Today’s medical technology has come so far that historically complex evaluations can now be easily undertaken at home. Case in point: the legendary blood pressure monitor and its now easy-to-use functionality that is helping save lives across the world.
But how does the humble yet imperative blood pressure monitor (BPM) work? Let’s find out below:
The measurement techniques
The digital BPM utilises an inflation device to pump the cuff surrounding the wrist or upper arm with enough air pressure to inhibit the blood’s ability to flow in the main artery. This pressure is then slowly released, enlisting a digital solenoid valve up to the point of the blood flowing through the person’s artery.
The blood pressure is then measured by a sensor and the signal from the sensor is conditioned with an instrumentation amplifier
The user interface
Typically BPMs utilise a basic monochrome LCD with 100 segments or less than a driver integrated with a microcontroller can easily drive. Backlighting is also an added feature using one or numerous white light emitting diodes (LEDs).
One or multiple physical push buttons or switches are generally used to turn the power on and off and to produce the all-important measurement. A top quality BPM may include a colour LCD with touch screen to produce advanced user interface technology including touch menus, animations, graphics and more.
Audible notifications in the patient’s BPM can also be produced with simple beepers driven by one or two microcontroller port pins that contain pulse-width modulation (PWM) technology. More advanced voice announcements can easily be created by adding an amplified speaker with a digital-to-analog converter (DAC).
With recent technological advancements, health data aggregation, connectivity and sharing have become increasingly popular in the consumer health industry, with connected BPMs now containing the ability to upload data to a smart phone or computer for further medical analysis when needed. This data transfer is typically produced through a wireless Bluetooth Low-Energy (BLE) radio link or USB interface.
An advanced BPM may also enlist WiFi or other wireless networking to upload the imperative data to a remote digital health management program without needing a smartphone or computer.
Upper arm BPMs generally use multiple AA or AAA alkaline batteries whilst wrist monitors generally utilise two AAA batteries. Conversely, a high quality BPM may utilise a rechargeable Li-ion battery and a wall charger like you would find with tablets and smartphones.
The BPM’s analog circuitry and air pump need a 3.3V or 5V supply whilst the digital circuitry requires a 1.8V or 3.3V supply, depending on the technology utilised. In turn, a typical BPM requirespump/analog voltage to 5V to be regulated by a buck-boost switching regulator. What’s more, it requires a low-dropout linear regulator (LDO) for the 1.8V or 3.3V digital element.
To add more battery life, an automatic power shutdown is performed after a period of user inactivity, but a real-time clock (RTC) can always be powered on to provide the time whilst the BPM is not in use.