Objectives. In order to limit the variability of coronary flow velocity reserve (CFVR), we analyzed which factors independently affect CFVR and established a new parameter integrating these factors. Background. Coronary flow velocity reserve (CFVR) is a frequently used parameter for evaluating the physiological significance of epicardial stenosis and microvascular function. Since CFVR measurements are done in substantially different hemodynamic and clinical situations, interpretation of CFVR requires correction for major influencing factors. Methods. In 141 patients with angina-like symptoms and angiographically unobstructed coronary arteries, intracoronary Doppler measurements were performed in at least two coronary vessels. Coronary flow velocity reserve was calculated as the ratio of hyperemic average peak velocity (hAPV), after intracoronary bolus of adenosine, to baseline average peak velocity (bAPV). Results. Analysis of covariance revealed that only bAPV (p < 0.0001) and age (p < 0.0001) were independent factors influencing CFVR. Based on a regression model for estimation of predicted CFVR values, individual CFVR values (CFVR(ind)) obtained at different bAPV and age were transformed in corrected CFVR values (CFVR(corr)) by relating them to a mean bAPV of 15 cm/s and a mean age of 55 years. The transformation from CFVR(ind) into CFVR(corr) for the left anterior descending artery can be done by using the following equation: CFVR(corr) = 2.85*CFVR(ind)*10 (0.48*log(bAPV) + 0.0025*age - 1.16). When applying this new parameter to conditions assumed to cause microvascular dysfunction, analysis showed that only patients with diabetes showed a significant decrease of traditional CFVR and CFVR(corr), whereas a history of hypertension and current smoking habit had no influence on CFVR(corr). Conclusions. The concept of CFVR(corr) standardizes CFVR for bAPV and age as the major physiological determinants. Especially in patients with microvascular dysfunction, this approach may help to discriminate between conditions directly affecting vasodilator reserve and conditions primarily affecting bAPV. (C) 2000 by the American College of Cardiology.