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Human Microvascular Reactivity In Vivo Using Incident Dark Field Videomicroscopy

The microvasculature is increasingly recognized as a major contributor to many cardiovascular diseases including atherosclerosis and heart failure with preserved ejection fraction (HFpEF). Endothelial microvascular dysfunction, the inability to vasodilate to endothelial‐dependent agonists, precedes the development of large artery disease. While microvascular (dys)function can be assessed using invasive techniques (e.g., cardiac catheterization) there are limited strategies in which to assess microvascular function in a non‐invasive and cost‐effective manner. Recent advances in hand‐held vital microscopy allow for reliable direct imaging of the sublingual microcirculation at bedside. One of the latest advancements (Cytocam, Braedius Medical) utilizes state of the art incident dark field (IDF) technology to allow for quantification of total vascular density (TVD). We therefore hypothesized an increase in TVD in response to both an endothelial‐dependent, and ‐independent vasodilator. Cytocam‐IDF was optimized to measure in vivo sublingual microvascular response to topical application of the endothelial‐independent vasodilator nitroglycerin (NTG) (0.3mg) and the endothelial‐dependent dilator acetylcholine (5.5 ·10‐2 M). Five images were taken at baseline. Immediately following topical administration of acetylcholine, an additional 5 images were taken to compare TVD pre‐ and post‐treatment. The area was washed and after 30 min of rest, a NTG tablet was administered sublingually and additional 5 images were obtained. Massey's microcirculation image quality score was applied, and TVD was measured using the De Backer score manual analysis by two separate investigators to account for interobserver variability, with consensus achieved. Both NTG (12.6 mm/mm2± 0.5, n=7 compared to baseline 9.9 mm/mm2± 0.42, n=7) (Mean±SEM) and acetylcholine (13.1 mm/mm2± 0.3, n=3 compared to baseline 10.4 mm/mm2± 0.5, n=3) increased TVD. These data suggest that measurement of TVD in response to endothelium‐specific pharmacological agonists may allow for assessment of the human systemic microvasculature in vivo. This is a promising strategy that may allow for early detection of endothelial microvascular dysfunction prior to the onset of large artery disease or heart failure.