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Biomedical subjects

J E Cohen

Publications and source records attributed to J E Cohen.

At least 19 recordsLinked to original sources
PubMed2006

Domestic dogs and cats as sources of Trypanosoma cruzi infection in rural northwestern Argentina.

The reservoir capacity of domestic cats and dogs for Trypanosoma cruzi infection and the host-feeding patterns of domestic Triatoma infestans were assessed longitudinally in 2 infested rural villages in north-western Argentina. A total of 86 dogs and 38 cats was repeatedly examined for T. cruzi infection by serology and/or xenodiagnosis. The composite prevalence of infection in dogs (60%), but not in cats, increased significantly with age and with the domiciliary density of infected T. infestans. Dogs and cats had similarly high forces of infection, prevalence of infectious hosts (41-42%), and infectiousness to bugs at a wide range of infected bug densities. The infectiousness to bugs of seropositive dogs declined significantly with increasing dog age and was highly aggregated. Individual dog infectiousness to bugs was significantly autocorrelated over time. Domestic T. infestans fed on dogs showed higher infection prevalence (49%) than those fed on cats (39%), humans (38%) or chickens (29%) among 1085 bugs examined. The basic reproduction number of T. cruzi in dogs was at least 8.2. Both cats and dogs are epidemiologically important sources of infection for bugs and householders, dogs nearly 3 times more than cats.

Age Factors↗
PubMed2005

Body mass index and mortality in women: follow-up of the Canadian National Breast Screening Study cohort.

OBJECTIVE: The present study was conducted to examine the relationship between obesity and all-cause mortality in women. STUDY DESIGN AND SETTINGS: The subjects were women enrolled from 1980 to 1985 in a Canadian randomized trial, the National Breast Screening Study (NBSS) to evaluate the efficacy of mammographic screening. Mortality was ascertained by record linkage to the Canadian Mortality Data Base. Hazard ratios (HR) for the association between body mass index (BMI) and all-cause mortality were obtained from Cox proportional hazard regression models. RESULTS: During an average follow-up period of 16.5 years, 2566 deaths were identified among the 49 165 women, age 40-59 y at enrollment. The risk of all-cause death increased linearly above a BMI of 22 kg/m(2) and the trend was statistically significant. The HR (and 95% confidence intervals) in the various categories of BMI (kg/m(2)) were: BMI<18.5: 1.12 (0.99-1.25); BMI 18.5-21.9: 1.00 (reference); BMI 22-24.9: 1.15 (1.11-1.18); BMI 25.0-27.9: 1.28 (1.24-1.32); BMI 28.0 -29.9: 1.34 (1.29-1.39); BMI 30.0-34.9: 1.30 (1.25,1.35); and BMI > or =35.0: 1.40 (1.33-1.47). CONCLUSION: This study confirms the association of high BMI with increased all-cause mortality in women.

Adult↗
PubMed2005

Creatine phosphate administration preserves myocardial function in a model of off-pump coronary revascularization.

AIM: Off pump coronary artery bypass grafting (OPCAB) involves, and is occasionally impaired by obligatory regional myocardial ischemia, particularly with the use of proximal coronary in-flow occlusion techniques. Intracoronary shunts do not guarantee absence of distal ischemia given their small inner diameter and the presence of proximal coronary stenosis. Additional adjunctive measures to provide short-term myocardial protection may facilitate OPCAB. High-energy phosphate supplementation with creatine phosphate prior to ischemia may attenuate ischemic dysfunction. METHODS: In a rodent model of a transient coronary occlusion and myocardial ischemia, 36 animals underwent preischemic intravenous infusion of either creatine phosphate or saline, 10 minutes of proximal left anterior descending (LAD) occlusion, and 10 minutes of reperfusion. Rats underwent continuous intracavitary pressure monitoring and cellular ATP levels were quantified using a luciferin/luciferase bioluminescence assay. RESULTS: Within 2 minutes of ischemia onset, creatine phosphate animals exhibited statistically significant greater preservation of myocardial function compared to controls, an augmentation which persisted throughout the duration of ischemia and subsequent reperfusion. Furthermore, significantly greater cellular ATP levels were observed among creatine phosphate treated animals (344+/-55 nMol/g tissue, n=5) compared to control animals (160+/-9 nMol/g tissue, n=5)(p=0.014). CONCLUSIONS: A strategy of intravenous high-energy phosphate administration successfully prevented ischemic ventricular dysfunction in a rodent model of OPCAB.

Adenosine Triphosphate↗
PubMed2003

Dimensions underlying legislator support for tobacco control policies.

OBJECTIVE: To propose and test a new classification system for characterising legislator support for various tobacco control policies. DESIGN: Cross sectional study. SUBJECTS: Federal and provincial legislators in Canada serving as of October 1996 who participated in the Canadian Legislator Study (n = 553; response rate 54%). MAIN OUTCOME MEASURES: A three factor model (Voters, Tobacco industry, Other interest groups) that assigns nine tobacco control policies according to legislators' hypothesised perceptions of which group is more directly affected by these policies. RESULTS: Based on confirmatory factor analysis, the proposed model had an acceptable fit and showed construct validity. Multivariate analysis indicated that three of the predictors (believing that the government has a role in health promotion, being a non-smoker, and knowledge that there are more tobacco than alcohol caused deaths) were associated with all three factor scales. Several variables were associated with two of the three scales. Some were unique to each scale. CONCLUSIONS: Based on our analyses, legislator support for tobacco control policies can be grouped according to our a priori factor model. The information gained from this work can help advocates understand how legislators think about different types of tobacco control policies. This could lead to the development of more effective advocacy strategies.

Analysis of Variance↗
PubMed2003

What the public thinks about the tobacco industry and its products.

OBJECTIVES: To assess public attitudes toward the tobacco industry and its products, and to identify predictors of attitudes supportive of tobacco industry denormalisation. DESIGN: Population based, cross sectional survey. SETTING: Ontario, Canada. SUBJECTS: Adult population (n = 1607). MAIN OUTCOME MEASURES: Eight different facets of tobacco industry denormalisation were assessed. A denormalisation scale was developed to examine predictors of attitudes supportive of tobacco industry denormalisation, using bivariate and multivariate analyses. RESULTS: Attitudes to the eight facets of tobacco industry denormalisation varied widely. More than half of the respondents supported regulating tobacco as a hazardous product, fining the tobacco industry for earnings from underage smoking, and suing tobacco companies for health care costs caused by tobacco. Majorities also thought that the tobacco industry is dishonest and that cigarettes are too dangerous to be sold at all. Fewer than half of the respondents thought that the tobacco industry is mostly or completely responsible for the health problems smokers have because of smoking and that tobacco companies should be sued for taxes lost from smuggling. In particular, less than a quarter thought that the tobacco industry is most responsible for young people starting to smoke. Non-smoking, knowledge about health effects caused by tobacco, and support for the role of government in health promotion were independent predictors of support for tobacco industry denormalisation. CONCLUSIONS: Although Ontarians are ambivalent toward tobacco industry denormalisation, they are supportive of some measures. Mass media programmes aimed at increasing support for tobacco industry denormalisation and continued monitoring of public attitudes toward this strategy are needed.

Adolescent↗
PubMed2003

MRI and MRS of Coffin-Lowry syndrome: a case report.

MRI and MRS were used to examine the brain and the spine of a Coffin-Lowry syndrome (CLS) patient. There were moderately enlarged lateral and third ventricles and subarachnoid space with prominent Virchow-Robin spaces. MRS of basal ganglia and periventricular white matter was normal.

Brain↗
PubMed2002

Effects of partial housing improvement and insecticide spraying on the reinfestation dynamics of Triatoma infestans in rural northwestern Argentina.

The long-term effects on domiciliary reinfestation by Triatoma infestans of smoothing the plaster of indoor walls prior to insecticide application (in Amamá village) relative to only insecticide application (in Trinidad-Mercedes villages) were evaluated in rural northwestern Argentina from 1992 to 1997. All domestic and peridomestic areas of each house were sprayed with 2.5% suspension concentrate deltamethrin at 25 mg/m(2) in October 1992, and infestations were assessed by various methods every 6 months. Domiciliary infestation decreased from 72-88% in 1992 to 6-17% in late 1995, to increase moderately thereafter without returning to baseline rates. Peridomestic sites were the first in becoming reinfested, and reached more abundant T. infestans populations than domiciliary areas. Domiciliary infestation rates and bug abundances were not significantly different between communities during surveillance. Domiciliary infestation rates in well-plastered houses were very low (5-9%) and approximately stable until 1996, but in houses with regular or bad plaster they consistently increased from 5 to 19-21% in both communities. Logistic multiple regression analysis showed that the likelihood of domestic infestation assessed through householders' collections was significantly and positively associated with the occurrence of an infested peridomestic site in the respective house, the occurrence of high-density domestic infestations before interventions, and well-plastered walls in 1996. Combining insecticide spraying and partial improvement of walls controlled domestic infestations and transmission of Trypanosoma cruzi effectively, but was not sufficient to eliminate T. infestans from the study area or increase the effectiveness of careful chemical control.

Animals↗
PubMed2001

Global stability, local stability and permanence in model food webs.

The dynamical theory of food webs has been based typically on local stability analysis. The relevance of local stability to food web properties has been questioned because local stability holds only in the immediate vicinity of the equilibrium and provides no information about the size of the basin of attraction. Local stability does not guarantee persistence of food webs in stochastic environments. Moreover, local stability excludes more complex dynamics such as periodic and chaotic behaviors, which may allow persistence. Global stability and permanence could be better criteria of community persistence. Our simulation analysis suggests that these three stability measures are qualitatively consistent in that all three predict decreasing stability with increasing complexity. Some new predictions on how stability depends on food web configurations are generated here: a consumer-victim link has a smaller effect on the probabilities of stability, as measured by all three stability criteria, than a pair of recipient-controlled and donor-controlled links; a recipient-controlled link has a larger effect on the probabilities of local stability and permanence than a donor-controlled link, while they have the same effect on the probability of global stability; food webs with equal proportions of donor-controlled and recipient-controlled links are less stable than those with different proportions.

Animals↗
PubMed2001

Modeling household transmission of American trypanosomiasis.

American trypanosomiasis, or Chagas disease, caused by the protozoan parasite Trypanosoma cruzi and transmitted by blood-feeding triatomine bugs, is a chronic, frequently fatal infection that is common in Latin America. Neither adequate drugs nor a vaccine is available. A mathematical model calibrated to detailed household data from three villages in northwest Argentina shows that householders could greatly reduce the risk of human infection by excluding domestic animals, especially infected dogs, from bedrooms; removing potential refuges for bugs from walls and ceilings; and using domestically applied insecticides. Low-cost, locally practicable environmental management combined with intermittent use of insecticides can sustainably control transmission of T. cruzi to humans in rural Argentina and probably elsewhere.

Animals↗
PubMed2001

Transient dynamics and food-web complexity in the Lotka-Volterra cascade model.

How does the long-term behaviour near equilibrium of model food webs correlate with their short-term transient dynamics? Here, simulations of the Lotka -Volterra cascade model of food webs provide the first evidence to answer this question. Transient behaviour is measured by resilience, reactivity, the maximum amplification of a perturbation and the time at which the maximum amplification occurs. Model food webs with a higher probability of local asymptotic stability may be less resilient and may have a larger transient growth of perturbations. Given a fixed connectance, the sizes and durations of transient responses to perturbations increase with the number of species. Given a fixed number of species, as connectance increases, the sizes and durations of transient responses to perturbations may increase or decrease depending on the type of link that is varied. Reactivity is more sensitive to changes in the number of donor-controlled links than to changes in the number of recipient-controlled links, while resilience is more sensitive to changes in the number of recipient-controlled links than to changes in the number of donor-controlled links. Transient behaviour is likely to be one of the important factors affecting the persistence of ecological communities.

Computer Simulation↗
PubMed2001

Tobacco commerce on the internet: a threat to comprehensive tobacco control.

Although internet use continues to increase and e-commerce sales are expected to exceed US$1 trillion by the end of 2001, there have been few assessments in the literature regarding the implications of this medium for tobacco control efforts. This commentary explores the challenges that the internet may pose to the key components of a comprehensive tobacco control strategy, and pinpoints potential approaches for addressing these challenges. Four key challenges that the internet presents for tobacco control are identified: unrestricted sales to minors; cheaper cigarettes through tax avoidance and smuggling; unfettered advertising, marketing and promotion; and continued normalisation of the tobacco industry and its products. Potential strategies for addressing these challenges include international tobacco control agreements, national and state regulation, and legal remedies.

Advertising↗
PubMed2001

Combined endovascular treatment of dissecting vertebral artery aneurysms by using stents and coils.

OBJECT: With the recent development and refinement of endovascular stents, the significant potential for these devices in the treatment of wide-necked dissecting and fusiform aneurysms has become apparent. In this article the authors report on the use of stents and coils to treat dissecting and fusiform vertebral artery (VA) aneurysms. METHODS: Eight consecutive patients harboring eight dissecting aneurysms and one fusiform aneurysm of the VA were succesfully treated using a procedure in which the authors inserted an intravascular stent and secondary endosaccular coils when needed. In all but one patient complete aneurysm occlusion was achieved, and in all cases there was no neurological complication. Follow-up angiography examinations were performed in all patients (mean duration of follow-up angiography review 13.1 months, range 3-42 months). The patients remained stable throughout the clinical follow-up period (mean 14.1 months, range 4-42 months). No rebleeding was recorded. CONCLUSIONS: At present this combined approach represents a reliable and safe alternative for the treatment of VA dissecting aneurysms, especially in patients who cannot tolerate occlusion tests.

Adult↗
PubMed2000

Dynamic optimization of a linear-quadratic model with incomplete repair and volume-dependent sensitivity and repopulation.

PURPOSE: The linear-quadratic model typically assumes that tumor sensitivity and repopulation are constant over the time course of radiotherapy. However, evidence suggests that the growth fraction increases and the cell-loss factor decreases as the tumor shrinks. We investigate whether this evolution in tumor geometry, as well as the irregular time intervals between fractions in conventional hyperfractionation schemes, can be exploited by fractionation schedules that employ time-varying fraction sizes. METHODS: We construct a mathematical model of a spherical tumor with a hypoxic core and a viable rim, which is most appropriate for a prevascular tumor, and is only a caricature of a vascularized tumor. This model is embedded into the traditional linear-quadratic model by assuming instantaneous reoxygenation. Dynamic programming is used to numerically compute the fractionation regimen that maximizes the tumor-control probability (TCP) subject to constraints on the biologically effective dose of the early and late tissues. RESULTS: In several numerical examples that employ five or 10 fractions per week on a 1-cm or 5-cm diameter tumor, optimally varying the fraction sizes increases the TCP significantly. The optimal regimen incorporates large Friday (afternoon, if 10 fractions per week) fractions that are escalated throughout the course of treatment, and larger afternoon fractions than morning fractions. CONCLUSION: Numerical results suggest that a significant increase in tumor cure can be achieved by allowing the fraction sizes to vary throughout the course of treatment. Several strategies deserve further investigation: using larger fractions before overnight and weekend breaks, and escalating the dose (particularly on Friday afternoons) throughout the course of treatment.

Algorithms↗
PubMed2000

Heterogeneity among smokers and non-smokers in attitudes and behaviour regarding smoking and smoking restrictions.

OBJECTIVE: To determine if smokers and non-smokers cluster into meaningful, discrete subgroups with distinguishable attitudes and behaviours regarding smoking and smoking restrictions. DESIGN: Qualitative research with 45 smokers guided development of questionnaire items applied in a population based telephone survey of 432 current smokers and 1332 non-smokers in Ontario, Canada. METHODS: Cluster analysis of questionnaire items used to categorise adult smokers and non-smokers; comparison of clusters on sociodemographic characteristics and composite knowledge and attitude scores. RESULTS: Smokers clustered in three groups. "Reluctant" smokers (16%) show more concern about other people discovering that they smoke, but parallel "easygoing" smokers (42%) in supporting restrictions on smoking and not smoking around others. "Adamant" smokers (42%) feel restrictions have gone too far, and are less likely to accommodate non-smokers. Significant gradients across categories in the expected direction were observed with respect to smoking status, stage of change, knowledge, and attitude scores, and predicted compliance with restrictions, validating the proposed typology. Non-smokers also clustered into three groups, of which the "adamant" non-smokers (45%) are the least favourably disposed to smoking. "Unempowered" non-smokers (34%) also oppose smoking, but tend not to act on it. "Laissez-faire" non-smokers (21%) are less opposed to smoking in both attitude and behaviour. A significant gradient across categories in the expected direction was observed with respect to composite scores regarding knowledge of the health effects of active and passive smoking and a composite score on support for restrictions on smoking in public places. CONCLUSION: Recognition and consideration of the types of smokers and non-smokers in the population and their distinguishing characteristics could inform the development of tobacco control policies and programmes and suggest strategies to assist implementation.

Adult↗