Microcirculatory and Rheological Adaptive Mechanisms at High Altitude in European Lowlander Hikers and Nepalese Highlanders

Abstract

Background: Physical activity at high-altitudes is increasingly widespread, both for tourist trekking and for the growing tendency to carry out sports and training activities at high-altitudes. Acute exposure to this hypobaric–hypoxic condition induces several complex adaptive mechanisms involving the cardiovascular, respiratory and endocrine systems. A lack of these adaptive mechanisms in microcirculation may cause the onset of symptoms of acute mountain sickness, a frequent disturbance after acute exposure at high altitudes. The aim of our study was to evaluate the microcirculatory adaptive mechanisms at different altitudes, from 1350 to 5050 m a.s.l., during a scientific expedition in the Himalayas. Methods: The main haematological parameters, blood viscosity and erythrocyte deformability were assessed at different altitudes on eight European lowlanders and on a group of eleven Nepalese highlanders. The microcirculation network was evaluated in vivo by conjunctival and periungual biomicroscopy. Results: Europeans showed a progressive and significant reduction of blood filterability and an increase of whole blood viscosity which correlate with the increase of altitude (p < 0.02). In the Nepalese highlanders, haemorheological changes were already present at their residence altitude, 3400 m a.s.l. (p < 0.001 vs. Europeans). With the increase in altitude, a massive interstitial oedema appeared in all participants, associated with erythrocyte aggregation phenomena and slowing of the flow rate in the microcirculation. Conclusions: High altitude causes important and significant microcirculatory adaptations. These changes in microcirculation induced by hypobaric–hypoxic conditions should be considered when planning training and physical activity at altitude.

Hemorheological, cardiorespiratory, and cerebrovascular effects of pentoxifylline following acclimatization to 3,800 m

“…Like previous findings ( 13 ), high altitude caused a significant decrease in red blood cell deformability; however, pentoxifylline failed to rectify this decline. Pentoxifylline had no effect on whole blood and plasma viscosity, red blood cell deformability, or red blood cell aggregation.…”

“…It is therefore plausible that pentoxifylline at high altitude does not increase red blood cell deformability per se, but negates the decline in red blood cell deformability. Red blood cell deformability declines with greater altitude ( 13 ) and hypoxia ( 14 ).…”

“…Hypobaric hypoxia stimulates plasma volume decreases and erythropoiesis, leading to a rapid and sustained increase in whole blood viscosity ( 10 ), which can impede microvascular flow ( 11 , 12 ). Impaired red blood cell deformability independent of hemoconcentration may also contribute to this detriment in microcirculation flow ( 13 ). Acute hypoxia causes a decrease in red blood cell deformability in a dose-dependent manner ( 14 ), occurring with greater red blood cell oxidative stress ( 15 ).…”

“…Acute hypoxia causes a decrease in red blood cell deformability in a dose-dependent manner ( 14 ), occurring with greater red blood cell oxidative stress ( 15 ). Furthermore, lowlanders during ascent to high altitude (1,350 to 5,050 m) had a significant and progressive reduction in red blood cell deformability, which correlated with an increase in altitude ( 13 ). We therefore reasoned that hypoxic exposure would decrease red blood cell deformability.…”