Research Center for High Altitude Medicine

Xining, China

Research Center for High Altitude Medicine

Xining, China
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Simonson T.S.,University of California at San Diego | Wei G.,Research Center for High Altitude Medicine | Wagner H.E.,University of California at San Diego | Wuren T.,Research Center for High Altitude Medicine | And 7 more authors.
Experimental Physiology | Year: 2014

New Findings: What is the central question of this study? Is Tibetan and Chinese highlanders' blood oxygen-binding affinity (P50) different from that of other populations (at altitude or sea level), and does Tibetan P50 relate to haemoglobin concentration and/or exercise capacity at altitude? What is the main finding and its importance? Tibetans and Chinese at 4200 m have slightly lower P50 than sea-level residents. During maximal exercise at 4200 m, reduced P50 does not enhance pulmonary gas exchange, impair systemic oxygen extraction or affect peak exercise capacity. Oxygen saturation measurements based upon forehead oximetry are sufficiently reduced during exercise at altitude (and accurate compared with those obtained from arterial blood by co-oximetry) to determine P50 reliably. High-altitude natives are challenged by hypoxia, and a potential compensatory mechanism could be reduced blood oxygen-binding affinity (P50), as seen in several high-altitude mammalian species. In 21 Qinghai Tibetan and nine Han Chinese men, all resident at 4200 m, standard P50 was calculated from measurements of arterial PO2 and forehead oximeter oxygen saturation, which was validated in a separate examination of 13 healthy subjects residing at sea level. In both Tibetans and Han Chinese, standard P50 was 24.5 ± 1.4 and 24.5 ± 2.0 mmHg, respectively, and was lower than in the sea-level subjects (26.2 ± 0.6 mmHg, P < 0.01). There was no relationship between P50 and haemoglobin concentration (the latter ranging from 15.2 to 22.9 g dl-1 in Tibetans). During peak exercise, P50 was not associated with alveolar-arterial PO2 difference or peak O2 uptake per kilogram. There appears to be no apparent benefit of a lower P50 in this adult high-altitude Tibetan population. © 2014 The Authors.


PubMed | University of California at San Diego, Federal University of Rio Grande do Sul and Research Center for High Altitude Medicine
Type: Journal Article | Journal: Experimental physiology | Year: 2014

High-altitude natives are challenged by hypoxia, and a potential compensatory mechanism could be reduced blood oxygen-binding affinity (P50), as seen in several high-altitude mammalian species. In 21 Qinghai Tibetan and nine Han Chinese men, all resident at 4200m, standard P50 was calculated from measurements of arterial PO2 and forehead oximeter oxygen saturation, which was validated in a separate examination of 13 healthy subjects residing at sea level. In both Tibetans and Han Chinese, standard P50 was 24.51.4 and 24.52.0mmHg, respectively, and was lower than in the sea-level subjects (26.20.6mmHg, P<0.01). There was no relationship between P50 and haemoglobin concentration (the latter ranging from 15.2 to 22.9gdl(-1) in Tibetans). During peak exercise, P50 was not associated with alveolar-arterial PO2 difference or peak O2 uptake per kilogram. There appears to be no apparent benefit of a lower P50 in this adult high-altitude Tibetan population.


Wagner P.D.,University of California at San Diego | Simonson T.S.,University of California at San Diego | Wei G.,Research Center for High Altitude Medicine | Wagner H.E.,University of California at San Diego | And 4 more authors.
Experimental Physiology | Year: 2015

Despite residence at >4000 m above sea level, many Tibetan highlanders, unlike Andean counterparts and lowlanders at altitude, exhibit haemoglobin concentration ([Hb]) within the typical sea-level range. Genetic adaptations in Tibetans are associated with this relatively low [Hb], yet the functional relevance of the lower [Hb] remains unknown. To address this, we examined each major step of the oxygen transport cascade [ventilation (VE), cardiac output (QT) and diffusional conductance in lung (DL) and muscle (DM)] in Tibetan males at maximal exercise on a cycle ergometer. Ranging from 15.2 to 22.9 g dl-1, [Hb] was negatively associated with peak O2 uptake per kilogram (r = -0.45, P < 0.05) and both cardiac output (QT/kg: r = -0.54, P < 0.02) and muscle O2 diffusion conductance (DM/kg: r = -0.44, P < 0.05) but not ventilation, arterial partial pressure of O2 or pulmonary diffusing capacity. Most variance in peak O2 uptake per kilogram was attributed to QT, DM and arterial partial pressure of CO2 (r2 = 0.90). In summary, lack of polycythaemia in Tibetans is associated with increased exercise capacity, which is explained by elevated cardiac, muscle and, to a small extent, ventilatory responses rather than pulmonary gas exchange. Whether lower [Hb] is the cause or result of these changes in O2 transport or is causally unrelated will require additional study. © 2015 The Physiological Society.


Simonson T.S.,University of California at San Diego | Wei G.,Research Center for High Altitude Medicine | Wagner H.E.,University of California at San Diego | Wuren T.,Research Center for High Altitude Medicine | And 4 more authors.
Journal of Physiology | Year: 2015

Key points: We hypothesized that sea-level range haemoglobin concentration ([Hb]) at altitude, previously linked with adaptive genetic factors in Tibetans, would be associated with greater exercise capacity, explained by changes in steps of the oxygen transport system in this population. In 21 Tibetan and 9 Han Chinese males resident at 4200-4300 m, we measured [Hb], ventilation, volumes of O2 and CO2 utilized at peak exercise (V˙O2 and V˙CO2), heart rate, cardiac output and arterial blood gas variables at peak exercise on a cycle ergometer and determined oxygen (O2) diffusion capacity in lung and muscle. Tibetans with low [Hb] exhibit greater peak V˙O2 kg-1, which was explained mostly by variation in cardiac output, ventilation and O2 diffusional conductances in muscle. These results suggest that polycythaemia may be an excessive response to low PO2 at altitude. Tibetans living at high altitude have adapted genetically such that many display a low erythropoietic response, resulting in near sea-level haemoglobin (Hb) concentration. We hypothesized that absence of the erythropoietic response would be associated with greater exercise capacity compared to those with high [Hb] as a result of beneficial changes in oxygen transport. We measured, in 21 Tibetan males with [Hb] ranging from 15.2 g dl-1 to 22.9 g dl-1 (9.4 mmol l-1 to 14.2 mmol l-1), [Hb], ventilation, volumes of O2 and CO2 utilized at peak exercise (V˙O2 and V˙CO2), heart rate, cardiac output and arterial blood gas variables at peak exercise on a cycle ergometer at ∼4200 m. Lung and muscle O2 diffusional conductances were computed from these measurements. [Hb] was related (negatively) to V˙O2 kg-1 (r = -0.45, P< 0.05), cardiac output kg-1 (QT kg-1, r = -0.54, P < 0.02), and O2 diffusion capacity in muscle (DM kg-1, r = -0.44, P<0.05), but was unrelated to ventilation, arterial partial pressure of O2 (PaO2) or pulmonary diffusing capacity. Using multiple linear regression, variance in peak V˙O2 kg-1 was primarily attributed to QT, DM, and PCO2 (R2 = 0.88). However, variance in pulmonary gas exchange played essentially no role in determining peak V˙O2. These results (1) show higher exercise capacity in Tibetans without the erythropoietic response, supported mostly by cardiac and muscle O2 transport capacity and ventilation rather than pulmonary adaptations, and (2) support the emerging hypothesis that the polycythaemia of altitude, normally a beneficial response to low cellular PO2, may become maladaptive if excessively elevated under chronic hypoxia. The cause and effect relationships among [Hb], QT, DM, and PCO2 remain to be elucidated. © 2015 The Authors. The Journal of Physiology. © 2015 The Physiological Society.


PubMed | University of California at San Diego and Research Center for High Altitude Medicine
Type: Journal Article | Journal: Experimental physiology | Year: 2015

What is the topic of this review? Recent developments link relatively lower hemoglobin concentration in Tibetans at high altitude to exercise capacity and components of oxygen transport. What advances does it highlight? Haemoglobin concentration (ranging from 15.2 to 22.9gdl(-1) ) in Tibetan males was negatively associated with peak oxygen (O2 ) uptake per kilogram, cardiac output and muscle O2 diffusion conductance. Most variance in the peak O2 uptake per kilogram of Tibetan males was attributed to cardiac output, muscle diffusional conductance and arterial partial pressure of CO2 . The mechanisms underlying these differences in oxygen transport in Tibetans require additional analyses. Despite residence at >4000m above sea level, many Tibetan highlanders, unlike Andean counterparts and lowlanders at altitude, exhibit haemoglobin concentration ([Hb]) within the typical sea-level range. Genetic adaptations in Tibetans are associated with this relatively low [Hb], yet the functional relevance of the lower [Hb] remains unknown. To address this, we examined each major step of the oxygen transport cascade [ventilation (VE), cardiac output (QT) and diffusional conductance in lung (DL) and muscle (DM)] in Tibetan males at maximal exercise on a cycle ergometer. Ranging from 15.2 to 22.9gdl(-1) , [Hb] was negatively associated with peak O2 uptake per kilogram (r=-0.45, P<0.05) and both cardiac output (QT/kg: r=-0.54, P<0.02) and muscle O2 diffusion conductance (DM/kg: r=-0.44, P<0.05) but not ventilation, arterial partial pressure of O2 or pulmonary diffusing capacity. Most variance in peak O2 uptake per kilogram was attributed to QT, DM and arterial partial pressure of CO2 (r(2) =0.90). In summary, lack of polycythaemia in Tibetans is associated with increased exercise capacity, which is explained by elevated cardiac, muscle and, to a small extent, ventilatory responses rather than pulmonary gas exchange. Whether lower [Hb] is the cause or result of these changes in O2 transport or is causally unrelated will require additional study.

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