Physiol Meas. 2021 Jun 10. doi: 10.1088/1361-6579/ac0a34. Online ahead of print.
ABSTRACT
OBJECTIVE: Filtering can change the timing of pulse feature points on photoplethysmography (PPG) signals. We aim to quantitatively investigate the effect of measurement site and type of pulse feature on the filtering-induced time shift (TS).
APPROACH: 60-second PPG signals were measured from six body sites [finger, wrist under (volar), wrist upper (dorsal), earlobe, and forehead] of 36 healthy adults. Using infinite impulse response digital filters, PPG signals were prefiltered (band-pass, pass and stop bands: >0.5Hz and <0.2Hz for high-pass filter, <20Hz and >30Hz for low-pass filter) then filtered (low-pass, pass and stop bands: <3Hz and >5Hz). Four pulse features (peak, valley, maximal first derivative, and maximal second derivative) were extracted. For each subject, overall TS and intra-subject TS variability in feature points were calculated as the mean and standard deviation of TS between prefiltered and filtered PPG signals in 50 cardiac cycles. Statistical test was performed to investigate the effect of measurement site and type of pulse feature on overall TS and intra-subject TS variability.
RESULTS: Measurement site, type of pulse feature, and their interaction had significant impacts on the overall TS and intra-subject TS variability (p<0.001 for all). Valley and maximal second derivative showed higher overall TS than peak and maximal first derivative. Finger has higher overall TS and lower intra-subject TS variability than other measurement sites.
SIGNIFICANCE: Measurement site and type of pulse feature can significantly influence the timing of feature point on filtered PPG signals. Filtering parameters should be quoted to support the reproducibility of PPG-related studies.
PMID:34111855 | DOI:10.1088/1361-6579/ac0a34
