Reproducibility of flow mediated skin fluorescence to assess microvascular function

Abstract

Objective: Recent technical developments enable skin fluorescence to be quantified in vivo in humans. The present study aimed at determining whether flow mediated skin fluorescence was reproducible, sensitive to changes within an individual, and if it could differ between patients with coronary artery disease and healthy volunteers.

Methods: First, forearm flow mediated skin fluorescence recorded during and after brachial artery occlusion was assessed following successive forearm occlusion periods (1, 2, 3 and 5min) and expressed as ischemic and hyperemic responses (as % of baseline). Secondly, 3min flow mediated skin fluorescence was assessed before and after 10min local cooling to 15°C. In a third protocol, the inter-day reproducibility of ischemic and hyperemic responses to 3min occlusion was tested at an interval of 7days, and compared between healthy controls and patients with coronary artery disease (CAD).

Results: In the first protocol, we observed a time dependent increase in the ischemic and hyperemic responses to occlusion. Next, we observed a lower hyperemic response after local cooling (9.8±4.2 versus 17.8±2.5% respectively, P<0.001), while in contrast, the ischemic response was higher and exhibited greater variability (23±15 versus 11.8±6.4%; P=0.028). In the third protocol, the inter-day reproducibility of flow mediated skin fluorescence for a 3min occlusion period was excellent. The ischemic response was significantly lower in CAD patients than in healthy controls (6.7±4.8% vs 14.7±6.8% respectively, P<0.001). Similarly, the hyperemic response was significantly decreased in the CAD group compared to healthy controls (11.6±3.6% vs 19.5±5.4% respectively, P<0.001).

Conclusion: We show that quantifying the ischemic and hyperemic flow mediated skin fluorescence is feasible, reproducible, sensitive to acute changes in skin blood flow, and distinguishes patients populations. However, more data are needed to evaluate the correlation with other methods or specific biochemical endothelial markers.

Keywords: Brachial artery occlusion, coronary artery disease; Flow mediated skin fluorescence; Microcirculation; NADH fluorescence.