This article shows how to implement a system that can measure arterial blood pressure values. design. It contains descriptions of the hardware, the software architecture, the packages employed in the implementation, and the application-specific software developed for creating the system.

Flexis BPM Reference Design Block Diagram

How to start
The project consists of:

• The BPM system
• A cuff
• A PC software interface
• A 1321x-SRB (sensor reference board) for ZigBee communication

Install the PC software, which enables the user to download data from the system onto a computer.

1. First double-click on the Freescale SMAC GUI installer.
2. Click on the Next button. Now you will see a window that shows the installation route where the GUI will be installed.
3. Click on the Next button to continue.The system will now install the necessary files into your system. At the end of the installation you should see a window saying that the installation has been completed.
4. You will then be prompted to install the USBIO driver package. This package installs the USB drivers onto your computer.
5. Obey the instructions to install these drivers.
6. After the program has finished installing the driver, you will see the Installation Complete window.
7. After the USBIO driver package installation is complete, you will be asked to install the Freescale ZigBee/802.15.4 MAC COM device driver set. It is important that the user also install this driver so that the system will work properly.

Sensor Reference Board Setup

1. Attach the sensor reference board (SRB) when the power switch is in the OFF position.
2. Turn on the SRB. If necessary, install the new USB hardware on your computer.
3. Click on Next.
4. Your system will then find the necessary files and install the USB device on your PC. After the installation has finished you will see a screen that says “Completing the Found New Hardware Wizard.”
5. After it has installed, you will then be asked to install the COM device.
6. Click on Next.
7. Your system will then install the necessary DLL files. After they have been installed you will see a screen that says “Completing the Found New Hardware Wizard.”
8. After the hardware has been installed you will be able to use the SRB with the Blood Pressure Monitor Demo.

BPM Setup

1. Select the desired Flexis MCU and place it into the BPM reference design socket. Select MC9S08QE128 for down-ramp measurement or MCF51QE128 for up-ramp measurement.
2. Power on the BPM reference design.
3. Connect the USB connector to the BPM reference design. After it is connected, the PC will see that a new hardware device has been found and will ask you if you want to install its driver.
4. Install the new hardware driver onto the PC.

The design for the BPM PCB was made with the intention of isolating the different blocks of the system to avoid letting coupling noise into the lines of the instrumentation amplifier. The power is segmented through the use of 0 Ω resistors for debugging. These resistors can be replaced by ferrite cores to suppress EMI and noise coming from the different portions of the board. Ground distribution was implemented using a star configuration. Another feature of the board is the test socket which eases the change between the S08 and the ColdFire device.

The purpose of the blood pressure monitor is to indicate the pulse pressure (the systolic pressure minus the diastolic pressure) of a patient. This is implemented through the use of a cuff wrapped around the patient’s arm, and measuring the pressure and pressure differential of that cuff while air is put into or out of the system. Moreover, the blood pressure monitor must be able to perform many other functions, such as:

• Display information
• Provide audio feedback
• Keep statistical records
• Using USB or ZigBee communications, send statistical feedback to a PC for further analysis

The system uses MRAM to store data. To do this, the MCU dedicates eight complete ports for MRAM use. The MRAM is part of the hardware independent layer and is used by the voice generator module to read raw audio to reproduce. The MRAM is also used by the blood pressure monitor to store the last five readings.

Schematic

Bill of Materials

Note: this is just a part of schematic and BOM. Please contact us if you need all the schematics and BOM.

This article serves only as a proof of concept for this application and is not authorized for use in safety-critical applications such as a U.S. Food and Drug Administration (FDA) class 3 application.

Read the Italian version: Come realizzare uno sfigmomanometro (misuratore di pressione arteriosa)

Source: Medical Applications

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