Speckle Contrast Optical Spectroscopy Improves Cuffless Blood Pressure Accuracy

For decades, blood pressure monitoring has relied on a 19th-century invention: the inflatable cuff. Whether at the doctor’s office or at home, the process is the same—wrap, squeeze, release, repeat. But while the cuff has become a clinical staple, it’s far from perfect. It’s bulky, uncomfortable, and offers only a snapshot of a person’s cardiovascular health. Now, researchers at Boston University have taken a major step toward replacing the cuff with something far more elegant: a wearable optical system that uses light and machine learning to estimate blood pressure continuously and noninvasively.

The technology is based on speckle contrast optical spectroscopy (SCOS), a technique that measures blood flow by analyzing the way coherent light scatters off moving red blood cells. When laser light hits tissue, it creates a grainy interference pattern—called a speckle pattern—that changes as blood flows. By capturing and analyzing these fluctuations, SCOS can provide detailed information about both blood flow and blood volume. While SCOS has previously been used for brain and tissue monitoring, this is one of the first times it’s been applied to blood pressure estimation.

In a study published in Biomedical Optics Express, the team—led by Professor Darren Roblyer and doctoral student Ariane Garrett—tested the SCOS system on 30 volunteers. Measurements were taken from the wrist and finger, both at rest and during leg press exercises designed to induce blood pressure changes. The researchers found that combining blood flow and volume data from SCOS improved blood pressure estimation accuracy by up to 31% compared to using blood volume alone. That’s significant, because most commercial optical monitors today rely solely on photoplethysmography (PPG), which tracks blood volume but not flow.

The implications are big. Hypertension affects nearly half of all adults in the U.S. and is the leading cause of cardiovascular disease. Yet many cases go undetected, especially in people with “masked hypertension,” where blood pressure appears normal in a clinical setting but spikes during daily life. A wearable SCOS device could provide continuous, real-world monitoring, offering a more accurate picture of cardiovascular health and enabling earlier intervention.

The project began as a collaboration between Boston University and Meta’s Reality Labs, with the goal of exploring how optical signals could be used to track cardiovascular metrics. In 2023, the team showed that features extracted from SCOS blood flow waveforms were strongly correlated with blood pressure. The new study builds on that work, demonstrating that these waveforms can be used to predict blood pressure in real time.

What sets SCOS apart is its ability to capture both blood flow and volume simultaneously, offering a richer dataset than traditional optical methods. And because it’s noninvasive and doesn’t require compression, it could be integrated into wearable devices like smartwatches or rings—making blood pressure monitoring as seamless as checking your steps.