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

Physiological parameters and training characteristics of endurance runners at Ethiopian Youth Sports Academy (2400 meters above sea level) and Guna Athletics Sport Club (3100 meters above sea level) training camps: a comparative cross-sectional study

BACKGROUND

Endurance performance is impacted by physiological, anthropometrical, diet, genetic, psychological, and training characteristics. Altitude can affect physiological parameters (like maximum oxygen utilization, arterial oxygen saturation (SaO2), heart rate, and blood pressure) and training characteristics (duration, frequency, and training load). Thus, this study compared physiological parameters and training characteristics between endurance runners at Ethiopian Youth Sports Academy (EYSA) and Guna Athletics Sport Club (GASC) located which are located at elevation of 2400 and 3100 meters, respectively.

METHODS

A comparative cross-sectional study design was used from September to November 2021. Data was obtained from a total of 120 eligible participants (30 runners and 30 controls at GASC, and 30 runners and 30 controls at EYSA). Sociodemographic and training characteristics were assessed using self-administered standardized questionnaires. SaO2 and heart rate were measured using finger pulse-oximetry (Nellcor, Oxim N-65; Covidien, Dublin, Ireland). Blood pressure was measured by Folee Digital Blood Pressure Monitor DX-B1 (Jiangsu Folee Medical Equipment Co., Ltd., Zhenjiang, China).

RESULTS

The runners of GASC had significantly lower resting SaO2, SaO2 immediately after maximal exertion, training (frequency and load) than runners of EYSA in both sexes. Runners of Guna Athletics Sport Club (RGASC) had significantly higher maximum oxygen utilization (VO2max) than Runners Ethiopian Youth Sports Academy (REYSA) in both sexes. Severe exercise-induced hypoxemia (EIAH) and moderate EIAH were developed by male runners of GASC and EYSA respectively. Besides, female runners GASC and EYSA developed moderate and mild EIAH, respectively.

CONCLUSIONS

Conclusively, there were significant differences in physiological parameters and training load between RGASC and REYSA. High altitude (3100 meters) may have a greater impact on the above variables than moderate hypoxia (2400 meters above sea level). Hence, endurance runner coaches should give emphasis to these variables.

Women at Altitude: Sex-Related Physiological Responses to Exercise in Hypoxia

Sex differences in physiological responses to various stressors, including exercise, have been well documented. However, the specific impact of these differences on exposure to hypoxia, both at rest and during exercise, has remained underexplored. Many studies on the physiological responses to hypoxia have either excluded women or included only a limited number without analyzing sex-related differences. To address this gap, this comprehensive review conducted an extensive literature search to examine changes in physiological functions related to oxygen transport and consumption in hypoxic conditions. The review encompasses various aspects, including ventilatory responses, cardiovascular adjustments, hematological alterations, muscle metabolism shifts, and autonomic function modifications. Furthermore, it delves into the influence of sex hormones, which evolve throughout life, encompassing considerations related to the menstrual cycle and menopause. Among these physiological functions, the ventilatory response to exercise emerges as one of the most sex-sensitive factors that may modify reactions to hypoxia. While no significant sex-based differences were observed in cardiac hemodynamic changes during hypoxia, there is evidence of greater vascular reactivity in women, particularly at rest or when combined with exercise. Consequently, a diffusive mechanism appears to be implicated in sex-related variations in responses to hypoxia. Despite well-established sex disparities in hematological parameters, both acute and chronic hematological responses to hypoxia do not seem to differ significantly between sexes. However, it is important to note that these responses are sensitive to fluctuations in sex hormones, and further investigation is needed to elucidate the impact of the menstrual cycle and menopause on physiological responses to hypoxia.

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.

Deep Genome Resequencing Reveals Artificial and Natural Selection for Visual Deterioration, Plateau Adaptability and High Prolificacy in Chinese Domestic Sheep

Sheep were one of the earliest domesticated animals. Both artificial and natural selection during domestication has resulted in remarkable changes in behavioral, physiological, and morphological phenotypes; however, the genetic mechanisms underpinning these changes remain unclear, particularly for indigenous Chinese sheep. In the present study, we performed pooled whole-genome resequencing of 338 sheep from five breeds representative of indigenous Chinese breeds and compared them to the wild ancestors of domestic sheep (Asian mouflon, Ovis orientalis) for detection of genome-wide selective sweeps. Comparative genomic analysis between domestic sheep and Asian mouflon showed that selected regions were enriched for genes involved in bone morphogenesis, growth regulation, and embryonic and neural development in domestic sheep. Moreover, we identified several vision-associated genes with funtional mutations, such as PDE6B (c.G2994C/p.A982P and c.C2284A/p.L762M mutations), PANK2, and FOXC1/GMSD in all five Chinese native breeds. Breed-specific selected regions were determined including genes such as CYP17 for hypoxia adaptability in Tibetan sheep and DNAJB5 for heat tolerance in Duolang sheep. Our findings provide insights into the genetic mechanisms underlying important phenotypic changes that have occurred during sheep domestication and subsequent selection.

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.

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.

The effects of classic altitude training on hemoglobin mass in swimmers

Aim of the study was to determine the influence of classic altitude training on hemoglobin mass (Hb-mass) in elite swimmers under the following aspects: (1) normal oscillation of Hb-mass at sea level; (2) time course of adaptation and de-adaptation; (3) sex influences; (4) influences of illness and injury; (5) interaction of Hb-mass and competition performance. Hb-mass of 45 top swimmers (male 24; female 21) was repeatedly measured (~6 times) over the course of 2 years using the optimized CO-rebreathing method. Twenty-five athletes trained between one and three times for 3-4 weeks at altitude training camps (ATCs) at 2,320 m (3 ATCs) and 1,360 m (1 ATC). Performance was determined by analyzing 726 competitions according to the German point system. The variation of Hb-mass without hypoxic influence was 3.0 % (m) and 2.7 % (f). At altitude, Hb-mass increased by 7.2 ± 3.3 % (p < 0.001; 2,320 m) and by 3.8 ± 3.4 % (p < 0.05; 1,360 m). The response at 2,320 m was not sex-related, and no increase was found in ill and injured athletes (n = 8). Hb-mass was found increased on day 13 and was still elevated 24 days after return (4.0 ± 2.7 %, p < 0.05). Hb-mass had only a small positive effect on swimming performance; an increase in performance was only observed 25-35 days after return from altitude. In conclusion, the altitude (2,320 m) effect on Hb-mass is still present 3 weeks after return, it decisively depends on the health status, but is not influenced by sex. In healthy subjects it exceeds by far the oscillation occurring at sea level. After return from altitude performance increases after a delay of 3 weeks.

High serum testosterone levels are associated with excessive erythrocytosis of chronic mountain sickness in men

Chronic mountain sickness (CMS) is characterized by excessive erythrocytosis (EE) secondary to hypoventilation. Erythropoietin (Epo) and testosterone regulate erythrocyte production. Low thyroid hormone levels are also associated to hypoventilation. Hence, these hormones can play a role in etiopathogeny of EE. The purpose of this study was to elucidate the effect of sexual and thyroid hormones and Epo in residents from Lima (150 m) and Cerro de Pasco (4,340 m), Peru, and the response to human chorionic gonadotrophin stimulation (hCG). Three groups, one at low altitude and two at high altitude [1 with hemoglobin values >16-21 g/dl and the second with Hb >or=21 g/dl (EE)], were studied. hCG was administered intramuscularly in a single dose (1,000 IU), and blood samples were obtained at 0, 6, 12, 24, 48, and 72 h after injection. High-altitude natives present similar levels of gonadotropins and thyroid hormones but lower dehydroepiandrosterone sulphate (DHEAS) levels (P < 0.01) and greater Epo (P < 0.01), 17alpha-hydroxyprogesterone (P < 0.01), and testosterone levels (P < 0.01) than those at 150 m. Serum testosterone levels (524.13 +/- 55.91 microg/dl vs. 328.14 +/- 53.23 ng/dl, means +/- SE; P < 0.05) and testosterone/DHEAS ratios are higher (7.98 +/- 1.1 vs. 3.65 +/- 1.1; P < 0.01) and DHEAS levels lower in the EE group (83.85 +/- 14.60 microg/dl vs. 148.95 +/- 19.11 ug/dl; P < 0.05), whereas Epo was not further affected. Testosterone levels were highest and DHEAS levels lowest in the EE group at all times after hCG stimulation. In conclusion, high androgen activity could be involved in the etiopathogeny of CMS. This evidence provides an opportunity to develop new therapeutic strategies.