Abstract P017: Reliability of Near-Infrared Spectroscopy in the Evaluation of Forearm Microvascular Function

Background: The assessment of microvascular reactivity by near-infrared spectroscopy (NIRS) was shown to be associated with cardiovascular status and the number of cardiovascular risk factors and could be of interest in cardiac or high-risk patients. However, the reliability of NIRS parameters measured at the arm has never been studied and should be known before they could be used in research and clinical settings. The aim of this study was to measure the absolute and relative reliability of the most commonly used NIRS parameters during post-occlusive hyperaemia in healthy young men. Methods: 18 healthy men (33.56±7.88 years), without any cardiovascular risk factors (dyslipidemia, hypertension, abdominal obesity, diabetes and smoking) or cardiac symptoms had their fasting microvascular function evaluated twice, on two mornings separated by at least 7 days. Briefly, NIRS optodes were placed on the brachio-radialis muscle and a pressure cuff was installed on the upper-arm of subjects and inflated at 80mm Hg over the systolic blood pressure. NIRS parameters were registered continuously for 2 minutes at rest, 5 minutes during occlusion and 5 minutes post-occlusion. NIRS parameters listed in the table below were then analyzed. Results: CV (%) SEM Pearson r ICC mVO 2 (ml/min/100g) 6.51 0.0043 0.90 0.90 Half time to O 2 Hb max (sec) 20.04 4.15 0.79 0.78 Time to O 2 Hb max (sec) 15.61 8.24 0.79 0.75 O 2 Hb max (%) 6.68 2.39 0.70 0.66 tHb max (%) 13.32 1.66 0.31 0.31 Time to tHb max (sec) 19.61 4.73 0.86 0.85 AUC O2Hb 16.15 184.01 0.83 0.83 AUC tHb 18.59 175.04 0.80 0.80 AUC HHb 20.37 159.38 0.63 0.63 mVO 2 : muscle oxygen consumption, O 2 Hb : oxyhaemoglobin, tHb: total haemoglobin and HHb: deoxyhaemoglobin Conclusion: Reliability of most NIRS parameters was strong (Half time to O 2 Hb max and Time to O 2 Hb max) and very strong (mVO 2 , Time to tHb max and AUC O 2 Hb and tHb). The Coefficient of variations were below 10% for mVO 2 , and O 2 Hb max, and between 10 and 20% for the other parameters, which is in line with previous data at the calf level in healthy subjects and peripheral artery disease patients. We can therefore conclude that NIRS parameters evaluated during brachial post-occlusive hyperaemia were reliable and can be used by physicians and investigators to establish thresholds of relevancy for NIRS parameter changes and to estimate sample sizes in clinical studies.