Finally, you no longer have to roll up your sleeves when measuring your blood pressure

Translated by EEtimes, Maurizio Di Paolo Emilio

Devices such as blood pressure monitors, electrocardiographs, and oxygen sensors have become the new darlings of the consumer market, and interest in patient monitoring is growing as these applications go mainstream. Maxim Integrated is making it easier to enter this market with a reference design for a cuffless blood pressure monitor.

Home, hospital and image processing diagnostics are three fundamental areas of the e-health industry, and wearable devices can measure a variety of important parameters. Depending on the needs, the location of the device on the body can significantly affect what can and cannot be measured.

Let's first learn some basic knowledge about blood pressure. Blood pressure is the source of the power of blood pushing against the arterial walls. When the heart beats and contracts, it causes blood to flow through the arteries in other parts of the body. This force creates pressure on the arteries, which is called systolic blood pressure. The average systolic blood pressure is equal to or less than 120 mmHg. The lower value of arterial pressure is called diastolic blood pressure, and its reasonable value is equal to or less than 80 mmHg.

Until now, accurate monitoring of arterial blood pressure has only been possible with mechanical and bulky medical devices that wrap tightly around your arm. But Maxim's integrated solution offers the possibility of easier blood pressure tracking.

Designers can develop blood pressure diagnostic solutions through the MAXREFDES220# reference design, which includes a complete integrated optical sensor module, a microcontroller sensor center, and a detection algorithm. The measurement method is to place your finger on the instrument for 30-45 seconds, allowing you to measure blood pressure anytime, anywhere.

The Maxim Integrated MAXREFDES220# reference design includes everything you need to prototype finger-based heart rate and blood oxygen saturation (SpO2), including the MAX30101 or MAX30102 high-sensitivity optical sensor, and the MAX32664D sensor IC hub with integrated algorithms. And using the MAX30101 and MAX32664, it provides an integrated hardware and software solution for multiple finger-based applications. The MAX32664 firmware provides digital signal processing functions to process the data. The reference design also includes a three-axis accelerometer to compensate for motion artifacts. The integrated optical module and algorithms in the IC hub sensor, as well as the optical system design guide, enable customers to easily integrate finger-based blood pressure solutions into their devices. A MAX32630FTHR is also provided to emulate the host system to simplify development.

The MAXREFDES220# meets Class II regulatory limits and provides the following accuracy:

Systolic blood pressure error: Median = 1.7 mmhg, Std = 7.4 mmhg

Diastolic blood pressure error: Median = 0,1mmHg, Std = 7,6mmhg

The Class II regulatory limits are mean error ≤ 5 mmHg and Std deviation ≤ 8 mmHg.

The MAX30101 is an integrated pulse oximetry and heart rate monitoring module with low-noise optical and electronic components, and communication is through a standard I2C-compatible interface.

The principle of pulse oximetry is to use the ability of blood to absorb light of different wavelengths, which depends on the different concentrations of oxygen. The wavelength of adult hemoglobin is generally around 805 nanometers, and the wavelength varies with the degree of oxygenation.

The current method for measuring the percentage of oxygenated red blood cells is to use a finger-type photoelectric sensor. When measuring, just put the sensor on the human finger, use the finger as a transparent container for hemoglobin, use red light with a wavelength of 660nm and near-infrared light at 940nm as the incident light source, and measure the light transmission intensity through the tissue bed to calculate the hemoglobin concentration and blood oxygen saturation. The instrument can display the human body's blood oxygen saturation, providing a continuous and non-destructive blood oxygen measurement instrument for clinical use. This requires a microelectronic solution with low bias current, high impedance and fast 16-bit performance to process the output of the photodiode that detects these wavelengths. The oversampling, filtering and signal processing process then removes the low-level signal in the motion artifact for pulse frequency measurement.

The MAX32664D is derived from the MAX32664 series of sensors and hubs, and is specifically designed for finger measurement of blood pressure, heart rate, and blood oxygen saturation SpO2. Combined with the MAX30101 pulse oximeter and heart rate monitoring module, it provides raw data to the host device through its I2C with Maxim's BPT algorithm. This algorithm is integrated on a separate micro sensor hub, which greatly simplifies product design, freeing up the main system microcontroller to share resources and horsepower with the algorithm, a problem that always causes great trouble to software engineers.

Thanks to advances in technology, healthcare is becoming more and more convenient. More precise patient guidance has effectively reduced costs, and patients can even be monitored outside the hospital. This frequent feedback on one's own health status can encourage people to work harder to maintain healthy habits.