A blood pressure meter, also known as blood pressure cuff, is a device used to measure a person’s blood pressure. Blood pressure is an important measure of cardiovascular health and is an indicator of how blood circulates through the body. There are two main types of blood pressure meters: aneroid (mechanical) and digital.
The process of measuring blood pressure involves measuring two different pressures: the systolic pressure and the diastolic pressure. Systolic pressure is the highest pressure in the arteries during the contraction of the heart (when it pumps blood), while diastolic pressure is the lowest pressure in the arteries when the heart is at rest between beats.
Here’s how each type of blood pressure meter works:
Aneroid (mechanical) sphygmomanometer
The inflatable cuff is placed around the arm, approximately at the level of the heart and above the elbow.
The doctor or health professional will use a stethoscope to listen for the sounds of blood flow in the brachial artery (located in the crease of the elbow).
The cuff is then slowly inflated until the blood pressure is high enough to stop blood flow in the artery.
Air is then slowly released from the cuff while watching the manometer (pressure gauge) and listening to blood flow through the stethoscope.
When the first sound (called the Korotkoff sound) is heard, the pressure at that time is recorded as the systolic pressure.
When the sound disappears, the pressure at that time is recorded as the diastolic pressure.
Over the years, blood pressure measurement devices have evolved from traditional aneroid sphygmomanometers to the more modern and convenient digital sphygmomanometers. One of the key advances in these digital devices is their ability to detect swings in blood pressure.
Digital sphygmomanometers use a method called oscillometry to detect swings in blood pressure. Oscillometry is based on the analysis of cuff pressure fluctuations caused by pulsatile blood flow in the underlying artery. These fluctuations occur due to changes in arterial volume during the cardiac cycle.
Oscillation detection process in the digital sphygmomanometer
- Cuff Placement: As with the aneroid sphygmomanometer, the inflatable cuff is placed around the arm at the level of the heart and above the elbow. The cuff should fit snugly but not too tight.
- Cuff Inflation: When the digital device is turned on, it automatically begins to inflate the cuff. During the inflation process, the cuff puts pressure on the artery, compressing it and temporarily stopping blood flow.
- Controlled Deflation: As the cuff slowly deflates, the pressure exerted on the artery decreases. At this time, blood flow begins to resume in the brachial artery, and arterial volume varies with each heartbeat.
- Oscillation Detection: The digital sphygmomanometer is equipped with a sensitive pressure sensor that measures oscillations in cuff pressure caused by pulsatile blood flow. These oscillations are most prominent when the cuff pressure is between the systolic and diastolic pressure.
- Oscillation analysis and blood pressure calculation: A microprocessor built into the device analyzes the detected oscillations and determines the point of maximum amplitude of the oscillations, which corresponds to the mean arterial pressure (MAP). The microprocessor then uses manufacturer-specific algorithms to calculate systolic and diastolic pressures from the MAP and oscillation characteristics.
- Display of results: Once the systolic and diastolic pressures have been calculated, the digital sphygmomanometer displays the values on the device screen. Typically, the screen shows the systolic pressure at the top, the diastolic pressure at the bottom, and the heart rate (beats per minute) somewhere nearby. Some devices can also display a blood pressure rating based on guidelines set by medical organizations, such as the American Heart Association, to help users understand if their blood pressure is within a normal range or requires medical attention.
Advantages and considerations when using a digital sphygmomanometer
The advantages can be listed as follows:
- Easy to use: Digital sphygmomanometers are easy to use and do not require specialized skills to operate. This makes them ideal for home blood pressure monitoring.
- Comfort: These devices typically inflate and deflate the cuff automatically, reducing discomfort and ensuring a more consistent measurement.
- Speed: Measuring blood pressure with a digital sphygmomanometer is fast, which can be useful in emergency medical care situations.
On the other hand, although digital sphygmomanometers are usually accurate, they can go out of calibration over time. It is important that the devices are checked and recalibrated periodically by professionals or according to the manufacturer’s recommendations. To obtain accurate readings, it is also important to follow the manufacturer’s instructions and medical recommendations, such as sitting in a comfortable and relaxed position, not talking during the measurement, and placing the cuff correctly on the arm.
Remember that digital devices may be sensitive to electronic interference, such as that produced by nearby mobile phones or electronic devices. Make sure there are no sources of interference near the sphygmomanometer during use.