Dynamic Spectrum for noninvasive blood component analysis and its advances

Noninvasive blood component analysis by spectroscopy has broad prospects that based on Dynamic Spectrum (DS) can effectively suppress the influences of individual differences (such as skin, muscle, fat) and the variations of measurement conditions, which shows its potential in the clinical applications. The purpose of this article is to review the starting point and the advances of DS, to assess the current situation of the field and to explore future directions. The principle of DS and the error sources of noninvasive blood component analysis were introduced. An overview of the six stages of noninvasive blood component analysis, including sensing principle, acquisition methods of spectral photoplethysmography (photoplethysmography signal at multiple wavelengths) signals, spectral photoplethysmography (SPPG) preprocessing, DS extraction methods from SPPG, the quality evaluation for DS and modeling methods, was presented. Finally, the existing issues of DS are discussed and the future directions are predicted.