Excessive Erythrocytosis Is Not Associated With Altered Iron Homeostasis in Men From the World's Highest City

Expedition 5300: limits of human adaptations in the highest city in the world

Exposure to chronic hypobaric hypoxia imposes a significant physiological burden to more than 80 million humans living above 2500 m throughout the world. Among them, 50 000 live in the world's highest city, La Rinconada, located at 5000-5300 m in southern Peru. Expedition 5300 is the first scientific and medical programme led in La Rinconada to investigate the physiological adaptations and altitude-related health issues in this unique population. Dwellers from La Rinconada have very high haemoglobin concentration (20.3 ± 2.4 g/dL; n = 57) and those with chronic mountain sickness (CMS) exhibit even higher concentrations (23.1 ± 1.7 g/dL; n = 150). These values are associated with large total haemoglobin mass and blood volume, without an associated iron deficit. These changes in intravascular volumes lead to a substantial increase in blood viscosity, which is even larger in CMS patients. Despite these large haematological changes, 24 h blood pressure monitoring is essentially normal in La Rinconada, but some results suggest impaired vascular reactivity. Echocardiography revealed large right heart dilatation and high pulmonary arterial pressure as well as left ventricle concentric remodelling and grade I diastolic dysfunction. These changes in heart dimension and function tend to be more severe in highlanders with CMS. Polygraphy evaluations revealed a large reduction in nocturnal pulse oxygen saturation (median SpO2 = 79%), which is even more severe in CMS patients who also tended to show a higher oxygen desaturation index. The population of La Rinconada offers a unique opportunity to investigate the human responses to chronic severe hypoxia, at an altitude that is probably close to the maximum altitude human beings can permanently tolerate without presenting major health issues.

High altitude polycythemia and its maladaptive mechanisms: an updated review

High altitude polycythemia is a maladaptation of highlanders exposed to hypoxic environment, leading to high blood viscosity and severe cardiorespiratory dysfunction. Prolonged hypoxia causes respiratory depression and severe hypoxemia, and further mediates changes in genetic and molecular mechanisms that regulate erythropoiesis and apoptosis, ultimately resulting in excessive erythrocytosis (EE). This updated review investigated the maladaptive mechanisms of EE, including respiratory chemoreceptor passivation, sleep-related breathing disorders, sex hormones, iron metabolism, and hypoxia-related factors and pathways.