Haffke et al. used peripheral arterial tonometry (PAT) in patients after COVID-19 who had myalgia, encephalomyelitis, and chronic fatigue syndrome and compared markers of endothelial dysfunction such as Endothelin-1 (ET-1), Angiopoietin-2 (Ang-2), Endocan (ESM-1), intreleukon-8 (IL-8) and Angiotensin-Converting Enzyme (ACE). Here, ACE is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.