Table 1: Comparison of noninvasive techniques for assessing endothelial function.

Technique Equipment Cost Skill level Test time Validity Reliability Ref PWA Applanation tonometry Medium US$15,000 Low 35 mins Medium* Medium-high* d = 0.9–2.3% [6–9] FMD (i) Ultrasound (ii) Tourniquet High >US$50,000 High 20 mins High Medium CV: 14–50% [10–16] Plethysmography Strain-gauge Low US$10,000 Med. 30 mins Medium Medium CV: 8–27% [17–20]

FMD: flow-mediated dilation; CV: coefficient of variation; d: sample bias (mean difference); PWA: pulse wave analysis. *Further study is needed to corroborate these findings.