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The sounds in the measurement of blood pressure

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Many of you will know how to measure blood pressure. It attacks the sfignomanometro all'avanbraccio, it supports the stethoscope on the cubital fossa , the sfigno swells and then slowly deflates, the first sound heard is the systolic pressure (the maximum), the last sound you hear is to the diastolic (minimum).

But the problem is because the measurement is performed so that is why you hear that sound?

Until now, intuitively, I understood why when the pressure exceeds the systolic sfigno ie the maximum did not feel anything, and because of that limit is back down to hear the sound of the heartbeat.

Why, of course, if you compress the artery sfigno "stronger" of the boost given from the heart, the artery is occluded and then there is no passage of blood and therefore no noise. As the artery is reopened, down to the pressure exerted externally by sfigno, at that time the blood begins to pass and then the noises start.

But why, when the pressure drops below the pressure from sfigno minimum, these noises cease? Why I no longer feel the heartbeat in the cubital fossa?

The explanation, with hindsight it is also simple and, having discovered today, there I want to participate.

Take it away. Let for a moment losing the sfignomanometro. How come if you support the stethoscope on the cubital fossa or otherwise on any street not hear anything?

To understand this let us consider a more simple and we use the hose to water the garden. When using do not hear any sound through the pipe. Now we take a point of the tube and pieghiamolo up to interrupt the flow of water. Slowly begin to re-open the tube and you will notice that the passage choke in the water produces a whistle.

This whistle was not present when the tube comes straight from the swirling water at the chokepoint that produces mini vortices, and transforms the movement of water, usually laminar , moving in a turbulent .

It is then easy to include the presence of the sounds during blood pressure measurement.

When the pressure is greater than the systolic sfigno, there are sound because the artery is occluded. With the external pressure exerted by sfigno and between the systolic and diastolic artery semi-compressed motion is turbulent and therefore the turbulence produces the sounds we hear in the stethoscope. When the pressure drops below the diastolic blood returns to laminar flow and, as in the garden hose, every sound ceases.

The nice thing is that I also found that these sounds have a name, by those who observed them for the first time, that Nikolai Korotkoff , and therefore are called Korotkoff sounds , I also discovered that there is no Korotkoff only sound but there are four that are heard every time we measure blood pressure.

The first sound, corresponding to the opening of the artery, resembles a short-term stakes. The second is a longer piece of noise as if rubbing the blood on the walls of the artery. The third sound is more defined and looks like knocking on a door. The fourth and last, the third comes from but it is as if it were more muffled.

If you want to hear them, are present in this video from 2:12 minutes

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