Cardiorespiratory Coordination in Hypercapnic Test Before and After High-Altitude Expedition.

Valentina V Gultyaeva,Vladimir N Melnikov,Margarita I Zinchenko,Dmitriy Y Uryumtsev,Natalia V Balioz,Sergey G Krivoschekov

doi:10.3389/fphys.2021.673570

Abstract

Coordination of cardiovascular and respiratory systems enables a wide range of human adaptation and depends upon the functional state of an individual organism. Hypoxia is known to elicit changes in oxygen and carbon dioxide sensitivity, while training alters cardiorespiratory coordination (CRC). The delayed effect of high altitude (HA) acclimatization on CRC in mountaineers remains unknown. The objective of this study was to compare CRC in acute hypercapnia in mountaineers before and after a HA expedition. Nine trained male mountaineers were investigated at sea level before (Pre-HA) and after a 20-day sojourn at altitudes of 4,000–7,000 m (Post-HA) in three states (Baseline, Hypercapnic Rebreathing, and Recovery). A principal component (PC) analysis was performed to evaluate the CRC. The number of mountaineers with one PC increased Post-HA (nine out of nine), compared to Pre-HA (five out of nine) [Chi-square (df = 1) = 5.14, P = 0.023]; the percentage of total variance explained by PC1 increased [Pre-HA median 65.6 (Q1 64.9/Q3 74.9), Post-HA 75.6 (73.3/77.9), P = 0.028]. Post-HA, the loadings of the expired fraction of O2, CO2, and ventilation onto PC1 did not change, and the loading of heart rate increased [Pre-HA 0.64 (0.45/0.68) and Post-HA 0.76 (0.65/0.82), P = 0.038]. During the Recovery, the percentage of total variance explained by PC1 was higher than during the Baseline. Post-HA, there was a high correlation between the Exercise addiction scores and the eigenvalues of PC1 (r = 0.9, P = 0.001). Thus, acute hypercapnic exposure reveals the Post-HA increase in cardiorespiratory coordination, which is highly related to the level of exercise addiction.

Highlights

Ascent to high altitude (HA) is accompanied by the process of acclimatization to chronic hypoxia
Later we revealed that cardiorespiratory coherence changes in response to hypoxic exposure depend upon fitness status (Uryumtsev et al, 2020)
We suggested that exercise addiction, which has been found in extreme sports (Heirene et al, 2016), could be correlated with cardiorespiratory coordination

Summary

Introduction

Ascent to high altitude (HA) is accompanied by the process of acclimatization to chronic hypoxia. Hypoxia is known to cause changes in the brain regulatory circuits, leading to alterations in blood flow and ventilatory sensitivity to oxygen and to carbon dioxide (Lindsey et al, 2018). Ventilatory and cerebrovascular hypercapnic response patterns show similar plasticity in CO2 sensitivity following hypoxic acclimatization, suggesting an integrated control mechanism (Smith et al, 2017). There are studies that describe the hematological (He et al, 2013) and hormonal changes (Liu et al, 2017), increased hypoxic tolerance, hypoxic ventilatory response and cerebral oxygenation (Cheung et al, 2014), and elevated sympathetic nervous system activity (Sander, 2016) after return to sea level. We are not aware of any studies that concern the delayed effects of HA acclimatization on the integration of cardiovascular and respiratory systems

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Conclusion