed1989

Initial assessment data from a 43-site program for homeless chronic mentally ill veterans.

In May 1987 the Veterans Administration established the Homeless Chronically Mentally Ill Veterans Program at 43 sites to provide outreach, health care, and residential rehabilitation services. Intake assessment data on 10,529 homeless veterans screened as potential candidates for clinical services during the program's first 11 months are presented. With a median age of 40, the homeless veterans were considerably younger than veterans in the general U.S. population. More had served in the Vietnam era than in other military eras. Almost three-fifths were white, and a third were black; more than 40 percent were receiving some form of public support. Almost half manifested one or more severe psychiatric symptoms at screening, and almost two-thirds had previously been hospitalized for either a psychiatric or a substance abuse problem.

Adult↗
PubMed1989

Image understanding system for histopathology.

An image understanding machine vision system for histological diagnoses is based on three interacting expert systems: a diagnostic expert system utilizing terms familiar to pathologists, an interpretive expert system relating human diagnostic concepts to computable histometric features and a scene segmentation expert system which extracts the diagnostic information from the imagery. The control software for the image understanding system resides on a multiprocessor computer. This article details measures to maintain system efficiency and to accommodate the requirements of interprocess communication and processing task scheduling.

Diagnosis, Computer-Assisted↗
PubMed1989

Mechanism of inhibition of prostaglandin H synthase by eugenol and other phenolic peroxidase substrates.

The mechanism of inhibition of prostaglandin H synthase (PHS) by eugenol was investigated using purified apoenzyme reconstituted with either manganese protoporphyrin IX (Mn-PHS) or hematin (Fe-PHS). Eugenol stimulated Fe-PHS activity at low concentrations and inhibited at higher concentrations, an activity typical of many phenolic compounds. Eugenol was also an excellent reducing cosubstrate for the peroxidase, being cooxidized to a reactive quinone methide in the process. Higher concentrations of eugenol were required to inhibit Fe-PHS than Mn-PHS (which retains cyclooxygenase activity but not peroxidase activity). Inhibition by eugenol was highly dependent on arachidonic acid concentration. In experiments using Mn-PHS, eugenol increased the time required for the initiation of O2 consumption after addition of arachidonic acid and also inhibited the rate of O2 uptake. Eugenol did not, however, affect the total amount of O2 consumed. The addition of 10 microM hydroperoxide (prostaglandin G2) to these incubations did not prevent the inhibitory effects of eugenol. Other phenolic compounds, including guaiacol, butylated hydroxyanisole, and acetaminophen inhibited Mn-PHS in a manner similar to eugenol. These results demonstrate that eugenol and other phenolic compounds specifically inhibit the cyclooxygenase component of PHS and that this inhibition occurs in addition to, or independent of, the effect of these compounds on peroxide tone or their peroxidative metabolism. We suggest that this inhibition is due to competition with arachidonic acid for the active site of PHS.

Animals↗
PubMed1989

Expert systems in histopathology. III. Representation of knowledge as "structured objects".

In designing expert systems for histopathology, the representation of knowledge as "structured objects" may offer advantages over the use of a set of rules. A structured-object representation using straightforward, descriptive, declarative statements can allow consideration of the relationships between the facts and constraining conditions of a domain in a richer, more complex and more complete manner. The use of associative (semantic) networks and frames to organize histopathologic knowledge as structured objects is discussed and demonstrated with examples that consider the complex tissue structures found in the kidney and thyroid. As an example, the design and function of a structured object-based expert system for follicular thyroid aspirates is discussed, including a consideration of the types of information that such a system would require. Such a system utilizes model-based reasoning rather than the rule-based reasoning of rule-based expert systems.

Diagnosis, Computer-Assisted↗
PubMed1989

Baroreceptor, not left ventricular, dysfunction is the cause of hemodialysis hypotension.

Many patients with chronic renal failure experience profound hypotension during hemodialysis. This has been attributed both to autonomic and ventricular dysfunction. In an attempt to distinguish which, if either, is important in this role, we assessed both autonomic and left ventricular function in 10 such patients. Cardioactive medication was stopped 24 hours prior to the investigations. Autonomic function was assessed from day/night blood pressure and heart rate variation and from the hemodynamic response to tilting and the Valsalva maneuver using an intra-arterial ambulatory monitoring technique. Left ventricular function was assessed scintigraphically both before and during hemodialysis. Day/night variation was significantly reduced in the patients with chronic renal failure (BP 13/7 +/- 8/6 mmHg, HR 5 +/- 4) compared with a control population (BP 36/28 +/- 10/5 mmHg, HR 19 +/- 6). Nine patients had a "square wave" response to the Valsalva maneuver. Both of these abnormalities are usually seen in patients with heart failure and are attributed to volume overload and a consequent failure of baroreceptor response. Blood pressure fell during hemodialysis (mean fall 40/22 +/- 20/10 mmHg) in all patients, but heart rate did not change (-2 +/- 16) despite the hypotension. All patients had a normal or high resting ejection fraction (mean 66%, range 55-79%), and there was no change during dialysis. This indicates that the hypotension was not due to left ventricular dysfunction in this group of patients, but to a failure of the baroreceptor response to volume depletion during hemodialysis.

Adult↗
PubMed1988

Cytotoxicity of butylated hydroxyanisole and butylated hydroxytoluene in isolated rat hepatocytes.

The effects of the antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on isolated rat hepatocytes were investigated. Both antioxidants were observed to be cytotoxic in a concentration-dependent manner at concentrations ranging from 100 to 750 microM. At equimolar concentrations BHT was more cytotoxic than BHA. Their toxicity appeared to be independent of their metabolism to reactive intermediates since inhibitors of cytochrome P-450 (metyrapone, SKF 525-A and piperonyl butoxide) had no effect on the cytotoxicity and N-acetylcysteine was also without protective effect. In addition, deuterated BHT was equitoxic with BHT. Only low temperature incubation (4 degrees), which has previously been shown to inhibit the insertion of these compounds into biomembranes, was effective in inhibiting the cytotoxic effects. Using isolated rat liver mitochondria we observed that both BHA and BHT inhibited respiratory control primarily by stimulating state 4 respiration and thus acting as membrane uncouplers. BHA and BHT also effectively dissipated membrane potential across the mitochondrial membrane and caused the release of calcium and mitochondrial swelling. These mitochondrial effects were reflected by a rapid decrease in ATP levels in intact hepatocytes which preceded cell death. These results suggest that the observed cytotoxicity of BHA and BHT to hepatocytes is related to their effects on biomembranes and mitochondrial bioenergetics.

Adenosine Triphosphate↗
PubMed1988

Anti-Klebsiella K30 phospholipid antibodies in systemic lupus erythematosus: antigen cross-reactions and idiotypic sharing with antibodies to DNA and Klebsiella K30 polysaccharide.

Patients with systemic lupus erythematosus were examined for the presence of serum antibodies reactive with phospholipids (PL) extracted from the membranes of Klebsiella K30 (K30PL). Affinity-purified anti-K30PL antibodies were tested for their ability to cross-react with other PL antigens or DNA and for the presence of idiotypic markers known to be associated with anti-DNA antibodies or antibodies to Klebsiella K30 polysaccharide (K30p). Affinity-purified antibodies to K30PL, phosphatidylserine (PS), or phosphatidylinositol (PL) uniformly cross-reacted with each other. Analysis of the PL preparations by thin-layer chromatography and reversed-phase high-performance liquid chromatography (HPLC) showed the presence of several components. Lupus sera reacted with one component mainly in the HPLC-fractionated K30PL preparation, although this component appeared to be present in the other PL preparations. Direct-binding and inhibition studies showed that affinity-purified antibodies to the K30PL extract, PS, or PI reacted poorly with DNA. However, the anti-K30PL antibodies possessed a prominent anti-DNA idiotypic marker (AM Id) in 61% of the patients and an anti-K30p idiotypic marker (SP Id) in 94% of the patients. The results thus show that anti-K30PL antibodies are idiotypically related to anti-DNA and anti-K30p antibody subpopulations, although they do not share the same antigen-binding characteristics.

Antibodies, Antinuclear↗
PubMed1988

Statistical design of the Women's Health Trial.

The National Cancer Institute has initiated a randomized trial to determine whether a low fat diet can reduce the incidence of breast cancer among women at increased risk for this disease. A feasibility trial involving 303 women has been conducted to examine recruitment strategies, study short-term compliance and, more generally, develop and refine trial procedures. The feasibility trial group also developed a detailed full-scale trial design plan, and randomization of participants to such a trial is currently underway. The purpose of this report is to describe the major design features of this Women's Health Trial, with particular emphasis on the statistical aspects of the design. The trial is planned to last 10 years and to include 32,000 participants. Of these 32,000 women, 12,800 will be assigned to a low fat diet intervention, and the other 19,200 will constitute a control group. The sample size of 32,000 arises from a range of estimates and assumptions pertaining to (a) the incidence of breast cancer at enrollment corresponding to selected eligibility criteria, (b) the relative risk of breast cancer as a function of a woman's history of dietary fat intake, (c) compliance assumptions in terms of average percent fat in the intervention and control groups as a function of time from randomization, and (d) rates of competing causes of death. These estimates and assumptions will be discussed, as will the robustness of the intended sample sizes to departures from such design assumptions.

Aged↗
PubMed1988

Perioperative hypertension. The primary care physician's role.

Questions concerning the proper management of hypertension in surgical patients often arise in primary care practice. Currently available literature and our own clinical experience lead us to make the following recommendations. 1. Continue antihypertensive therapy up to and including the morning of surgery, when the dose should be given with a small sip of water. 2. If possible, adjust antihypertensive therapy so blood pressure is less than 160/90 mm Hg for at least two weeks prior to surgery. 3. Discontinue all monoamine oxidase inhibitors at least one week prior to surgery and substitute alternative antihypertensive or antidepressant medication as necessary. 4. Be attentive to the patient's preoperative volume status and any evidence of cardiovascular disease. 5. In patients with postoperative hypertension, search for specific aggravating factors and treat them primarily. 6. Discuss with the anesthesiologist any difficulties in blood pressure control.

Antihypertensive Agents↗