This is what I don't understand, but maybe it is because I am a scientist and not an engineer. An SpO2 monitor simply bounces red light (and possibly some other wavelengths) off of tissue and measures the returning light. Since the more oxygen is bound to haemoglobin, the redder blood gets, it is a really simple measurement - even trivial. I have built many for research purposes in my lab. I suppose these patents could be about calibration, optimisation, miniaturisation, or signal processing (e.g., heart rate detection), but fundamentally it is just about bouncing red light off of blood and measuring the return signal. I hope this wasn't the Patent Office running amok handing out patents for ideas that are obvious.