Cuffless Evaluation of Arterial Pressure Waveform using Flexible Force Sensor: A Proof of Principle

In recent years, thin, flexible force sensors have appeared and been widely used as pressure sensors. These sensing elements are now emerged into robotics, sport, and instrumentation applications due to their thin and flexible construction with the ability to operate at low pressures. However, their potential applications in medical instrumentation as a noninvasive force/pressure sensing element has not been explored widely. In this work, we investigated the performance of a commercial flexible force sensing resistor (FSR) to assess arterial pressure waveform (in units of mmHg) from the captured skin surface pressure, with a one-time calibration. Extensive in-vitro experimental work on this approach was conducted using a fully automated arterial flow phantom. The phantom was specially designed to resemble the anatomy of the human neck, comparing a carotid vessel encompassed with a tissue-like silicone material. The pulsatile flow of blood mimicking fluid with programmable flow rate and pulse rate provided an in-vitro system simulating blood circulation through the human carotid artery. A custom hand-held probe and signal acquisition hardware was developed to acquire the pulsatile force acting on the tissue surface due to the transmural pressure. A calibration model was developed to estimate the morphology of true transmural pressure, using a clinical-grade catheter inserted into the phantom as the reference standard. Following the one-time calibration, FSR sensor continuously captured arterial pressure waveform with a root-mean-square-error less than 8 mmHg. Studies were conducted under various simulated test conditions and evaluated the accuracy of pressure wave assessment. The effect of operator dependent hold-down pressure on the sensing performance of FSR was also investigated. Overall, the proposed approach provided a cost-effective system for continuous assessment of arterial pressure waveform with potential applications in unobtrusive, long-term monitors.