Figure 1.

Study design Days 5 and 42. Eighteen subjects underwent the same protocol on Days 5 and 42. Subjects received saline, acetylcholine (Ach), stored blood, and then Ach again to assess the effect of blood transfusion on the vascular endothelial response to Ach. At baseline subjects received an infusion of 0.9% normal saline (NS) at 2 ml per minute. This was followed by sequential infusions of Ach at increasing rates of 7.5, 15, and 30 μg per minute, which corresponded with infusion flow doses of 15, 30, and 60 ml per hour. A washout period of 30 minutes was followed by red blood cell infusion and repeated Ach infusion. Blood was transfused for a total duration of 9–12 minutes. The rates of blood infusion were 5 ml per minute for 2 minutes (300 ml/h), 10 ml per minute for 2 minutes (600 ml/h), and then 15 ml per minute until the unit was completed (900 ml/h). Continuous forearm blood flow measurements were performed at each baseline and infusion stage. Venous blood draws were performed before onset of the study and then again after blood infusion.