2.2. Endothelial function assessment

Peripheral microvascular endothelial function was assessed using RH-PAT in a designated quiet, temperature controlled and uniformly lit room. Subjects were instructed to fast for 4-hours prior to the study and to abstain from coffee or tobacco on the day of the examination. All vasoactive medications were discontinued for 24-hours prior to testing. A fitted blood pressure cuff was placed on one arm, and the finger cuffs of the Endo-PAT 2000 device (designed by Itamar Medical Ltd, Caesarea, Israel) was placed on the middle finger of each hand [13]. The EndoPAT 2000 is a Food and Drug Administration–approved noninvasive device allows continuous recording of the Peripheral Arterial Tone signal measured from the fingertip by recording finger arterial pulsatile volume changes. The interpretation is operator independent.

The reactive hyperemia protocol consists of the following sequence. A five-minute baseline measurement, after which a blood pressure cuff on the test arm is inflated to 60 mmHg above baseline systolic blood pressure, or at least 200 mmHg for five minutes (occlusion of pulsatile arterial flow confirmed by the reduction of the PAT tracing to zero) after which the cuff is deflated, and the post-deflation PAT tracing is recorded for an additional six minutes. The ratio of the PAT signal after cuff release to baseline is calculated through a computer algorithm automatically normalizing for baseline signal, and indexed to the contralateral arm. A calculated RH-PAT index ≤ 2.0 is a clinically used cut-off value for diagnosis of PED at Mayo Clinic and we have previously demonstrated that RH-PAT index ≤ 2.0 correlated with reduced exercise capacity and greater dyspneic symptoms [14]. Several studies have shown a good association between PED assessment using EndoPAT and other methods, such as intra-arterial acetylcholine infusion and brachial artery Doppler ultrasound following reactive hyperemia [15], [16], [17].