Blood pressure

The blood pressure is the pressure of the blood in a blood vessel. In the jargon, the term vessel pressure will be used. It is the force per unit area that is exerted between the blood and blood vessel walls of the arteries, capillaries and veins, with the blood pressure usually the pressure in the larger arteries is intended. Blood pressure is usually given in mm Hg ( millimeters of mercury ). Within the EU, this is also the legal unit of measurement for blood pressure.

  • 5.1 Short-term arterial pressure regulation
  • 5.2 Medium-term arterial pressure regulation
  • 5.3 Long-term arterial pressure regulation
  • 5.4 Organ-specific pressure regulation


The blood pressure should be under normal conditions and without taking into account individual differences, ideally at 120 /80 mm Hg.

From 140 /90 mm Hg one speaks internationally defined by high blood pressure, which adversely affects health and life expectancy. This value is also recommended in the joint guidelines of the European Societies of Hypertension and Cardiology, as amended in 2013 as the target for almost all patients.

In various areas of the circulatory system there are different pressure ratios. When speaking without immediate addition of the blood pressure, then you usually mean arterial pressure in the large arteries at heart level (BD or BP common is the synecdoche RR for Riva - Rocci ), which is usually measured at the brachial artery of the upper arm. In addition, the central venous pressure is also of medical interest.

The blood pressure readings are overprints from the atmosphere and are not in the SI unit Pascal (Pa), but in the traditional unit mm Hg ( millimeters of mercury ) indicated because earlier for pressure measurement usually mercury manometer were used.

The type of arterial pressure is conventionally as a number pair of systolic (maximum value depends inter alia on the cardiac output ) and diastolic pressure (minimum value, in cardiac filling phase and, therefore, among other things, also depends on the elasticity and the filling state of the great vessels ). We then say, for example, " 105 to 70 ".

At rest, the normal systolic arterial pressure from 13.3 to 17.4 kPa ( 100-130 mm Hg) and the diastolic value from 8.0 to 11.3 kPa ( 60-85 mm Hg). In addition, the mean arterial pressure and pulse amplitude, see (difference between systolic and diastolic arterial pressure value ) application. The mean blood pressure data correspond to those lying down. When standing, the blood pressure due to gravity in the lower half of the body is higher than lying down, while it is above the hydrostatic indifference level lower than when lying down.

In the rescue medicine the fingernail test is a method of orienting determination of peripheral blood circulation situation, which allows a rough conclusion on the circulatory situation, especially in little time for the investigation of any injuries, such as disasters and accidents. Here, the nail is pressed briefly into the nail bed, so that this colored white. If the time is up for re- coloring more than one second, there is a lack of blood supply. However, previous injuries or nail polished nails can distort this result.

Physiology of the arterial pressure

The systolic arterial pressure generated by the ejection force of the heart. The diastolic arterial pressure corresponds to the continuous pressure in the arterial vascular system. The compliance of the large arteries and their Windkessel function limit the ejection systolic value and, through its buffer function for one, albeit lower, blood flow in diastole.

Physical exertion to take cardiac output and blood flow to the periphery. The vascular resistance decreases. The systolic arterial pressure rises more sharply than the diastolic value.

Measurement of the arterial pressure

One distinguishes the direct ( invasive and bloody ) arterial pressure measurement by a pressure sensor in a blood vessel of the indirect ( non-invasive, bloodless ) measurement, which is performed by means of a blood pressure cuff to a limb.

The direct arterial pressure measurement is used primarily by anesthesiologists to monitor during surgery and intensive care units.

The indirect measurement of arterial pressure is due to the rapid and safe implementation today the drug of choice in most fields of medicine. One differentiates the manual measurement of the automatic means of a digital device (see sphygmomanometer ). The manual measurement can be auscultation, palpation or oscillatory performed.


For the arterial pressure measurement to determine two values: the upper or first value is called the systolic arterial pressure. He characterizes the pressure in the heart at the moment in which the heart muscle squeezes maximum. Once relaxed, the heart muscle, the arterial pressure at the second or lower value (diastolic arterial pressure) decreases.

The increase in systolic arterial pressure exertion and stress can be the cause.


The diastolic arterial pressure is due to the resistance ratios in the blood vessels. So deposits in the blood vessels (atherosclerosis ) can increase the arterial pressure.


The arterial pressure is not a fixed value and fluctuates daily routine, depending on what activity is being exercised. During physical exertion, stress and excitement, he increases in physical and mental rest periods it drops.

Suffers a man, however, under arterial hypertension (high blood pressure ), the pressure in the blood vessels remains elevated even at rest: The heart has to constantly pump with increased effort. This overloads the heart and vessel walls. An arterial pressure exists when repeated measurement, a value of more than 140/90 mm Hg is reached.

Hypertension is recognized as a risk factor for developing cardiovascular disease. Come to the risk factor arterial hypertension still overweight or obese ( very overweight ) and another risk factor, such as diabetes (diabetes), smoking, or dyslipidemia (increased cholesterol and LDL ) was added, there is a significantly increased risk in the course of living a heart - cardiovascular disease to suffer. It is also described by the cardiometabolic risk factors.

Classification of blood pressure values ​​according to WHO / ISH

The World Health Organization (WHO ) published in 1999 together with the International Society of Hypertension (ISH ) 2003 revised WHO / ISH hypertension guidelines ( German WHO / ISH guidelines high blood pressure) with the following classification.

Arterial pressure regulation

The arterial pressure must be within certain bandwidths move, because both too high and too low arterial pressure damage the organism or individual organs. At the same time, the arterial pressure must but even under changing loads (eg a hard endurance run or rest, sleep ) to be adjusted.

Necessary prerequisite of arterial pressure control is that the body can measure the arterial pressure in the vessels themselves. In the aorta, carotid arteries, as well as other major arteries in the chest and neck measure pressure-sensitive sensory cells, the baroreceptors, the stretching of the arterial wall.

Short-term arterial pressure regulation

The mechanisms of short-term arterial pressure regulation fall within seconds. The most important mechanism here is the Barorezeptorenreflex. Stretches a higher pressure (and thus a higher volume ) of the arterial wall, the baroreceptors send out a reflex inhibitory impulses to the sympathetic nervous system in the circulatory center of the medulla oblongata ( extended spinal cord). At excessively low arterial blood pressure values ​​, the number of inhibitory impulses is however more from reflex, so it comes to irritation of the sympathetic nerve in the medulla oblongata. Due to a decrease in the inhibition the ejected from the heart blood volume is thus increased, additionally, it may come to vasoconstriction in the skin, kidneys and gastrointestinal tract. In the right and left atrium are stretch receptors that respond in a similar manner.

Medium-term arterial pressure regulation

This is particularly the renin -angiotensin -aldosterone system call. Decreases renal blood flow from (for example, by a generalized arterial pressure or renal artery narrowing), this leads to increased renin release in the kidney and ultimately leading to an increase in concentration of the strong vasoconstrictor angiotensin II

Long-term arterial pressure regulation

About the regulation of blood volume and thus blood pressure in this case the kidney is particularly involved. With increasing mean arterial pressure, the pressure is lowered by Druckdiurese and increasing fluid excretion. With drop in blood pressure or blood volume ADH ( antidiuretic hormone) is secreted from the posterior pituitary, and thus the water reabsorption in the distal tubule and collecting duct of the kidney by incorporation of aquaporins stimulates 2 (water channels). About special V1 receptors ADH acts in addition blood vessel narrowing. It comes on the already mentioned renin -angiotensin -aldosterone system, ultimately to the release of aldosterone, which also contributes through enhanced retention of water and sodium in the kidney to maintain blood pressure over volume increase. When the blood volume exerts increased pressure on the atria, there transmitters, such as ANP are released, which also increase the fluid excretion in the kidney.

See also: kidney functions

Organ-specific pressure regulation

To ensure a uniform blood supply, some institutions are able to respond directly to variations in blood pressure. This mechanism is referred to as the Bayliss effect or myogenic autoregulation, since the vascular muscles even without assuming the regulation.


  • At low blood pressure see hypotension.
  • Too high venous blood pressure see venous hypertension (peripheral ) and central venous blood pressure.

Static blood pressure

Under the static blood pressure is defined as a pressure of about 6 to 7 mm Hg, which sets in at a standstill of the heart while lying down in the vessels. The static blood pressure is an indicator of the filling state of the receptacles. It depends on the blood volume and vascular capacity.