Blood pressure is the force that blood exerts against the walls of arteries as it flows through them. It is measured in millimetres of mercury (mmHg) and expressed as two numbers, systolic pressure (the top number) and diastolic pressure (the bottom number). Systolic pressure is the pressure in the arteries when the heart contracts and pumps blood out, while diastolic pressure is the pressure in the arteries when the heart is relaxed and filling with blood.
Korotkoff Sounds
Korotkoff sounds are the sounds heard during blood pressure measurement using a sphygmomanometer (blood pressure cuff) and a stethoscope. These sounds are used to determine the systolic and diastolic blood pressure values. The Korotkoff sounds are named after Nikolai Korotkoff, a Russian physician who first described them in 1905. They are created by the turbulent flow of blood in the brachial artery as the pressure in the cuff is gradually released.
There are five phases of Korotkoff sounds:
- Phase I: The first sound heard as the cuff is slowly deflated is a clear, tapping sound. This sound corresponds to the systolic blood pressure.
- Phase II: A swishing or whooshing sound follows the tapping sound, which corresponds to the transitional phase between the systolic and diastolic pressure.
- Phase III: The sound becomes louder and more distinct, similar to the tapping sound heard in Phase I.
- Phase IV: The sounds become softer, muffled, and have a “blowing” quality.
- Phase V: The sounds disappear completely. This is the diastolic blood pressure.
The first and fifth phases are the most important in determining blood pressure values. The systolic pressure is determined by the onset of Phase I, while the diastolic pressure is determined by the disappearance of Phase V.
It’s important to note that factors such as the position of the arm, the size of the cuff, and the rate of cuff deflation can all affect the accuracy of blood pressure measurement using the Korotkoff sounds. Therefore, proper technique and calibration of the equipment are essential for accurate measurement.
How to take a manual blood pressure
To take a resting blood pressure manually, you will need a blood pressure cuff, a stethoscope, and a sphygmomanometer (an instrument used to measure blood pressure).
Here are the steps to take a resting blood pressure manually:
- Find a quiet and comfortable room for the person to rest in for at least 5 minutes prior to measurement.
- Have the person sit down in a chair with their feet flat on the ground and their arm resting on a flat surface, such as a table, at heart level.
- Wrap the blood pressure cuff snugly around the person’s upper arm, with the lower edge of the cuff about 2.5 cm (1 inch) above the bend of the elbow.
- Locate the person’s brachial artery by gently feeling for a pulse on the inside of their arm, just below the elbow.
- Place the stethoscope over the brachial artery, and place the earpieces of the stethoscope in your ears.
- Inflate the cuff by squeezing the bulb or pressing the button on the sphygmomanometer until the pressure in the cuff is about 20-30 mmHg above the expected systolic pressure (usually around 160 mmHg).
- Gradually release the pressure in the cuff by opening the valve on the sphygmomanometer. You should be able to hear the person’s pulse through the stethoscope.
- Listen for the first clear sound of the pulse, which indicates the systolic pressure. This is the pressure when the heart is contracting.
- Continue to listen as you gradually release more pressure from the cuff. The sound will become muffled or disappear briefly and then return. The point at which the sound disappears completely is the diastolic pressure. This is the pressure when the heart is relaxed between beats.
- Record the systolic and diastolic pressures in millimetres of mercury (mmHg).
- Deflate the cuff and remove it from the person’s arm.
It’s important to take multiple measurements at different times of day to get an accurate resting blood pressure reading. Additionally, it’s best to have a healthcare professional show you how to take a blood pressure manually to ensure accuracy. Always consult a medical professional if you are concerned or for a diagnosis.