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

Abstract

Pulse detection has in recent years received extensive attention in physiological health monitoring, and continuous blood pressure estimation models based on pulse waveform analysis have shown great promises. Two widely used technologies for noninvasive detection of the pulse waveform are photoplethysmography and tonometry. Although the signals from PPG and tonometry are rooted in different physiological mechanisms, the technologies are typically used separately. The simplistic approach of estimating cardiovascular responses based on single sensor sources is discorrelated with the complexity of the human body. To acknowledge this, we have developed a low-cost, low-power sensor prototype combining PPG and force-sensing capabilities. The proposed solution is able to accurately detect the pulse waveform, both optically and tactually, in addition to estimating the sensor interface pressure. We hypothesize that the combined solution can be used to ameliorate one or more of the challenges associated with the separate technologies in physiological monitoring, and thus potentially give continuous pulse waveform based blood pressure estimation models valuable additional inputs, ultimately leading to increased estimation accuracies and measurement confidence.

Wrist ballistocardiography and invasively recorded blood pressure in healthy volunteers during reclining bike exercise

“…A wearable tonometer integrated in the same wristband was placed above the radial artery immediately below the wrist of participants' dominant hand. The device consisted of a linear array of silicone polymer-covered MEMS pressure sensors (BMP390, Bosch Sensortec Gmbh, Germany) to increase the viable placement area (Solberg et al, 2019).…”

Embedded Soft Inductive Sensors to Measure Arterial Expansion of Tubular Diameters in Vascular Phantoms

“…This is tuned with an adjustment screw on the laser to hit the target regardless of the different diameters of the tubes. γ is calculated using (7) and a caliper measurement of the diameter of the tube.…”

“…However, in cases where the interaction between the model vessel and the surrounding tissue is of interest, this is not feasible. In the case of radial tonometry, a technology that is seeing interest for applications in wearable blood pressure monitoring [7]- [9], the interaction between the vessel wall, the underlying bone, and the tissue between the vessel and skin surface are all important. This can be achieved by placing the vessel model inside tissue-mimicking material, obstructing view of the tube [10].…”