Summary
Background: Accurate and early diagnosis of various diseases and pathological conditions require
analysis techniques that can capture time-varying (TV) dynamics. In the pursuit of
promising TV signal processing methods applicable to real-time clinical monitoring
applications, nonstationary spectral techniques are of great significance.
Objectives: We present two potential practical applications of such techniques in quantifying
TV physiological dynamics concealed in photoplethysmography (PPG) signals: early detection
of blood-volume loss using a non-parametric approach known as variable frequency complex
demodulation (VFCDM), and accurate detection of abrupt changes in respiratory rates
using a parametric approach known as combined optimal parameter search and multiple
mode particle filtering (COPS-MPF).
Methods: The VFCDM technique has been tested using ear-PPG signals in two study models: mechanically
ventilated patients undergoing surgery in operating room settings and spontaneously
breathing conscious healthy subjects subjected to lower body negative pressure (LBNP)
in laboratory settings. Extraction of respiratory rates has been tested using COPS-MPF
technique in finger-PPG signals collected from healthy volunteers with abrupt changes
in respiratory rate ranging from 0.1 to 0.4 Hz.
Results: VFCDM method showed promise to detect the blood loss noninvasively in mechanical
ventilated patients well before blood losses become apparent to the physician. In
spontaneously breathing subjects during LBNP experiments, the early detection and
quantification of blood loss was possibleat 40% of LBNP tolerance. COPS-MPF showed
high accuracy in detecting the constant as well as sudden changes in respiratory rates
as compared to other time-invariant methods.
Conclusion: Integration of such robust algorithms into pulse oximeter device may have significant
impact in real-time clinical monitoring and point-of-care healthcare settings.
Keywords
Time-frequency spectral analysis - autoregressive modeling - optimal parameter search
- photoplethysmography - respiratory rate - hypovolemia