Figure 6.

Quadratic classification of PPG signals measured before and after the simulated heat stress induction based on the optimal feature (entropy of the filtered PPG signal) and RMSSD. Here, RMSSD stands for the square root of the mean of the squares of the successive heartbeats intervals; SE stands for sensitivity; and PP stands for positive predictivity. (a) At rest vs. after exercise 1; (b) at rest vs. after exercise 2; (c) at rest vs. after exercise 3. The plus signs refer to subjects measured at rest, while the diamond signs refer to subjects measured after exercise (the simulated heat stress induction).