Hemoglobin mass and peak oxygen uptake in untrained and trained residents of moderate altitude

Recommendations for Women in Mountain Sports and Hypoxia Training/Conditioning

The (patho-)physiological responses to hypoxia are highly heterogeneous between individuals. In this review, we focused on the roles of sex differences, which emerge as important factors in the regulation of the body's reaction to hypoxia. Several aspects should be considered for future research on hypoxia-related sex differences, particularly altitude training and clinical applications of hypoxia, as these will affect the selection of the optimal dose regarding safety and efficiency. There are several implications, but there are no practical recommendations if/how women should behave differently from men to optimise the benefits or minimise the risks of these hypoxia-related practices. Here, we evaluate the scarce scientific evidence of distinct (patho)physiological responses and adaptations to high altitude/hypoxia, biomechanical/anatomical differences in uphill/downhill locomotion, which is highly relevant for exercising in mountainous environments, and potentially differential effects of altitude training in women. Based on these factors, we derive sex-specific recommendations for mountain sports and intermittent hypoxia conditioning: (1) Although higher vulnerabilities of women to acute mountain sickness have not been unambiguously shown, sex-dependent physiological reactions to hypoxia may contribute to an increased acute mountain sickness vulnerability in some women. Adequate acclimatisation, slow ascent speed and/or preventive medication (e.g. acetazolamide) are solutions. (2) Targeted training of the respiratory musculature could be a valuable preparation for altitude training in women. (3) Sex hormones influence hypoxia responses and hormonal-cycle and/or menstrual-cycle phases therefore may be factors in acclimatisation to altitude and efficiency of altitude training. As many of the recommendations or observations of the present work remain partly speculative, we join previous calls for further quality research on female athletes in sports to be extended to the field of altitude and hypoxia.

Regulation of haemoglobin concentration at high altitude

Lowlanders sojourning for more than 1 day at high altitude (HA) experience a reduction in plasma volume (PV) that increases haemoglobin concentration and thus restores arterial oxygen content. If the sojourn extends over weeks, an expansion of total red cell volume (RCV) occurs and contributes to the haemoconcentration. While the reduction in PV was classically attributed to an increased diuretic fluid loss, recent studies support fluid redistribution, rather than loss, as the underlying mechanism. The fluid redistribution is presumably driven by a disappearance of proteins from the circulation and the resulting reduction in oncotic pressure exerted by the plasma, although the fate of the disappearing proteins remains unclear. The RCV expansion is the result of an accelerated erythropoietic activity secondary to enhanced renal erythropoietin release, but a contribution of other mechanisms cannot be excluded. After return from HA, intravascular volumes return to normal values and the normalisation of RCV might involve selective destruction of newly formed erythrocytes, although this explanation has been strongly challenged by recent studies. In contrast to acclimatised lowlanders, native highlanders originating from the Tibetan and the Ethiopian plateaus present with a normal or only mildly elevated haemoglobin concentration. Genetic adaptations blunting the erythropoietic response to HA exposure have been proposed as an explanation for the absence of more pronounced haemoconcentration in these populations, but new evidence also supports a contribution of a larger than expected PV. The functional significance of the relatively low haemoglobin concentration in Tibetan and Ethiopian highlanders is incompletely understood and warrants further investigation.

The relationship between hemoglobin and [Formula: see text]: A systematic review and meta-analysis

OBJECTIVE

There is widespread agreement about the key role of hemoglobin for oxygen transport. Both observational and interventional studies have examined the relationship between hemoglobin levels and maximal oxygen uptake ([Formula: see text]) in humans. However, there exists considerable variability in the scientific literature regarding the potential relationship between hemoglobin and [Formula: see text]. Thus, we aimed to provide a comprehensive analysis of the diverse literature and examine the relationship between hemoglobin levels (hemoglobin concentration and mass) and [Formula: see text] (absolute and relative [Formula: see text]) among both observational and interventional studies.

METHODS

A systematic search was performed on December 6th, 2021. The study procedures and reporting of findings followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Article selection and data abstraction were performed in duplicate by two independent reviewers. Primary outcomes were hemoglobin levels and [Formula: see text] values (absolute and relative). For observational studies, meta-regression models were performed to examine the relationship between hemoglobin levels and [Formula: see text] values. For interventional studies, meta-analysis models were performed to determine the change in [Formula: see text] values (standard paired difference) associated with interventions designed to modify hemoglobin levels or [Formula: see text]. Meta-regression models were then performed to determine the relationship between a change in hemoglobin levels and the change in [Formula: see text] values.

RESULTS

Data from 384 studies (226 observational studies and 158 interventional studies) were examined. For observational data, there was a positive association between absolute [Formula: see text] and hemoglobin levels (hemoglobin concentration, hemoglobin mass, and hematocrit (P<0.001 for all)). Prespecified subgroup analyses demonstrated no apparent sex-related differences among these relationships. For interventional data, there was a positive association between the change of absolute [Formula: see text] (standard paired difference) and the change in hemoglobin levels (hemoglobin concentration (P<0.0001) and hemoglobin mass (P = 0.006)).

CONCLUSION

These findings suggest that [Formula: see text] values are closely associated with hemoglobin levels among both observational and interventional studies. Although our findings suggest a lack of sex differences in these relationships, there were limited studies incorporating females or stratifying results by biological sex.

Effect of hypobaric hypoxia on hematological parameters related to oxygen transport, blood volume and oxygen consumption in adolescent endurance-training athletes

Objective

To analyze the effect of altitude on hematological and cardiorespiratory variables in adolescent athletes participating in aerobic disciplines.

Methods

21 females and 89 males participated in the study. All were adolescent elite athletes engaged in endurance sports (skating, running and cycling) belonging to two groups: permanent residents in either low altitude (LA, 966 m) or moderate altitude (MA, 2640 m). Hematocrit (Hct), hemoglobin concentration ([Hb]), total hemoglobin mass (Hbt), blood, plasma and erythrocyte volumes (BV, PV and EV), VO₂peak and other cardiorespiratory parameters were evaluated.

Results

Sex differences were evident both in LA and HA skating practitioners, the males having higher significant values than the females in oxygen transport-related hematological parameters and VO₂peak. The effect of altitude residence was also observed in Hct, [Hb], Hbt and EV with increased (14%–18%) values in the hematological parameters and higher EV (5%–24%). These results matched the significantly higher values of VO₂peak measured in MA residents. However, BV and PV did not show differences between LA and MA residents in any case. Sports discipline influenced neither the hematological variables nor most of the cardiorespiratory parameters.

Conclusions

LA and MA adolescent skaters showed sex differences in hematological variables. Endurance-trained male adolescent residents at MA had an increased erythropoietic response and a higher VO₂peak compared to their counterparts residing and training at LA. These responses are similar in the three aerobic sports studied, indicating that the variables described are highly sensitive to hypoxia irrespective of the sports discipline.

Validation of Maximal, Submaximal, and Nonexercise Indirect [Formula: see text]O2max Estimations at 2600 m Altitude

Aim: To study the criterion validity of three indirect maximal oxygen uptake ([Formula: see text]O₂max) assessment equations at altitude. Methods: We studied 64 young adults (53% men) at Bogota, Colombia (2600 m altitude). Direct [Formula: see text]O₂max was measured by indirect calorimetry using a maximal incremental treadmill protocol. Indirect [Formula: see text]O₂max was estimated by two exercise field tests (the 20-m shuttle-run test [20-MST] and the 2-km walking test (UKK)) and one nonexercise method (the perceived functional ability-physical activity rating questionnaire [PFA-PAR]). Altitude-adjusted PFA-PAR was estimated as a 13% linear reduction in PFA-PAR. We calculated Lin concordance coefficients (LCC) and standard error of the estimates (SEEs), and we performed Bland-Altman analyses for each indirect method. Results: Mean [Formula: see text]O₂max was 41.2 ± 5.8 mL/kg/min in men and 32.2 ± 3.6 mL/kg/min in women. We found the highest agreement with direct [Formula: see text]O₂max for the 20-MST (LCC = 0.79, SEE = 3.91 mL/kg/min), followed in order by the altitude-adjusted PFA-PAR (LCC = 0.71, SEE = 4.12 mL/kg/min), the UKK (LCC = 0.67, SEE = 5.48 mL/kg/min), and the unadjusted PFA-PAR (LCC = 0.57, SEE = 4.75 mL/kg/min). The unadjusted PFA-PAR tended to overestimate [Formula: see text]O₂max, but Bland-Altman analysis showed that this bias disappeared after altitude adjustment. Conclusion: Several maximal, submaximal, and nonexercise methods provide estimates of [Formula: see text]O₂max with acceptable validity for use in epidemiological studies of populations living at moderate altitude.

The increase in hemoglobin concentration with altitude varies among human populations

Decreased oxygen availability at high altitude requires physiological adjustments allowing for adequate tissue oxygenation. One such mechanism is a slow increase in the hemoglobin concentration ([Hb]) resulting in elevated [Hb] in high-altitude residents. Diagnosis of anemia at different altitudes requires reference values for [Hb]. Our aim was to establish such values based on published data of residents living at different altitudes by applying meta-analysis and multiple regressions. Results show that [Hb] is increased in all high-altitude residents. However, the magnitude of increase varies among the regions analyzed and among ethnic groups within a region. The highest increase was found in residents of the Andes (1 g/dL/1000 m), but this increment was smaller in all other regions of the world (0.6 g/dL/1000 m). While sufficient data exist for adult males and females showing that sex differences in [Hb] persist with altitude, data for infants, children, and pregnant women are incomplete preventing such analyses. Because WHO reference values were originally based on [Hb] of South American people, we conclude that individual reference values have to be defined for ethnic groups to reliably diagnose anemia and erythrocytosis in high-altitude residents. Future studies need to test their applicability for children of different ages and pregnant women.

Diurnal changes of arterial oxygen saturation and erythropoietin concentration in male and female highlanders

In Caucasians and Native Americans living at altitude, hemoglobin mass is increased in spite of erythropoietin concentrations ([Epo]) not markedly differing from sea level values. We hypothesized that a nocturnal decrease of arterial oxygen saturation (SaO₂) causes a temporary rise of [Epo] not detected by morning measurements. SaO₂ (continuous, finger oximeter) and [Epo] (ELISA, every 4 h) were determined in young highlanders (altitude 2600 m) during 24 h of usual daily activity. In Series I (six male, nine female students), SaO₂ fell during the night with the nadir occurring between 01:00 and 03:00; daily means (range 92.4–95.2%) were higher in females (+1.7%, P < 0.01). [Epo] showed opposite changes with zenith occurring at 04:00 without a sex difference. Mean daily values (22.9 ± 10.7SD U/L) were higher than values obtained at 08:00 (17.2 ± 9.5 U/L, P < 0.05). In Series II (seven females), only SaO₂ was measured. During follicular and luteal phases, SaO₂ variation was similar to Series I, but the rhythm was disturbed during menstruation. While daily [Epo] variations at sea level are not homogeneous, there is a diurnal variation at altitude following changes in SaO₂. Larger hypoventilation‐dependent decreases of alveolar PO₂ decreases during the night probably cause a stronger reduction of SaO₂ in highlanders compared to lowlanders. This variation might be enlarged by a diurnal fluctuation of Hb concentration. In spite of a lower [Hb], the higher SaO₂ in women compared to men led to a similar arterial oxygen content, likely explaining the absence of differences in [Epo] between sexes.

Hematocrit and Hemoglobin Levels of Nonhuman Apes at Moderate Altitudes: A Comparison with Humans

Mortola, Jacopo P. and DeeAnn Wilfong. Hematocrit and hemoglobin levels of nonhuman apes at moderate altitudes: a comparison with humans. High Alt Med Biol. 17:323-335, 2016.-We asked to what extent the hematologic response (increase in hematocrit [Hct] and in blood hemoglobin concentration [Hb]) of humans to altitude hypoxia was shared by our closest relatives, the nonhuman apes. Data were collected from 29 specimens of 7 species of apes at 2073 m altitude (barometric pressure Pb = 598 mm Hg); additional data originated from apes located at a lower altitude (1493 m, Pb = 639 mm Hg). The human altitude profiles of Hct and Hb between sea level and 3000 m were constructed from a compilation of literature sources that (all combined) comprised data sets of 10,000-12,000 subjects for each gender. These human data were binned for 0-250 m altitude (sea level) and for each 500 m of progressively higher altitudes. Values of Hb and Hct of both men and women were significantly higher than at sea level at the 1500 bin (1250-1750 m); hence, the altitude threshold for the human hematological responses must be between 1000 and 1500 m. In the nonhuman apes, no increase in Hct or Hb was apparent at 1500 m; at 2000 m, the increase was significant only for the Hb of females. At either altitude in the group of nonhuman apes, the increase in Hct was much less than in humans, and that of Hb was significantly less at 1500 m. We conclude that lack of, or minimal, hematopoietic response to moderate altitude can occur in mammalian species that are not genetically adapted to high altitudes. Polycythemia is not a common response to altitude hypoxia and, at least at moderate altitudes, the degree of the human response may represent the exception among apes rather than the rule.

Hemoglobin Mass and Aerobic Performance at Moderate Altitude in Elite Athletes

Fore more than a decade, the live high-train low (LHTL) approach, developed by Levine and Stray-Gundersen, has been widely used by elite endurance athletes. Originally, it was pointed out, that by living at moderate altitude, athletes should benefit from an increased red cell volume (RCV) and hemoglobin mass (Hbmass), while the training at low altitudes should prevent the disadvantage of reduced training intensity at moderate altitude. VO2max is reduced linearly by about 6-8 % per 1000 m increasing altitude in elite athletes from sea level to 3000 m, with corresponding higher relative training intensities for the same absolute work load. With 2 weeks of acclimatization, this initial deficit can be reduced by about one half. It has been debated during the last years whether sea-level training or exposure to moderate altitude increases RCV and Hbmass in elite endurance athletes. Studies which directly measured Hbmass with the optimized CO-rebreathing technique demonstrated that Hbmass in endurance athletes is not influenced by sea-level training. We documented that Hbmass is not increased after 3 years of training in national team cross-country skiers. When athletes are exposed to moderate altitude, new studies support the argument that it is possible to increase Hbmass temporarily by 5-6 %, provided that athletes spend >400 h at altitudes above 2300-2500 m. However, this effect size is smaller than the reported 10-14 % higher Hbmass values of endurance athletes living permanently at 2600 m. It remains to be investigated whether endurance athletes reach these values with a series of LHTL camps.

AltitudeOmics: rapid hemoglobin mass alterations with early acclimatization to and de-acclimatization from 5260 m in healthy humans

It is classically thought that increases in hemoglobin mass (Hbmass) take several weeks to develop upon ascent to high altitude and are lost gradually following descent. However, the early time course of these erythropoietic adaptations has not been thoroughly investigated and data are lacking at elevations greater than 5000 m, where the hypoxic stimulus is dramatically increased. As part of the AltitudeOmics project, we examined Hbmass in healthy men and women at sea level (SL) and 5260 m following 1, 7, and 16 days of high altitude exposure (ALT1/ALT7/ALT16). Subjects were also studied upon return to 5260 m following descent to 1525 m for either 7 or 21 days. Compared to SL, absolute Hbmass was not different at ALT1 but increased by 3.7±5.8% (mean ± SD; n = 20; p<0.01) at ALT7 and 7.6±6.6% (n = 21; p<0.001) at ALT16. Following descent to 1525 m, Hbmass was reduced compared to ALT16 (−6.0±3.7%; n = 20; p = 0.001) and not different compared to SL, with no difference in the loss in Hbmass between groups that descended for 7 (−6.3±3.0%; n = 13) versus 21 days (−5.7±5.0; n = 7). The loss in Hbmass following 7 days at 1525 m was correlated with an increase in serum ferritin (r = −0.64; n = 13; p<0.05), suggesting increased red blood cell destruction. Our novel findings demonstrate that Hbmass increases within 7 days of ascent to 5260 m but that the altitude-induced Hbmass adaptation is lost within 7 days of descent to 1525 m. The rapid time course of these adaptations contrasts with the classical dogma, suggesting the need to further examine mechanisms responsible for Hbmass adaptations in response to severe hypoxia.

Hemoglobin oxygen affinity in patients with cystic fibrosis

In patients with cystic fibrosis lung damages cause arterial hypoxia. As a typical compensatory reaction one might expect changes in oxygen affinity of hemoglobin. Therefore position (standard half saturation pressure P₅₀st) and slope (Hill’s n) of the O₂ dissociation curve as well as the Bohr coefficients (BC) for CO₂ and lactic acid were determined in blood of 14 adult patients (8 males, 6 females) and 14 healthy controls (6 males, 8 females). While Hill’s n amounted to approximately 2.6 in all subjects, P₅₀st was slightly increased by 1mmHg in both patient groups (controls male 26.7±0.2, controls female 27.0±0.1, patients male 27.7±0.5, patients female 28.0±0.3 mmHg; mean and standard error, overall p<0.01). Main cause was a rise of 1–2 µmol/g hemoglobin in erythrocytic 2,3-biphosphoglycerate concentration. One patient only, clearly identified as an outlier and with the mutation G551D, showed a reduction of both P₅₀st (24.5 mmHg) and [2,3-biphosphoglycerate] (9.8 µmol/g hemoglobin). There were no differences in BCCO₂, but small sex differences in the BC for lactic acid in the controls which were not detectable in the patients. Causes for the right shift of the O₂ dissociation curve might be hypoxic stimulation of erythrocytic glycolysis and an increased red cell turnover both causing increased [2,3-biphosphoglycerate]. However, for situations with additional hypercapnia as observed in exercising patients a left shift seems to be a more favourable adaptation in cystic fibrosis. Additionally when in vivo PO₂ values were corrected to the standard conditions they mostly lay left of the in vitro O₂ dissociation curve in both patients and controls. This hints to unknown fugitive factors influencing oxygen affinity.

Efficacy of residence at moderate versus low altitude on reducing acute mountain sickness in men following rapid ascent to 4300 m

To determine if residence at moderate (~2000 m) compared to low (<50 m) altitude reduces acute mountain sickness (AMS) in men during subsequent rapid ascent to a higher altitude. Nine moderate-altitude residents (MAR) and 18 sea-level residents (SLR) completed the Environmental Symptoms Questionnaire (ESQ) at their respective baseline residence and again at 12, 24, 48, and 72 h at 4300 m to assess the severity and prevalence of AMS. AMS cerebral factor score (AMS-C) was calculated from the ESQ at each time point. AMS was judged to be present if AMS-C was ≥0.7. Resting end-tidal CO2 (PETco2) and arterial oxygen saturation (Sao2) were assessed prior to and at 24, 48, and 72 h at 4300 m. Resting venous blood samples were collected prior to and at 72 h at 4300 m to estimate plasma volume (PV) changes. MAR compared to SLR: 1) AMS severity at 4300 was lower (p<0.05) at 12 h (0.50±0.69 vs. 1.48±1.28), 24 h (0.15±0.19 vs. 1.39±1.19), 48 h (0.10±0.18 vs. 1.37±1.49) and 72 h (0.08±0.12 vs. 0.69±0.70); 2) AMS prevalence at 4300 was lower (p<0.05) at 12 h (22% vs. 72%), 24 h (0% vs. 56%), 48 h (0% vs. 56%), and 72 h (0% vs. 45%); 3) resting Sao2 (%) was lower (p<0.05) at baseline (95±1 vs. 99±1) but higher (p<0.05) at 4300 at 24 h (86±2 vs. 81±5), 48 h (88±3 vs. 83±6), and 72 h (88±2 vs. 83±5); and 4) PV (%) did not differ at 72 h at 4300 m in the MAR (4.5±6.7) but was reduced for the SLR (-8.1±10.4). These results suggest that ventilatory and hematological acclimatization acquired while living at moderate altitude, as indicated by a higher resting Sao2 and no reduction in PV during exposure to a higher altitude, is associated with greatly reduced AMS after rapid ascent to high altitude.

Effect of six days of staging on physiologic adjustments and acute mountain sickness during ascent to 4300 meters

This study determined the effectiveness of 6 days (d) of staging at 2200 m on physiologic adjustments and acute mountain sickness (AMS) during rapid, high-risk ascent to 4300 m. Eleven sea-level (SL) resident men (means +/- SD; 21 +/- 3 yr; 78 +/- 13 kg) completed resting measures of end-tidal CO(2) (Petco(2)), arterial oxygen saturation (Sao(2)), heart rate (HR), and mean arterial pressure (MAP) at SL and within 1 h of exposure to 4300 m in a hypobaric chamber prior to 6 d of staging at 2200 m (preSTG) and on the summit of Pikes Peak following 6 d of staging at 2200 m (postSTG). Immediately following resting ventilation measures, all performed submaximal exercise ( approximately 55% of altitude-specific maximal oxygen uptake) for approximately 2 h on a bicycle ergometer to induce higher levels of AMS. AMS-C, calculated from the Environmental Symptoms Questionnaire, was measured following 4 h and 8 h of exposure at preSTG and postSTG, and the mean was calculated. Resting Petco(2) (mmHg) was unchanged from SL (39.8 +/- 2.6) to preSTG (39.3 +/- 3.0), but decreased (p < 0.05) from preSTG to postSTG (32.8 +/- 2.6). Resting Sao(2) (%) decreased (p < 0.05) from SL (97 +/- 2) to preSTG (80 +/- 4) and increased (p < 0.05) from preSTG to postSTG (83 +/- 3). Resting HR (bpm) and MAP (mmHg) did not change in any of the test conditions. The incidence and severity of AMS-C decreased (p < 0.05) from preSTG (91 +/- 30%; 1.05 +/- 0.56) to postSTG (45 +/- 53%; 0.59 +/- 0.43), respectively. These results suggest that modest physiologic adjustments induced by staging for 6 d at 2200 m reduced the incidence and severity of AMS during rapid, high-risk ascent to 4300 m.

Effects of various training modalities on blood volume

It is controversially discussed whether soccer games should be played at moderate (2001-3000 m) and high altitudes (3001-5500 m) or should be restricted to near sea level and low altitude (501-2000 m) conditions. Athletes living at altitude are assumed to have a performance advantage compared with lowlanders. One advantage of altitude adaptation concerns the expansion of total hemoglobin mass (tHb-mass), which is strongly related to endurance performance at sea level. Cross-sectional studies show that elite athletes posses approximately 35% higher tHb-mass than the normal population, which is further elevated by 14% in athletes native to altitude of 2600 m. Although the impact of this huge tHb-mass expansion on performance is not yet investigated for altitude conditions, lowland athletes seek for possibilities to increase tHb-mass to similar levels. At sea level tHb-mass is only moderately influenced by training and depends more on genetic predisposition. Altitude training in contrast, using either the conventional altitude training or the live high-train low (>14 h/day in hypoxia) protocol for 3-4 weeks above 2500 m leads to mean increases in tHb-mass of 6.5%. This increase is, however, not sufficient to close the gap in tHb-mass to elite athletes native to altitude, which may be in advantage when tHb-mass has the same strong influence on aerobic performance at altitude as it has on sea level.

Arterial oxygen saturation and hemoglobin mass in postmenopausal untrained and trained altitude residents

Because of lacking ventilatory stimulation by sex hormones in postmenopausal women (PW), one might expect a lowered arterial oxygen saturation (S(O(2))) in hypoxia and therefore a stronger erythropoietic reaction than in young women (YW). Nine untrained (UTRPW) and 11 trained (TRPW) postmenopausal altitude residents (2600 m) were compared to 16 untrained (UTRYW) and 16 trained young women (TRYW) to check this hypothesis and to study the combined response to hypoxia and training. S(O(2)) was decreased in PW (89.2% +/- 2.2 vs. 93.6 +/- 0.7% in YW, p < 0.01). Hb mass, however, was similar in UT (UTRYW: 9.2 +/- 0.9 g/kg(1), UTRPW: 8.7 +/- 1.0 g/kg). But if body fat rise with age was excluded by relation to fat-free mass, Hb mass was increased in UTRPW (+1.2 g/kg, p < 0.05) compared to UTRYW. Training caused a similar rise of Hb mass in PW and YW (0.3 g/kg per mL/kg x min(1) rise in V(O(2peak))). There was no difference in erythropoietin among the groups. Ferritin was higher in PW than YW. The results show that female hormones and fitness level have to be considered in studies on erythropoiesis at altitude. The role of erythropoietin during chronic hypoxia still has to be clarified.

Physical fitness and hematological changes during acclimatization to moderate altitude: a retrospective study

While high altitude adaptations have been studied extensively, limited research has examined moderate altitude (MA: 1500 to 3000 m) adaptations and their time course, despite the fact that millions of people sojourn to or reside at MA. We retrospectively examined long-term MA acclimatization by analyzing recurring physical fitness test results and hematological data among 2147 college-age male cadets previously residing at either sea level (SL) or MA and currently attending the U.S. Air Force Academy (USAFA), a unique, regimented, and well-controlled military university located at 2210 m. Significant (p < 0.01) differences were found in aerobic and anaerobic fitness test scores between former SL and MA subjects, with MA subjects scoring 27 points (8%) higher during a 1.5-mile aerobic fitness run and 18 points (6%) higher than SL subjects in the anaerobic fitness test for 2 yr. These differences may be partly explained by the hematological differences observed. Hemoglobin concentration ([Hb]) was significantly (p < 0.001) higher (6.3%; approximately 1 g/dL) in MA subjects prior to arrival at USAFA and acutely, but the difference between altitude conditions was gone at the next retrospective blood draw (+17 months). After 2.5 yr at USAFA, former SL residents had significantly (p < 0.001) higher [Hb] by +10%, or 1.5 g/dL versus prearrival values. This study suggests that significant hematological acclimatization occurs with MA exposure and requires greater than 7 months to reach stability. The altitude-induced erythropoiesis may explain in part the improvements in aerobic performance, but altitude-related anaerobic differences still remain after hematological acclimatization.

Extracellular pH defense against lactic acid in untrained and trained altitude residents

The assumption that buffering at altitude is deteriorated by bicarbonate (bi) reduction was investigated. Extracellular pH defense against lactic acidosis was estimated from changes (Delta) in lactic acid ([La]), [HCO3-], pH and PCO2 in plasma, which equilibrates with interstitial fluid. These quantities were measured in earlobe blood during and after incremental bicycle exercise in 10 untrained (UT) and 11 endurance-trained (TR) highlanders (2,600 m). During exercise the capacity of non-bicarbonate buffers (betanbi=-Delta[La]. DeltapH(-1)-Delta[HCO3-]. DeltapH(-1)) amounted to 40+/-2 (SEM) and 28+/-2 mmol l(-1) in UT and TR, respectively (P<0.01). During recovery beta (nbi) decreased to 20 (UT) and 16 (TR) mmol l(-1) (P<0.001) corresponding to values expected from hemoglobin, dissolved protein and phosphate concentrations related to extracellular fluid (ecf). This was accompanied by a larger decrease of base excess after than during exercise for a given Delta[La]. betabi amounted to 37-41 mmol l(-1) being lower than at sea level. The large exercise betanbi was mainly caused by increasing concentrations of buffers due to temporary shrinking of ecf. Tr has lower betanbi in spite of an increased Hb mass mainly because of an expanded ecf compared to UT. In highlanders betanbi is higher than in lowlanders because of larger Hb mass and reduced ecf and counteracts the decrease in [HCO3-]. The amount of bicarbonate is probably reduced by reduction of the ecf at altitude but this is compensated by lower maximal [La] and more effective hyperventilation resulting in attenuated exercise acidosis at exhaustion.

Erythropoietin regulations in humans under different environmental and experimental conditions

In the adult human, the kidney is the main organ for the production and release of erythropoietin (EPO). EPO is stimulating erythropoiesis by increasing the proliferation, differentiation and maturation of the erythroid precursors. In the last decades, enormous efforts were made in the purification, molecular encoding and description of the EPO gene. This led to an incredible increase in the understanding of the EPO-feedback-regulation loop at a molecular level, especially the oxygen-dependent EPO gene expression, a key function in the regulation loop. However, studies in humans at a systemic level are still very scanty. Therefore, it is the purpose of the present review to report on the main recent investigations on EPO production and release in humans under different environmental and experimental conditions, including: (i) studies on EPO circadian, monthly and even annual variations, (ii) studies in connection with short-, medium- and long-term exercise at sea-level which will be followed (iii) by studies performed at moderate and high altitude.

The optimised CO-rebreathing method: a new tool to determine total haemoglobin mass routinely

A routine method to determine total haemoglobin mass (tHb) in clinical practice and sports medicine is non-existent. Radioactive tracers or other dilution procedures like the common CO-rebreathing method (Proc(com)) are impractical, the latter in particular because of the relatively long time of respiration. According to the multicompartment model of Bruce and Bruce (J Appl Physiol 95:1235-1247, 2003) the respiration time can be considerably reduced by inhaling a CO-bolus instead of the commonly used gas mixture. The aim of this study was to evaluate this theoretical concept in practice. The kinetics of the HbCO formation were compared in arterialised blood sampled from an hyperaemic earlobe after inhaling a CO-bolus (Proc(new)) for 2 min and a CO-O(2) mixture (Proc(com)) for approximately 10 min. The reliability of Proc(new) was checked in three consecutive tests, and phlebotomy was used to determine the validity. VO(2max) was determined with and without previous application of Proc(new) and the half-time of HbCO was registered also in arterialised blood after resting quietly and after the VO(2max) test. Proc(new) yielded virtual identical tHb values compared to Proc(com) when HbCO determined 5 min after starting CO-rebreathing was used for calculation. The typical error of Proc(new) was 1.7%, corresponding to a limit of agreement (95%) of 3.3%. The loss of 95 g (19) haemoglobin was detected with an accuracy of 9 g (12). After application of Proc(new) VO(2max) was reduced by 3.0% (3.7) (P=0.022) and half-time was lowered from 132 min (77) to 89 min (23) after the VO(2max) test. Inhaling a CO-bolus markedly simplifies the CO-rebreathing method without reducing validity and reliability and can be used for routine determination of tHb for various indications.

Drugs for increasing oxygen and their potential use in doping: a review

Blood oxygenation is a fundamental factor in optimising muscular activity. Enhancement of oxygen delivery to tissues is associated with a substantial improvement in athletic performance, particularly in endurance sports. Progress in medical research has led to the identification of new chemicals for the treatment of severe anaemia. Effective and promising molecules have been created and sometimes used for doping purposes. The aim of this review is to present methods, and drugs, known to be (or that might be) used by athletes to increase oxygen transport in an attempt to improve endurance capacity. These methods and drugs include: (i) blood transfusion; (ii) endogenous stimulation of red blood cell production at altitude, or using hypoxic rooms, erythropoietins (EPOs), EPO gene therapy or EPO mimetics; (iii) allosteric effectors of haemoglobin; and (iv) blood substitutes such as modified haemoglobin solutions and perfluorochemicals. Often, new chemicals are used before safety tests have been completed and athletes are taking great health risks. Such new chemicals have also created the need for new instrumental strategies in doping control laboratories, but not all of these chemicals are detectable. Further progress in analytical research is necessary.

Blood volume and hemoglobin mass in endurance athletes from moderate altitude

PURPOSE

To determine whether total hemoglobin (tHb) mass and total blood volume (BV) are influenced by training, by chronic altitude exposure, and possibly by the combination of both conditions.

METHODS

Four groups (N = 12, each) either from locations at sea level or at moderate altitude (2600 m) were investigated: 1) sea-level control group (UT-0 m), 2) altitude control group (UT-2600 m), 3) professional cyclists from sea level (C-0 m), and 4) professional cyclists from altitude (C-2600 m). All subjects from altitude were born at about 2600 m and lived all their lives (except during competitions at lower levels) at this altitude. tHb and BV were determined by the CO-rebreathing method.

RESULTS

VO2max (mL x kg(-1) x min(-1)) was significantly higher in UT-0 m (45.3 +/- 3.2) than in UT-2600 m (39.6 +/- 4.0) but did not differ between C-0 m (68.2 +/- 2.7) and C-2600 m (69.9 +/- 4.4). tHb (g x kg(-1)) was affected by training (UT-0 m: 11.0 +/- 1.1, C-0 m: 15.4 +/- 1.3) and by altitude (UT-2600 m: 13.4 +/- 0.9) and showed both effects in C-2600 m (17.1 +/- 1.4). Because red cell volume showed a behavior similar to tHb and because plasma volume was not affected by altitude but by training, BV (mL x kg(-1)) was increased in C-0 m (UT-0 m: 78.3 +/- 7.9; C-0 m: 107.0 +/- 6.2) and in UT-2600 m (88.2 +/- 4.8), showing highest values in the C-2600 m group (116.5 +/- 11.4).

CONCLUSION

In endurance athletes who are native to moderate altitude, tHb and BV were synergistically influenced by training and by altitude exposure, which is probably one important reason for their high performance.

Effects of intermittent exposure to high altitude on blood volume and erythropoietic activity

The purpose of this review is to describe changes in blood volume and erythropoietic activity occurring under different types of intermittent exposure to hypoxia. These hypoxic episodes can vary from a few seconds or minutes to hours, days, or even weeks. Short hypoxic episodes like sleep apnea only lead to a small increase in hemoglobin concentration, which is mainly due to a hormonal-mediated decrease in plasma volume. In most of these cases the cumulative time spent under hypoxia does not exceed the critical threshold of about 90 min. Endurance athletes and mountaineers who voluntarily expose themselves to hypoxia for some hours or during the night while spending the day at normoxia ("sleep high-train low" concept) do improve their physical performance. Despite raising erythropoietic activity, indicated by elevated plasma concentrations of EPO and the transferrin receptor, the postulated increase in red cell volume has not satisfactorily been proved. Frequent changes between low and high altitudes, which are usual in some South American and Asian countries, provoke similar adaptations in red cell mass as occur in high altitude residents. However, the plasma volume decreases at altitude and increases again when staying at sea level. Even after more than 20 yr of regular moving between low and high altitude, the total blood volume, hemoglobin concentration and hematocrit, as well as the plasma EPO concentration, noticeably oscillate during every hypoxic-normoxic cycle. We assume these changes to be an optimal rapid adaptation of the oxygen transport system to the prevailing hypoxic or normoxic environment. However, possible risks for the organism cannot be excluded.