103 Rational and Design of the MICORDIS study brachial artery using an inflatable blood-pressure cuff. After 5 min of inflation the cuff is deflated, which induces reactive hyperemia. During this hyperemic period, a second flow measurement is performed.49 The EndoPAT displays the pulse amplitude response to hyperemia, and automatically calculates the Reactive Hyperemia Index (RHI) as the post-to pre-occlusion PAT-ratio on the index finger of the occluded arm, divided by the corresponding ratio from the contralateral, control arm.49, 50 The RHI is assumed to reflect systematic microvascular function, and a cut-off value of RHI <1,67 is used to diagnose peripheral microvascular dysfunction.51 OBJECTIVES The primary objective of the MICORDIS study is a difference in MBV in INOCA patients compared to healthy controls, evaluated at baseline, during hyperinsulinemia and during increased myocardial contraction. Secondary objectives of the study are: 1) sex differences in MBV, MBF, ΔMBV, baseline characteristics, cardiovascular risk factors, depression, stress level, blood parameters and physiological indexes in patient group; 2) differences in baseline characteristics, cardiovascular risk factors, depression, stress level and physiological indexes between patient and control group; 3) comparison of MBV, MBF and ΔMBV at baseline and after HE-clamp and dobutamine of the patient and control group; 4) MBV, MBF and ΔMBV compared between insulin resistant subjects and noninsulin resistant subjects; 5) correlation between MBV (+other related variables) measured with MCE and MBV measured with CMR; 6) difference in peripheral endothelial function between INOCA patients and healthy controls; and 7) differences in protein expression and phosphorylation of microvascular endothelial cells compared between patient and control group. STATISTICAL ANALYSIS AND SAMPLE SIZE CALCULATION The expected effect size was estimated based on a study of Rinkevich et al.52 Rinkevich compared the MBV between healthy controls and patients with Syndrome X using dipyridamole as a stimulus of MBV. A reduced MBV in non-obstructive CAD patients compared to healthy controls is the primary endpoint of our study. We expect the difference in MBV to be greater during stimulation with insulin and dobutamine, compared to dipyridamole as stimulus on MBV, making the data of Rinkevich appropriate for the use of sample size calculations. To detect a mean difference in MBV of 25 (MBV determined with MCE is dimensionless), we calculated a sample size of 24 patients per group to achieve a power of 80%, assuming a standard deviation of 30 in both groups. This calculation assumed the 5% significance level, using a two-sided independent sample t-test. To 5
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