How is blood pressure is measured?
1 Answer
An instrument called a sphygmomanometer is used to measure blood pressure.
Explanation:
There are three types of sphygmomanometers: digital, aneroid, and mercury.
A digital sphygmomanometer measures blood pressure by detecting tiny pressure differences in the brachial artery that result from systole and diastole.
Both mercury and aneroid sphymomonometers work using the same underlying principles and are both considered manual since a practitioner with a stethoscope is required to use it.
- A stethoscope is placed over the brachial artery and the cuff is manually inflated.
- The practitioner continues to inflate the cuff until no noises are heard. This usually occurs near 140-160 mmHg, and at that pressure the artery is fully closed off. As a result, no blood is passing through the artery and no sound from the whooshing blood can be heard.
- Air is let out of the cuff at a slow rate, and as blood rushes back into the artery, whooshing and throbbing noises are once again heard. The pressure at which noise returns is known as the systolic pressure.
- When the artery is still partially occluded, blood is still not flowing through it uniformly and noise continues to be made. However, once the artery fully opens back up again, no more noise is heard and the pressure at which this occurs is noted as the diastolic pressure.
The above image shows how sound is heard through the stethoscope. You can also see the oscillating pressure that's found in the artery (this is what's detected by digital sphygmomanometers).
The systolic and diastolic blood pressures together form a patient's
These words, systole and diastole, refer to phases of the cardiac cycle. Systole is the phase when blood is pushed out of the heart and to the rest of the body (hence the higher blood pressure), and diastole is the period in the heart when the heart refills with blood.
