Methods
We therefore aimed to demonstrate in vivo the presence of endothelial dysfunction in COVID-19 patients without cardiovascular risk factors or pre-existing cardiac conditions. We used the Endo-PAT 2000, a device able to measure endothelial vasodilation function in a rapid and non-invasive way (5). The device records endothelium-mediated changes in the digital pulse waveform known as the Peripheral Arterial Tone (PAT) signal, measured with a pair of plethysmographic probes situated on the index finger of both patient’s hands. Endothelium-mediated changes in the PAT signal are elicited by creating a downstream hyperemic response, induced by blood flow occlusion in the brachial artery for 5 minutes using an inflatable cuff on one arm. The response to reactive hyperemia is evaluated automatically by the device, and a PAT ratio is calculated using the post- and pre-occlusion PAT values relative to the occluded arm (compared to the measurements from the contralateral arm, which serves as control for non-endothelial dependent systemic effects). The Reactive Hyperemia Index (RHI) is then calculated as the ratio of Pulse Wave Amplitude (PWA) measured during the 60-second period after cuff deflation divided by the average PWA measured before cuff inflation; RHI values below 1.67 are suggestive of endothelial dysfunction.