Reliability of the power spectral density for photoplethysmography under a pulsed magnetic field stimulus

We have compared the aging index of the second derivatives of photoplethysmography (PPG) with the power spectral density (PSD) from PPG signals to investigate the effect of a strong pulsed electromagnetic field (PEMF) on the improvement of vascularization in the capillary vessels of the finger. The PEMF stimulator was composed of an elliptical coil of 10 turns and 12 cm × 5 cm, and its maximum field and transition time were 0.48 T and 0.102 ms, respectively. It is not easy to analyze the stimulus effect of blood vessel from raw signals of PPG, and aging index of vascularization from the second derivatives of PPG. A PSD analysis in the frequency domain was introduced to reduce artifacts due to change in the posture of the subjects, the environment, acoustic noise, etc. For ages in the 50s, the PSD analysis before and after PEMF stimulus was rather more reliable than the second derivatives of the PPG.