An unobtrusive PEP estimation method using hand-to-hand impedance plethysmography

There is currently a wide interest in developing wearable devices for the estimation of cuffless blood pressure (CBP) based on pulse transit time (PTT) measurements. However, to make the measurement more convenient for the user, many devices measure pulse arrival time (PAT), the time difference between the ECG and a distal pulse wave, typically in the hands, using, for example, photoplethysmography (PPG). The drawback of this procedure is that PAT includes not only PTT but also the pre-ejection period (PEP), which can limit the reliability of the measurements. On the other hand, the measurement of the PEP usually involves the placement of sensor elements on the torso by specialized operators, which greatly limits the measurement of this parameter outside of hospital settings. In this work, we present an unobtrusive method for the estimation of PEP using hand-to-hand impedance plethysmography (hh-IPG). To validate the feasibility of the presented approach, hh-IPG and reference impedance cardiography (ICG) signals were recorded sequentially for 2 min from 9 subjects with a wide age range. The results obtained show a strong correlation (R = 0.90) between the PEP estimate obtained with hh-IPG and the reference PEP obtained with ICG, which opens up the possibility of incorporating this measurement in a much more convenient and non-invasive way in wearable devices in the near future.Clinical Relevance- The hh-IPG method offers a non-invasive, stable, and user-friendly alternative to traditional impedance cardiography (ICG) for pre-ejection period (PEP) estimation. Its consistent performance with lower variability supports its application in wearable devices and telemedicine platforms.