Blood pressure monitor trades compression for US

By Theresa Pablos, AuntMinnie staff writer

September 1, 2020 -- Researchers from Japan have developed a blood pressure monitor that utilizes a tiny ultrasound probe instead of compression to monitor systolic and diastolic changes. The science behind the prototype was presented as a virtual poster at the 2020 European Society of Cardiology (ESC) Conference. Lead author Dr. Kazunori Uemura, PhD, and his team from the National Cerebral and Cardiovascular Center in Japan designed the ultrasound-based monitor to unobtrusively track blood pressure on-the-go. Once calibrated, the ultrasound-based device produced blood pressure readings comparable to conventional technology in dogs.

"This method reliably tracks [blood pressure] changes without occlusive cuff inflation," the authors wrote in their poster abstract.

Monitoring blood pressure out-of-the-office and at regular intervals is important for hypertension diagnosis and management, but current compression-based blood pressure monitors can interfere with the daily lives of patients. Uemura and colleagues saw ultrasound as a potential alternative to compression-based technology.

The cuff they created utilizes a tiny ultrasound probe about half the size of a box of matches. The probe sits snugly in between a patient's skin and the larger blood pressure cuff.

Upon mild cuff inflation, the ultrasound transducer's 65 piezoelectric elements measure changes to an artery situated underneath the probe. Uemura and colleagues use these measurements to calculate estimated diastolic and systolic blood pressure.

(A) Schematic illustration of the cuff and ultrasound probe wrapped around the upper arm and positioned over the brachial artery. (B) Longitudinal cross section illustration of the ultrasound probe and inflated cuff. When the cuff is inflated, the device tracks the ultrasonic dimension of the brachial artery. Image courtesy of Dr. Kazunori Uemura, PhD.
The authors tested the cuff's accuracy for blood pressure monitoring on the right femoral artery of six anesthetized dogs. Measurements taken with the ultrasound-based device correlated strongly with compression-based readings, according to coefficient of determination (R2) analysis.

With just one-time calibration, the diastolic blood pressure readings had a bias of 3.9 ± 7.9 mmHg. This measurement fell within the acceptable bias range of < 5 ± < 8 mmHg set by the Association for the Advancement of Medical Instrumentation (AAMI).

However, with one-time calibration, the systolic blood pressure readings had a bias of 2.6 ± 18.9 mmHg, outside of the AAMI acceptable range. To improve the systolic readings, the authors added machine learning and a support vector algorithm to the initial, one-time calibration. The new analysis yielded systolic measurements with a bias of 0.7 ± 6.9 mmHg, meeting the AAMI guidelines.

"Once calibrated, this method measures [diastolic blood pressure] accurately," the authors wrote. "With the aid of machine learning, precision in [systolic blood pressure] prediction was greatly improved to acceptable levels."

This type of ultrasound-based technology is a long way from use in the clinic, and the research team still has yet to test the device's accuracy on people. But if the cuff holds up in further testing, the combination of ultrasound and machine learning could lead to better mobile blood pressure monitoring.

"This method with machine learning approach has potential for stress-free [blood pressure] measurement in ambulatory [blood pressure] monitoring," the authors concluded.

Carotid lumen size linked to death from all causes

By Theresa Pablos, AuntMinnie staff writer

August 21, 2020 -- Could ultrasound measurements of the carotid lumen diameter be a better measure than carotid intima-media thickness (CIMT) for predicting mortality from cardiovascular disease? Lumen diameter indeed could add new information, according to a study in the Journal of the American Heart Association.

Researchers from Germany found that lumen diameter measurements of the carotid artery derived from ultrasound scans predicted mortality from both cardiovascular disease and from all causes. And they believe that it provides more information than CIMT.

CIMT has been used as a noninvasive biomarker for cardiovascular disease risk stratification and the risk of future cardiovascular events, the authors report. Both the coronary and carotid arteries distend during the early stages of atherosclerosis, a phenomenon that can be detected and measured on ultrasound scans.

But recent research has raised doubts about the reliability of CIMT for predicting individual outcomes. The new evidence, published on August 4, demonstrates that lumen size might be a better predictor of death from both cardiovascular and noncardiovascular events, with larger lumens indicating higher risk.

"Our results suggest that [lumen diameter] may be superior to CIMT," wrote the authors, led by Dr. Felix Fritze from the University of Greifswald's medical school in Greifswald, Germany.

The team of German researchers compared the effectiveness of CIMT and lumen diameter using data from a prior study that conducted baseline screenings and 10- and 15-year follow-up exams on the population of a German village.

As part of the baseline assessment, individuals underwent carotid ultrasonography. The original research team also recorded relevant health information, including cholesterol levels, diabetes status, and mortality outcomes.

For the new analysis, Fritze and colleagues created various models to analyze data from 2,751 participants, including 506 who died during the original study. Their further cardiovascular mortality analysis used outcomes from all but 214 of the participants with unknown causes of death.

The researchers found that individuals with the largest CIMT measurements had the highest hazard ratio (HR) for all-cause mortality, at 1.73, compared with a hazard ratio for lumen diameter of 1.29 and the combination of CIMT and lumen diameter at 1.26.

The model using lumen diameter alone was significantly associated with death from all causes, deaths attributed to cardiovascular events, and deaths attributed to noncardiovascular events. On the other hand, the model using CIMT alone was significantly associated with all-cause mortality and noncardiovascular mortality -- but not cardiovascular mortality.

To help determine the likelihood of their models predicting future values, the authors conducted an Akaike information criterion (AIC) analysis. In this analysis, the lumen diameter model came out on top for both all-cause mortality and cardiovascular mortality. It also came in second for cardiovascular mortality, just behind a model that combined lumen size and CIMT values.

Furthermore, the lumen diameter model remained significant for all-cause mortality even after the researchers excluded people with chronic kidney disease, prior myocardial infarction, and type 2 diabetes. The same wasn't true for the CIMT model.

Lumen diameter vs. CIMT for predicting mortality
Model	Rank (AIC)
	All-cause mortality	Cardiovascular mortality	Noncardiovascular mortality
Lumen diameter	No. 1	No. 1	No. 2
Lumen diameter + CIMT	No. 2	No. 2	No. 1
CIMT	No. 3	No. 5	No. 3
None	No. 4	No. 4	No. 4
Lumen diameter ÷ CIMT	No. 5	No. 3	No. 5

The authors do not know why the model using lumen diameter performed much better than CIMT in their analysis. They hypothesized it could be because lumen size is related to CIMT but is also much easier to measure.

"The larger caliber of [lumen diameter] compared with CIMT may improve manual measurement accuracy and thus may be more applicable for an outpatient setting," they wrote.

It's important to note the study only included white participants from one part of Germany, so the results may not be applicable to a more diverse population. As a result, the authors called for follow-up research with more robust patient populations to verify their findings.

"To the best of our knowledge, this is the first study to compare the informative value of CIMT and [lumen diameter] with regard to all-cause, cardiovascular, and noncardiovascular mortality associations," they concluded. "We report that [lumen diameter] provides more information than CIMT."