Apparatus, systems and methods are provided for using the PG waveform to determine peripheral venous and arterial saturations. Generally, saturations are determined by isolating an indicator of venous or arterial blood volume in each of a plurality of PG waveforms and using the isolated indicators to determine saturation in the corresponding region of the vasculature. Indicators may include respiratory induced variations of AC and/or DC components of the PG waveforms, peaks of the PG waveforms, troughs of the PG waveforms, venous pulsations of the PG waveforms, etc. Indicators may further be isolated in either the time or frequency domain. The isolated indicators may advantageously be normalized, e.g., based on a baseline of the PG waveform or a derivative thereof.
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