Effect of Filtering on Pulse Wave Transit Time Measured by Photoplethysmography

The waveform of a photoplethysmography
$(PPG)$
signal depends on the measurement site and individual physiological conditions. Pulse transition time
$(PTT)$
is an important physiological parameter for blood pressure estimation.
$PTT$
can be derived from electrocardiogram
$(ECG)$
and
$PPG$
waveform features. Filtering can change
$PPG$
signal waveform and the timing of
$PPG$
feature points. We aim to quantitatively investigate the filtering-induced
$PTT$
changes at different measure sites in healthy subjects of different ages. The
$ECG$
, and fingertip and earlobe
$PPG$
signals were recorded simultaneously from 58 young
$(age < =50)$
and 40 old
$(age > 50)$
healthy adults. The
$PPG$
signals were preprocessed and then filtered (low-pass, pass and stop bands:
$< 3 \ Hz \ and > 5 \ Hz$
. The
$PTT$
difference between the preprocessed and filtered
$PPG$
signals was calculated and analyzed using analysis of variance (ANOVA) and paired tests. The results show significant effect of age and measurement site on filtering-induced
$PTT$
difference and its relative difference
$p < 0.05$
for all). We conclude that the physiological factor including measurement site and age should be considered in PTT-based blood pressure estimation methods.