PubMed Health⌕ Search

Biomedical subjects

G E Swan

Publications and source records attributed to G E Swan.

At least 19 recordsLinked to original sources
PubMed2000

Biobehavioral characteristics of nondemented older adults with subclinical brain atrophy.

OBJECTIVE: To characterize the risk factors and neuropsychological performance of two subgroups of community-dwelling, white elderly men free of severe cognitive impairment (n = 383; mean age, 72.9 +/- 3.0 years) who differ on volumetric measurements of total brain parenchyma and white matter hyperintensity (WMH) volumes. METHODS: Group comparisons were made of cerebrovascular disease risk factors measured at the time of imaging and at three prior examinations extending over 25 years of adult life. Measures of verbal memory and speed psychomotor processing at the time of imaging and 10 years before imaging were also available. RESULTS: Compared with those in the "nonatrophy" group, individuals in the subgroup with "atrophy" (defined by low total brain volume and high WMH volume) were older, reported a higher level of depressive symptomatology, experienced a steeper decline in diastolic blood pressure (DBP) and a steeper increase in pulse pressure, were less physically active, had smoked for more years, and had a higher prevalence of several cardiovascular disease indicators, including an ankle/arm systolic blood pressure ratio less than 0.9, and hypertension. After multivariate analysis, the 25-year decline in DBP, the number of years smoked, and an ankle/arm index of less than 0.9 remained significant discriminators of the two groups. Lower levels of speeded performance at the time of imaging and a steeper 10-year decline in cognitive performance on selected tests were also observed in the atrophic group. CONCLUSION: Community-dwelling older adults with volumetric brain measurements associated with accelerated aging are distinguishable on the basis of several health-related characteristics. These individuals also perform less well on certain tasks involving executive functioning.

Adult↗
PubMed2000

Contribution of genetic and environmental influences to ankle-brachial blood pressure index in the NHLBI Twin Study. National Heart, Lung, and Blood Institute.

The ankle-brachial index (ABI) is widely used in the clinical diagnosis of peripheral arterial disease. The contributions of genetic and environmental influences to normal and abnormal ABI values are unknown. In this study, the authors used available data on 94 monozygotic pairs and 90 dizygotic pairs of elderly, White, male twins examined in 1995-1997 to investigate the contributions of genetic and environmental influences to normative ABI values. Within-twin-pair correlations for normative ABI values were statistically significant, and the correlation in monozygotic twin pairs was significantly greater than that in dizygotic pairs. Structural equation modeling of the variance-covariance matrices of monozygotic and dizygotic twins indicated that 48% of the observed variability in ABI values could be attributed to additive genetic effects. In contrast, concordance rates for low ABI values (ABI< or =0.9) for both monozygotic and dizygotic twins were significantly greater than would be expected by chance alone, but within-pair monozygotic similarity was not significantly greater than dizygotic similarity. A matched-cotwin analysis in 21 pairs that were discordant for low ABI values found that twins with low ABI values were physically less active and more likely to be persistent smokers than their normal-control brothers. These findings reinforce the role of individual health practices (e.g., physical activity, smoking) in the manifestation of peripheral arterial disease among subjects matched for age, genetics, and early shared environment.

Aged↗
PubMed2000

Ten-year follow-up for male twins divided into high- or low-risk groups for ischemic heart disease based on risk factors measured 25 years previously.

PURPOSE: To undertake medical follow-up in white males in the National Heart, Lung, and Blood Institute (NHLBI) twin study, previously divided on the basis of cardiovascular disease risk factors. METHODS: Tree structured survival analysis (TSSA) used at a mean age of 63 years to classify twins into high and low risk subgroups for ischemic heart disease (IHD) found that subjects at a mean age of 48 years were at highest risk with high systolic blood pressures and low high density lipoprotein cholesterol levels. Low risk subjects had lower blood pressures, better pulmonary function tests, and a negative family history for IHD or low post load plasma glucose levels. Medical record review was performed ten years later at the 4th Examination of the NHLBI twin cohort conducted in 1995-1997. RESULTS: The percentage of men in the NHLBI twin study who died nearly tripled (from 9.3% to 25.8%) in the ten-year period between the ages of 63 and 73 years. Deaths have tended to remain higher in DZ than MZ twins (27.8% versus 23.7%). At Exam 4, the relative risk of IHD (fatal or non-fatal) was 5.24 times higher for those in the high risk group than those in the low risk class (95% confidence limit 2.72-10.07, p < 0.0001 and 5.86 for any cardiovascular disease (95% confidence limit 3.03-11.33). The proportion of deaths from IHD in subjects with a high risk profile at entry was 51.7%, and 70.0% had died from all cardiovascular related disease. CONCLUSION: The present results indicate TSSA remained effective in classifying subjects into subgroups with greater risk of morbidity and mortality related to cardiovascular disease after ten additional years.

Aged↗
PubMed2000

Segregation analysis of drinking problem in elderly men and their first-degree relatives from the Western Collaborative Group Study.

PURPOSE: The purpose of this study is to determine the mode of inheritance of alcohol-related drinking problems. METHODS: Family history was collected by interview from 493 elderly male participants (probands) in a follow-up cardiovascular exam of healthy white men living in the San Francisco Bay Area and Los Angeles. Segregation analysis was used to test for the presence of a major gene effect underlying the liability to develop an alcohol-related drinking problem. RESULTS: The results showed that the liability to drinking problem is due, in part, to a single major gene with no residual effects from shared familial influences. CONCLUSIONS: These results suggest that at least one major gene is involved in the genetic predisposition to develop drinking problem in late adulthood.

Adult↗
PubMed2000

Longitudinal changes in the contribution of genetic and environmental influences to symptoms of depression in older male twins.

Genetically informative longitudinal data on self-reported symptoms of depression allow for an investigation of the causes of stability and change in depression symptoms throughout adult life. In this report, the authors investigated the relative contribution of genetic and environmental influences to symptoms of depression in 83 monozygotic and 84 dizygotic male twin pairs from the National Heart, Lung, and Blood Institute (NHLBI) Twin Study. Participants first completed the Center for Epidemiologic Studies-Depression (CES-D) scale in 1985-1986 and again during 1995-1997. Mean age of twins at baseline was 63 years, range 59 to 70. From cross-sectional genetic analyses we estimated the heritability of CES-D to be 25% (95% confidence interval [CI], 11%-39%) at baseline and 55% (95% CI, 40%-71%) at follow-up. Fitting longitudinal genetic models to the two-wave data, we found that stability of symptoms over the 10-year follow-up was due primarily to continuity of genetic influences.

Adult↗
PubMed2000

A genetic analysis of smoking behavior in family members of older adult males.

AIMS: To conduct a genetic study of smoking behavior in 493 three-generation families. DESIGN: Complex segregation analysis and maximum likelihood statistics were used to describe the familial clustering of ever-smoking under several transmission models. SETTING: The Western Collaborative Group Study, an ageing and health study currently in its 39th year of follow-up. PARTICIPANTS: Probands were male participants who were of mean age 71.6 years at the time of the family history interview in 1986-88. MEASUREMENTS: Data were collected via an interview that focused on the family smoking history of participants. Smoking histories of all first-degree relatives were obtained from probands. FINDINGS: Evidence for genetic transmission was indicated by rejection of both the environmental and sporadic models in favor of a Mendelian genetic model with residual familial effects from spouses and both parents. CONCLUSIONS: The best-fitting model was that of a dominant major gene with low estimated frequency and residual familial correlations. This is the first study to date to model the familial transmission of ever-smoking in three-generation families.

Aged↗
PubMed2000

A high-performance liquid chromatographic method for the determination of monofluoroacetate.

A simple isocratic high-performance liquid chromatographic (HPLC) method for the quantitative analysis of monofluoroacetic acid (MFA), the toxic substance of Dichapetalum cymosum, in plant material, rumen contents (gastric contents), and liver samples is described. A suitable HPLC column that gives optimum sensitivity, accuracy, precision, and separation of MFA is identified. A C-610 organic acid analysis column at ambient temperature with 0.02M H3PO4 as an eluent and ultraviolet detection at 210 nm is utilized to quantitate MFA. Using this method, the average percentage recovery in plant material, bovine liver, and rumen samples is 94.8%, and a detection limit of 12 microg/L is achievable.

Animals↗
PubMed2000

The contribution of genetic influences to measures of lower-extremity function in older male twins.

Tests of balance, gait, and endurance were administered to 95 monozygotic (MZ) and 92 dizygotic (DZ), white male twins aged 68 to 79 years who had been born in the United States. Within-twin-pair correlations were calculated for each individual task and for an overall summary performance score. These were subjected to structural equation modeling to determine the contributions of genetic and environmental influences to individual differences in performance scores. MZ intraclass correlations were significant and greater than DZ correlations for the 8-foot walk and the repeated chair stands task, but not for the standing balance task. The heritability of the lower-extremity summary score was 57%, of which 39% was due to additive genetic effects and 18% due to nonadditive effects. In addition, we found that genetic influences contributed primarily to twin similarity in the poorest quartile of performance, whereas shared environmental influences contributed to twin similarity in the best quartile.

Aged↗
PubMed2000

The joint effect of apolipoprotein E epsilon4 and MRI findings on lower-extremity function and decline in cognitive function.

BACKGROUND: Cognitive decline and poor physical function are risk factors for disability in old age and may occur more often in subjects with the apolipoprotein E epsilon4 (ApoE-epsilon4) allele. The objective of this study was to investigate the joint effect of ApoE-epsilon4 and structural changes detected on MRI brain scans on cognitive decline and lower-extremity function. METHODS: Brain MRI (1.5 T), neuropsychological tests, and lower-extremity physical function tests were administered to World War II male veteran twins ages 69 to 80. Quantification of MRI scans used a previously published algorithm to segment brain images into total cerebral brain (TCB), cerebrospinal fluid (CSF), and white-matter hyperintensity (WMH) volumes. A short battery of physical performance tests was used to assess lower-extremity function. Ten-year changes in performance on the Mini-Mental State Exam (MMSE), the Benton Visual Retention Test (BVRT), and the Digit Symbol Substitution (DSS) test were used to assess cognitive decline. RESULTS: For the sample as a whole, the comparison of subjects by median split of total cerebral brain volume found that those with brain volumes below the median performed worse on tests of gait and balance (p < .01) and experienced greater cognitive decline on the MMSE and BVRT cognitive test batteries (both p < .01). In addition, subjects with WMH volumes above the median had poor performance on the standing balance tasks and experienced greater decline on the DSS test (p < .01). Stratified analyses revealed that the joint effect of radiological findings and the ApoE-epsilon4 allele on cognitive decline and lower-extremity function was often greater than that expected from the separate effects combined. CONCLUSIONS: We conclude that radiological findings in conjunction with ApoE-epsilon4 may single out a group at higher risk for dementia. We speculate that the observed interaction effect may be due to increased susceptibility to brain injury or impaired repair mechanisms in subjects with ApoE-epsilon4.

Aged↗
PubMed2000

Clinical, cardiopulmonary and haemocytological effects of xylazine in goats after acute exposure to different environmental temperature and humidity conditions.

This study was carried out to assess the influence of xylazine administration on clinical, cardiopulmonary and haemocytological variables after acute exposure to different environmental conditions. Xylazine hydrochloride was administered intravenously at 0.1 mg/kg body mass to 6 clinically healthy, castrated male goats. All animals were exposed for 60 min to 3 sets of climatic conditions: 14 degrees C, 33% relative humidity; 24 degrees C, 55% RH, and 34 degrees C, 65% RH. The variables that were measured for a period of 60 min after xylazine administration were sedation, analgesia, salivation, urination, ventilation rate, heart-rate, mean arterial blood pressure, oesophageal temperature, haematocrit, mean corpuscular volume and mean corpuscular haemoglobin concentration. Xylazine induced sedation, analgesia, salivation and urination independently of the 3 environmental conditions. Environment had no influence on the onset, duration and recovery from sedation. In the 14 degrees C environment, xylazine resulted in a significant decrease in ventilation and heart-rate from baseline values. Significant changes in mean arterial blood pressure, haemoglobin concentration, mean corpuscular volume, haematocrit and red cell count were observed in the 3 environments. Total plasma protein was significantly altered at 24 degrees C and 34 degrees C. Acute exposure of goats to different environmental conditions had no significant influence on the clinical, cardiopulmonary and haemocytological variables. Physiological changes induced by xylazine were therefore independent of the environment.

Adrenergic alpha-Agonists↗
PubMed2000

Stability and partitioning of closantel and rafoxanide in ruminal fluid of sheep.

The stability and the partitioning of closantel and rafoxanide in ruminal fluid (RF) was examined in vitro. Stability was evaluated in two studies in a ruminal fluid-artificial saliva (RF-AS) mixture containing either drug. Drug concentrations were measured in samples collected sequentially from four batches of RF-AS fortified with either closantel or rafoxanide in one study and in four separately incubated aliquots of a RF-AS mixture of each drug in the second study at the start and at various intervals during a 24 h incubation period. The viability of the in vitro RF-AS incubation model was validated by the presence of digoxin degradation (T1/2 of 39,1 +/- 13 h) and by the absence of significant time related differences (P> 0,5) in volume of gas produced, pH and methylene blue reduction time of the RF-AS drug mixture. Partitioning of closantel and rafoxanide was determined by measuring the relative drug concentration of the fluid and particulate phases in RF fortified with either drug at different concentrations. Closantel and rafoxanide were shown to be stable in a RF-AS mixture and were not subjected to any significant biodegradation. An initial marked reduction in drug concentration measured in the RF-AS mixture during the first 2 h of incubation was attributed to the attachment of both drugs onto particulate matter. This was subsequently confirmed in the partitioning study. More than 80% of closantel and rafoxanide was shown to be associated with the particulate phase of RF

Animals↗
PubMed2000

Morphological changes associated with the development of the rumino-reticulum in growing lambs fed different rations.

Morphological changes associated with rumino-reticular development was compared in two groups of SA Mutton Merino lambs (n = 12) fed different diets at 3-5 weeks, 17-19 weeks and 31-33 weeks of age. Diet groups were identified as MMH or MHH according to the sequence at which the full-milk replacement (M) or hay (H) diet were fed to the lambs over the three study phases (phases I, II and III) preceding each age period. Prominent differences in the morphology (size and volume) and function (pH, proteolytic activity and microbial population) of the rumino-reticulum were observed in indicator lambs (n = 2) killed at every age period and also between milk-fed and hay-fed lambs. The size of the rumino-reticulum was rudimentary at 3-5 weeks of age and remained underdeveloped in lambs at 17-19 weeks of age which had received a full-milk replacement diet during phase II. One lamb, slaughtered at 3 weeks of age, showed a large distended rumen with severe sloughing of the surface cells of the stratum corneum. The size of the rumino-reticulum increased in size (2 x) in lambs which were fed hay relative to the milk-fed lambs during phase II and reached adult proportions in all lambs at 31-33 weeks of age. Ultrastructural examination showed that rumen papillae were more developed in lambs fed hay during phase II when compared to those of milk-fed lambs. Rumen papillae were best developed in phase III lambs.

Aging↗
PubMed1999

Midlife cardiovascular risk factors and brain morphology in identical older male twins.

OBJECTIVE: Structural changes in the human brain have been reported to a greater extent in subjects with cardiovascular risk factors. We conducted a matched co-twin analysis of elderly monozygotic twins from the National Heart, Lung, and Blood Institute Twin Study to examine the association between midlife cardiovascular risk factors and MRI-based measures of brain atrophy. METHODS: Brain MRIs (1.5-T) were obtained from 74 monozygotic, white, male, World War II veteran twins born in the United States from 1917 to 1927 and age 68 to 79 at the time of the brain scan. A semiautomated algorithm was used to segment brain images into total brain, CSF, and white matter hyperintensity volumes. Cardiovascular risk factors, medical history variables, and health practices were available from data collected over 25 years of adult life. RESULTS: Independent of shared genetic or familial influences, within-pair differences in midlife glucose levels, high-density lipoprotein cholesterol, and systolic blood pressure were significantly associated with differences in white matter hyperintensities. Within-pair differences in coronary heart disease history and in current consumption of alcohol and level of physical activity were significantly associated with differences in brain parenchyma. In addition, within-pair differences in white matter hyperintensity volumes were significantly associated with differences in performance on cognitive and physical function tests and self-reports of depression symptoms. CONCLUSION: Independent of age effects and shared genetic or familial influences, midlife cardiovascular risk factors and lifetime health practices were predictive of structural brain changes in old age.

Brain↗
PubMed1999

Differential genetic influence for components of memory in aging adult twins.

OBJECTIVE: To investigate the relative proportion of genetic and environmental contributions to verbal memory in community-dwelling World War II veteran twins. DESIGN: The California Verbal Learning Test (CVLT) was administered to 94 monozygotic (MZ) and 89 dizygotic (DZ) elderly male twin pair participants in the fourth examination of the National Heart, Lung, and Blood Institute Twin Study. SETTING: Subjects voluntarily participated on an outpatient basis at a research or medical center facility in 1 of 4 sites in the United States. PARTICIPANTS: Subjects had a mean age of 71.8 years (SD, 2.9 years), a mean educational level of 13.6 years (SD, 2.8 years), and no history of stroke and/or a Mini-Mental State Examination score of 23 or greater. MAIN OUTCOME MEASURES: Twin pair similarity in performance on 4 factor analytically derived components of the CVLT measuring verbal learning and memory, response discrimination, learning strategy, and recognition memory. RESULTS: The MZ intraclass correlation was significantly larger than the DZ correlation for verbal learning and memory (I<.001) but not for the other 3 components of memory. Using maximum likelihood methods, the best-fitting genetic model indicated that verbal learning and memory has a substantial genetic component (56% of total variance), whereas response discrimination has a much smaller, although still detectable, genetic component (24% of total variance). There is no evidence of genetic influence on learning strategy or recognition memory. CONCLUSION: Differential contribution of genetic and environmental influences to specific components of memory suggest that, in this group of elderly male twin pairs, some components may be more amenable to intervention than others.

Aged↗
PubMed1999

Implications of genetic epidemiology for the prevention of tobacco use.

Genetic epidemiology is the study of the pattern of common disease incidence in families and populations in order to infer the genetic basis of the disease. Genetic epidemiological studies are usually undertaken in advance of DNA-based studies aimed at genetic dissection. Truly transdisciplinary work on the prevention of tobacco use involving genetic epidemiology has not been conducted to date. As we prepare to move to the next generation of research on nicotine dependence, we have the advantage of being able to employ newly developed biobehavioral measures and to learn from previously encountered difficulties in the field of psychiatric genetics. Recent theoretical developments in the area of adolescent substance use clearly identify a role for both direct and indirect susceptibility to regular tobacco use that is in part determined by genetic factors. A logical next step for transdisciplinary work in this area is to design and implement a developmental study of substance use in children and their family members. A key step in the design and implementation of this longitudinal approach will be the utilization of measurement methods that determine with as much precision as possible the social, cultural, behavioral, and genetic factors that place adolescents at risk for tobacco dependence. The extent to which environmental risk factors interact with genetic risk factors to increase susceptibility to nicotine addiction is unknown. It is unlikely that knowledge of genetic risk factors alone will lead to effective prevention strategies. A longitudinal family study designed around the framework of a transdisciplinary theory of adolescent substance use offers the potential to be highly informative in the next generation of research on tobacco prevention.

Adolescent↗