Smartphone Pulse Transit Time Sensing
Seismo is a smartphone application that uses seismocardiography (SCG) and photoplethysmography (PPG) to compute pulse transit time. See our paper for more details.
Pulse transit time (PTT) is inversely correlated with blood pressure, making it a promising technique for non-invasive, continuous estimation of blood pressure. Seismo measures PTT using a smartphone's built-in sensors. The accelerometer is used to detect the physical vibration of the heart when the phone is placed on the user's chest; from this signal, called seismocardiography (SCG), the time of the aortic valve opening can be detected. Simultaneously, the camera and flash are used to illuminate the capillaries in the fingertip, enabling detection of the pulse's arrival at the finger. The difference in timing between the pulse origin at the heart and its arrival at the fingertip is the PTT. After an individualized calibration, the PTT reading can be converted to an approximate blood pressure reading.