A method 100 and apparatus for determining SpO2, of a subject from an optical measurement is disclosed herein. In a described embodiment, the method 100 includes obtaining a PPG(red) signal and a PPG(IR) signal at steps 102 and 104, and pairing the PPG(red) and PPG(IR) signals at step 106 in which an amplitude of each cardiac rhythm cycle of the first signal is aligned to an amplitude of a respective cardiac rhythm cycle of the second signal to form a plurality of paired windows. At step 108, the method further includes, for each paired window, calculating values of a ratio R from the paired first and second signals and based on the calculated R values, binning the calculated R values into predetermined frequency bins at step 110. At steps 112 and 114, at least one of the frequency bins is selected to derive a revised ratio, Rrev and at step 116, SpO2 is derived from the revised ratio Rrev. A zoning schema for deriving SpO2 is also disclosed.本文中揭露一種用以自光學測量測定受測者之SpO2的方法100及裝置。在所描述實施例中,方法100包括:在步驟102及104中獲得一PPG(red)信號及一PPG(IR)信號;以及在步驟106中使該PPG(red)信號及該PPG(IR)信號成對,其中第一信號之每一心節律週期的振幅與第二信號之相應的心節律週期的振幅對準來形成多個成對窗口。在步驟108中,該方法進一步包括,針對每一成對窗口,根據成對的第一信號及第二信號計算比率R的值,並基於所計算出的R值,在步驟110中將所計算出的該等R值分群至預定的頻率槽中。在步驟112及114中,其中至少一頻率槽被選來導出一校訂比率Rrev,且在步驟116中,自該校訂比率Rrev導出SpO2。用以導出SpO2之分區模式亦被揭露。100‧‧‧方法102~116‧‧‧步驟
