An easy-to-use hand-to-hand impedance-based sensor to obtain carotid pulse arrival time

Abstract

Pulse arrival times (PATs) are time intervals between the electrocardiogram (ECG) and an arterial pulse wave (APW) widely used to obtain cuffless blood pressure (BP). Although some distal APWs can be easily measured using, for example, a photoplethysmography (PPG) sensor on a finger, proximal APWs, such as the one of the carotid in the neck, are much more difficult to obtain for unskilled users. To overcome this, we propose an impedance-based sensor using only two electrodes in contact with each upper extremity (one to inject current and one to measure voltage at each hand or wrist), which can measure both ECG and an APW [an impedance plethysmogram, (IPG)] to obtain the PAT. Since the injected current flows from hand to hand across the upper torso, we hypothesize that the measured IPG should be sensitive to the arrival of the APW near the heart and, therefore, that the obtained PAT could be used as a surrogate of a proximal PAT even when measured on the hands. We have verified this by comparing the hand-to-hand impedance PAT obtained with the sensor with a gold-standard proximal PAT obtained in the carotid by tonometry in a cohort of 84 volunteers aged 20-61 years, showing a correlation of r=0.90 between the two. These results support the feasibility of future inclusion of these proximal PAT measurements in easy-to-use devices to obtain cuffless BP or other cardiovascular information with improved performance by nonspecialist users outside clinical settings.