Red cell properties and optimal oxygen transport

Why Are High-Altitude Natives So Strong at Altitude? Maximal Oxygen Transport to the Muscle Cell in Altitude Natives

In hypoxia aerobic exercise performance of high-altitude natives is suggested to be superior to that of lowlanders; i.e., for a given altitude natives are reported to have higher maximal oxygen uptake (VO2max). The likely basis for this is a higher pulmonary diffusion capacity, which in turn ensures higher arterial O2 saturation (SaO2) and therefore also potentially a higher delivery of O2 to the exercising muscles. This review focuses on O2 transport in high-altitude Aymara. We have quantified femoral artery O2 delivery, arterial O2 extraction and calculated leg VO2 in Aymara, and compared their values with that of acclimatizing Danish lowlanders. All subjects were studied at 4100 m. At maximal exercise SaO2 dropped tremendously in the lowlanders, but did not change in the Aymara. Therefore arterial O2 content was also higher in the Aymara. At maximal exercise however, fractional O2 extraction was lower in the Aymara, and the a-vO2 difference was similar in both populations. The lower extraction levels in the Aymara were associated with lower muscle O2 conductance (a measure of muscle diffusion capacity). At any given submaximal exercise intensity, leg VO2 was always of similar magnitude in both groups, but at maximal exercise the lowlanders had higher leg blood flow, and hence also higher maximum leg VO2. With the induction of acute normoxia fractional arterial O2 extraction fell in the highlanders, but remained unchanged in the lowlanders. Hence high-altitude natives seem to be more diffusion limited at the muscle level as compared to lowlanders. In conclusion Aymara preserve very high SaO2 during hypoxic exercise (likely due to a higher lung diffusion capacity), but the effect on VO2max is reduced by a lower ability to extract O2 at the muscle level.

Phenotypic plasticity in blood-oxygen transport in highland and lowland deer mice

In vertebrates living at high altitude, arterial hypoxemia may be ameliorated by reversible changes in the oxygen-carrying capacity of the blood (regulated by erythropoiesis) and/or changes in blood-oxygen affinity (regulated by allosteric effectors of hemoglobin function). These hematological traits often differ between taxa that are native to different elevational zones, but it is often unknown whether the observed physiological differences reflect fixed, genetically based differences or environmentally induced acclimatization responses (phenotypic plasticity). Here, we report measurements of hematological traits related to blood-O2 transport in populations of deer mice (Peromyscus maniculatus) that are native to high- and low-altitude environments. We conducted a common-garden breeding experiment to assess whether altitude-related physiological differences were attributable to developmental plasticity and/or physiological plasticity during adulthood. Under conditions prevailing in their native habitats, high-altitude deer mice from the Rocky Mountains exhibited a number of pronounced hematological differences relative to low-altitude conspecifics from the Great Plains: higher hemoglobin concentrations, higher hematocrits, higher erythrocytic concentrations of 2,3-diphosphoglycerate (an allosteric regulator of hemoglobin-oxygen affinity), lower mean corpuscular hemoglobin concentrations and smaller red blood cells. However, these differences disappeared after 6 weeks of acclimation to normoxia at low altitude. The measured traits were also indistinguishable between the F1 progeny of highland and lowland mice, indicating that there were no persistent differences in phenotype that could be attributed to developmental plasticity. These results indicate that the naturally occurring hematological differences between highland and lowland mice are environmentally induced and are largely attributable to physiological plasticity during adulthood.

Hematological indices in elite cyclists

BACKGROUND

Blood testing is a major concern in sports. Sporting federations have introduced cut-off values for hematological variables to limit blood manipulations. To date, no reference margins have been established to adjust single- or multivariable blood tests to the exercise adapted blood cell system of athletes. We studied hemoglobin (Hb), hematocrit (Hct), blood cell variables and changes in vascular volumes in male and female national team cyclists to evaluate the influence of exercise on these variables and the results of blood tests, and to estimate normal ranges in athletes for blood tests.

METHODS

1628 blood samples of 169 male and 55 female athletes were considered. Samples were analyzed automatically, blood cell indices and vascular volumes were calculated. Overall averages and seasonal differences were estimated.

RESULTS

Hb-average was: 15.4 +/- 0.8 g dL(-1) for male and 13.9 +/- 0.7 g dL(-1) for female cyclists, Hct: 45 +/- 2.9% and 40.7 +/- 2.7%. Blood variables and vascular volumes showed significant seasonal changes. 1-6% of all samples were found above the currently used limits for blood testing. This is in accordance with the data from the normal population. Nevertheless, EPO misuse or blood manipulations cannot totally be excluded.

CONCLUSION

Athletes display seasonal adaptations in their blood profile which should be considered in testing regulations. The presented data might be used as reference values for indirect single- and multivariable blood tests.

Increased brain capillaries in chronic hypoxia

The effect of chronic hypobaric hypoxia (28 days, 455 Torr) on the organization of brain vessels was studied in Balb/c mice. In comparison to age-matched controls kept at sea level, emulsion-perfused capillaries in hypoxic mice showed marked dilation in all brain areas studied. Capillary length per unit volume of tissue (Lv) was increased in the cerebellar granular layer, the caudate nucleus, the globus pallidus, the substantia nigra, the superior colliculus, and the dentate gyrus. There was a selective increase of Lv in the hippocampus (CA1 strata pyramidale and lacunosum and CA3 strata pyramidale and oriens) and in somatosensory cortex layers V and VI, motor cortex layers II, III, V, and VI, and auditory cortex layers II and III. An increase in capillary surface area per unit volume of tissue was also determined in several brain areas, including layer IV of somatosensory cortex, where Lv was not significantly increased. The O2 diffusion conductance and PO2 in the tissues were estimated with a mathematical model. The remodeling of capillary diameter and length during chronic hypoxia accounts for the significant increase of O2 conductance to neural tissues. Also the estimated tissue PO2 in chronic brain hypoxia is markedly increased in the caudate nucleus and the substantia nigra compared with acute hypoxia. These results suggest that formation of new capillaries is an important mechanism to restore the O2 deficit in chronic brain hypoxia and that local rates of energy utilization may influence angiogenesis in different areas of the brain.