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Digital Blood Pressure Monitor: How it Works

blood pressure medical device measurement sensor health

This page covers the basics of digital blood pressure monitors. We’ll explore how they work, along with some application notes and a list of manufacturers.

A digital blood pressure monitor is a device used to measure a person’s blood pressure. These devices typically feature an LCD display that shows the results clearly. They measure both diastolic and systolic blood pressure and pulse rates simultaneously. They can also detect and alert the user to irregular heartbeats.

At rest, a healthy young person will usually have a systolic arterial pressure of about 110 mmHg and a diastolic arterial pressure of about 70 mmHg.

Blood flow refers to the volume of blood flowing through tissue over a specific period, usually measured in ml/min. This flow is vital for transporting oxygen and nutrients in the blood. Blood flow depends on blood pressure, flowing from areas of high pressure to areas of low pressure. The greater the pressure difference, the higher the blood flow.

pressure changes on blood vessels

Blood is pumped from the left ventricle of the heart into the aorta, where it reaches its highest pressure. The blood pressure decreases as the blood moves away from the left ventricle until it reaches 0 mmHg at the right atrium of the heart. Figure 1 (above) illustrates the variation of blood pressure across different blood vessels.

Cuff Pressure Vs HeartBeat Signal

Let’s delve into how blood pressure monitoring works, referencing the curve in Figure 2 (above). This monitoring utilizes the oscillometric method, which relies on pressure pulsations recorded during measurements.

An occlusive cuff is placed on the left arm and connected to an air pump and pressure sensor. Here are the steps involved:

Step 1: The cuff is inflated until the pressure exceeds the typical systolic value.
Step 2: The cuff is slowly deflated.

As the cuff deflates and the systolic pressure is reached, pulsations begin to appear. These pulsations represent pressure changes resulting from the heart’s ventricle contractions. This is also used to calculate the heart’s beat rate. The pulsations increase in amplitude until the MAP (mean arterial pressure) value is reached and then decrease until they disappear. Systolic and diastolic values are calculated using algorithms, which can vary between different medical equipment manufacturers.

Digital Blood Pressure Monitor Application Note

Freescale has developed an affordable digital blood pressure monitor using its Kinetis K53 microcontroller units and other electronic devices like ADC/DAC, OpAmps, TRIAMPS, etc. This device calculates systolic and diastolic pressure.

The calculation assumes that systolic pressure is approximately equal to the pressure measurement recorded in the cuff when a pulse with 70% of the amplitude of the MAP pulse appears while the cuff pressure is above the MAP value. Diastolic pressure is approximately equal to the cuff pressure value registered when a pulse with 50% of the MAP pulse amplitude appears while the cuff pressure is under the MAP value.

For further details, visit www.freescale.com.