This paper presents three technical issues associated with arterial pulse signal measurements using a microfluidic-based tactile sensor: motion artifact, overlying tissue at an artery and inter-subject variation. Arising from the sensor-artery interaction upon hold-down pressure on the sensor, a measured pulse signal is a combination of the sensor design, hold-down pressure, overlying tissue at an artery, the arterial wall and the true pulse signal in the artery. Meanwhile, motion artifact causes change in the sensor-artery interaction and also plays a non-negligible role in a measured pulse signal. The influence of motion artifact on a measured pulse signal can be reduced by a sensor with high stiffness. To obtain a pulse signal at near-zero transmural pressure with reasonable accuracy, matching the sensor design with the overlying tissue at an artery is critical for achieving good conformity of the sensor to the artery (for signal transmission) with minimal distortion of the true one in the artery. For simplicity, a uniform layer is utilized to adjust the sensor design. While a uniform layer added to a sensor improves its conformity with the radial artery (RA) embedded deep under the skin, a uniform layer is also needed as a cushion to reduce suppression of the true pulse signal at the superficial temporal artery (STA) near the skin. Due to inter-subject variation (i.e, overlying tissue and artery size), the absolute values of arterial indices derived from a measured pulse signal at the same artery are not comparable between subjects. Post-exercise recovery of arterial indices derived from measured pulse signals is suggested to serve as a better assessment of the cardiovascular (CV) system.

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