Abstract
An increased and more effective microvascular perfusion is postulated to play a key role in the physiological adaptation of Sherpa highlanders to the hypobaric hypoxia encountered at high altitude. To investigate this, we used Lempel-Ziv complexity (LZC) analysis to explore the spatiotemporal dynamics of the variability of the skin microvascular blood flux (BF) signals measured at the forearm and finger, in 32 lowlanders (LL) and 46 Sherpa highlanders (SH) during the Xtreme Everest 2 expedition. Measurements were made at baseline (BL) (LL: London 35 m; SH: Kathmandu 1300 m) and at Everest base camp (LL and SH: EBC 5,300 m). We found that BF signal content increased with ascent to EBC in both SH and LL. At both altitudes, LZC of the BF signals was significantly higher in SH, and was related to local slow-wave flow-motion activity over multiple spatial and temporal scales. In SH, BF LZC was also positively associated with LZC of the simultaneously measured tissue oxygenation signals. These data provide robust mechanistic information of microvascular network functionality and flexibility during hypoxic exposure on ascent to high altitude. They demonstrate the importance of a sustained heterogeneity of network perfusion, associated with local vaso-control mechanisms, to effective tissue oxygenation during hypobaric hypoxia.
Highlights
Sherpas highlanders (SH) are known to demonstrate considerable tolerance to hypobaric hypoxia, the mechanisms behind this adaptation are not well understood[1]
Artefact-free skin blood flux (BF) and tissue oxygenation signals (Fig. 1) of sufficient length for LZ complexity (LZC) analysis at both BL and Everest Base Camp (EBC), were obtained in 32 LL (16 M/16 F), age 46(14)y, BMI 24.3(3.3) kg/m2 (mean(SD)) and 46 Sherpa highlanders (SH) (23 M/23 F), age 28(6)y (p = 0.0001, SH vs LL) and BMI 23.8(3.4) kg/m2 (p > 0.05, SH vs LL) who represented a subset of the 144 participants from the Xtreme Everest 2 research expedition (XE2)[28]
We have previously shown using time and spectral domain analysis of BF signals that SH, when exposed to hypobaric hypoxia, demonstrated superior preservation of peripheral microcirculatory perfusion compared to LL and that in SH differences in local myogenic and neurogenic control may play a key role in their www.nature.com/scientificreports adaptation to high altitude by sustaining local perfusion and tissue oxygenation
Summary
Sherpas highlanders (SH) are known to demonstrate considerable tolerance to hypobaric hypoxia, the mechanisms behind this adaptation are not well understood[1]. Www.nature.com/scientificreports as well as higher frequency cardiac and respiratory rhythms to microvascular perfusion has been assessed using spectral analysis of blood flux (BF) signals obtained using non-invasive laser Doppler fluximetry in the skin[14] This has led to the suggestion that measurement of flow-motion activity may provide an early indicator of declining function (for review see[15]). The rhythmical oscillatory processes that determine flow-motion, and that operate across differing time-scales in the range ~0.6–100 seconds, have been explored using multiscale non-linear analysis of the laser Doppler BF signal[22,23,26] To date these studies have shown multiscale complexity analysis to be a good predictor of the variability of the signal over multiple time scales[22,23,26]. They have shown that multiscale non-linear analysis may provide novel mechanistic insight into the extent to which the BF signal is modulated by the different frequency bands under differing (patho)physiological conditions[24,27]
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