- Flow-mediated vasodilatation test (study days 0 and 29) - An ultrasound device for measuring the size of the brachial artery (artery in the upper arm) is placed just above the elbow. The size of the artery is measured before and 5 minutes after blood flow to the arm is stopped for 5 minutes, using a blood pressure cuff. The artery is also measured before and after taking nitroglycerin, a medicine that dilates blood vessels. These measurements tell how well the drug treatment works on the cells lining the brachial artery, which is an indicator of coronary artery function. This test takes about 1.5 hours.