By Crystal Zhu
Hypertension, often called the “silent killer,” affects nearly half of all adults in the United States, according to the American Heart Association. Globally, high blood pressure (BP) contributes to an estimated 7.5 million deaths each year. Yet despite its prevalence, most people only check their blood pressure a few times a year at a clinic, if at all, leaving many cases undetected until serious complications arise. Engineers are working to change that by rethinking how we monitor this vital sign. From light-based photoplethysmography (PPG) to bioimpedance and capacitive sensors, new wearable devices promise to make continuous, noninvasive blood pressure (cNIBP) monitoring as effortless as wearing a smartwatch. To catch cardiovascular disease before it strikes, healthcare must move beyond the clinical blood pressure cuff toward continuous, wearable BP monitoring that empowers people to track and manage their health at home.
In hospitals, the gold standard for measuring BP is an invasive arterial line (IAL), a slender catheter inserted directly into an artery and connected to a pressure transducer. It captures every pulse with pinpoint accuracy, so it is an essential tool for patients in intensive care. But this method is not one you’d want to take home since it’s uncomfortable, risky, and impractical outside a hospital setting.
For decades, the inflatable arm cuff has been the noninvasive alternative. It’s reliable for single intermittent readings but far from perfect for long-term use, as the cuff only provides a snapshot—a single measurement in time. Hypertension, however, doesn’t stay still. Blood pressure fluctuates throughout the day, rising with stress, activity, or posture, so a few isolated readings cannot capture the full picture.
This gap between invasive precision and noninvasive convenience has driven engineers to develop wearable systems that capture BP continuously without needles or cuffs. These devices rely on detecting secondary signals that correlate with BP: changes in light absorption, electrical impedance, or even minute displacements of the skin. The challenge lies in translating these signals into accurate BP readings that can match the gold standard of an arterial line. Over the past two decades, innovations in biomedical sensing, signal processing, and machine learning have brought this vision closer to reality.
The first major leap toward cNIBP came from photoplethysmography (PPG), a technique that shines light into the skin and measures how much is reflected back, a principle already used in pulse oximeters and smartwatches. Blood absorbs light differently depending on its volume, so the PPG waveform mirrors the pulsations of arterial blood flow.
Researchers soon realized that PPG could be used not only to measure heart rate but also to infer pulse transit time (PTT): the time it takes a pulse wave to travel between two points in the vascular system. Because PTT shortens as arteries stiffen, engineers began using it as a surrogate for BP monitoring. Still, light can be fickle. PPG signals are sensitive to skin tone, motion, and ambient light. Engineers tackled these challenges by turning to multi-wavelength photoplethysmography (MWPPG), which uses multiple colors of light to penetrate the skin at different depths and separate noise from vascular motion, producing a clearer view of blood flow.
While light-based systems illuminated the way, others looked to electricity for answers. Bioimpedance sensing sends a tiny alternating current through the skin and measures how easily it passes through. Blood, being a conductor, changes the tissue’s electrical impedance as it pulses through arteries, revealing valuable information about circulation and blood pressure.
But the human body isn’t static; every movement can distort the signal. So modern bioimpedance devices incorporate contact pressure sensors that maintain consistent skin-electrode coupling. In a 2023 study, Namkoong et al. demonstrated this approach with a dual-channel bioimpedance system, shown in Figure 1, in which electrodes placed along the radial artery capture impedance changes while monitoring contact pressure in real time. By stabilizing the interface between sensor and skin, their design enables continuous readings without light or cuffs, making bioimpedance especially promising for long-term wear and exercise monitoring.
Figure 1: Contact pressure-guided continuous BP measuring device. a) 2-channel bioimpedance measurements are taken along the radial artery in the wrist. b) The arterial blood volume changes with increasing contact pressure. Figure adapted from Namkoong et al. 2023.
The newest frontier in cNIBP technology uses capacitive sensing, a method that detects the microscopic movements of the skin as the artery expands and contracts with each heartbeat. Unlike optical or electrical systems, capacitive sensors track arterial wall motion directly, offering high sensitivity and opening up possibilities for continuous monitoring in patients like newborns or elderly individuals with fragile skin.
Recent clinical research has shown that capacitive sensors combined with advanced signal processing and machine learning can achieve accuracy comparable to invasive arterial measurements, demonstrating that cuffless monitoring can be both precise and gentle. Though still emerging, this same sensing principle could one day help millions monitor cardiovascular health from home.
Each of these sensing methods tells a piece of the same story: engineers are redefining what it means to monitor health. By turning blood pressure from an occasional measurement into a continuous stream of information, we can transform how doctors diagnose, how patients manage, and how society prevents disease.
But for that vision to work, accuracy isn’t enough. These devices must also be comfortable, affordable, and accessible. They must adapt to different bodies, lifestyles, and skin tones. They must protect privacy while integrating seamlessly into telehealth systems. The tools we build today will decide whether blood pressure remains a silent killer or becomes a silent guardian—a constant, unobtrusive reminder that our
hearts are still beating as they should. The next time you glance at your smartwatch or fitness tracker, imagine a future where it quietly keeps you one step ahead of heart disease. The future of cardiovascular care will not wait for clinics. It will reach millions in their homes, on their wrists, and through the devices they already use. And it will be engineered.
References:
American Heart Association. (2025). What is high blood pressure? https://www.heart.org/en/health-topics/high-blood-pressure/the-facts-about-high-blood-pressure
Healthline Editorial Team. (2025). What percent of deaths are due to hypertension (high blood pressure)? Healthline. https://www.healthline.com/health/high-blood-pressure-hypertension/percent-of-deaths-due-to-hy pertension
Liu, J., Yan, B. P., Zhang, Y.-T., Ding, X.-R., Su, P., & Zhao, N. (2019). Multi-Wavelength Photoplethysmography Enabling Continuous Blood Pressure Measurement With Compact Wearable Electronics. IEEE Transactions on Biomedical Engineering, 66(6), 1514–1525. https://doi.org/10.1109/TBME.2018.2874957
Muntner, P., Carey, R. M., Gidding, S., Jones, D. W., Taler, S. J., Wright Jr., J. T., & Whelton, P. K. (2018). Potential US population impact of the 2017 ACC/AHA High Blood Pressure Guideline. Circulation, 137(2), 109-118. https://doi.org/10.1161/CIRCULATIONAHA.117.032582
Namkoong, M., McMurray, J., Branan, K., Hernandez, J., Gandhi, M., Ida-Oze, S., Coté, G., & Tian, L. (2023). Contact Pressure-Guided Wearable Dual-Channel Bioimpedance Device for Continuous Hemodynamic Monitoring. Advanced Materials Technologies, 9(3), 2301407. https://doi.org/10.1002/admt.202301407
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