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Blood pressure

Abbreviation: RR (after the inventor of the instrumental blood pressure measurement Scipione Riva-Rocci)
German: Blutdruck

1 Definition

Blood pressure is the pressure that prevails in a certain part of the cardiovascular systems. In medical language, mostly arterial blood pressure in the big arteries is meant.

2 Background

The blood pressure can be measured in different sections of the vascular system. Clinically, not only the arterial blood pressure, but also the blood pressure in other vascular sections is relevant, eg.

The following specifications pirmarily refer to the arterial blood pressure.

3 Classification

3.1 ...According to cardiac phase

In order to better estimate the organ perfusion, in the field of intensive care, a third parameter is used next to these two, namely the mean arterial pressure (MAP).

Systolic blood pressure is generated by the ejection force of the heart. Diastolic blood pressure is maintained when the aortic valve is closed, mainly by the blood volume and the elasticity of the arteries (pressure reservoir function). When vascular elasticity decreases (eg. In arteriosclerosis), at first, diastolic pressure increases, and later, also the systolic blood pressure is permanently increased.

3.2 ...according to measurement conditions

4 Measurement

The blood pressure measurement can be undertaken in two ways:

  • Bloody blood pressure measurement: A pressure sensor is brought directly into the vessel, and the pressure prevailing there is registered.
  • Bloodless blood pressure measurement: Indirect measurement method with pressure cuff at the upper arm or the wrist. Either acoustical via the Korotkoffís sounds or oscillometrically.

Clinically, the bloodless method is most common, whereas the bloody blood pressure measurement is only applied in intensive care or in clinical research.

4.1 Measurement value

The unit for the blood pressure is "mm Hg" millimeter mercury column. A common abbreviation for arterial blood pressure is RR, after Scipione Riva Rocci, 1863 to 1937, an Italian internal specialist.

4.2 Measurement error

Bloody blood pressure measurement is very precise due to the sensors used. A possible source of error, however, is the wrong calibration of the equipment to be used.

With the bloodless (indirect) measurement method after Riva-Rocci, the correct configuration of the cuff width is of utmost importance: due to the inversely proportional relation of the pressure to the surface, a too broad cuff leads to a too low measurement, whereas a too tight cuff leads to a too high measurement.

Further measurement errors can be caused by the presence of an auscultatoric gap or a too high pressure relief. These errors can be avoided by a simultaneous determination of the systolic pressure by palpitation while inflating the cuff, as well as by slowly releasing the air (3 mmHg/s).

Despite a correct measurement technique, depending on the situation, you can measure values that are not representative for the actual arterial blood pressure of the patient. Possibles causes include eg. the presence of an feces, or impulse to urinate, or the so-called white coat hypertension.

5 Reference range

The reference values for the systolic and the diastolic blood pressure are phrased as followed by the WHO:

Evaluation systolic value (mmHg) diastolic value (mmHg)
ideal < 120 < 80
normal < 130 < 85
highly normal 130-139 85-89
Hypertension grade 1 140-159 90-99
Hypertension grade 2 160-179 100-109
Hypertension grade 3 ‚â• 180 ‚â• 110

An elevated arterial blood pressure is called hypertension, while a decreased arterial blood pressure is called hypotension. More common, more dangerous, and therefore clinically relevant, is hypertension.

6 Regulation of the blood pressure

The blood pressure in the arteries may only alter within relatively narrow limits, since hypertension as well as hypotension can damage individual organs or vessel walls. At the same time, the blood pressure needs to bee adapted to a changing strain of the body. The basic prerequisite for the regulation of the blood pressure is its control via the baroreceptors. These can be found in the walls of the aorta and other large arteries in the region of the thorax and neck. The most important examples lie in the carotid sinus.

The receptors registrate the alternated blood pressure by the changes of the dilation of the vessel walls caused thereby, and they convey them to the medulla oblongata. The medulla now introduces measures to lower or rise the blood pressure. Here, it is important to note that there are different measures that can have either a short-term or a long-term effect. Alongside the baroreceptors, there are other factors such as the blood osmolarity that influence the blood pressure.

6.1 Short-term regulation

The signal of the baroreceptors, or also the stretch receptors in the atria control the sympathetic nervous system in the medulla oblongata. When blood pressure drops, the activity of the sympathetic nervous system increases, which induces blood pressure to rise again. It works the same way vice versa.

6.2 Medium-term regulation

Here, the receptors that control renal perfusion play an important role. When perfusion decreases, renin release rises, which again leads to a release of angiotensin II. This effects a constriction of the vessels and increases blood pressure.

6.3 Long-term regulation

The long-term regulation of the blood pressure, which is also the tardiest, is based on the alterations of the blood volume. The kidneys play an important role here, too, since they control how much water is excreted with urine. When the blood pressure rises, pressure diuresis increases the excretion of water, which causes the blood volume and thereby also the blood pressure to go down. This is promoted by ANP, which is released due to the increased pressure in the heart. If pressure and volume are too low, ADH increases the reabsorption of water in the kidneys.

7 Web links

This page was last edited on 15 May 2017, at 09:45.

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