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Biomedical subjects

D J Lynch

Publications and source records attributed to D J Lynch.

At least 19 recordsLinked to original sources
PubMed2005

Monte Carlo simulation of the spatial distribution of energy deposition for an electron microbeam.

Dosimetry calculations characterizing the spatial variation of the energy deposited by the slowing and stopping of energetic electrons are reported and compared with experimental measurements from an electron microbeam facility. The computations involve event-by-event, detailed-histories Monte Carlo simulations of low-energy electrons interacting in water vapor. Simulations of electron tracks with starting energies from 30 to 80 keV are used to determine energy deposition distributions in thin cylindrical rings as a function of penetration and radial distance from a beam source. Experimental measurements of the spatial distribution of an electron microbeam in air show general agreement with the density-scaled simulation results for water vapor at these energies, yielding increased confidence in the predictions of Monte Carlo track-structure simulations for applications of the microbeam as a single-cell irradiator.

Computer Simulation↗
PubMed2004

Analysis of low-energy electron track structure in liquid water.

An implementation is presented of interaction cross sections for non-relativistic electron track structure simulations. The model, incorporating liquid-phase cross sections for inelastic interactions and improved algorithms for elastic scattering, is applied to Monte Carlo simulation of the track structure of low-energy electrons. Benchmark distributions and mean values are presented for several measures of penetration distances that characterize the general physical extent of the track structure. The results indicate that, except for the last approximately 500 eV of energy loss, electron tracks have a quasi-linear character; this suggests that a major part of an electron track may be reasonably described by a lineal-energy-like characterization.

Algorithms↗
PubMed2004

Microdosimetry of electron microbeams.

Track structures of 25, 50 and 80 keV primary electrons, simulated by the detailed-history Monte Carlo method, were analyzed for the frequency distributions of energy deposited in spheres with a diameter of 1 microm, placed in a cylindrically symmetrical array around the projected initial direction of the primary electron. The frequency mean of specific energy, the dose mean of lineal energy, and the parameters of lognormal functions fit to the dose distributions were calculated as a function of beam penetration and radial distance from the projected beam axis. Given these data, the stochastics of dose and radiation quality for micrometer-scale sites targeted by a medium-energy electron microbeam can be predicted as a function of the site's location relative to the beam entry point.

Dose-Response Relationship, Radiation↗
PubMed2001

Microdosimetry of a 25 keV electron microbeam.

Electron microbeam experiments are planned or under way to explore in part the question regarding whether the bystander effect is a general phenomenon or is restricted to high-LET radiation. Since low-LET radiations scatter more readily compared to high-LET radiations, identifying bystander cells and assessing the potential dose that they may receive will be crucial to the interpretation of radiobiological results. This paper reports on initial calculations of the basic information needed for a stochastic model of the penetration of energetic electrons in tissue-like matter; the model will be used to predict doses delivered to adjacent regions in which bystander cells may reside. Results are presented of calculations of the stochastics of energy deposition by 25 keV electrons slowing down in a homogeneous water medium. Energy deposition distributions were scored for 1-micrometer spheres located at various penetration and radial distances up to 10 micrometer from the point of origin. The energy of 25 keV was selected because experiments are planned for that energy. At 25 keV there is a high probability that the entire electron track will be contained within a typical mammalian cell. Individual tracks are scored because of their primacy; data for higher doses can be obtained by convoluting single-track distributions. The event frequency decreases approximately exponentially after the first micrometer to 1% at about 8 micrometer of penetration. Radially, the 1% contour extends to 3.5 micrometer at a penetration of 5.5 micrometer. The frequency-mean energy deposited decreases from 1.5 to 1 keV/micrometer at a penetration of 3.5 micrometer, then increases back to about 1.5 at a penetration of 6.5 micrometer. The mean energy increases to about 3 keV/micrometer at a radial distance of 8.5 micrometer.

Computer Simulation↗
PubMed2000

Monte Carlo simulation of single-cell irradiation by an electron microbeam.

A model is presented for irradiation of a cellular monolayer by an electron microbeam. Results are presented for two possible window designs, cells plated on the vacuum-isolation window and cells plated on Mylar above the vacuum-isolation window. Even for the thicker dual-membrane window that facilitates tissue culture and allows the target cell to be centered relative to the electron beam, the majority of the calculated beam spreading was contained in a volume typical of the mammalian HeLa cell line. None of the 10(4) electrons simulated at 25 keV were scattered into the spatial region occupied by neighbors of the target cell. Dose leakage was largest at 50 keV where the mean energy deposited in all neighbors was 21% of that deposited in the target cell. This ratio was reduced to 5% at 90 keV, the highest beam energy simulated. Lineal energy spectra of energy deposition events scored in the nucleus of the target cell became progressively more like the gamma-ray spectrum as the electron beam energy increased. Hence, our simulations provide strong support for the feasibility of a low-LET, single-cell irradiator.

Cell Nucleus↗
PubMed2000

Type A behavior pattern, sex, and social support.

Low social support has been suggested as a contributing factor to cardiac disease in some individuals with Type A Behavior Pattern. A number of studies have focused on the relationship between social support and Type A traits in subjects without cardiac disease as a means of evaluating this hypothesis; however, results of these studies have been confusing. In the current study, involving samples of adolescents and working adults, there was a significant positive correlation between Type A scores and satisfaction with social support in men but not in women.

Adolescent↗
PubMed1997

Telephone counseling for patients with minor depression: preliminary findings in a family practice setting.

BACKGROUND: Depression is a frequently occurring condition in family practice patients, but time limitations may hamper the physician's ability to it treat effectively. Referrals to mental health professionals are frequently resisted by patients. The need for more effective treatment strategies led to the development and evaluation of a telephone-based, problem-solving intervention. METHODS: Patients in a family practice residency practice were evaluated through the Medical Outcomes Study Depression Screening Scale and the Diagnostic Interview Schedule to identify those with subthreshold or minor depression. Twenty-nine subjects were randomly assigned to either a treatment or comparison group. Initial scores on the Hamilton Depression Rating Scale were equivalent for the groups and were in the mildly depressed range. Six problem-solving therapy sessions were conducted over the telephone by graduate student therapists supervised by a psychiatrist. RESULTS: Treatment group subjects had significantly lower post-intervention scores on the Hamilton Depression Rating Scale compared with their pre-intervention scores (P < .05). Scores did not differ significantly over time in the comparison group. Post-intervention, treatment group subjects also had lower Beck Depression Inventory scores than did the comparison group (P < .02), as well as more positive scores for social health (P < .002), mental health (P < .05), and self-esteem (P < .05) on the Duke Health Profile. CONCLUSIONS: The findings indicate that brief, telephone-based treatment for minor depression in family practice settings may be an efficient and effective method to decrease symptoms of depression and improve functioning. Nurses in these settings with appropriate training and supervision may also be able to provide this treatment.

Counseling↗
PubMed1996

Implantable cardioverter-defibrillator: another device to cover.

The implantable cardioverter-defibrillator is a mechanical device developed to manage patients with life-threatening arrhythmias when pharmacologic control has failed or produced unacceptable side effects. It is a significant amount of foreign material with a generator pack (volume 113 to 145 cc, weight 197 to 235 gm) and two or three leads and patches that are inserted into or placed on the heart. Although it has worked very well in preventing premature death, there have been complications associated with the device itself. The most significant of these has been exposure and/or infection. We present three patients who have experienced this problem. Improved coverage has been accomplished by burying the implant beneath the rectus abdominis muscle in situations where skin and subcutaneous tissue alone have proved inadequate. By dividing one or two tendinous inscriptions and the anterior limb of the internal oblique fascia, a musculofascial pocket is created to contain the generator and lead wires. This provided satisfactory coverage in two of our three patients. The single failure resulted from external trauma to the abdominal wall.

Aged↗
PubMed1996

Alcohol withdrawal at home. Pilot project for frail elderly people.

The need for safe, accessible, client-centred, alcohol withdrawal services for seniors was recognized by health service workers in Victoria. A partnership of health and support service organizations developed and implemented a pilot project for treating alcohol withdrawal in the home. The project provided service that integrated well with a substance-abuse treatment program for seniors.

Activities of Daily Living↗
PubMed1994

Implantable cardioverter defibrillator patch erosion presenting as hemoptysis.

Although the internal cardioverter defibrillator has prevented many premature deaths from lethal ventricular arrhythmias, some complications have occurred with its use. We present a patient who developed a fistula between the left ventricle and a bronchus, caused by erosion of the ventricular patch. The patient's presenting symptom was hemoptysis. Physicians caring for patients with these devices should be aware of this potential problem.

Animals↗
PubMed1994

Screening women in family practice settings: association between depression and smoking cigarettes.

OBJECTIVE: The purpose of this survey study was to test female family practice outpatients for an association between depression and cigarette smoking. METHODS: The survey consisted of demographic items including questions on smoking, and an eight-item self-report depression screening instrument. Eighty percent of the women (ages 18-91) approached agreed to participate in this study (N = 695). RESULTS: Thirty-two percent scored positive for depression and 28% smoked cigarettes. Cigarette smokers had significantly higher depression scores than did nonsmokers, and heavier smokers (> 10/day) had higher scores than did smokers of 10 or fewer cigarettes/day. CONCLUSION: There appears to be an association between smoking and depression among female family practice patients. This warrants both patient care and research attention.

Adolescent↗
PubMed1992

Adherence to exercise interventions in the treatment of hypercholesterolemia.

The goals of this study were to determine the rate of adherence to exercise treatment of hypercholesterolemia and to identify personality and demographic factors associated with adherence. Of the 31 subjects entering the 26-week program, 12 attended 80% or more of the scheduled sessions. Adherence was positively associated with the perceived seriousness of hypercholesterolemia, the expectation of benefit from treatment, and depressed feelings of helplessness and hopelessness. Negative associations were identified between adherence and the perception of health status being under the control of chance or of powerful others. Older subjects were more likely to be adherers at 8 and 16 weeks but not at 26 weeks.

Adult↗
PubMed1992

Teaching interviewing skills: the effect of instructors' academic department.

This study examines student evaluations of an interviewing and communications skills course taught in small groups by members of psychiatry and family medicine departments. Student course evaluations for two academic years were analyzed by means of t-tests and multiple regression analyses to explore if the group leader's academic department affected the student's learning experience. Students taught by family medicine instructors rated significantly higher three aspects of the course: the usefulness of the role playing session, the credibility and realism of the videotaping session, and the recommendation that the course be continued. This study found the family medicine instructors to be valued teachers of interviewing and communication skills.

Attitude↗
PubMed1990

Assessment of a brief interviewing course using the Helping Relationship Inventory: an interviewing course assessment.

A brief second year interviewing course consisting of 9 hours of small group meetings was evaluated by administering the Helping Relationship Inventory (HRI). Other studies have used the HRI to assess longer interviewing courses that included both small groups and large class lectures. The purpose of this study was to use the HRI to see if objective improvement in communication skills could be found in this relatively brief interviewing course. One hundred and nine students, representing an 80% return rate, completed all questions on the HRI pre- and post-tests. Analysis of pre- and post-test data showed that students became significantly more understanding (p less than 0.0001) and significantly less 'supportive' or pacifying (p less than 0.0001) by the end of the course. There were no differences found on pre- and post-test HRI scores comparing males (n = 71) and females (n = 38). This study demonstrates that even brief small group interviewing courses can effect a positive change in students' communication skills.

Communication↗
PubMed1990

The Toledo Exercise and Diet Study. Results at 26 weeks.

This study was designed to test whether an exercise program is additive to diet counseling in lowering elevated blood cholesterol levels. From a screened population of 1024 subjects, we randomized 66 predominantly female subjects to two intervention groups: diet counseling and diet counseling with exercise. Subjects were selected who had elevated levels of serum low-density lipoprotein cholesterol, an average or low fitness level, and a diet high in saturated fat and cholesterol. After 26 weeks of intervention, 51 subjects exhibited significant decreases in serum levels of cholesterol, high-density lipoprotein cholesterol, triglycerides, and low-density lipoprotein cholesterol. The addition of exercise to diet counseling resulted in improved aerobic capacity, losses of body fat and weight, and further nonsignificant decreases in serum cholesterol and low-density lipoprotein cholesterol levels. Since these results differ from data acquired in individuals with normal to borderline serum cholesterol levels, further studies appear indicated in hypercholesterolemic subjects, especially in women.

Adult↗
PubMed1989

Type A and social support.

This investigation tested Matthews's hypothesis, which proposed that reduced social support may be one of the mediators of susceptibility to coronary disease in Type A individuals. In addition, sex differences were hypothesized to be an important aspect of the findings. Subjects were 72 women and 57 men undergraduate students who completed the Jenkins Activity Survey (JAS) and the Sarason Social Support Questionnaire. For women, both the Type A and Speed and Impatience subscales of the JAS were negatively related to satisfaction with social support. For men, however, Type A scores on JAS were positively correlated with satisfaction with social support. The implications of these findings, particularly with regard to the importance of separate analyses by sex, are discussed.

Adult↗
PubMed1989

Students' reactions as guides to course revisions.

Items on four course changes made in response to students' evaluations of a course on interviewing were rated higher by the 3 succeeding classes of students, indicating changes improved the students' perceptions of the course.

Attitude of Health Personnel↗