Monitoring Vital Signs with Ultrasound

You’ve entered an Emergency Room filled with people who, like you, are all seeking medical help. People are scattered around the ER, all the beds are full, and the average wait time in Canada is eight hours. A nurse has checked all your vital signs. Your body temperature, blood oxygenation (SpO2), heart rate (HR), and blood pressure (BP) were all within acceptable limits. Your condition was also assessed using the Canadian Triage and Acuity Scale (CTAS) using a 5-point scale (Level 1= most critically ill) to Level 5 (least critically ill). A verbal review of your medical history takes into account other important parameters, such as known chronic conditions, your reported pain level, behavioural aspects, fitness level and pharmaceutical history. All tests were within acceptable limits. But after a number of hours, the pain that brought you to the ER has returned with even more urgency. You’re now seriously regretting the short walk you took for some fresh air.

Fortunately, the nurse had applied a wearable ultrasound device that continually transmits your pertinent information. That device has now alerted ER staff to the rapid deterioration in your condition.

It may sound slightly futuristic, but continuous remote vital sign monitoring could be right around the corner. A recent article in ScienceDirect.com entitled “Improving trauma victim monitoring on the field with new photoplethysmography sensors” stated that “...even very simple diagnostic devices would be useful. These devices should be simple to use, low cost and possibly disposable.”

The flexibility offered by wearable monitoring systems will dramatically reduce the reliance on dedicated, instrumented beds, easily the most expensive real estate in an emergency room.  A cost-benefit analysis would prove both the economic and medical advantages of remote vital sign monitoring.

Beyond the introductory scenario above, these ultrasound sensors could offer “decision support” for a more effective and accurate diagnosis based on the patient’s recorded overall health status and behavioural history.

It would allow extended monitoring of patients receiving an early discharge if their status seemed stable and manageable. Extending ultrasound monitoring beyond hospital premises will also streamline the flow of ER patients, increasing the quality, and quantity, of medical care.

Monitoring patients with specific chronic diseases, or following major surgery with disposable, wearable ultrasound transducers will offer constant, regular surveillance to identify early problematic signs.

In mass casualty situations, a small medical team of first responders must make critical, often life-or-death decisions based on the estimated status of numerous victims. By attaching wearable body sensor units to each victim, and centralizing the monitoring of their vital signs, lives would be saved.

In a typical hospital ER, these wearable systems will need to be able to scale up to 150 patients, with low power consumption that allows sustained operation for up to 10 hours. 

What are today’s challenges?

Ultrasound transducers, the handheld units that produce and receive sound waves, send the information to a computer where those signals are interpreted to create the sonogram - an image of subsurface tissue within the body.

Current ultrasound transducers are not designed to be wearables. They are designed and built to be operated by a skilled technician who literally conducts the exam. In effect, this operator dependence has been an impediment to the development of disposable, wearable devices.

Cost is also a major consideration in healthcare. Traditional ultrasound equipment for bedside monitoring is relatively expensive, with each unit costing more than $50,000. Even portable units can cost as much as $5,000.  A transducer’s cost, depending on its function, ranges from $1000 to $15,000, and must be disinfected after each use. The requirement for an expert operator also contributes to the cost of each exam.

In fact, the biggest obstacle that remains whether implementing a portable or cart-based ultrasound system, is that both currently rely on operator dependence. 

The most popular technical approach to gain portability is photoplethysmography (PPG) - an optical measurement of the blood flow in capillaries using at least two different wavelengths. These pulse oximeters collect the data from PPG via attachment to fingers, wrists or earlobes. This data measures the vital signs of blood oxygen saturation and pulse rate. Any irregularity in heart rate or palpitations is important, but more difficult to detect using PPG.

Ultrasound can also be used for a more accurate estimation of respiration rate (RR), which is generally considered to be a more sensitive indicator than pulse oximeters regarding changes in a patient’s health status. Monitoring breathing rate is a must in patients with COVID-19 or chronic obstructive pulmonary disease (COPD).

And tomorrow’s opportunities?

Blood pressure monitoring is a technical challenge in continuous monitoring. But wearable ultrasound patches can provide more information than PPG regarding irregular heart rhythm. Cardiac issues such as arrhythmia, tachycardia, bradycardia or ischemia can all lead to stroke or heart failure.

An alternative BP monitoring system was presented by Sonus Microsystems in 2025 using a wireless patch applied to the neck over the carotid artery using AI models to extract the BP data. And in 2024, an innovative technique called resonance sonomanometry was introduced by a team from Caltech (resonance sonomanometry for non-invasive, continuous monitoring of blood pressure). It takes advantage of the superior characteristics of ultrasonic waves to measure the changes in the diameter of the artery resulting from the pressure of the blood flowing through it. 

The most restrictive issue today that is stagnating breakthroughs in ultrasound technology is that all current transducers rely on conventional manufacturing methods lacking the ability to make a wearable device. They are designed to be operated by a skilled technician and the conventional manufacturing methods lack the ability to make them a wearable device. 

However, innovative developments in manufacturing technology by Sonus Microsystems will bridge that gap. 

Sonus’ polymer-based ultrasound systems are the world’s first truly wearable ultrasound systems, leveraging the flexibility, scalability and low cost of polymer MEMS (microelectromechanical systems) technology. Given their wide fractional bandwidth and easily adaptable design, these PolyCMUTs (polymer-based capacitive micromachined ultrasonic transducers) are ideally suited to wearable ultrasound systems.

Ultrasonic transducers, used either as independent units, or in combination with temperature sensors and pulse oximeters, will ultimately untether thousands of patients and bring the benefits of continuous vital sign monitoring to medical practitioners. With these recent technological advances, such as wearable devices, the cost and quality of Canadian healthcare will take a sizable step forward. 

And an increasingly aging, but active population will applaud.