Biomedical subjects

J R Turner

Publications and source records attributed to J R Turner.

At least 73 records · Page 4Linked to original sources

PubMed1995

Parental history of hypertension and cardiovascular response to stress in Black and White men.

White offspring of hypertensives typically exhibit an elevated cardiovascular response to stress. Studies of Black offspring of hypertensives have been fewer, with inconsistent results. This may be due, in part. to incomplete characterizations of hemodynamic responses. This study examines cardiovascular reactivity in Black and White offspring of hypertensives with a particular focus on vascular resistance responses. A total of 62 healthy normotensive men, 41 with a parental history of hypertension (PH+: 21 Blacks, 20 Whites), and 21 without parental hypertension (PH-: 7 Blacks, 14 Whites) engaged in a series of laboratory tasks. Both Black and White PH+ participants exhibited elevated diastolic blood pressure (DBP) responses, but to different patterns of stressor tasks. Familial differences in total peripheral resistance response were also obtained for Black and White participants in a comparison across all tasks, but were particularly evident in tasks when PH+ participants had elevated DBP responses. These results suggest that a parental history of hypertension is an important moderator of cardiovascular, and in particular peripheral vascular, responses to stress in Black and White individuals.

Journal Article↗

PubMed1995

Total skin electron therapy at two energies on a linear accelerator.

We have implemented the AAPM Task Group 30 recommendations with respect to Total Skin Electron Therapy (TSET) for the treatment of Mycosis Fungoides. Extensive measurements have been performed on the Varian 2100c linear accelerator with a water equivalent phantom, cylindrical phantoms and an anthropomorphic phantom to validate the 12 beam technique and to measure calibration factors. The technique was developed at 2.5 MeV and 3.5 MeV (mean energy at the surface) with the energy degrading screen at 30 cm from the patient. Field flatness over the treatment area was within +/- 3% with no significant regional variation of energy. The bremstrahlung contamination was .06-1.2%. The absolute calibration of absorbed dose to the patient required the measurement of the ratio "skin dose to calibration point dose", this was confirmed by measurements with a parallel plate ionization chamber and thermoluminescence dosimetry. The results indicate the care that must be taken with ionization chamber measurements under TSET condition to avoid erroneous readings due to the "polarity effect". A protocol is suggested for the practical implementation and quality assurance of the technique. The results of two successful treatments are presented and compared with the predicted results from phantoms.

Biophysical Phenomena↗

PubMed1994

Conjugal transfer of cosmid DNA from Escherichia coli to Saccharopolyspora spinosa: effects of chromosomal insertions on macrolide A83543 production.

Cosmid pOJ436, containing large inserts of Saccharopolyspora spinosa (Ss) DNA, was transferred by conjugation from Escherichia coli to Ss an integrated into the chromosome, apparently by homologous recombination, at high frequencies (10(-5) to 10(-4) per recipient). Transfer was mediated by the plasmid RP4 (RK2) transfer functions in E. coli, and the RK2 oriT function located on pOJ436 [Bierman et al., Gene 116 (1992) 43-49]. pOJ436 lacking Ss DNA, or containing a small insert (approx. 2 kb) of Ss DNA, conjugated from E. coli and integrated at either of two bacteriophage phi C31 attB sites at low frequency (approx. 10(-7) per recipient). Exconjugants containing homologous inserts or inserts at the phi C31 attB sites were stable in the absence of antibiotic selection, and most produced control levels of tetracyclic macrolide A83543 factors. Some exconjugants contained similar kinds of large deletions and were defective in macrolide production.

Anti-Bacterial Agents↗

PubMed1994

Intertask consistency of hemodynamic responses to laboratory stressors in a biracial sample of men and women.

Cardiovascular responses were examined in a community sample of 128 subjects, comprised of 58 African American and 70 Caucasian American men and women. Subjects completed a battery of laboratory stressors including mental arithmetic, reaction time, a speech task, and the cold pressor test. In addition to systolic and diastolic blood pressures, the underlying hemodynamic parameters of cardiac output and total peripheral resistance were assessed. In order to explore intertask consistency of response in both ethnic groups and both gender groups, correlational analyses were conducted separately for each group. For the psychological tasks, unanimously significant coefficients were observed. Intertask consistency between psychological tasks and the cold pressor was also considerable, but was somewhat less impressive (particularly for blood pressure) than that observed among the psychological tasks themselves. With regard to hemodynamic responses, cardiac output and total peripheral resistance demonstrated intertask consistency equal to, if not greater than, that shown by systolic and diastolic blood pressure, this consistency being evident for each ethnic and each gender group.

Adolescent↗

PubMed1994

Total-body irradiation on an isocentric linear accelerator: a radiation output compensation technique.

A treatment technique for total-body irradiation (TBI) is proposed that combines arc therapy with dynamic output control to achieve high-grade dose uniformity. The patient lies on a low couch and receives exposure in the prone and supine positions from a modulated arcing beam. The technique has been validated using a personal computer to control the linear accelerator and we demonstrate that only minor alterations to current dynamic therapy systems would be required. We have examined the practical application of this treatment with emphasis on methods of conformal therapy where an optimized dose distribution is prepared from a matrix of caliper measurements taken from the patient. This technique provides a means for regular TBI treatment on a computer-controlled linear accelerator that is easy to set up, requires short exposure times and is comfortable for the patient.

Equipment Failure Analysis↗

PubMed1994

Comparison of cardiac versus vascular reactors and ethnic groups in plasma epinephrine and norepinephrine responses to stress.

This study examined differences in plasma epinephrine (EPI) and norepinephrine (NOREPI) responses to stressors in 67 healthy African-American and Caucasian American men and women of the ages 18 to 49. Subjects were divided into three groups: (a) those who showed high blood pressure (BPI responses to stress associated with consistently high cardiac output (CO) increases with no substantial increases in total peripheral resistance (TPR), labeled cardiac reactors: (b) those with equally high BP increases associated with consistently higher TPR increases and lesser CO increases. labeled vascular reactors; (c) those who showed mixed hemodynamic responses or were low BP reactors. Ethnic and gender group differences in EPI and NOREPI responses were also examined. Cardiac reactors, vascular reactors and mixed + low reactors did not differ in EPI or NOREPI levels at baseline. During stressors, cardiac reactors showed greater increases in plasma EPI than vascular reactors or others during math, reaction time, and passive and active speech tasks: they also showed a weak trend toward greater NOREPI increases during these challenges as well. No differences were seen during the cold pressor: this stressor evoked the least change in EPI of all tasks, whereas the active speech elicited the greatest increases in both EPI and NOREPI of all tasks. Vascular reactors did not differ from mixed + low reactors in EPI or NOREPI reactivity, and men and women did not differ in EPI or NOREPI reactivity to any task. In contrast, Black subjects showed greater increases in NOREPI levels across all stressors compared to White subjects. These findings have implications for investigations of the role of sympathetic nervous system activity in the pathogenesis of hypertension in both African-American and Caucasian American populations.

Journal Article↗

PubMed1994

Field size dependence of effective source distance and field factors of a 9 MeV electron beam.

Effective source distances and field factors were measured for a number of square and rectangular fields using a 9 MeV electron beam from a Varian 2100-C linear accelerator. Mathematical relationships between effective source distance and field size, and field factor and field size were derived. For 9 MeV electrons, effective source distance is dependent on the field area and applicator cone, while field factors are dependent on the elongation of the field, the field area and applicator cone. Measured field factor data for rectangular fields were compared to field factors obtained using the "square root" method and found to agree to within 0.5%. In some instances, field factors can vary up to 10% for the same field size in different electron applicator cones.

Electrons↗

PubMed1993

Race and gender comparisons: I. Hemodynamic responses to a series of stressors.

A sample of 155 adults, age 18-49 years, including nearly equal subgroups of Black and White men and women, underwent evaluation of cardiovascular reactivity during 5 behavioral stressors. Among the men, overall blood pressure increases to tasks did not differ, but Blacks showed generally higher total peripheral resistance, whereas Whites showed greater heart rate and cardiac output increases. Among the women, the same racial-group differences were evident during certain tasks, but not during others. Men showed greater overall systolic blood pressure increases than did women, and they also showed less recovery toward baseline levels in systolic and diastolic pressure and stroke volume 5 min after the stressors. Other gender differences were task specific. The possible contributions of structural changes in the myocardium and vasculature, of altered sympathetic receptor distribution, and of task-specific behavioral factors influencing task involvement are discussed.

Adolescent↗

PubMed1993

Race and gender comparisons: II. Predictions of work blood pressure from laboratory baseline and cardiovascular reactivity measures.

In 148 Black and White men and women, laboratory measures of blood pressure (BP), heart rate, stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) during baseline and 5 stressors were examined in relationship to ambulatory systolic (SBP) and diastolic (DBP) blood pressures at work. Baseline BP strongly predicted mean work levels in all groups. For White men and Black women, higher SV and CO responses to the active speech and averaged across all tasks predicted higher work SBP individually and also when added to a model based on baseline SBP, age, and diary information. For White women, higher SBP increases to the passive speech similarly predicted mean work SBP. For Black men, higher TPR response to the cold pressor test correlated with higher work SBP but did not improve a predictor model involving baseline SBP and age. Reactivity measures did not consistently contribute to prediction of work DBP.

Adult↗

PubMed1993

Radiation hazards during cobalt 60 plaque therapy for choroidal melanoma.

Prompted by the concerns of the staff and patients, radiation hazards from Cobalt 60 (Co 60) plaque therapy for choroidal melanoma were recently assessed when two patients were concurrently treated at Christchurch Hospital. The risks from radiation to the attending medical staff, nursing personnel from the operating theatre and ward, and the patients' visitors were investigated. The radiation dose for all staff and visitors involved with the two patients was found to be well below the recommended weekly limits set by the International Commission on Radiological Protection. Our department code of practice to minimise radiation hazard during plaque therapy has been revised.

Brachytherapy↗

PubMed1993

Postural stability of hemodynamic responses during mental challenge.

Laboratory stress testing is typically conducted while subjects are seated, whereas real-life stressors may often be encountered while standing. The present study of 20 healthy young men evaluated blood pressure and underlying hemodynamic adjustments to a standardized mental arithmetic task performed twice while seated and twice while standing. Blood pressure increased during mental arithmetic in both postures, but the underlying hemodynamic determinants of the pressor responses were different for the two postures. Augmented cardiac output was responsible for increasing blood pressure during seated task performance, whereas increased vascular resistance was the mechanism for the pressor response to the task performed while standing. Blood pressure and hemodynamic responses were reproducible subject characteristics for a given posture; test-retest correlations were significant for all cardiovascular measures. However, seated blood pressures responses were not significantly correlated with standing blood pressure responses. In contrast, significant between-posture correlations were found for cardiac output and vascular resistance responses. This preliminary evidence of postural stability of the hemodynamic determinants of blood pressure responses during stress is consistent with growing evidence that hemodynamic response tendencies are robust characteristics of reactivity. Ambulatory monitoring of hemodynamic response patterns during real-life stress may reveal more idiosyncratic profiles of stress reactivity than are displayed by blood pressure responses alone.

Adult↗

PubMed1992

Substrate specificity of isopenicillin N synthase.

Highly purified isopenicillin N synthase (IPNS) from two sources (naturally occurring in Penicillium chrysogenum and that expressed in Escherichia coli via a cloned gene derived from Cephalosporium acremonium) have been isolated and utilized in vitro to test synthetic modifications of the natural substrate, (L-alpha-amino-delta-adipyl)-L-cysteinyl-D-valine (ACV). A very sensitive procedure utilizing the ability of beta-lactams to induce the synthesis of beta-lactamase was employed to determine whether an ACV analogue could serve as a substrate for IPNS. A wide variety of amino and carboxyl terminal tripeptide substitutions were examined and found to elicit positive beta-lactamase induction profiles. However, none of these modifications were found to function as efficiently as a substrate as ACV. One of the beta-lactam products which was formed from the reaction of IPNS and the tripeptide analogue was independently synthesized and evaluated for antibacterial activity. Modification of the L-cysteine residue in the second position of ACV resulted in tripeptides that were unable to serve as substrates. Conversion of the D-valine residue in the third position of ACV to an aromatic amino acid or to a highly electronegative residue such as trifluorovaline resulted in elimination of substrate activity and creation of an inhibitor of the enzyme.

Amino Acid Sequence↗

PubMed1992

Stress-induced changes in the rate of sodium excretion in healthy black and white men.

The effects of exposure to competitive mental stressors on rates of excretion of sodium (Na), potassium (K) and fluid, together with cardiovascular responses, were evaluated in 14 black and 14 white normotensive men after 3 days of controlled diet (200 mEq Na, 100 mEq K daily). In the first hour of a 5-hr protocol, subjects ingested a standard dinner and drank 1 liter of water. In hours 2-5, they voided to provide urine collections every 30 min, and drank 200 ml additional water after each collection. Hours 1-2 were for stabilization of excretion, hour 3 was baseline, hour 4 was stress and hour 5 was post-stress rest. During stress, 20 men showed faster natriuresis and 8 showed slower natriuresis than at baseline. These subgroups did not differ in any excretion measure at baseline. During stress, the slow stress natriuresis group showed slower excretion of potassium and fluid as well as sodium; slow natriuresis and kaliuresis persisted 30 min after stress. Creatinine clearance rate was also decreased, but only during the first 30 min of stress. Slow stress natriuresis subjects were found to have higher blood pressures during baseline and stress, greater heart rate and cardiac output increases during stress, and a larger percentage had hypertensive parents (63 vs 37%) compared to fast stress natriuresis subjects. Slow stress natriuresis was observed in 50 vs 17% of men with resting diastolic levels above vs below 80 mmHg, and in 43% of blacks vs 18% of whites tested. Overall, black subjects tended to excrete sodium more slowly than whites at baseline, and showed significantly lesser increases in sodium excretion rate when pressures rose during stress.

Adult↗

PubMed1992

Reactivity to stress and psychological adjustment in adults with pituitary insufficiency.

OBJECTIVE: Hypopituitary adults who were affected during childhood have a below-average rate of marriage, a rate of unemployment that exceeds national norms, and often indicate dissatisfaction with their life circumstances. We undertook the present study to determine the effects of short stature versus those of pituitary hormone deficiency. DESIGN AND PATIENTS: We compared hypopituitary adults (n = 25) with normal short adults (n = 25) who were matched for height, sex, age and socioeconomic status. MEASUREMENTS: In these two groups of subjects, we compared the physiological responses to a simulated social stressor, a public speaking task, and we measured the psychometric attributes that are indicators of social assertiveness and extraversion. RESULTS: Before, during and after the stress of public speaking, patients with multiple pituitary hormone deficiencies (n = 20) had lower mean systolic and diastolic blood pressures than controls, while patients with isolated growth hormone deficiency (n = 5) were equivalent to controls. The reactivity to stress, assessed using delta scores based on changes in blood pressure and heart rate, was also decreased in multiple hormone deficient patients. Psychometric test results indicated that patients with multiple hormone deficiencies showed lower openness, lower assertiveness, greater neuroticism and a tendency towards less extraversion than did controls. The responses of patients with isolated GH deficiency on the psychometric tests were not statistically different from controls, but the number of subjects in this group (n = 5) was too small to draw conclusions. CONCLUSIONS: The impaired cardiovascular responses to stress in patients with multiple hormone deficiencies, compared to short control subjects and to patients with GH deficiency leads us to conclude that factors other than stature and GH are responsible for these observations. The differences might be related to insufficiency of catecholamines or cortisol in the patients with multiple hormone deficiencies. These hormonal deficiencies might also account for the socially inhibited behaviour of these patients. Our results suggest that more attention needs to be directed at preparing hypopituitary patients for the challenges of adulthood. Also, these patients may be helped by more intensive efforts at hormonal replacement in adulthood.

Adolescent↗

PubMed1992

Characterization of a novel regulatory gene governing the expression of a polyketide synthase gene in Streptomyces ambofaciens.

A key step in the biosynthesis of macrolide antibiotics is the assembly of a large macrocyclic lactone ring by a multienzyme protein complex called the polyketide synthase. In the species Streptomyces ambofaciens, the polyketide synthase for the assembly of the 16-membered ring of the macrolide antibiotic spiramycin is encoded by the biosynthetic gene srmG. Here we show that the accumulation of transcripts from the srmG promoter is governed by the regulatory gene srmR, whose predicted product, a 65 kDa polypeptide, is not significantly similar in its deduced amino acid sequence to that of previously reported proteins in the protein databases. The srmR gene product is also required for the accumulation of transcripts from srmX, an additional gene in the vicinity of srmR, but not for the accumulation of transcripts from srmR itself. Interestingly, mutations in srmR prevent the accumulation of transcripts from the spiramycin resistance gene srmB, but this is an indirect consequence of the failure of srmR mutants to produce spiramycin, which is an inducer of its own resistance gene. The possibility that srmR is the prototype for a new class of regulatory genes governing early events in the biosynthesis of macrolide antibiotics is discussed.

Amino Acid Sequence↗

PubMed1992

Comparison of impedance cardiographic measurements using band and spot electrodes.

The comprehensive assessment of cardiac function using impedance cardiography has led to increasingly widespread use of the technique in psychophysiology. Disposable adhesive band electrodes have been the most widely used electrode type, but spot electrode configurations present attractive alternatives in terms of convenience and subject comfort. The present study was designed to evaluate whether one such spot electrode configuration yielded the same information as the more standard band electrodes for cardiac output and systolic time interval measurement. Male and female healthy adult subjects (N = 20) were tested. Comparisons between spot and band electrodes were made for the absolute magnitude of cardiac output and systolic time intervals, as well as for responses to the highly reproducible effects of bicycle exercise. Consistent with previous findings, systolic time interval measurements were unaffected by electrode type. However, for cardiac output measurements, differences between spot and band electrode measurements were found. Under resting conditions, the absolute magnitudes of cardiac output values measured using spot electrodes were smaller than for band electrodes. Subtle, yet significant differences were also found for cardiac output responses to exercise, with spot electrodes indicating greater increases in cardiac output than band electrodes. At the same time, anticipated gender differences found for cardiac output at rest and in response to exercise were unaffected by electrode type. Overall, these findings suggest that when comparing the results of studies that have utilized different impedance electrode types, it would be prudent to remain alert to the possibility of confounding influences.

Adult↗

PubMed1992

Job strain and ambulatory work blood pressure in healthy young men and women.

The effect of high job strain (defined as high psychological demands plus low decision latitude at work) on blood pressure was determined in 129 healthy, nonhypertensive men (n = 65) and women (n = 64). Blood pressure measures included mean screening levels obtained in a clinical environment, mean ambulatory levels from one 8-hour workday, and the change in levels from screening to mean work levels. In male workers, men with high and low job strain showed similar blood pressures at screening, but men with high job strain showed greater increases from screening to work, resulting in higher mean work blood pressure. Occupational status was unrelated to job strain or blood pressure in men. In female workers, women with high and low job strain did not differ in any measure of blood pressure; however, there were trends for higher occupational status and greater skill discretion to be associated with higher blood pressure responses at work in women.

Adolescent↗

PubMed1991

Intracellular sites for storage and recycling of C3b receptors in human neutrophils.

Upon activation of human neutrophils, C3b receptors (type 1 complement receptors, CR1) are rapidly translocated from an intracellular pool to the surface, increasing plasma membrane expression 6- to 10-fold. This is followed by reinternalization and degradation of the receptors, even in the absence of ligand. Upregulation of surface CR1 may occur without exocytosis of primary or secondary granules, and intracellular CR1 in resting neutrophils does not sediment with these granules on density gradient fractionation. To directly localize the intracellular pools of CR1, we used immunoelectron microscopy of fixed, permeabilized cells. In resting neutrophils, CR1 is associated with the membranes of smooth-surfaced, empty-appearing vesicles whose irregular borders clearly distinguish them from primary and secondary granules. After activation by fMet-Leu-Phe, the intracellular pool is primarily found in large, conspicuous, multivesicular bodies. These bodies also incorporate colloidal gold from the extracellular fluid, suggesting that they are formed by endocytosis. Thus, the sites in which CR1 is stored in resting cells, and recycled in activated cells, are structurally unique and morphologically distinguishable.

Cell Compartmentation↗