Recruitment of non‐perfused sublingual capillaries increases microcirculatory oxygen extraction capacity throughout ascent to 7126 m

Abstract

Key pointsr A physiological response to increase microcirculatory oxygen extraction capacity at high altitude is to recruit capillaries. r In the present study, we report that high altitude-induced sublingual capillary recruitment is an intrinsic mechanism of the sublingual microcirculation that is independent of changes in cardiac output, arterial blood pressure or systemic vascular hindrance.r Using a topical nitroglycerin challenge to the sublingual microcirculation, we show that high altitude-related capillary recruitment is a functional response of the sublingual microcirculation as opposed to an anatomical response associated with angiogenesis.r The concurrent presence of a low capillary density and high microvascular reactivity to topical nitroglycerin at sea level was found to be associated with a failure to reach the summit, whereas the presence of a high baseline capillary density with the ability to further increase maximum recruitable capillary density upon ascent to an extreme altitude was associated with summit success.Abstract A high altitude (HA) stay is associated with an increase in sublingual capillary total vessel density (TVD), suggesting microvascular recruitment. We hypothesized that microvascular recruitment occurs independent of cardiac output changes, that it relies on haemodynamic changes within the microcirculation as opposed to structural changes and that microcirculatory function is related to individual performance at HA. In 41 healthy subjects, sublingual handheld vital microscopy and echocardiography were performed at sea level (SL), as well as at 6022 m Matthias Peter Hilty has found that, during his education and throughout his board certification in General Internal Medicine and Intensive Care Medicine, his main interests lie in the foundations of human physiology, in addition to their application in clinical practice. Studies of the response of the macro-and microcirculation to critical illness and high altitude environments have lead to his high appreciation of the contrast between witnessing cardiovascular pathophysiology during field studies, in laboratory settings and at the bedside. Hoping to support the upcoming challenge to translate these findings to clinical use, Dr Hilty is applying advanced computational techniques for the objective assessment of a patient's microcirculation. M. P. Hilty and othersJ Physiol 597.10 (C2) and 7042 m (C3), during ascent to 7126 m within 21 days. Sublingual topical nitroglycerin was applied to measure microvascular reactivity and maximum recruitable TVD (TVD NG ). HA exposure decreased resting cardiac output, whereas TVD (mean ± SD) increased from 18.81 ± 3.92 to 20.92 ± 3.66 and 21.25 ± 2.27 mm mm −2 (P < 0.01). The difference between TVD and TVD NG was 2.28 ± 4.59 mm mm −2 at SL (P < 0.01) but remained undetectable at HA. Maximal TVD NG was observed at C3. Those who reached the summit (n = 15) demonstrated higher TVD at SL (P < 0.01), comparable to TVD NG in non-summiters (n = 21) at SL and in both groups at C2. Recruitment of sublingu...

MicroTools enables automated quantification of capillary density and red blood cell velocity in handheld vital microscopy

“…HVM imaging directly visualizes hemoglobin that is contained in red blood cells, as opposed to anatomical structures of the tissue, thereby defining the functional component of the microcirculation in terms of oxygen carrying capacity. Thus, the boundaries of microvascular structures within an HVM image sequence are defined by the spatial arrangement and direction of movement of red blood cells, and structures not currently perfused by red blood cells may only be visualized using recruitment maneuvers as described elsewhere 22 . These structures, which may be further categorized into arterioles, capillaries, and venules in subsequent steps, are referred to as “vessels” in the current manuscript.…”

Microcirculation alterations in severe COVID-19 pneumonia

“…Patients severely affected with COVID-19 develop fever and hypoxemia. Therefore, hypoxia-induced capillary recruitment could be an explanation for the increased vascular density observed [ 9 , 10 ]. Besides, high metabolic activity and tissue hypoxia are recognized stimuli for vascular growth [ 11 ].…”

Exposure to acute normobaric hypoxia results in adaptions of both the macro- and microcirculatory system

“…In contrast, studies concerning the effects of hypoxia on the microcirculatory system are comparatively scarce. For example, previous studies reported an increase in sublingual microcirculatory blood flow and capillary density after ascent to high altitudes 19,20 , which suggests microvascular recruitment after exposure to hypobaric hypoxia 21 . However, recent studies also reported that the physiological adaptions to hypobaric hypoxia can differ substantially from those to normobaric hypoxia 22,23 , which is why the results of studies conducted in high altitude can not be fully applied to the normobaric environment.…”