A Theoretical Study of Sensor-Artery Interaction in Noninvasive Arterial Pulse Signal Measurement Using Tactile Sensors

Roman Roxas, Erika Osbourne, Dylon Johnson, Josh Wolbert, Adam Harnish, Dieu Nguyen, Camrie Stewart, Linda Vahala and Zhili Hao

Department of Mechanical and Aerospace Engineering, Old Dominion University, Norfolk, VA, USA

This paper presents a theoretical study of the sensor-artery interaction in an arterial pulse signal measurement using a tactile sensor. The sensor-artery interaction is first analyzed for pulse signal transmission into the sensor, from the perspective of elastic wave propagation, and then is examined for relating all the involved parameters to estimated arterial indices, for the purpose of providing guidance on sensor design optimization for improving measurement accuracy and a better interpretation of a measured pulse signal taking into account artery sites and individual variations.    

To assess arterial health, arterial pulse signals are noninvasively measured at the skin surface by a tactile sensor and are then utilized to estimate various arterial indices, which are indicative of arterial wall parameters (e.g., elasticity, viscosity and radius). Therefore, acquiring a pulse signal with minimum distortion holds the key for measurement accuracy in arterial indices. A measured pulse signal results from the sensor-artery interaction in a pulse signal measurement. To date, many experimental studies have established the importance of hold-down pressure exerted on a sensor in acquiring a pulse signal with maximum amplitude. Yet, very few theoretical studies exist on the effect of all the parameters involved in sensor-artery interaction on a measured pulse signal and consequently estimated arterial indices.

Acting as an excitation source, a pulse signal in an artery initiates an elastic wave propagating in the overlying tissue above the artery and is completely reflected back into the tissue, if no sensor is placed above the artery. To noninvasively measure a pulse signal in an artery, a tactile sensor is placed at the skin surface above the artery. By exerting hold-down pressure on the sensor, the pulse signal is transmitted into the sensor at the skin surface. Meanwhile, motion artifacts (e.g., respirations and body shift of a person) also play a role in how the pulse signal is transmitted into the sensor. As such, a measured pulse signal results from the sensor-artery interaction: a combination of the true pulse signal in an artery, the arterial wall, overlying tissue at the artery and the sensor, under the influence of hold-down pressure and motion artifacts. From the perspective of elastic wave propagation, the sensor-artery interaction is first analyzed for the effect of all the involved parameters on pulse signal transmission into the sensor. Afterwards, from the perspective of lumped-element modeling, the sensor-artery interaction is analyzed for the effect of all the involved parameters on estimated arterial indices. The developed theoretical theories on the sensor-artery interaction are further qualitatively validated by some experimental data and the related experimental findings in the literature. The full paper will present the details about the theoretical study of the sensor-artery interaction.