Korotkoff noises

Diastolic blood pressure was first determined by the military doctor Nikolai Sergeyev Korotkoff, who developed this method as part of his dissertation in St. Petersburg in 1905 (Eckert 2006). Even after more than 100 years, blood pressure measurement using Korotkoff's tones is still considered the gold standard for blood pressure measurement (Lin 2022).

Korotkoff murmurs are arterial circulatory murmurs that occur during indirect blood pressure measurement (Babbs 2015) and can be heard by auscultation above the brachial artery (Campbell 2023).

Korotkoff noises are divided into 5 phases:

• Phase I:

This is characterized by the first appearance of a murmur, the so-called systolic blood pressure value (Niebauer 2015).

• Phase II:

The noise takes on a hissing or blowing character due to a drop in pressure (Niebauer 2015).

• Phase III:

In this phase, the hissing sounds become louder (Niebauer 2015).

• Phase IV:

Now there is a more or less abrupt quietening of the Korotkoff sounds (Niebauer 2015). In this phase, the diastolic value is read if the end of the Korotkoff sounds is < 40 mmHg (Hiddemann 2000).

• Phase V:

The sounds disappear completely (Niebauer 2015). Reading of the diastolic blood pressure (Hiddemann 2000).

The duration of the individual phases depends on age. For example, phases II and III increase in length with age, while phases I and IV decrease at the same time (Campbell 2023).

A distinction is made in Korotkoff murmurs between a:

• 1. systolic murmur

This is the first audible sound when the pressure of the cuff is released. The measured value at which the noise is first perceived thus characterizes the systolic blood pressure value (Herold 2018).

• 2. diastolic murmur

The diastolic murmur, on the other hand, is the last audible murmur. This measured value indicates the diastolic blood pressure value (Herold 2018).

• Korotkoff tones up to 0 mmHg audible:

This may be the case if

- there is an increased cardiac output or hypercirculation, which may be the case, for example:

- in the case of anemia

- with fever

- during pregnancy (Herold 2018)

- in the case of a large AV fistula

- in the case of severe aortic regurgitation (Kasper 2015)

In this case, the diastolic value should be read in phase IV, i.e. as soon as the sound becomes quieter (Herold 2018).

• Auscultatory gap:

An auscultatory gap can occur if the cuff pressure was not inflated high enough. In this case, when the cuff pressure is released, the pause between the Korotkoff sounds occurs first and the next sound is mistaken for the start of the systolic pressure. To avoid this, the cuff should always be inflated high enough. The radial pulse can also be checked at the same time (Herold 2018).

• Quiet Korotkoff sounds

Auscultation can be difficult in very thin, seriously ill or elderly patients. In such cases, before inflating the cuff, it is advisable to raise the patient's arm above the patient's head height for approx. 30 seconds while the hand opens and closes 5-10 times. The regular measurement is then carried out. As a rule, the sounds can then be heard more clearly without affecting the blood pressure (Campbell 2023).

The noise itself is caused by the natural resonance of the equivalent spring-mass-damper system. The optimal systolic endpoint is the occurrence of Korotkoff murmurs, the optimal diastolic endpoint is their disappearance (Babbs 2015).

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