The influence of light noise on the error in estimating the level of fractional blood saturation using a multi-wave pulse oximeter

In connection with the development and implementation of modern optoelectronic technologies in various branches of medicine, it is important to ensure high-quality functioning of devices for non-invasive spectrophotometric diagnostics of physiological parameters under the infl uence of such specific external factors as light noise of natural and artificial light sources. A mathematical model of fixed-frequency light noise is presented and it is shown that such noise is an additive interference in relation to the useful photoplethysmographic signal of the pulse oximeter channel. It is shown that when using photoplethysmographic methods for studying oxygen status parameters, the intensity of optical radiation transmitted through biological tissue depends on the level of arterial blood oxygen saturation. A mathematical model of the photoplethysmographic signal has been developed that allows taking into account the pulse wave parameters – the frequencies of the first and second harmonics of arterial blood pulsation, respiratory contractions. The light noise level is normalized to the photoplethysmographic signal level using the signal-to-noise ratio. It has been found that at a signal-to-noise ratio of 10; 5; 1, the ratios of the constant and variable components of the photoplethysmographic signal change on average by 6.7, 11.4, 15.7 %, respectively, compared to the case of no additive interference. The effect of light noise of various levels on the quality of fractional blood saturation level assessment was investigated and it was found that with a signal/noise ratio of 10; 5; 1, the relative error of this assessment is 3.676; 6.115; 8.077 %, respectively. A physical experiment was conducted with the participation of 30 subjects to determine the effect of illumination on the quality of fractional blood saturation level assessment by a multiwave pulse oximeter. The experimental data confirmed the results of model studies for a signal/noise ratio of 10 and 5. The results obtained can be used in the design and development of noninvasive spectrophotometric diagnostic devices and assessment of their performance under conditions of destabilizing factors.

mathematical model, photoplethysmographic signal, light noise, biological tissue, fractional blood saturation level, fast Fourier transform, multiwave pulse oximeter