Calibration for massive physiological signal collection in hospital --
Sawtooth artifact in beat-to-beat pulse transit time measured from patient
Objective: Calibration is one of the most important initial steps in any
signal acquisition and experiment. It is however less discussed when massively
collecting physiological signals in clinical setting. Here we test an
off-the-shelf integrated Photoplethysmography (PPG) and electrocardiogram (ECG)
monitoring device for its ability to yield a stable Pulse transit time (PTT)
signal. Method: This is a retrospective clinical study using two databases: one
containing 35 subjects who underwent laparoscopic cholecystectomy, another
containing 22 subjects who underwent spontaneous breathing test in the
intensive care unit. All data sets include recordings of PPG and ECG using a
commonly deployed patient monitor. We calculated the PTT signal offline.
Result: We identify a novel constant oscillatory pattern in the PTT signal and
identify this pattern as the sawtooth artifact. We propose an approach based on
the de-shape method to visualize, quantify and validate this sawtooth artifact.
Conclusion: The PTT and ECG signals not designed for the PTT evaluation may
contain unwanted artifacts. The PTT signal should be calibrated before analysis
to avoid erroneous interpretation of its physiological meaning.