A crude video of Katherine E. Brandt’s “death rattle” appeared on Twitter on Saturday, about 11 hours before she succumbed to ovarian cancer. Her wife, Kimberly D. Acquaviva, had posted it there. For Acquaviva, a nursing professor at the University of Virginia whose scholarship focuses on end-of-life issues, academic interests and personal suffering have for the past six months uncomfortably intertwined.