Reduced insulin sensitivity in young, normoglycaemic subjects alters microvascular tissue oxygenation during postocclusive reactive hyperaemia.

New Findings: What is the central question of the study? Are measures of reduced insulin sensitivity in young, normoglycaemic subjects correlated with near-infrared spectroscopy-derived microvascular responsiveness [tissue oxygen saturation reperfusion rate (STO upslope)] during postocclusive reactive hyperaemia? What is the main finding and its importance? A sevenfold range of hepatic insulin sensitivity is significantly correlated (r = 0.44, P = 0.02) with STO upslope after transient tissue ischaemia. Near-infrared spectroscopy may be an important tool for determining altered microvascular function before onset of hyperglycaemia. Identification of pre-type 2 diabetes much earlier than with the present clinical criteria is important for pre-emptive measures against microvascular deterioration.

Abstract: Near-infrared spectroscopy (NIRS) measurement of postocclusive reactive hyperaemia (PORH) tissue oxygen saturation reperfusion rate [STO upslope (as a percentage per minute)] has recently been correlated with the percentage of flow-mediated dilatation (%FMD). Cardiovascular disease is associated with impairments in %FMD. Reduced insulin sensitivity may negatively affect the vascular system for many years before prediabetes/type 2 diabetes states. The aim of this study was to determine whether static and dynamic STO parameters during PORH are correlated with reduced insulin sensitivity in young, normoglycaemic subjects. Glucose and insulin were measured during an oral glucose tolerance test in 18- to 26-year-old, healthy subjects (11 men and 11 women), and STO was measured during PORH of antebrachial muscle. Hepatic (ISI ) and whole-body (ISI ) insulin sensitivities were calculated. The STO upslope was negatively correlated with minimal STO (r = -0.5, P = 0.01). The change of STO from minimum to baseline (ΔSTO ) was significantly negatively correlated with fasting insulin (r = -0.5, P = 0.01) and a positively correlated with ISI (r = 0.65, P = 0.001). The minimum STO was significantly negatively correlated with ISI , and STO upslope was significantly positively correlated with ISI (r = 0.44, P = 0.02). The minimum STO (a measure of O extraction while the cuff was inflated), ΔSTO (a measure of the amount of reperfusion) and STO upslope (a measure of responsiveness of the microcirculation to ischaemia) were all positively correlated with ISI , one of the longest-used measures of insulin sensitivity. The NIRS-derived STO might be a useful tool for assessing how levels of reduced insulin sensitivity in young, normoglycaemic adults affect the microvasculature.