Nonlinear population dynamics: models, experiments and data.
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Animals↗
Biomedical subjects
B Dennis
Publications and source records attributed to B Dennis.
Resonant population cycles in temporally fluctuating habitats.
Experiments with the flour beetle Tribolium have revealed that animal numbers were larger in cultures grown in a periodically fluctuating volume of medium than in cultures grown in a constant volume of the same average size. In this paper we derive and analyze a discrete stage-structured mathematical model that explains this phenomenon as a kind of resonance effect. Habitat volume is incorporated into the model by the assumption that all rates of cannibalism (larvae on eggs, adults on eggs and pupae) are inversely proportional to the volume of the culture medium. We tested this modeling assumption by conducting and statistically analyzing laboratory experiments. For parameter estimates derived from experimental data, our model indeed predicts, under certain circumstances, a larger (cycle-average) total population abundance when the habitat volume periodically fluctuates than when the habitat volume is held constant at the average volume. The model also correctly predicts certain phase relationships and transient dynamics observed in data. The analyses involve a thorough integration of mathematics, statistical methods, biological details and experimental data.
Animals↗
Provitamin A carotenoid intake and carotid artery plaques: the Atherosclerosis Risk in Communities Study.
We examined the cross-sectional association between intake of carotenoids with provitamin A activity and carotid artery plaques in 12,773 participants of the Atherosclerosis Risk in Communities Study aged 45-64 y. Usual diet was assessed with a 66-item food-frequency questionnaire. Plaques were examined by B-mode ultrasound of multiple carotid artery segments. In both women and men, those in the highest quintile of carotenoid consumption had a lower prevalence of plaques (women, 25.4%; men, 36.0%) than those in the lowest quintile of carotenoid consumption (women, 29.3%; men, 39.8%). The prevalence odds ratios contrasting extreme intake quintiles were 0.82 (95% CI: 0.70, 0.97) in women and 0.85 (95% CI: 0.72, 1.01) in men. The associations diminished slightly after potential confounders were adjusted for. In women, the inverse association was particularly strong for current smokers (adjusted odds ratio contrasting extreme quintiles: 0.67; 95% CI: 0.45, 0.98). In men, no such effect modification by smoking was seen. The inverse association was somewhat stronger in men aged 55-64 y than in those aged 45-54 y, whereas age made little difference in women. These findings, together with previous findings that carotenoid intake was unrelated to average carotid artery wall thickness, suggest that carotenoids may exert their influence later rather than earlier in the atherosclerotic process, and support the hypothesis that carotenoids or other plant-derived compounds may play a role in preventing arterial plaque formation.
Arteriosclerosis↗
Effects of reducing dietary saturated fatty acids on plasma lipids and lipoproteins in healthy subjects: the DELTA Study, protocol 1.
Few well-controlled diet studies have investigated the effects of reducing dietary saturated fatty acid (SFA) intake in premenopausal and postmenopausal women or in blacks. We conducted a multicenter, randomized, crossover-design trial of the effects of reducing dietary SFA on plasma lipids and lipoproteins in 103 healthy adults 22 to 67 years old. There were 46 men and 57 women, of whom 26 were black, 18 were postmenopausal women, and 16 were men > or =40 years old. All meals and snacks, except Saturday dinner, were prepared and served by the research centers. The study was designed to compare three diets: an average American diet (AAD), a Step 1 diet, and a low-SFA (Low-Sat) diet. Dietary cholesterol was constant. Diet composition was validated and monitored by a central laboratory. Each diet was consumed for 8 weeks, and blood samples were obtained during weeks 5 through 8. The compositions of the three diets were as follows: AAD, 34.3% kcal fat and 15.0% kcal SFA; Step 1, 28.6% kcal fat and 9.0% kcal SFA; and Low-Sat, 25.3% kcal fat and 6.1% kcal SFA. Each diet provided approximately 275 mg cholesterol/d. Compared with AAD, plasma total cholesterol in the whole group fell 5% on Step 1 and 9% on Low-Sat. LDL cholesterol was 7% lower on Step 1 and 11% lower on Low-Sat than on the AAD (both P<.01). Similar responses were seen in each subgroup. HDL cholesterol fell 7% on Step 1 and 11% on Low-Sat (both P<.01). Reductions in HDL cholesterol were seen in all subgroups except blacks and older men. Plasma triglyceride levels increased approximately 9% between AAD and Step 1 but did not increase further from Step 1 to Low-Sat. Changes in triglyceride levels were not significant in most subgroups. Surprisingly, plasma Lp(a) concentrations increased in a stepwise fashion as SFA was reduced. In a well-controlled feeding study, stepwise reductions in SFA resulted in parallel reductions in plasma total and LDL cholesterol levels. Diet effects were remarkably similar in several subgroups of men and women and in blacks. The reductions in total and LDL cholesterol achieved in these different subgroups indicate that diet can have a significant impact on risk for atherosclerotic cardiovascular disease in the total population.
Adult↗
Chaotic Dynamics in an Insect Population
A nonlinear demographic model was used to predict the population dynamics of the flour beetle Tribolium under laboratory conditions and to establish the experimental protocol that would reveal chaotic behavior. With the adult mortality rate experimentally set high, the dynamics of animal abundance changed from equilibrium to quasiperiodic cycles to chaos as adult-stage recruitment rates were experimentally manipulated. These transitions in dynamics corresponded to those predicted by the mathematical model. Phase-space graphs of the data together with the deterministic model attractors provide convincing evidence of transitions to chaos.
Journal Article↗
Dietary antioxidants and carotid artery wall thickness. The ARIC Study. Atherosclerosis Risk in Communities Study.
BACKGROUND: Evidence that dietary antioxidants may prevent atherosclerotic disease is growing. The relationship between the intake of dietary and supplemental vitamin C, alpha-tocopherol, and provitamin A carotenoids and average carotid artery wall thickness was studied in 6318 female and 4989 male participants 45 to 64 years old int he Atherosclerosis Risk in Communities Study. METHODS AND RESULTS: Intake was assessed by use of a 66-item semiquantitative food-frequency questionnaire. Carotid artery intima-media wall thickness was measured as an indicator of atherosclerosis at multiple sites with B-mode ultrasound. Among men and women > 55 years old who had not recently begun a special diet, there was a significant inverse relationship between vitamin C intake and average artery wall thickness adjusted for age, body mass index, fasting serum glucose, systolic and diastolic blood pressures, HDL and LDL cholesterol, total caloric intake, cigarette use, race, and education (test for linear trend across quintiles of intake, P = .019 for women and P = .035 for men). An inverse relationship was also seen between wall thickness and alpha-tocopherol intake but was significant only in women (test for linear trend, P = .033 for women and P = .13 for men). There was a significant inverse association between carotene intake and wall thickness in older men (test for linear trend, P = .015), but the association weakened after adjustment for potential confounders. No significant relationships were seen in participants < 55 years old. CONCLUSIONS: These data provide limited support for the hypothesis that dietary vitamin C and alpha-tocopherol may protect against atherosclerotic disease, especially in individuals > 55 years old.
Antioxidants↗
Dietary intake patterns and sociodemographic factors in the atherosclerosis risk in communities study. ARIC Study Investigators.
BACKGROUND: Comprehensive and up-to-date data on differences in dietary intake according to various sociodemographic factors are needed to understand the potential impact of dietary factors on disease risks in the United States. METHODS: Usual dietary intake assessed by a food frequency questionnaire was examined in relation to race, sex, and educational attainment using baseline data obtained from randomly selected samples of 15,800 middle-aged black and white men and women who participated in the Atherosclerosis Risk in Communities Study. RESULTS: In almost all comparisons, higher educational attainment was associated with recommended dietary intake patterns--lower per energy intakes of meats, eggs, chicken with skin, and whole milk and higher intakes of fruits, vegetables, fish, chicken without skin, and low-fat milk. As expected from these food intake patterns, higher educational attainment was associated with lower intakes of saturated fatty acid and cholesterol and with higher intakes of dietary fiber and various micronutrients. Compared with women's diets, men's diets were slightly more atherogenic (in whites only) based upon Keys score and had lower micronutrient levels. Although there were large differences in the food intakes between blacks and whites, the differences in nutrient intakes were generally smaller. However, intakes of cholesterol and vitamin A were somewhat higher and intakes of saturated fatty acid, calcium, and potassium were lower among blacks than in whites. CONCLUSIONS: This community-based study clearly demonstrated that regardless of race and sex, high educational attainment is associated with recommended dietary intake patterns. Continuing efforts to improve general educational level and to promote healthy dietary habits among those with low socioeconomic status are warranted.
Black or African American↗
Neurocognitive abilities for a clinically depressed sample versus a matched control group of normal individuals.
Depressed patients have been reported to show deficits in tasks that demand memory, planning/sequencing, speeded responding, and effortful responding. Many studies of depressed patients have used inadequate instrumentation or poor control groups. In this investigation, the cognitive performance of 44 patients diagnosed as clinically depressed was compared with the performance of a control group of normal individuals that closely matched the clinical group on the variables of age, gender, race or ethnic group, and educational attainment. The groups were compared on the tasks that compose the Kaufman Adolescent and Adult Intelligence Test (KAIT), which includes reliable and valid measures of most pertinent areas of purported deficit in depressed patients. Multivariate analyses of variance indicated that the depressed and control groups did not differ significantly on KAIT variables, but the depressed patients did differ significantly from the control group on the delayed versus immediate recall of verbal information.
Adolescent↗
Care study: severe needle phobia.
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Adult↗
Acquired lymphedema: a chart review of nine women's responses to intervention.
The medical records of nine women who had acquired lymphedema as a sequela to a modified radical mastectomy for breast cancer were analyzed to ascertain what factors, phenomena, or experiences in their lymphedema treatment may have influenced outcomes. The women were identified as having either successful or poor outcomes. Their conservative lymphedema treatment consisted of compression pumps, compression garments, and, in some cases, manual lymph drainage. The qualitative analysis of records implicated the following factors in the outcome of conservative lymphedema treatment for these women: (a) the amount of delay before starting compression treatment, (b) the size of the lymphedematous arm when treatment started, (c) the availability of social and financial supports, and (d) the presence of complicating health problems. The findings of this study cannot be generalized; however, further scientific inquiry into the phenomena that lie behind treatment outcome variations could lead to more effective treatment approaches.
Adult↗
Emergency department complaint frequency: variation by patient median household income.
STUDY OBJECTIVE: To determine whether emergency department complaint frequency varies with patient median household income, as approximated by patient residence zip code. DESIGN: All patient visits and complaints received in one ED were reviewed. Median household income of patient residence zip codes was obtained from available demographic data. Patients were categorized into seven income categories. EXCLUSIONS: Cases in which zip codes could not be determined or zip code income data could not be obtained; complaints from physicians, not patients; and data from zip codes remote from the hospital. SETTING: Nine hundred twenty-nine-bed teaching hospital. TYPE OF PARTICIPANTS: All ED visits and all ED complaints over a four-year period. STATISTICAL ANALYSIS: Armitage's chi 2 test for trend of proportions was used to compare complaint frequencies in different income groups. RESULTS: A total of 277,210 patient visits and 675 complaints met study criteria. Complaint frequencies ranged from 1.65 to 3.14 per thousand visits. Higher-income patients were more likely to complain than lower-income patients (P = .0000058). CONCLUSION: In this setting, ED patients residing in higher median income zip codes are more likely to register complaints than those from lower-income zip codes. Complaint frequencies from hospitals with different demographics may not be comparable.
Emergency Service, Hospital↗
HL7: facilitating multiple approaches to systems integration.
System interfaces of the 1980s are being replaced by system integration of the 1990s. Standards such as Health Level 7 (HL7) are facilitating this integration process. The authors dispel several persistent misconceptions about the HL7 standard and illustrate two working approaches to HL7-based networking.
Computer Communication Networks↗
Hemodynamic and endocrine effects of mental stress in untreated borderline hypertension.
Mental arithmetic and mirror tracing were compared in 40 untreated patients with borderline hypertension, tested in random sequence in standardized protocols. Both tasks significantly increased systolic and diastolic blood pressure, heart rate, cardiac index, plasma renin, and decreased peripheral resistance. Mental arithmetic also increased cholesterol, triglycerides and HDL; plasma catecholamines were not changed significantly. Lipid changes were correlated with blood pressure changes. These methods will be useful in exploring the relationships between hemodynamic reactivity to stress, and the presence and progression of atherosclerosis, as well as testing the effects of antihypertensive drugs on stress-induced changes that may influence atherosclerotic complications of hypertension.
Adult↗
Case study: a problem of "malignant hypertension".
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Adolescent↗
Nephrotoxicity of high- and low-osmolality contrast media.
Nephrotoxicity of radio-opaque contrast media (CM) is generally believed to involve toxic injury of proximal tubular cells. Measurement of urinary tubular enzyme excretion has been advocated as a sensitive marker of such toxic injury. It has been claimed that the new low-osmolality or nonionic CM reduce the incidence of nephrotoxicity but this remains uncertain. We studied 23 patients with normal renal function undergoing coronary angiography; patients were randomized into three groups receiving either diatrizoate (1,800 mmol/kg H2O), ioxaglate (600 mmol/kg H2O) or iohexol (850 mmol/kg H2O). Urinary excretion of a panel of enzymes increased significantly in all groups by 20 h (p less than 0.05 to less than 0.005). Alanine aminopeptidase excretion at 20 h was greater after the administration of high osmolality ionic CM than with the others but all three CM produced a similar pattern of enzyme excretion. No significant change in glomerular filtration rate was found in any group so the significance of the enzymuria remains uncertain.
Adult↗
Food choices among white adolescents: the Lipid Research Clinics Prevalence Study.
Food groups have been widely used in nutrition education but relatively few studies have employed food groups to interpret dietary intake. The 24-h dietary recalls of 534 male and 476 female adolescents, aged 10-19 yr, were analyzed using a food grouping scheme. Foods were grouped with emphasis placed on fats and carbohydrates. Frequency of use and contribution of food groups to the macronutrients were determined. When nutrient intake was analyzed as a percentage of total calories, both males and females were found to have similar profiles. More than 60% of each macronutrient was contributed by combinations of three major food groups. The meat/fish/poultry, milk/cheese/yogurt, and bread/cereal products food groups contributed 81.2% of the protein; milk/cheese/yogurt, bread/cereal products and sweets accounted for 63.0% of the carbohydrate intake; and 74.3% of the dietary fat consumption was attributable to the meat/fish/poultry, milk/cheese/yogurt, and fats food groups. There were no notable differences in the food groups used by males and females. However, differences between the sexes emerged when nutrient intakes as a percentage of calories were stratified and food group usage was investigated. Food groups associated with macronutrients that are believed to affect health status have been identified.
Adolescent↗
Cost-containment efforts.
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Cost Control↗
The NHLBI nutrition data system.
A standardized system for the collection and processing of dietary information in large-scale studies is described. Components of the system include interviewer and coder training, certification and continuing education, automated procedures for identifying and quantitating fat, guides for classifying and quantitating foods, system maintenance and quality control procedures, and a food table containing about 800 food items and 450 recipe items. The system is flexible enough to respond to market changes in formulation. Unique automated features make the system particularly useful in identifying and quantitating different dietary fats. These features could be modified to meet nutritional demands of other studies.
Cholesterol, Dietary↗