“…HR was elevated when participants were stressed, and PPG could accurately capture these physiological changes, including HR reduction during relaxing exercises [ 10 , 42 , 43 , 64 , 65 ]. In addition to stress, PPG also accurately detects patients who are depressed [ 32 - 34 , 37 , 38 , 40 , 41 , 44 , 45 , 48 , 49 , 52 , 54 ], including those with MDD. In other words, depression was associated with a lower HR in contrast to stress.…”