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

Photoplethysmography (PPG) involves measuringan optic signal related to the arterial volumetric pulsations ofblood, and has great potential in clinical applications due to itssimplicity and noninvasiveness. In the present study, we aimedto verify if the induced vasodilation and increase in terminalblood supply by local heating stimulation (LH) could help toimprove the correlation of harmonic components betweenradial BP and finger PPG waveforms. Trials were performedon male healthy volunteers (n=17) aged 25-31 years. LH wasperformed by placing a waterbag filled with 35oC water aroundthe lower arm. BP and PPG spectra were calculated from theaverages of all of the pulses during the entire measurementperiod for the amplitude proportion. For the first threeharmonics, the correlation coefficients for the regression linesbetween BP and PPG waveforms were significantly increasedfollowing LH. The present result illustrated improved BP-PPGcorrelations of harmonic components following LH. It impliesthat an appropriate environmental temperature could improvethe reconstruction of the BP waveform from noninvasive PPGmeasurements. The present frequency-domain analysis methodcould thus provide an alternative and more convenient methodfor acquiring the BP waveform, and hence bring new studydirections for further applications such as in evaluatingwhole-body responses of the microcirculatory blood supply tovarious treatment strategies, the augmentation indexcalculation, and telemedicine.