Figure 3. Representative images.

Representative still images of the sublingual microcirculation at sea level (A and C) and 7042 m (B and D), before and after recruitment of capillaries by topical application of nitroglycerin. Stimulation with topical nitroglycerin at sea level (C) lead to a recruitment of capillaries similar to that for exposure to high altitude (B); the highest capillary density was measured in summiters at 7042 m after stimulation with nitroglycerin (D). Moving image sequences are provided online via the Zenodo repository (Hilty et al. 2018).