Noninvasive Determination of Spatially Resolved and Time-Resolved Tissue Perfusion in Humans During Nitric Oxide Inhibition and Inhalation by Use of a Visible-Reflectance Hyperspectral Imaging Technique

Abstract

Background — Vascular disease is commonly associated with reduced local synthesis of nitric oxide (NO) and impaired tissue perfusion. We introduce a novel noninvasive, visible-reflectance, hyperspectral imaging technique for quantifying the percentage of hemoglobin existing as oxyhemoglobin (HbO 2 ) as an index of skin tissue perfusion. Methods and Results — To simulate vascular endothelial dysfunction, N G -monomethyl- l -arginine (L-NMMA) was infused into the brachial arteries of 9 healthy subjects for 5 minutes to inhibit forearm NO synthesis, first with the subject breathing room air and subsequently during NO inhalation at 80 ppm for 1 hour. Blood flow was measured by venous occlusion plethysmography, and the percentage of HbO 2 perfusing skin tissue was imaged noninvasively with a visible-reflectance hyperspectral technique. L-NMMA reduced blood flow by 31.7±4.9% and percentage of HbO 2 by 6.5±0.1 ( P =0.002 and P <0.001 versus baseline, respectively). With subjects inhaling NO, blood flow fell during L-NMMA infusion by only 10.9±7.3%, and the percentage of HbO 2 decreased by 3.6±0.1 ( P =0.007 and P <0.001, respectively, versus room air L-NMMA responses). Conclusions — Visible-reflectance hyperspectral imaging demonstrates (1) a significant decline in the percentage of HbO 2 in skin tissue when blood flow is reduced after inhibition of forearm NO synthesis and (2) restoration of HbO 2 toward basal values with improved blood flow during inhalation of NO. This imaging method may provide an effective approach for time-resolved noninvasive monitoring of skin hemoglobin oxygen saturation and assessment of responses to therapeutic interventions in patients with vascular disease.