The first clear tapping sound heard when measuring blood pressure is the systolic blood pressure. This is the first and highest pressure reading, which is the pressure in the arteries when the heart contracts.
sounds of Korotkoff are the sounds that medical personnel hear when they are taking blood pressure using a non-invasive procedure. They are named after Nikolai KorotkovRussian physician who discovered them in 1905 while working at the Imperial Medical Academy in Saint Petersburgthe Russian Empire.
The sounds heard during the measurement of blood pressure are not equal to heart sounds ear over the chest auscultation due to vibrations inside the ventricles associated with rapid closing of the valves. If one stethoscope is placed over the brachial artery at the antecubital fossa in a normal person (without arterial disease), no sounds should be audible. While the heart beats, these pulses are transmitted smoothly via laminar (not turbulent) blood flow through the arteries, and no sound is produced. Similarly, if the cuff of a sphygmomanometer is placed around a patient’s arm and inflated to a pressure above the patient’s systolic blood pressure, there will be no audible sound. This is because the pressure in the cuff is high enough to completely occlude the blood flow. This is similar to a tube or flexible pipe with fluid being compressed.
If the pressure drops to a level equal to the patient’s systolic blood pressure, the first Korotkoff sound will be heard. Since the pressure in the cuff is equal to the pressure produced by the heart, some blood will be able to pass through the arm when the pressure in the artery increases during systole. It is blood flows in spurts as the pressure in the artery rises above the pressure in the cuff and then drops back down beyond the cuff region, resulting in turbulence that produces an audible sound.
As the pressure in the cuff decreases further, tapping sounds continue to be heard as long as the pressure in the cuff is between systolic and diastolic pressures, as blood pressure continues to rise and fall below the pressure in the cuff.
Eventually, as the pressure in the cuff drops further, the sounds change in quality, then go muted, and finally disappear completely. This is because as the pressure in the cuff drops below the diastolic blood pressure, the cuff no longer provides any restriction to blood flow, allowing blood flow to return to being smooth without turbulence and therefore no longer producing any audible sound. .
Korotkoff’s Five Sounds
There are five Korotkoff sounds:
- Phase I: The first appearance of faint, repetitive, clear tapping sounds that gradually increase in intensity for at least two consecutive beats is systolic blood pressure.
- Phase II: There follows a brief period during which the sounds soften and take on a sibilant quality.
- Phase III: The return of the most acute sounds, which become clearer to recover, or even overcome, the intensity of the Phase I sounds.
- Phase IV: The distinct abrupt muffling of sounds, which become soft and breathy in quality.
- Phase V: The point at which all sounds finally disappear completely is diastolic pressure.
Korotkoff’s second and third sounds have no clinical significance.
In some patients, the sounds may completely disappear for a short period of time between Phase II and III, which is referred to as auscultatory gap.
Systolic and diastolic blood pressure
Traditionally, systolic blood pressure is considered the pressure at which the first Korotkoff sound is first heard, and diastolic blood pressure is the pressure at which the fourth Korotkoff sound is barely audible. However, recently there has been a move towards using the fifth Korotkoff sound (i.e. silence) as the diastolic blood pressure, as this has been found to be more reproducible.
For pediatricsthere has been controversy over whether or not to use auscultation of the fourth or fifth Korotkoff sound as an indicator of diastolic pressure. Current clinical practice guidelines recommend using the fifth Korotkoff sound (but if undetectable, use the fourth).
The average time of the first Korotkoff sound represents a reliable pressure marker of systole from heart. The time average of the fourth Korotkoff sound represents a reliable pressure marker of diastole from heart.
- Audio recordings of the sounds of Korotkoff. Slide seven of twenty-two, Cardiff University/Prfysgol Caerdydd.
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Source: Korotkoff sounds
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