1. A method for determining blood pressure for a subject using a sphygmomanometer having a cuff and a pressure sensor integrated therein, comprising: measuring an oscillometric cuff pressure waveform of the subject using the sphygmomanometer, where the oscillometric cuff pressure waveform indicates the time evolution of the pressure inside the cuff during inflation and deflation of the cuff; measuring volume of air pumped into and out of the cuff during inflation and deflation of the cuff; determining the cross-sectional area waveform of the artery underneath the cuff using the volume of air pumped into and out of the cuff and the measured oscillometric cuff pressure waveform; determining an envelope of the cross-sectional area waveform as a function of the measured oscillometric cuff pressure waveform; and determining, by the computer processor, blood pressure for the subject using the envelope.