 - Brachial artery reactivity test to measure blood vessel function: Before the exercise stress testing, subjects lie on a stretcher while the brachial artery artery in the forearm is imaged using a noninvasive ultrasound method. Artery size and blood flow velocity are measured before and after inflating a blood pressure cuff on the forearm. Vessel size and flow velocity measurements are repeated after 15 minutes and again after administration of nitroglycerin under the tongue. 