Browsing by Autor "Gary M. Brittenham"

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Hemoglobin concentration of high‐altitude Tibetans and Bolivian Aymara
(Wiley, 1998) Cynthia M. Beall; Gary M. Brittenham; Kingman P. Strohl; John Blangero; Sarah Williams‐Blangero; Melvyn C. Goldstein; Michael J. Decker; Enrique Vargas; Mercedes Villena; Rudy Soria
Elevated hemoglobin concentrations have been reported for high-altitude sojourners and Andean high-altitude natives since early in the 20th century. Thus, reports that have appeared since the 1970s describing relatively low hemoglobin concentration among Tibetan high-altitude natives were unexpected. These suggested a hypothesis of population differences in hematological response to high-altitude hypoxia. A case of quantitatively different responses to one environmental stress would offer an opportunity to study the broad evolutionary question of the origin of adaptations. However, many factors may confound population comparisons. The present study was designed to test the null hypothesis of no difference in mean hemoglobin concentration of Tibetan and Aymara native residents at 3,800–4,065 meters by using healthy samples that were screened for iron deficiency, abnormal hemoglobins, and thalassemias, recruited and assessed using the same techniques. The hypothesis was rejected, because Tibetan males had a significantly lower mean hemoglobin concentration of 15.6 gm/dl compared with 19.2 gm/dl for Aymara males, and Tibetan females had a mean hemoglobin concentration of 14.2 gm/dl compared with 17.8 gm/dl for Aymara females. The Tibetan hemoglobin distribution closely resembled that from a comparable, sea-level sample from the United States, whereas the Aymara distribution was shifted toward 3–4 gm/dl higher values. Genetic factors accounted for a very high proportion of the phenotypic variance in hemoglobin concentration in both samples (0.86 in the Tibetan sample and 0.87 in the Aymara sample). The presence of significant genetic variance means that there is the potential for natural selection and genetic adaptation of hemoglobin concentration in Tibetan and Aymara high-altitude populations. Am J Phys Anthropol 106:385–400, 1998. © 1998 Wiley-Liss, Inc.
Hemoglobin concentration of high-altitude Tibetans and Bolivian Aymara
(Wiley, 1998) Cynthia M. Beall; Gary M. Brittenham; Kingman P. Strohl; John Blangero; Sarah Williams‐Blangero; Melvyn C. Goldstein; Michael J. Decker; Enrique Vargas; Mercedes Villena; Rudy Soria
Elevated hemoglobin concentrations have been reported for high-altitude sojourners and Andean high-altitude natives since early in the 20th century. Thus, reports that have appeared since the 1970s describing relatively low hemoglobin concentration among Tibetan high-altitude natives were unexpected. These suggested a hypothesis of population differences in hematological response to high-altitude hypoxia. A case of quantitatively different responses to one environmental stress would offer an opportunity to study the broad evolutionary question of the origin of adaptations. However, many factors may confound population comparisons. The present study was designed to test the null hypothesis of no difference in mean hemoglobin concentration of Tibetan and Aymara native residents at 3,800-4,065 meters by using healthy samples that were screened for iron deficiency, abnormal hemoglobins, and thalassemias, recruited and assessed using the same techniques. The hypothesis was rejected, because Tibetan males had a significantly lower mean hemoglobin concentration of 15.6 gm/dl compared with 19.2 gm/dl for Aymara males, and Tibetan females had a mean hemoglobin concentration of 14.2 gm/dl compared with 17.8 gm/dl for Aymara females. The Tibetan hemoglobin distribution closely resembled that from a comparable, sea-level sample from the United States, whereas the Aymara distribution was shifted toward 3-4 gm/dl higher values. Genetic factors accounted for a very high proportion of the phenotypic variance in hemoglobin concentration in both samples (0.86 in the Tibetan sample and 0.87 in the Aymara sample). The presence of significant genetic variance means that there is the potential for natural selection and genetic adaptation of hemoglobin concentration in Tibetan and Aymara high-altitude populations.
Percent of oxygen saturation of arterial hemoglobin among Bolivian Aymara at 3,900–4,000 m
(Wiley, 1999) Cynthia M. Beall; Laura Almasy; John Blangero; Sarah Williams‐Blangero; Gary M. Brittenham; Kingman P. Strohl; Michael J. Decker; Enrique Vargas; Mercedes Villena; Rudy Soria
A range of variation in percent of oxygen saturation of arterial hemoglobin (SaO2) among healthy individuals at a given high altitude indicates differences in physiological hypoxemia despite uniform ambient hypoxic stress. In populations native to the Tibetan plateau, a significant portion of the variance is attributable to additive genetic factors, and there is a major gene influencing SaO2. To determine whether there is genetic variance in other high-altitude populations, we designed a study to test the hypothesis that additive genetic factors contribute to phenotypic variation in SaO2 among Aymara natives of the Andean plateau, a population geographically distant from the Tibetan plateau and with a long, separate history of high-altitude residence. The average SaO2 of 381 Aymara at 3,900–4,000 m was 92 ± 0.15% (SEM) with a range of 84–99%. The average was 2.6% higher than the average SaO2 of a sample of Tibetans at 3,800–4,065 m measured with the same techniques. Quantitative genetic analyses of the Aymara sample detected no significant variance attributable to genetic factors. The presence of genetic variance in SaO2 in the Tibetan sample and its absence in the Aymara sample indicate there is potential for natural selection on this trait in the Tibetan but not the Aymara population. Am J Phys Anthropol 108:41–51, 1999. © 1999 Wiley-Liss, Inc.
Percent of oxygen saturation of arterial hemoglobin among Bolivian Aymara at 3,900-4,000 m
(Wiley, 1999) Cynthia M. Beall; Laura Almasy; John Blangero; Sarah Williams‐Blangero; Gary M. Brittenham; Kingman P. Strohl; Michael J. Decker; Enrique Vargas; Mercedes Villena; Rudy Soria
A range of variation in percent of oxygen saturation of arterial hemoglobin (SaO2) among healthy individuals at a given high altitude indicates differences in physiological hypoxemia despite uniform ambient hypoxic stress. In populations native to the Tibetan plateau, a significant portion of the variance is attributable to additive genetic factors, and there is a major gene influencing SaO2. To determine whether there is genetic variance in other high-altitude populations, we designed a study to test the hypothesis that additive genetic factors contribute to phenotypic variation in SaO2 among Aymara natives of the Andean plateau, a population geographically distant from the Tibetan plateau and with a long, separate history of high-altitude residence. The average SaO2 of 381 Aymara at 3,900-4,000 m was 92+/-0.15% (SEM) with a range of 84-99%. The average was 2.6% higher than the average SaO2 of a sample of Tibetans at 3,800-4,065 m measured with the same techniques. Quantitative genetic analyses of the Aymara sample detected no significant variance attributable to genetic factors. The presence of genetic variance in SaO2 in the Tibetan sample and its absence in the Aymara sample indicate there is potential for natural selection on this trait in the Tibetan but not the Aymara population.
Respiratory and hematological adaptations of young and older Aymara men native to 3600M
(Wiley, 1992) Cynthia M. Beall; Kingman P. Strohl; Barbara Gothe; Gary M. Brittenham; Gerardo Barragán Mejía; Enrique Vargas
This paper reports the results of a study designed to test the hypothesis that an inevitable concomitant of aging at high altitudes is chronic mountain sickness resulting from excess erythrocytosis secondary to exaggerated hypoxemia caused by aging processes in the respiratory system. It compares age differences in respiratory system function in oxygenating the blood measured as percent O<sub>2</sub> saturation of arterial hemoglobin during wakefulness and sleep and in erythrocytosis measured as hemoglobin concentration in 17 young (22-35 years) and 16 older (47-68 years) rural and urban resident Bolivian Aymara men, healthy lifelong residents of 3,500-4,000 m who were tested at 3,600 m. The results do not support the hypothesis. Older urban men are significantly more hypoxemic during wakefulness and sleep than young urban men, while there are no age differences in the degree of hypoxemia among the rural residents. However, older urban men do not have the higher hemoglobin concentration predicted by the hypothesis. Both urban and rural older men have lower hemoglobin concentration than their young counterparts, a finding not attributable to age differences in nutritional status or testosterone concentration. Despite their relatively low hemoglobin concentration, older men have estimated arterial O<sub>2</sub> content in the normal sea level range for young men and in this sense retain the capacity to adapt to high altitude at least through the seventh decade of life.
Salivary testosterone concentration of Aymara men native to 3600 m
(Informa, 1992) Cynthia M. Beall; Carol M. Worthman; Joy F. Stallings; Kingman P. Strohl; Gary M. Brittenham; Gerardo Barragán Mejía
This paper explores the possibility that variation in the normal physiological range of testosterone concentration modulates men's adaptation to hypobaric high-altitude hypoxia through stimulating haemoglobin production and/or causing respiratory disturbances and exacerbated hypoxaemia during sleep. These effects of testosterone are observed clinically at sea level and have potentially opposing consequences at high altitude, the former perhaps enhancing and the latter diminishing the effectiveness of adaptations to hypoxia. Seventeen young (average age 27 years) and 22 older (average age 57 years) healthy adult high altitude native Aymara men tested at 3600 m have average morning salivary testosterone concentrations of 282 and 241 pmol/l, respectively. The 31 urban men of both age groups have higher testosterone concentrations than the eight rural men and have mean haemoglobin concentrations significantly 0.7-1.0 g/dl higher within the normal high-altitude range, consistent with known effects of testosterone at sea level. Older urban men have slightly more frequent respiratory disturbances during sleep, associated with significantly greater hypoxaemia. There appear to be modest benefits to testosterone concentrations in the upper end of the observed range; however, the direction of these responses towards more haemoglobin production and more hypoxaemia during sleep of older men suggests the hypothesis that very high testosterone concentrations such as those in the upper ranges of sea level values could compromise adaptation to high altitude, particularly among older men.