Fig. 2

Typical example of PPG waveform measured in the upper arm. Waveform shown in (a) was recorded before application of the capsaicin patch, whereas that in (c) was recorded at about 15-th minute of the patch application. Black curves in (a) and (c) show synchronously recorded ECG. Thick lines in (b) and (d) show the shape of the signal after averaging over 20 cardiac cycles