Sphygmomanometer
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Introduction (what is the sphygmanomometer? What does it do/what is it used for?[edit | edit source]
A sphygmanomometer is used to indirectly measure arterial blood pressure. [1]
The Device[edit | edit source]
This is the blood pressure cuff that one would see in the Doctor's office, or in a medical clinic/setting. This is seen in the pictur eto the right.
The sphygmanomometer consists of [1][2] :
- An inflatable arm cuff
- A bulb pump for pumping air into the cuff, and a valve/dial for letting air out of the cuff
- A column of mercury, to display the changing pressure
- A pressure meter (manometer), which measures the air pressure, with the help of the rising mercury
In addition to the sphygmanomometer, a stethoscope is also used to listen to the sounds of blood flowing through the brachial artery. [2] See the auscultation page for guidelines on proper placement and usage of the stethoscope.
Definitions[edit | edit source]
Blood Pressure: Pressure exerted on the walls of blood vessels while blood is moving around the body. This is measured in mmHg and displayed as 'systolic blood pressure/diastole blood pressure' mmHg. [2]
Normal blood pressure: Normal blood pressure values are generally around 120/80 [3]. Above 140/90 mmHg, this would be considered high blood pressure, and is classified as hypertension.[2][3]
Systole: The contraction phase of the cardiac cycle, when the heart fills with blood. [1]
Diastole: The relaxation phase of the cardiac cycle, when the heart empties the blood. [1]
Systolic Pressure: Pressure that is exerted on the arteries as blood is leaving the heart during ventricular systole. [1]
Diastolic Pressure: Pressure that is exerted on the arteries during ventricular relaxation (diastole). [1]
Procedure (how to measure someone's blood pressure)[edit | edit source]
Locate the brachial pulse, in the elbow crease (cubital fossa), with the index and middle fingers. If it is not easily located, it ca be found using the head of the stethoscope. [4]
The cuff is wrapped around the middle of the upper arm, so it surrounds the brachial artery. [1] The bottom of the cuff should be 1 inch from the cubital fossa. [4] It should be placed relatively snug, but not too tight to make the person uncomfortable. [1]
Before inflating the cuff with the bulb pump, ensure that the airflow valve on the bulb pump is closed, by screwing it clockwise. [4]
With the bulb pump, pump air into the cuff until the pressure exceeds arterial pressure by about 30mmHg [1] [4]. Due to this pressure being greater than arterial pressure, the brachial artery is squeezed closed and blood flow is stopped. [1]
When you place the head of the stethoscope over the brachial artery (in the cubital fossa), there would be no sound due to the absence of blood flow. [1]
Gently open the airflow valve. You will notice the pressure in the cuff begins to decline, and will quickly fall below the arterial pressure. [1] There should only be a change of 2-3mmHg per heartbeat when you first open the air valve. [4]
The blood will be able to flow through the artery and will create a turbulent flow. This turbulent flow will create sharp sounds, which are heard through the stethoscope. These sharp sounds are known as Korotkoff sounds. [1]
The pressure at which the first tapping sound (Korotkoff sound) is heard represents systolic blood pressure. This can be read on the mercury meter/dial. [1] This occurs when the cuff pressure decreases and is unable to keep the brachial artery closed during systole. As the artery is gradually opening and blood flow is gradually increasing, turbulence is reduced and produces a sound. [1]
Once the sounds are heard, the valve is slowly released to enable the blood flow to increase, and the cuff pressure to decrease. [1][4]
There will be a series of louder, more pronounced sounds, at varying pitches, as the turbulence decreases and blood flow increases. [1]
Diastolic pressure will be reached when the sounds heard in the stethoscope are no longer heard. This occurs because the turbulent flow diminishes. [1]
Since the brachial artery will be open during systole and diastole, there won’t be any turbulence, and no sounds will be heard. [1]
Guidelines (sitting, patient)[edit | edit source]
Here are some rules and guidelines for when having your blood pressure measured: [5][4]
- No food or drink within 30 minutes
- Empty your bladder beforehand
- Ensure that your body is relatively warm (not cold) to avoid inaccurate results
- No talking during the procedure
- The cuff is against your bare skin, sleeves loosely rolled up
- Sitting up straight on a chair with your back supported - sit quietly for a few minutes prior to measuring
- Feet flat on the floor in front of you, with your legs uncrossed
- Rest your left forearm with the cuff on a table/surface at chest height, your palm should be facing up - use the left arm since it is closer to the heart, but can also compare both sides
- Ensure that the cuff fits well around your arm - you don't want it too loose, or too tight that it is uncomfortable and restricting
Korotkoff sounds[edit | edit source]
The Korotkoff sounds are the loud thumping sounds you'll hear through the stethoscope while deflating the sphygmanomometer.
Systolic blood pressure is indicated by the first Korotkoff sound that is heard. [1]
Diastolic blood pressure is indicated after all Korotkoff sounds have been heard through the stethoscope. [1]
Factors affecting arterial Blood Pressure[edit | edit source]
Things that can affect your true blood pressure reading include:
- Being nervous or anxious, therefore raising one's blood pressure [5]
- Having eaten or drank 30 minutes before the blood pressure reading, which includes alcohol or caffeine, raising the blood pressure [5]
- Having exercised within 30 minutes of the blood pressure reading [5]
- Having smoked within 30 minutes of the blood pressure reading [5]
- your posture/the way you are sitting - crossing your legs and letting your arm hang at your side can cause the blood pressure to go up [5] - *see "Guidelines" above for details on posture
Note the definition White Coat Syndrome - this is when someone's blood pressure is consistently/purposely higher in the lab/Doctor's office setting, most likely due to nervousness, anxiety, or similar factors.
Indications, Contraindications, and risks[edit | edit source]
there are no risks to having your blood pressure taken with sphygmanomometry. However, there may be some discomfort when the cuff is inflated. [4]
Resources[edit | edit source]
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References[edit | edit source]
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 Powers, Scott K. Howley, Edward T. editors. Circulatory Responses to Exercise. Exercise Physiology - Theory and Application to Exercise and Performance. 10th Ed. New York: McGraw-Hill Education. 2018. p194-220
- ↑ 2.0 2.1 2.2 2.3 National Library of Medicine. What is blood pressure and how is it measured? Available from: https://www.ncbi.nlm.nih.gov/books/NBK279251/ (accessed on 13 May 2022)
- ↑ 3.0 3.1 MedlinePlus - Trusted Health Information for you. Available from: https://medlineplus.gov/lab-tests/measuring-blood-pressure/ (accessed on 13 May 2022)
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 WebMD. Checking Your Blood pressure. Available from: https://www.webmd.com/hypertension-high-blood-pressure/monitoring-blood-pressure#1 (accessed on 13 May 2022)
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Centre for Disease Control and Prevention. High Blood Pressure. Available from: https://www.cdc.gov/bloodpressure/measure.htm#:~:text=these%20additional%20tips.-,How%20do%20health%20care%20professionals%20measure%20my%20blood%20pressure%3F,will%20measure%20your%20blood%20pressure. (accessed on 12 May 2022)
