Cutaneous Microvascular Blood Flow and Reactivity in Hypoxia.

Benedikt Treml,Martin Burtscher,Iris Steiner,Hans Knotzer,Werner Pajk,Karl-Heinz Stadlbauer,Michael Pilch,Axel Kleinsasser

doi:10.3389/fphys.2018.00160

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.

Highlights

The issue how microcirculation and microcirculatory blood flow are influenced by a hypoxic stimulus is still a matter of debate and under investigation
We looked at reactive hyperemia in hypoxia and at the effect of hypoxic acclimatization
Unpublished observation from our group showed that a “wash out-period” of 1 month following a short exposure to hypoxia seems to be long enough to normalize the hypoxic ventilatory response (HVR) increase to baseline

Summary

Introduction

The issue how microcirculation and microcirculatory blood flow are influenced by a hypoxic stimulus is still a matter of debate and under investigation. From animal experiments we know that microcirculatory blood flow in the skeletal muscle decreases during normobaric hypoxia and that functional capillary density is significantly reduced (Saldívar et al, 2003). These observations were supported by other animal experiments reporting similar results (Fisher et al, 1992). Cutaneous hypoxia alone does not affect microcirculation (Siebenmann et al, 2017) Another small study in 11 subjects observed an increase in forearm skin blood flow after systemic hypoxia, without impact of local regulatory factors (Paparde et al, 2015)

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Conclusion