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pulseenvelopes

Estimates lower and upper PPG envelopes using pulse-anchored interpolation.

Syntax

function [lowerEnvelope, upperEnvelope] = pulseenvelopes(ppg, fs, nD, varargin)

Description

LOWERENVELOPE = PULSEENVELOPES(PPG, FS, ND) estimates the lower envelope of a photoplethysmographic (PPG) signal by selecting one local minimum per pulse within a window before each pulse detection time ND and interpolating these anchor points. PPG is a numeric vector, FS is the sampling rate in Hz (positive scalar), and ND contains pulse detection times in seconds (typically returned by pulsedetection). LOWERENVELOPE is a column vector with the same length as PPG.

[LOWERENVELOPE, UPPERENVELOPE] = PULSEENVELOPES(PPG, FS, ND) also returns the upper envelope by selecting one local maximum per pulse within a window after each detection and interpolating these anchor points.

[...] = PULSEENVELOPES(..., 'Name', Value) specifies additional parameters using name-value pairs: - 'WindowA' - Window width in seconds for searching the upper envelope after each detection (default: 400e-3) - 'WindowB' - Window width in seconds for searching the lower envelope before each detection (default: 300e-3)

Source Code

View source code

Examples

% Pulse detection on the LPD-filtered signal
[b, delay] = lpdfilter(fs, 8, 'PassFreq', 7.8, 'Order', 100);
dppg = filter(b, 1, ppg);
dppg = [dppg(delay+1:end); zeros(delay, 1)];
nD = pulsedetection(dppg, fs);

% Estimate envelopes
[lowerEnv, upperEnv] = pulseenvelopes(ppg, fs, nD);

t = (0:length(ppg)-1)/fs;
figure;
plot(t, ppg, 'k'); hold on;
plot(t, lowerEnv, 'b', 'LineWidth', 1.5);
plot(t, upperEnv, 'r', 'LineWidth', 1.5);
legend('PPG', 'Lower envelope', 'Upper envelope');
xlabel('Time (s)'); ylabel('Amplitude');

View detailed example

See Also

Module: PPG | Last Updated: 2026-01-27