Cuffless blood pressure device ‘promising’—but concerns remain

A team of Japanese researchers has developed a cuffless blood pressure-measuring device that requires only a small sensor on the index finger. They believe the device could lead to a “paradigm shift” in how blood pressure (BP) is monitored, potentially replacing the cuff-based techniques that have been the standard for the last 120 years.

“The CLB (cuffless blood pressure estimation) is technically comparable to standard cuff-based devices and provides various advantages for BP recording, such as more comfortable monitoring during a variety of life activities,” lead author Naoki Watanabe, MD, from the department of cardiology at Nagoya University Graduate School of Medicine, and colleagues wrote in JACC: Basic to Translational Science.

“CLB enables patients to share more accurate and reliable data of ambulatory BP monitoring with their physicians. Collectively, CLB is expected to lower the incidence of cardiovascular events by collecting BP data that are unmeasurable by current diagnostic modalities.”

The device captures changes in peripheral blood volume using a light-emitting diode and a photodetector, a process called photoplethysmography (PTG). Data from five consecutive pulse wave intervals are averaged and digitalized and then entered into a proprietary algorithm to estimate diastolic and systolic BP.

To test the device, the researchers studied 172 individuals—66.9 percent male with an average age of 47.6—under various conditions. BP was measured in static and dynamic settings, as well as at least one month later to determine reproducibility.

As the finger sensor performed measurements on each participant’s right hand, BP was measured using the standard cuff-based technique in the upper left arm. BP data was highly consistent across the two techniques, except for diastolic BP under dynamic conditions.

“Previous reports have consistently reported similar evidence that exercise alters the relationship between pulse transit time and arterial blood pressure, which is more sensitive to the case of peripheral measurement of DBP than to the measurement of SBP by pulse transit time,” Watanabe et al. wrote. “This alteration is believed to result from changes in the correlation between pulse transit time (i.e., pulse wave velocity) and arterial wall distensibility in response to exercise. To overcome this physiological limitation, further improvement in the CLB is necessary.”

The authors noted previous attempts have been made to create cuff-free devices for BP estimation. One device is commercially available but requires both PTG and electrocardiogram (ECG) data, whereas their device requires only PTG data to be plugged into the algorithm.

A major limitation of the new method is it still must be calibrated using a cuff-based measurement.

“We are not yet free from the cuff, and our device is therefore termed ‘cuff-less,’ not ‘cuff-free,’” the authors wrote.

In a related editorial, Florian Rader, MD, MSc, and Ronald G. Victor, MD—both with Cedars-Sinai Heart Institute in Los Angeles—described the study statistics as “promising.”

“One advantage of this method to other similar methods, such as pulse transition time-based algorithms, is that PTG does not require an electrode to time the pulse wave analysis with the electrical activation of the left ventricle (i.e., QRS complex), thus making this technology potentially more versatile and ‘wearable,’” they wrote. “In addition, this new device provides much improved patient comfort compared with ambulatory BP monitoring, an advantage that also was demonstrated by surveying subjects in this study.”

However, Rader and Victor pointed out several additional limitations with the study. To name a few:

  • Several of the study’s coauthors are employees of the manufacturer and three of them hold the patent for the device, a significant conflict of interest. Rader and Victor said an independent validation of the device is advisable, although not required by international standards.
  • The editorialists are concerned a single calibration with a cuff-based measurement might not be sufficient given that changes in body position, exercise, body hydration and perspiration could alter the waveform signal of the wearable device.
  • Only 30 percent of participants in the study had hypertension; more work is needed to evaluate the device in a hypertensive population.
  • Measurements were conducted in a completely still position, which doesn’t accurately reflect the conditions in which a wearable device is used.

“We welcome the attempt to advance the rather static field of BP monitoring and appreciate the meticulous conduct of the experiments in this study,” Rader and Victor wrote. “However, this new technology needs to be further evaluated to address our concerns … before it can be recommended as a more convenient alternative to existing rigorously validated ambulatory, clinic, or home oscillometric BP monitors for the assessment and management of (hypertension).”