Brachial ultrasound reactivity study-A baseline ultrasound image (picture produced using sound waves) of the brachial artery (artery located at the bend of the arm) is taken and blood flow measurements are recorded. Then, a pressure cuff is placed around the upper forearm, inflated for 5 minutes to stop blood flow to the forearm, and then released. Images of the artery and flow measurements are repeated. After a 15-minute rest, new baseline images are taken and flow measurements obtained. A small amount of nitroglycerin is then sprayed under the tongue and after 3 minutes, blood flow measurements and brachial artery images are recorded once more.