Correlation of Harmonic Components between the Blood Pressure and Photoplethysmography Waveforms Following Local-Heating Stimulation

Photoplethysmography (PPG) involves measuring an optic signal related to the arterial volumetric pulsations of blood, and has great potential in clinical applications due to its simplicity and noninvasiveness. In the present study, we aimed to verify if the induced vasodilation and increase in terminal blood supply by local heating stimulation (LH) could help to improve the correlation of harmonic components between radial BP and finger PPG waveforms. Trials were performed on male healthy volunteers (n=17) aged 25-31 years. LH was performed by placing a waterbag filled with 35 o C water around the lower arm. BP and PPG spectra were calculated from the averages of all of the pulses during the entire measurement period for the amplitude proportion. For the first three harmonics, the correlation coefficients for the regression lines between BP and PPG waveforms were significantly increased following LH. The present result illustrated improved BP-PPG correlations of harmonic components following LH. It implies that an appropriate environmental temperature could improve the reconstruction of the BP waveform from noninvasive PPG measurements. The present frequency-domain analysis method could thus provide an alternative and more convenient method for acquiring the BP waveform, and hence bring new study directions for further applications such as in evaluating whole-body responses of the microcirculatory blood supply to various treatment strategies, the augmentation index calculation, and telemedicine.