Acute hypoxaemia and vascular function in healthy humans

Area of Science:

• Cardiovascular Physiology
• Hypoxia Research
• Vascular Function

Background:

• Endothelium-dependent flow-mediated dilatation (FMD) is known to be impaired by acute moderate hypoxia.
• The effects of milder hypoxia on FMD and the impact of acute hypoxia on endothelium-independent glyceryl trinitrate (GTN)-induced dilatation were previously unknown.
• High altitude and acute normobaric hypoxia equivalent to high altitude impair vascular function.

Purpose of the Study:

• To investigate whether flow-mediated dilatation (FMD) is impaired to the same degree during exposure to milder hypoxia compared to moderate hypoxia.
• To assess whether smooth muscle vasodilatory capacity, measured by glyceryl trinitrate (GTN)-induced dilatation, is impaired during acute hypoxic exposure.
• To determine the graded impairment of vascular function under varying levels of acute hypoxia.

Main Methods:

• Brachial FMD was measured at baseline and after 30 minutes of mild or moderate normobaric hypoxia in healthy adults.
• Glyceryl trinitrate (GTN)-induced dilatation was assessed after hypoxic exposures and in a normoxic control condition.
• A time-control trial under normoxia was conducted to account for potential effects of rest and inactivity on FMD.

Main Results:

• A graded impairment in both FMD and GTN-induced dilatation was observed during acute exposure to mild and moderate hypoxia.
• Reductions in FMD and GTN-induced dilatation were significantly greater during moderate hypoxia compared to mild hypoxia.
• Allometrically corrected FMD was attenuated in both mild and moderate hypoxia, and GTN-induced dilatation also showed significant impairment.

Conclusions:

• Acute exposure to mild and moderate hypoxia causes a graded impairment in both endothelium-dependent FMD and endothelium-independent smooth muscle function.
• The observed impairments in vascular function appear to be influenced by shear patterns and a decline in smooth muscle vasodilator capacity.
• Findings suggest that even short-term exposure to reduced oxygen levels can negatively impact vascular health, with implications for individuals at high altitude or with respiratory compromise.