What is disclosed is a system and method for determining a pulse transit time for a subject. In one embodiment, the system comprises a handheld wireless cellular device configured with a sensor to acquire an electrocardiogram (ECG) signal from the subject and a photodetector generating a time-series signal in response to continuously sensing a reflection of source light off a region of exposed skin of the subject where a photoplethysmographic (PPG) signal can be detected by the photodetector. In one embodiment, the time-series signal is a PPG signal. In another embodiment, the time-series signal is processed to extract a PPG signal. A temporally overlapping segment of the PPG and ECG signals is analyzed to obtain a pulse transit time between a reference point on the PPG signal and a reference point on the ECG signal. The pulse transit time is used to assess pathologic conditions such as peripheral vascular disease.
