- Forearm blood-flow test (study days 1 and 30): Small tubes are inserted into an artery and vein in the forearm at the inside of the elbow. Blood pressure cuffs are placed around the upper arm and wrist, and a strain gauge (a rubber band-like device) is placed around the forearm. When the blood pressure cuffs are inflated, blood flows into the forearm, stretching the strain gauge at a rate proportional to the blood flow. When the devices are in place, a salt water solution is injected in the small tube in the artery. After 20 minutes, small doses of the following drugs are given through the catheter at various intervals: 1) L-NMMA (blocks production of nitric oxide, a substance produced by the blood vessels that causes them to dilate); 2) sodium nitroprusside (dilates blood vessels, increasing blood flow); 3) acetylcholine (lowers blood pressure); and 4) acetylcholine plus L-NMMA. The effect of the different drugs on blood flow in the forearm is measured. The study takes about 2 hours to complete.