MODEL RELEASED. Blood donation. Nurse attaching an inflatable cuff around the upper arm of a blood donor. The cuff is part of a sphygmomanometer, or blood pressure gauge, that is used to measure a person's blood pressure. Mobile blood units travel to prearranged areas, such as shopping centres and work places, so that potential blood donors can attend at their convenience. Donor blood is given to patients in transfusions to replace lost blood, for example during surgery or after accidents.