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.