The Importance of Assessment of Endothelial Function According to the Time Course of Flow-mediated Dilation of the Brachial Artery

Ultrasonography is widely used to evaluate atherosclerosis. Therefore, many ultrasound parameters exist, each with its own clinical implications. Many reports have shown that these ultrasound parameters are useful for evaluating the progression of atherosclerosis or the risk of cardiovascular disease in healthy persons and in persons with cardiovascular risk factors. Ultrasound parameters are categorized as either structural or functional parameters. Particularly in the early stage of atherosclerosis, functional parameters are useful for evaluating the risk of the further development of atherosclerosis. We have also reported that the pulsatility index of the brachial artery is related to atherothrombotic infarctions in high-risk elderly subjects. Next, we studied flow-mediated dilation (FMD) as a functional parameter in the early stage of atherosclerosis. FMD is believed to be associated with endothelial nitric oxide (NO) synthesis. Furthermore, NO has the ability to prevent progression in the early stage of atherosclerosis. Guideline for FMD measurement have already been established. FMD has been defined as the rate of brachial artery vasodilation 60 seconds after a sphygmomanometric cuff is deflated after being inflated for 5 minutes to a pressure 50 mmHg greater than the systolic blood pressure. In several prospective studies, FMD measured according to these guidelines was shown to be a predictor of cardiovascular disease. We have also already reported a cross-sectional study in which FMD of the brachial artery based on this guideline was found to be associated with diabetic retinopathy in elderly persons who had diabetes but no cardiovascular disease. However, because these guidelines are based on the results of a study of healthy young adults, it remains to be seen whether these guidelines can be applied to elderly persons or persons with cardiovascular risk factors such as diabetes, hypertension, and dyslipidemia. Furthermore, because vasodilation occurred continuously for several minutes after sphygmomanometric cuff deflation, the time course of FMD of the brachial artery must be assessed. Therefore, we evaluated the time course of flow-mediated dilation of the brachial artery with a UNEXEF18G (UNEX Corp., Nagoya, Japan), which can continuously measure brachial artery vasodilation. Vasodilation measured 60 seconds after sphygmomanometric cuff deflation on the basis of the International Brachial Artery Reactivity Task Force guidelines designated FMD60, and the maximum vasodilation obtained during continuous measurement of the brachial artery was designated MaxFMD. Furthermore, the elapsed time from sphygmomanometric cuff deflation to MaxFMD was designated peak time (PT). Using these parameters, we evaluated the relationship between the time course of flow-mediated dilation of the brachial artery and aging, diabetes, hypertension, and dyslipidemia. Regarding the effect of age-related alteration of the time course of FMD of the brachial artery, we showed in