ALLPCB
Background
Arterial stiffness is characterized by hardening and narrowing of arterial walls. Cardiovascular events caused by arterial stiffness, such as myocardial infarction and stroke, remain leading causes of death worldwide. Quantitative assessment of arterial stiffness has a long history. Pulse wave velocity (PWV) is a parameter proportional to vascular elastic modulus (or stiffness level) and is widely considered an effective indicator of arterial stiffness. PWV is typically determined by measuring the pulse transit time (PTT) between two locations separated by a distance S on the same artery (two-point method), i.e., PWV = S / PTT. Clinical PWV measures include brachial-ankle PWV (baPWV) and carotid-femoral PWV (cfPWV), both obtained using the two-point method.
Such measurements generally require skilled operators and expensive, bulky medical equipment (for example, Omron Colin automatic arterial stiffness detector, cost about $60,000), partly due to strict synchronization requirements for two sensors. In addition, hospital PWV measurements are often brief, which may be insufficient for accurate arterial stiffness diagnosis. Therefore, there is a need for wearable devices that provide continuous, noninvasive, and accurate PWV monitoring for arterial stiffness assessment, which would be especially valuable in areas with limited equipment and specialist resources.
Flexible pressure sensors convert mechanical stimuli into electrical signals and are widely used for continuous arterial pulse detection because they can be conformally laminated to skin for long-term monitoring. Although substantial effort has been made to measure PWV, existing flexible pressure sensor–based PWV acquisition still relies on the two-point method, where two sensors simultaneously detect pulse waves at different arterial locations (mainly joints). This approach has two drawbacks. First, body motion severely affects pulse detection by joint-mounted wearable sensors. For example, radial artery pulse detection at the wrist is common, but signals often become undetectable when the wrist is flexed. Second, synchronizing two electrical recording channels adds challenges to circuit and algorithm design. An alternative is a single flexible pressure sensor to develop single-point PWV monitoring. However, building a wearable system based on a single flexible sensor is challenging: it requires highly stable and reliable pulse-wave detection and an effective method to compute PWV from a single sensor signal.
Highlights
- This work reports a single-point strategy based on stable fingertip pulse monitoring, using a flexible ion-electronic pressure sensor to measure heart-to-fingertip PWV (hfPWV).
- The ion-electronic sensor demonstrates high pressure resolution on the order of 0.1 Pa across a wide linear range, allowing capture of characteristic peaks in fingertip pulse waves.
- An arterial stiffness assessment model based on hfPWV was established. Its accuracy is comparable to existing clinical standards and was validated clinically.
