What you don't know might hurt you. Such is the case with high blood pressure, or hypertension. "In terms of hypertension, the statistics are pretty frightening. Around a third of all people in the U.S. suffer from hypertension. Unfortunately about half of those don't know they have it," noted Andrew Baker during a November talk at IDTechEx Show! in Santa Clara.
Baker is managing director of advanced sensor products in the Industrial & Healthcare Business Unit at Maxim. In his role, he gets a front-row seat into a variety of ailments—and how technology can help people better manage them.
Of hypertension, he said, "If you don't catch this silent killer, then hospitalization is the biggest cost." Citing research from the U.S. Centers for Disease Control and Prevention, Baker said that hypertension costs the U.S. $48B and causes 410,000 deaths per year, while half of hypertensive adults do not have their conditions under control.
The best path for preventing hypertension is to know your numbers. Table 1 illustrates normal numbers, as well as numbers of concern.
| Normal | Elevated | Hypertension/Stage 1 | Hypertension/Stage 2 | Hypertensive Crisis |
|---|---|---|---|---|
| Less than 120 systolic and less than 80 diastolic | 120 - 129 systolic and less than 80 diastolic | 130 - 139 systolic or 80 - 89 diastolic | 140 - 180 systolic or 90 - 120 diastolic | Higher than 180 systolic or higher than 120 diastolic |
Measuring blood pressure at rest (ideally at the same time each day) is the clinically recognized approach. However, there are some things that can get in the way of an accurate measurement. One big factor is the "white coat effect." Ever feel anxious while at the doctor's office? This anxiety can elevate your blood pressure, even though it is consistently normal when you check it at home. There's also a condition called masked hypertension, when blood-pressure levels are normal at a clinic but elevated at home. Baker noted that 10 to 20% of the general population could suffer from masked hypertension. Infrequent measures of blood pressure aren't going to catch many of the issues, he said.
Continuous blood-pressure monitoring from wearables such as smartwatches can help users uncover potential health problems early on.
Why Wearables Are Best for Measuring Blood Pressure
Measuring blood pressure has its roots in the 18th century. English clergyman and physiologist Stephen Hales conducted the first recorded blood-pressure measurement. He inserted tiny tubes into blood vessels and experimented on donkeys and horses. In 1896, Dr. Scipione Riva-Rocci introduced the mercury-sphygmomanometer, a cuff- and pump-based device that provided the first means for mass measurement of blood pressure. In 1905, Dr. N.C. Korotkoff introduced the auscultatory method for measuring arterial pressure.
While the core methods for measuring blood pressure haven't changed that much, the emergence of healthcare wearables brings the benefits of continuous monitoring. "I would consider it the wild west now—there are a lot of devices that claim to measure blood pressure," said Baker. "We feel that wearables is really the best method to measure blood pressure. It gives you a better window throughout the day as well as continuous measuring."
Wearables that utilize biosensors and sophisticated algorithms use electrocardiogram (ECG) and photophlethysmography (PPG) to derive pulse transit time and trending blood-pressure readings. One of the keys to accuracy is to gather a lot of data and apply machine learning to certain aspects of the PPG signal to look for changes, said Baker. In the U.S., end devices that show systolic and diastolic levels require clearance from the Food and Drug Administration (FDA).
To help designers quickly prototype solutions that measure finger-based heart rate and SpO2 levels, Maxim has a new reference design, the MAXREFDES220#. This cuffless blood-pressure measurement solution meets Class-II regulatory accuracy limits and can be embedded into wearables or smartphones. MAXREFDES220# consists of the MAX30101 or MAX30102 high-sensitivity optical sensor and the MAX32664D sensor hub IC with built-in algorithms. Maxim has pulled together data gathered from clinical trials to improve the accuracy of its algorithms.
"The other secret about measuring a good PPG signal is to ensure the fidelity of the signal. For the fidelity of a signal you need a good sensor," said Baker, who highlighted the continued signal-to-noise ratio (SNR) improvements of Maxim's PPG analog front-end products.
With wearables, users have a comfortable and convenient way to detect blood-pressure problems early on, when they can potentially prevent bigger issues through medication and lifestyle changes, said Baker. "The key about wearables is passive harvesting of a signal. When you have to ask an individual to do something, there's usually a compliance problem. We feel that wearables is really the way forward to solve this big problem," he said.
In addition to sensor products, wearable health solutions also depend on good power and battery management solutions as well as microcontrollers. Learn more the underlying technologies and access tutorials, reference designs, and trainings from Maxim's wearable health page.
