Guangkun Nie

Potassium in the blood is like salt in a soup: just a bit too much, and the heart starts to falter. Doctors usually monitor this mineral with blood draws from a vein, but for people with kidney disease or a weak heart, frequent lab visits become a ordeal.

You sleep, but your heart keeps telling stories. The rhythm of beats, the pauses between them, the respiratory waves — all shift from one sleep stage to the next. In a sleep lab, this is read from a host of sensors on the head, face, legs, and chest. It's cumbersome, expensive, and not something you can do at home.