Table 3 Summary of features extracted from the ECG.

From: Features from the photoplethysmogram and the electrocardiogram for estimating changes in blood pressure

Feature notation and publication

Description or formula

Hjorth mobility28

Estimate of the signal’s mean frequency (Equation SI 1)

Hjorth complexity28

Estimate of the signal’s bandwidth (Equation SI 2)

Fractal dimension28

Computed using Higuchi’s algorithm61 with \(k_{max} = 17\)

Shannon entropy (SE)28

Uncertainty of information content based on probability distribution (Equation SI 3)

Approximate entropy (approxEnt) *

Quantifies regularities of signal

Sample entropy (sampEnt) *

approxEnt computed without self comparisons

Multi-level sample entropy (MSE) *

Course approximations of sample entropy, computed at scales 2, 4, 6, 8

  1. * Indicates features that, to the authors’ knowledge, have not been previously implemented for BP estimation. Full details of the algorithms and equations used for computing each feature can be found in Supplementary Information SI: 2.
Back to article page