A method is provided for determining pulse transit time of a subject as a function of blood pressure. The method includes: measuring a proximal waveform indicative of the arterial pulse at a proximal site of the subject； measuring a distal waveform indicative of the arterial pulse at a distal site of the subject； defining a relationship between the proximal waveform and the distal waveform in terms of unknown parameters of a nonlinear model； determining the unknown parameters of the nonlinear model from the measured proximal waveform and the measured distal waveform； and determining pulse transit time for the subject as a function of blood pressure from the parameters of the nonlinear model. The nonlinear model can account for arterial compliance and peripheral wave reflection, where the arterial compliance depends on blood pressure.
