Influence of Photoplethysmogram Signal Quality on Pulse Arrival Time during Polysomnography

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. 2023 Feb 16;23(4):2220. doi: 10.3390/s23042220

Algorithm 1 ECG-Guided PPG Signal-Quality Assessment.

1:
procedure Identifying R and T Waves in ECG Signals
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$ECG$ → $R waves$ → $R waves positions$
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$R waves positions$ → $T waves positions$
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procedure Determining the Locations of PPG Pulse Onsets
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$PPG onsets$ = $\min (PPG (R waves positions : T waves positions))$
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$PPG onsets$ → $PPG onsets positions$
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procedure Assessing the Variability in PPG Pulse Amplitudes
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step 1: PPG Envelope Estimation
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for i = 1: length( $PPG onsets positions$ ) - 1 do
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$e_{P P G} (i)$ = $m a x$ ( $P P G$ ( $PPG onsets positions$ (i): $PPG onsets positions$ (i+1)))
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end
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step 2: Absolute Second Derivative of PPG Envelope Estimation
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for i = 1: length( $e_{P P G}$ ) - 2 do
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$| {e^{″}}_{P P G} (i) | = | e_{P P G} (i + 2) - 2 \cdot e_{P P G} (i + 1) + e_{P P G} (i) |$
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end
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step 3: Absolute Second Derivative of PPG Envelope Smoothing
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$o r d e r = 5$
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$| {e^{″}}_{P P G} {(i) |}_{s}$ = median filter( $| {e^{″}}_{P P G} (i) |$ , order)
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step 4: Absolute Second Derivative of PPG Envelope Offsetting
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k-subtraction constant; $N = l e n g t h (| {e^{″}}_{P P G} |_{s})$
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$| {e^{″}}_{P P G} |_{c e n t e r} = {| {e^{″}}_{P P G} |}_{s} (r o u n d (0.25 \cdot N) : r o u n d (0.75 \cdot N))$
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$| {e^{″}}_{P P G} {(i) |}_{o} = | {e^{″}}_{P P G} {(i) |}_{s} - k \cdot m e a n (| {e^{″}}_{P P G} |_{c e n t e r})$
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procedure Identifying Low-Quality PPG Pulse Waves
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thresholds: $θ_{1}$ and $θ_{2}$
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if $(| {e^{″}}_{P P G} |_{o} < θ_{1}) & (e_{P P G} > θ_{2})$ then
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$S Q I = 1$ $-High Quality$
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otherwise
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$S Q I = 0$ $-Low Quality$
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end