Apparatus, systems and methods are provided for analyzing relative compliance in the peripheral vasculature that generally involve generating a plethysmograph (PG) signal, generating one or more pressure waveforms and comparing the pressure waveform(s) relative to the PG signal to determine compliance indexes associated particular regions of the vasculature. A relative compliance ratio may also be determined by comparing arterial and venous relative compliance indexes. Apparatus, systems and methods are also provided for analyzing a PG waveform that generally involve generating a plethysmograph (PG) signal and comparing amplitude modulation of the PG signal relative to baseline modulation of the PG signal to estimate a relationship between left ventricular end diastolic pressure and stroke volume. The estimated relationship may account for a phase offset for the time between when changes in venous return affect left ventricular end diastolic pressure and stroke volume.
