Abstract: An active hand gripper for use in a blood drawing apparatus provides a tactile signal to a blood donor reminding the donor to periodically squeeze the hand gripper, thereby increasing donor venous pressure and the related blood flow rate from the donor into the blood drawing apparatus. The tactile signal may be generated, for example, in response to a measured decrease in line pressure; or in response to a projected decrease in line pressure based on analysis of current and past flow parameters; or at pre-set intervals based on a target gripping frequency; or based on the donor's pattern of actual gripping. The gripper can be configured for autonomous operation such that the gripper itself contains circuitry for determining when the tactile signal should be issued, or the gripper can receive a trigger signal from a controller within the blood drawing apparatus.