Test of a processing algorithm for NIR laser diodes based pulse oximetry

Abstract

Pulse oximeters are used for the non-invasive monitoring of arterial blood haemoglobin oxygen saturation. The photoplethysmographic (PPG) signals measured at two specific wavelengths are decomposed into its variable (E-AC) and the constant component (E-DC) for deriving a parameter related to the arterial blood oxygen saturation (So(2)) Previously it has been reported a signal processing algorithm for a near infrared (NIR) laser diodes based transmittance pulse oximetry system. The proposed algorithm permits the numeric separation of the variable and constant parts of the signals for two wavelengths, to derive a quotient (q) proportional to the So(2) levels. The E-DC is obtained by a low pass filtering and E-AC by a pass-band one, followed by a non-linear filtering. The non-linear filter is based on the reduction of the E-AC peak-to-peak frequency distribution for the analyzed time interval (histogram reduction). In the present study is exposed the influence of Bessel filters cut-off frequencies and histogram reduction percentage on q values. The test has been conducted on PPG signals recorded through experimental studies on human healthy volunteers using the NIR laser diodes based transmittance pulse oximetry system. The sources of artefacts and noise in the laser diodes PPG signals are discussed.