Pulse wave response characteristics for thickness and hardness of the cover layer in pulse sensors to measure radial artery pulse

Abstract

BackgroundPiezo-resistive pressure sensors are widely used for measuring pulse waves of the radial artery. Pulse sensors are generally fabricated with a cover layer because pressure sensors without a cover layer are fragile when they come into direct contact with the skin near the radial artery. However, no study has evaluated the dynamic pulse wave response of pulse sensors depending on the thickness and hardness of the cover layer. This study analyzed the dynamic pulse wave response according to the thickness and hardness of the cover layer and suggests an appropriate thickness and hardness for the design of pulse sensors with semiconductor device-based pressure sensors.MethodsPulse sensors with 6 different cover layers with various thicknesses (0.8 mm, 1 mm, 2 mm) and hardnesses (Shore type A; 30, 43, 49, 71) were fabricated. Experiments for evaluating the dynamic pulse responses of the fabricated sensors were performed using a pulse simulator to transmit the same pulse wave to each of the sensors. To evaluate the dynamic responses of the fabricated pulse sensors, experiments with the pulse sensors were conducted using a simulator that artificially generated a constant pulse wave. The pulse wave simulator consisted of a motorized cam device that generated the artificial radial pulse waveform by adjusting the stroke of the cylindrical air pump and an air tube that conveyed the pulse to the artificial wrist.ResultsThe amplitude of the measured pulse pressure decreased with increasing thickness and hardness of the cover layer. Normalized waveform analysis showed that the thickness rather than the hardness of the cover layer contributed more to waveform distortion. Analysis of the channel distribution of the pulse sensor with respect to the applied constant dynamic pressure showed that the material of the cover layer had a large effect.ConclusionsIn this study, in-line array pulse sensors with various cover layers were fabricated, the dynamic pulse wave responses according to the thickness and the hardness of the cover layer were analyzed, and an appropriate thickness and hardness for the cover layer were suggested. The dynamic pulse wave responses of pulse sensors revealed in this study will contribute to the fabrication of improved pulse sensors and pulse wave analyses.

Accuracy Evaluation of Robotic Tonometry Pulse Sensor System Based on Radial Artery Pulse Wave Simulator

“…Peng and Lu [26] introduced a flexible 5 x 5 capacitive pressure sensor array for determining pulse patterns. Jun et al [7] used a circular array sensor with 7 independent pressure sensors to estimate the direction of the radial artery and reported a study on the development of a 7-channel pulse sensor array [18]. These studies emphasize the importance of locating the maximum pulse amplitude on the radial artery.…”

“…Main hardware components of a robotic applanation tonometry pulse sensor system and movement axis definitions for robot manipulation and the center position of the cross line, one can easily mark the approximate location of the radial artery pulse. A piezo-resistive pulse sensor used to measure the radial pulse wave was fabricated using an arrangement of 6 in-line sensor cells (C33, EPCOS, Germany), and the surface of the pulse sensor as coated with silicone to prevent fracturing of the sensor cells due to contact with the wrist skin [18].…”

A Transfer Function Model Development for Reconstructing Radial Pulse Pressure Waveforms Using Non-Invasively Measured Pulses by a Robotic Tonometry System

“…The in-line arrangement ensures a sufficiently large sensing area for pulse measurements. The surface of the pulse sensor is coated with silicone to prevent the sensor cells from fracturing by the contact force with the wrist skin [ 18 ]. The RTS employs a 2-axis inclinometer (SCA100T-D01, Murata, Manufacture Co., Shinjuku City, Japan) to measure the tilt of the pulse sensor relative to the skin surface along the gravitational axis.…”

A Combined Photoplethysmography and Force Sensor Prototype for Improved Pulse Waveform Analysis

“…In our work, the pressure sensor elements are embedded in a soft silicone rubber (Ecoflex 00-10, Smooth-On) with a thickness of 1.55 mm, the same as the height of the PPG element. The soft silicone rubber was chosen because attenuation and distortion of pressure waves are typically reduced in softer materials [17]. The surface layer of the sensor is covered by the same silicone rubber mixed with graphite powder (Fig.…”