Cutaneous Microvascular Blood Flow and Reactivity in Hypoxia

Abstract

As is known, hypoxia leads to an increase in microcirculatory blood flow of the skin in healthy volunteers. In this pilot study, we investigated microcirculatory blood flow and reactive hyperemia of the skin in healthy subjects in normobaric hypoxia. Furthermore, we examined differences in microcirculation between hypoxic subjects with and without short-term acclimatization, whether or not skin microvasculature can acclimatize. Fourty-six healthy persons were randomly allocated to either short-term acclimatization using intermittent hypoxia for 1 h over 7 days at an FiO2 0.126 (treatment, n = 23) or sham short-term acclimatization for 1 h over 7 days at an FiO2 0.209 (control, n = 23). Measurements were taken in normoxia and at 360 and 720 min during hypoxia (FiO2 0.126). Microcirculatory cutaneous blood flow was assessed with a laser Doppler flowmeter on the forearm. Reactive hyperemia was induced by an ischemic stimulus. Measurements included furthermore hemodynamics, blood gas analyses and blood lactate. Microcirculatory blood flow increased progressively during hypoxia (12.3 ± 7.1–19.0 ± 8.1 perfusion units; p = 0.0002) in all subjects. The magnitude of the reactive hyperemia was diminished during hypoxia (58.2 ± 14.5–40.3 ± 27.4 perfusion units; p = 0.0003). Short-term acclimatization had no effect on microcirculatory blood flow. When testing for a hyperemic response of the skin's microcirculation we found a diminished signal in hypoxia, indicative for a compromised auto-regulative circulatory capacity. Furthermore, hypoxic short-term acclimatization did not affect cutaneous microcirculatory blood flow. Seemingly, circulation of the skin was unable to acclimatize using a week-long short-term acclimatization protocol. A potential limitation of our study may be the 7 days between acclimatization and the experimental test run. However, there is evidence that the hypoxic ventilatory response, an indicator of acclimatization, is increased for 1 week after short-term acclimatization. Then again, 1 week is what one needs to get from home to a location at significant altitude.

Sustained vasomotor control of skin microcirculation in Sherpas versus altitude‐naive lowlanders: Experimental evidence from Xtreme Everest 2

“…Consistent with our findings in skin are those of Treml et al (2018) using LDF, who found that lowlanders, on exposure to normobaric hypoxia, demonstrated a reduced hyperaemic response after occlusion. There was a trend towards reduced RH in lowlanders with ascent to high altitude, and flowmotion activity in the endothelial band was greater at altitude in both forearm and finger vascular beds of Sherpas.…”

“…There was a trend towards reduced RH in lowlanders with ascent to high altitude, and flowmotion activity in the endothelial band was greater at altitude in both forearm and finger vascular beds of Sherpas. Consistent with our findings in skin are those of Treml et al (2018) using LDF, who found that lowlanders, on exposure to normobaric hypoxia, demonstrated a reduced hyperaemic response after occlusion. Moreover, reduced skeletal muscle microvascular reactivity has been demonstrated in lowlanders ascending to EBC using near-infrared spectroscopy (Martin, Levett, Bezemer, Montgomery, & Grocott, 2013).…”

“…at 6 and 12 h of exposure to normobaric hypoxia (fraction of inspired O 2 equivalent to 4500 m altitude;Treml et al, 2018). However, as the degree of hypoxia increases at higher altitudes, possible dysregulation and disruption of microcirculatory flow might occur, affecting lowlanders to a greater degree.…”

Four Weeks of Hypoxia Training Improves Cutaneous Microcirculation in Trained Rowers

“…The microcirculation is associated with hypoxia adaptation (Ovadia-Blechman et al 2015, Treml et al 2018. Hypoxia causes cutaneous vasodilation and robust increase in cutaneous blood flow in healthy humans (Simmons et al 2007, Lawley et al 2014.…”

“…Intermittent hypoxia training had greater positive effect on hemodynamics, microvascular endothelial function, and work capacity of untrained healthy men (Shatilo et al 2008). However, the issue of how a hypoxia stimulus influences the microcirculation and microcirculatory blood flow is still debating and under investigated (Rowell et al 1982, Simmons et al 2007, Siebenmann et al 2017, Treml et al 2018. Paparde et al (2015) found that acute systemic hypoxia causes sympathetic stimulation to heart which results in increased heart rate and larger cardiac output, and which could be the reason of forearm skin blood flow increase in acute systemic hypoxia.…”