Date: August 7, 2024
Source: Caltech / PNAS Nexus (Resonance Sonomanometry)

A team at Caltech has developed a new method to measure true blood pressure continuously without needles. The technique is called resonance sonomanometry. It uses sound waves and ultrasound imaging to track blood pressure from an artery—without squeezing the arm like a cuff and without placing an invasive arterial line.

In a small clinical study, the early device produced results similar to a standard blood pressure cuff, and it can capture the full blood pressure waveform (the shape of pressure over each heartbeat).

Key takeaways

Here are the quick key facts you need to know about this technology:

• It’s noninvasive (no catheter in the artery)
• Continuous monitoring (not just one reading at a time)
• Can measure at different places on the body, not only the upper arm
• May reduce the need for risky arterial lines (a-lines) in some hospital patients
• Prototype is an armband today; the team says it could become a watch-sized device or skin patch later

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What’s new: Resonance sonomanometry (sound + ultrasound)

The device gently “buzzes” the skin with sound waves to make an artery vibrate. Then ultrasound measures how the artery “rings.” The vibration frequency changes when blood pressure changes—similar to how a guitar string changes pitch when you tighten it. That resonance signal is used to calculate absolute (true) blood pressure, not just “higher or lower than before.”

The prototype is being developed and tested with a Caltech spin-off called Esperto Medical.

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Explainer: Why continuous blood pressure is a big deal

Blood pressure problems are common and serious:

• High blood pressure (hypertension) raises risk of stroke, heart attack, and kidney disease.
• Low blood pressure (hypotension) can mean organs are not getting enough oxygen.

Doctors often want continuous readings, especially for sick patients. One or two cuff readings can miss sudden drops or spikes.

Previous technologies (and their limits)

1) Arm cuffs (manual or automatic):

• Good for routine checks
• Not continuous
• Mainly works on the arm
• Can miss changes between readings

2) Arterial line / “a-line” (catheter in an artery):

• The current best way to get continuous true blood pressure + waveform
• But it is invasive and can carry risks (infection, bleeding, complications)

3) Cuff-free wearable estimates (pulse-based methods):
Many newer devices try to estimate BP from pulse signals (often using optical sensors).

• Can be convenient
• Often needs calibration with a cuff
• May give relative BP changes instead of true absolute pressure
• Can be hard to use in emergencies where clinicians need “put it on and it works”

Caltech’s approach aims to deliver hospital-grade continuous BP without the needle – and without time-consuming calibration steps.

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What it may mean for the future of blood pressure monitoring

If larger studies confirm accuracy and reliability, this could lead to:

• Easier continuous monitoring in hospitals without defaulting to an arterial line
• Better at-home blood pressure tracking, because it could be “wear it and forget it”
• Stronger care in remote and low-resource settings, where continuous monitoring is hard today
• More use of the full waveform to help spot heart and circulation problems earlier

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What to watch next

This is still early-stage technology. Key next steps will likely include:

• Larger clinical trials in more patient groups
• Testing during movement and real hospital workflows
• Regulatory clearance and integration with hospital monitors

Biomedforum will keep you posted if any new medical devices are manufactured using resonance sonomanometry!