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Biomedical subjects

S A Barton

Publications and source records attributed to S A Barton.

At least 37 records · Page 2Linked to original sources
PubMed1988

A digital system for generating dynamic sinusoidal gas concentration signals.

A computer-controlled gas-mixing system is presented. It is capable of mixing four gases, the concentration of three of which will follow a path to be determined by the user. For our purposes the output O2 fraction is maintained constant and the levels of Ar and N2O vary sinusoidally and independently, with periods between 0.25 and 30 min. A fourth gas, N2 is necessary to make the sum of the individual fractions 100%. The system uses banks of between one and four solenoid valves each linked via a sonic choke to a common mixing chamber. A regime of pulse frequency modulation is employed. All calculations and timing of valve switching are performed by a dedicated microcomputer built for the purpose. The device has been used to provide respiratory gas forcing functions for a program of research in respiratory monitoring.

Humans↗
PubMed1988

A compensation method for membrane-covered (Clark) electrodes.

Membrane-covered electrodes (Clark electrodes) are widely used for monitoring blood gases, particularly PO2. A method of compensating for the inherently limited speed of response of Clark electrodes is presented. The theoretical response in the time domain is related to that in the frequency domain, and the latter is deduced from measurement of the former. Although the response functions are both infinite series, both responses are nevertheless completely defined by a single time parameter Te characteristic of the electrode under given measurement conditions. Practical verification was performed using electrodes in the double-pulsed mode, but the theory is applicable equally to direct-current-polarized and simply pulsed electrodes.

Algorithms↗
PubMed1987

Body circumferences as alternatives to skinfold measurements of body fat distribution in Mexican-Americans.

The ratios of circumferences (waist/hip, waist/thigh) have been proposed in lieu of skinfold measurements for studies of obesity and body fat distribution. The purpose of this paper is to present our experience in measuring a series of body circumferences and skinfolds in an obese population, and seek the relationship between these two kinds of variables as indicators of fatness and body fat distribution using canonical correlation analysis. With this method, weighted vectors of circumferences on the one hand and skinfolds on the other, are formed in such a way that the correlation between the two sets of variables is maximized. The weights (regression coefficients) and their signs help us select the best combination of circumferences which describe a component of centralized obesity. Our experience showed that 21 percent of women would have been excluded from this multivariate analysis due to skinfolds what could not be measured (mainly due to poor fold definition). Few men were so excluded (6 per cent), and almost all circumferences could be measured in both sexes. A first canonical correlation was substantial (0.84 in women, 0.89 in men) and appeared to relate to level of fatness. A second canonical correlation was moderate (0.59 in women, 0.42 in men) and statistically significant (P less than 0.01) in both sexes. Only in women was it independent of age, but in both sexes it reflected differences in central and peripheral (especially lower limb) fat. The simple waist/thigh ratio correlated well with the second canonical variate (0.79 in women, 0.67 in men).(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1986

Genetic polymorphism and fertility parameters in the Aymara of Chile and Bolivia.

To determine whether increased fitness in natural populations is associated with heterozygosity, several studies have attempted to correlate heterozygosity at one or a few genetic loci with fitness-related quantitative traits. The results have been equivocal at best. Furthermore, data on fertility-related parameters and the extent of genetic polymorphism at a large number of loci in man are quite scanty. This report examines the association of four fertility-related parameters (number of pregnancies, number of livebirths, number of children surviving at least one year and number of children alive at the time of the survey) with heterozygosity at 17 polymorphic immunological and biochemical systems in the Aymara of Chile and Bolivia. Women 45 years of age and above, on whom complete fertility histories and phenotype data are available, were included in the study (n = 190). None of the fertility parameters seem to be correlated with heterozygosity, as measured by the proportion of polymorphic loci. For some individual loci, however, an association between heterozygous state and fertility parameters exists. Even in these cases, heterozygosity did not always confer higher fertility. To see whether these negative results are due to heterogeneity in the data, the total sample was divided according to altitude of residence and ethnicity. The conclusions remained the same, indicating that the lack of association of these fertility parameters with genetic polymorphism is not due to population heterogeneity alone. Reproductive fitness differentials, therefore, were not detectable in the Aymara by heterozygosity determined by the polymorphic genetic systems scored by serological and electrophoretic techniques.

Adolescent↗
PubMed1986

Risk of postmenopausal hip fracture in Mexican American women.

To assess the risk of hip fracture in Mexican Americans, the ethnicity of 80 women aged 50 years and over admitted with hip fractures to a Texas hospital was compared with that of age-matched women hospitalized for other reasons. The risk of fracture for Mexican Americans was only 35 per cent that of Whites (95% CI = 19 per cent, 65 per cent). This finding was confirmed in a chart survey performed in a second hospital population. These results suggest that Mexican American women may receive less potential benefit from preventive measures for hip fracture than Whites.

Aged↗
PubMed1983

Diabetes among Mexican Americans in Starr County, Texas.

An increasing body of evidence suggests that diabetes mellitus constitutes a major health burden among the Mexican-American population. For example, county-wide death rates in Texas attributable to diabetes from 1970-1981 range from 2.5-52.0 diabetes deaths per 1000 total deaths with the highest rates generally occurring in counties whose populations are more than 75% Spanish ancestry. To assess the prevalence and morbidity of noninsulin-dependent diabetes mellitus among Mexican Americans, 14% of the Starr County, Texas, population (97% Mexican-American) was randomly sampled. The reference population, sampling strategy, and screening results are described. Age-specific prevalences of diabetes for males ranged from 0% in males aged 15-24 years to 17.6% in those above 75 years of age. Rates for females ranged from 0.4% in those aged 15-24 years to a high of 19.0% in the 55- to 64-year age group. In both sexes, the rates are relatively low for persons under age 45 with a sharp increase in those aged 45-54 years and high rates prevailing in the older age groups. Comparisons of the rates in Starr County to those of the general US population indicate a two- to fivefold greater risk in Starr County. In terms of impact on this community, these results imply that over 50% of individuals older than 35 years are directly affected by diabetes by virtue of their having the disease or by being a first-degree relative of a diabetic.

Adolescent↗
PubMed1981

2,3-Diphosphoglycerate and night vision.

Recovery of night vision at altitude has been examined in relationship to changes of 2,3,diphosphoglycerate (DPG). It appears that, if DPG influences night adaptation, its effect is small. Inter-individual variability is large, both in terms of DPG and performance on the MESOP, the device used to measure dark adaptation.

2,3-Diphosphoglycerate↗
PubMed1978

The Aymara of Western Bolivia. II. Maxillofacial and dental arch variation.

Maxillofacial and dental arch dimensions of the Bolivian Aymara population are age and sex dependent. Interpopulational comparisons reveal these dimensions to differ from those seen in Aleuts, Australian aborigines, and Swedes, but to be similar to those of the indigenous Taiwanese. Finally, these dimensions are not the same in Aymara of unmixed ancestry, and Mestizos residing in the same villages.

Adolescent↗
PubMed1978

The Aymara of Western Bolivia. IV. Gene frequencies for eight blood groups and 19 protein and erythrocyte enzyme systems.

A total of 315 individuals, mainly of Aymara origin, from western Bolivia were examined for genetic variation at eight red cell antigen and 19 serum protein and red cell enzyme loci. The gene frequencies for polymorphic loci and the discovery of several rare variants are discussed in terms of previous work among the Aymara and the closely related Quechua. The effect of inclusion of related individuals in the sample on gene frequency, variance of gene frequency and genetic distance, is discussed.

Blood Group Antigens↗
PubMed1976

High altitude, indigenous origin, and continuous cardiac monitoring.

Tape monitoring of the electrocardiogram among ambulant individuals with and without cardiac disease has been practicable for some years now. It has, however, found greater acceptance and utilization in diagnosis, early detection of silent ischemic heart disease (17), and the evaluation of the effectiveness of different dysrhythmia treatment modalities than as a means to examine differences in cardiovascular response to environmentally stressful situations. This study illustrates its practicability under field conditions substantially more rigorous than in most prior uses, and its applicability to our further understanding of the cardiovascular changes associated with adaptation to the hypoxia of altitude.

Adolescent↗
PubMedDate not supplied

Genetic components of variations of red cell glycolytic intermediates at two altitudes among the South American Aymara.

Red cell haemoglobin (Hb), haematocrit (Ht), 2,3-diphosphoglycerate (DPG), and adenosine triphosphate (ATP) levels were measured in 876 individuals from six villages at two altitude levels (altiplano and coast) of the Departmento de Arica of Northern Chile. Of these, data on 761 individuals are subjected to analysis to search for the evidence of genetic adaptation to a hypoxic environment at a high altitude. Total phenotypic variance for each of the variables is higher at the altiplano as compared to their counterparts at the coastal level. Data on 1127 pairs of relatives of six degrees of relationships are used to determine the genetic component of variation in each of these four traits. To a certain extent the larger familial correlations as well as higher variances at altiplano are explained by the apparent assortative mating (which may again be due to their restricted population size) at the higher elevation. Yet, at least in three variables (Hb, Ht, and DPG) no reduction in the additive genetic component of variation is noticed at the higher altitude. ATP seems to have the highest degree of genetic component of variance, particularly at the coastal level. Some implications of these results are discussed in the light of their roles in the glycolytic pathway.

2,3-Diphosphoglycerate↗
PubMedDate not supplied

Immunoglobulin (Gm and Km) allotypes in the Aymara of Chile and Bolivia.

Immunoglobulin (Gm and Km) allotype and haplotype frequencies are presented for 1707 individuals from Northern Chile and Western Bolivia, subdividing them by ethnicity and altitude of residence. The haplotype distribution of Gm as well as Km loci in these populations suggest that in almost all of the ethnicity x altitude subdivisions of this population considerable admixture of Amerindian and Caucasian genes have occurred. The haplotype frequency heterogeneity and the analysis of departure from Hardy-Weinberg expectations demonstrate that while some local variation in haplotype frequencies at the Gm and Km loci exists in this region, there is no clear evidence suggesting that the pattern of variation is due to an adaptation to the hypoxia of altitude. We conclude that such differences in haplotype frequencies are probably due to random genetic drift and differential admixture of Amerindian and Caucasian genes that have occurred in the past.

Bolivia↗
PubMedDate not supplied

Gender and treatment differences in knowledge, health beliefs, and metabolic control in Mexican Americans with type 2 diabetes.

PURPOSE: The purpose of this project was to describe metabolic control, knowledge, and health beliefs of Mexican Americans with type 2 diabetes. METHODS: The study site was Starr County, Texas, a border community located on the Rio Grande River and bordering northern Mexico. Of the total sample of 360 persons, 252 agreed to participate in this intervention study and were randomized either to the treatment group or the control group that waited 1 year to begin the intervention. RESULTS: The majority of individuals were Spanish-speaking females with a mean age of 54 years and a mean diabetes duration of 8 years. For those treated with diet only, males exhibited higher fasting blood glucose levels than females. Gender effects were seen for cholesterol level, with females exhibiting higher levels than males. Males expressed stronger perceptions of control and social support for diet. Bivariate relationships were found between acculturation and diabetes knowledge. The health belief subscales of control and impact on job together explained 16% of the variance in HbA1c values. CONCLUSIONS: Males and females held differing beliefs about ability to control their diabetes and degree of social support for diet. The impact of gender differences on ability to integrate diabetes self-care and on effectiveness of diabetes programs has not been determined but should be considered in future research.

Attitude to Health↗
PubMedDate not supplied

Symptom-related self-care of Mexican Americans with type 2 diabetes: preliminary findings of the Starr County Diabetes Education Study.

Starr County, Texas, a Texas-Mexico border community, was the site of a study involving culturally-appropriate education and group support for Mexican Americans with type 2 diabetes. Data were collected from 63 subjects on frequency of diabetes-related symptoms during the previous month and on self-care symptom treatments. On average, subjects were 57-year-old females, diagnosed with diabetes for 10 years, and exhibiting HbA1c levels of 12.5%. Almost 50% experienced excessive urination, excessive thirst, shakiness/nervousness, and numbness and/or tingling in their extremities. More than 50% of those who experienced symptoms did not view them as serious. Only one subject checked blood sugar levels when symptoms occurred. Significantly higher mean glycosylated hemoglobin levels were found for individuals who experienced dizziness and/or chest pain compared with those who did not. A variety of self-care treatments were employed, including over-the-counter medications and home remedies.

Adult↗