Fig. 5.

Hypoxia defense and vulnerability in oxygen sensitive tissues of mammals. Blue boxes indicate the breadth of protective mechanisms for preventing tissue injury during hypoxia in the general vascular system, cardiac and skeletal muscle, brain and neural tissues, and renal tissues of diving-adapted mammals. Red arrows indicate increased levels relative to terrestrial mammals (proportional increases shown in parentheses); blue arrows denote decreases. Pink boxes show the broad range of hypoxia-related symptoms reported for patients with COVID-19 infections. (Note mild to marked cases are combined for this general review.) See Machhi et al. (Machhi et al., 2020) for a review of the full list of symptoms relative to severity of infection. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)