Devices such as blood pressure monitors, electrocardiographs, and oxygen sensors have now become part of the consumer market, and with the mainstreaming of these applications the interest in patient monitoring is growing. Maxim Integrated is making it even easier to jump into this market with a reference design for a cuffless blood pressure monitor.
The electro-medical industry is divided into three basic areas: the home, the hospital, and diagnostics for image processing. A wearable device allows measuring a wide range of vital parameters. Depending on the general objective, some values are more important than others. The position of the device on the body significantly affects what can or cannot be measured.
Figure 1: MAXREFDES220#, a ready-to-use solution
Blood pressure is the force of the blood that pushes against the walls of the arteries. When the heart is beating, it contracts and makes the blood flow through the arteries in the rest of the body. This force creates pressure on the arteries and is known as systolic pressure. Average systolic blood pressure is equal to or less than 120 mm of mercury. The lower value of arterial pressure is known as diastolic pressure with a reasonable value equal to or less than 80 mm of mercury.
Until now, accurate monitoring of arterial pressure could only be achieved with mechanical and bulky medical devices in the form of a tightly wrapped cuff. The new Maxim Integrated solution offers the possibility of tracking blood pressure more easily.
Designers can develop blood pressure diagnostic solutions with the MAXREFDES220# reference design consisting of a complete integrated optical sensor module, a microcontroller sensor hub, and a detection algorithm. The measurement is done by placing the finger on a device for 30-45 seconds to measure blood pressure anywhere and at any time (while resting).
The reference design includes the MAX30101 or MAX30102 high-sensitivity optical sensor, as well as the MAX32664D sensor IC hub with integrated algorithms. Integrated optical modules and the algorithms in the IC hub sensor, along with a guide to optical system design, allow customers to easily integrate the finger-based blood pressure solution into their devices (figure 1).
The MAXREFDES220# meets the Class II regulatory limits provides the following accuracies:
- Systolic error: Media = 1.7mmHg, Deviation Std = 7.4mmHg
- Diastolic error: Media = 0.1mmHg, Deviation Std = 7.6mmHg
- For reference, the Class II regulatory limits are Mean Error ≤ 5 mmHg and Std Deviation ≤ 8mmHg.
MAX30101 is an integrated pulse oximetry and a heart rate monitoring module with low noise optical and electronic elements to facilitate the design process for mobile and wearable devices. Communication takes place through a standard interface compatible with I2C (figure 2).
Figure 2: a system diagram of MAX30101
Pulse oximetry exploits the ability of blood to absorb light at different wavelengths depending on the greater or lesser concentration of oxygen. Adult hemoglobin typically has a wavelength near 805 nm; the wavelength varies with oxygenation levels. Calculating the percentage of oxygenated red blood cells, two other wavelengths are used: usually 660 and 940 nm. Microelectronic solutions with low bias current, high impedance, and fast 16-bit performance are required to process the outputs of the photodiodes that detect these wavelengths. The oversampling, filtering, and signal processing procedures then clean up the low-level signals from motion artifacts to allow for pulse frequency measurement.
MAX32664D is a variant of the MAX32664 family of sensors and hubs, specifically designed for finger-based measurement of blood pressure, heart rate, and SpO2. In combination with MAX30101 pulse oximetry and the heart rate monitor module and powered by Maxim’s BPT algorithm, it provides raw data to a host device through its I2C. The availability of the algorithm in a standalone sensor hub micro greatly simplifies product design, as it frees the main system microcontroller from having to share resources and horsepower with the algorithm, which always results in significant headaches for software engineers.
The world of healthcare is evolving, thanks to technology. More excellent patient orientation, intelligently reduced costs, and the possibility to follow people even outside hospital facilities. Having frequent feedback on one’s health could encourage people to work harder to maintain healthy habits.
>> This article was originally published on our sister site, EE Times.
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