The blood pressure (vessel pressure) is the pressure of the blood that prevails in blood vessels. It is defined as the force per area that is exerted between blood and the vessel walls of arteries, capillaries or veins. The term blood pressure usually refers to the pressure in the large arteries. The unit of measurement for blood pressure is mmHg (millimeter of mercury), this is also the legal unit of measurement for blood pressure in the EU and may only be used for this purpose.
In medical practice, blood pressure is usually understood as arterial blood pressure and measured in the arm arteries at heart level by applying a blood pressure cuff (see: Measuring blood pressure). This measurement gives two values, the systolic and the diastolic value. The systolic value arises during the ejection phase of the heart and is indicated by the upper value, the diastolic (lower) value describes the pressure that permanently prevails in the arterial vascular system. The blood pressure values for the arm artery should be about 130/80 mmHg.
Classification of blood pressure
The following list clarifies the classification of the measured blood pressure values and shows that above a value of 140/90 from to high blood pressure, the so-called arterial hypertension is spoken.
- <120/ <80
- 120-129/ 80-84
- High normal:
- 130-139/ 85-89
- high blood pressure Grade 1:
- 140-159/ 90-99
- high blood pressure Grade 2:
- 160-179/ 100-109
- high blood pressure Grade 3:
- >179/ >110
(from the guidelines of the German Hypertension League)
The pressure conditions in the various areas of the bloodstream are different. When "blood pressure" is used without a more detailed definition, it usually means arterial pressure in large vessels at heart level. This is usually measured in one of the large arteries in the arm (brachial artery).
The blood pressure readings are overpressures compared to the atmosphere. However, they are not given in the SI unit Pascal (Pa), but in the traditional unit mm Hg. This has a historical background, as blood pressure was previously measured using a mercury manometer. The blood pressure is then given in a pair of numbers consisting of a systolic and a diastolic value. The systolic is the maximum value, which is determined, among other things, by the cardiac output. The diastolic value is the minimum value in the heart filling phase. For this reason, it depends, among other things, on the elasticity and state of filling of the large vessels. For example, one speaks of a blood pressure of "110 to 70". The values can vary depending on the position of the body. Because of the force of gravity in the lower half of the body when standing, blood pressure is higher than when lying down, but above the hydrostatic level it is lower when standing than when lying down. As a rule, the mean blood pressure values correspond to the values when lying down.
Development of blood pressure
Of the systolic arterial pressure is caused by the Ejection capacity of the heart. The diastolic pressure corresponds to the constant pressure in the arterial vascular system. The Air vessel function and Extensibility (Compliance) of the large arteries limit the systolic value during ejection, so that the blood pressure cannot become too high in a healthy person. Through her Buffer function they also ensure a low blood flow during the diastole. You have to do this during physical exertion Cardiac output and blood circulation in the periphery increase and the Vascular resistance sinks. The systolic arterial blood pressure rises faster than the diastolic value.
Arterial regulation of blood pressure
Since both too high and too low arterial pressure can damage the organism as well as individual organs, the blood pressure must be regulated within certain ranges. However, it must also be possible to adjust and increase the arterial pressure with changing loads. The basic requirement for this regulation is that the body can measure the blood pressure itself. For this purpose, so-called baroreceptors are located in the aorta, carotid artery and other large vessels. These measure the expansion of the arteries and pass the information on to the autonomic nervous system. The body can adapt to the given conditions.
For a more detailed explanation, a distinction is made between short-term, medium-term and long-term blood pressure regulation. The mechanisms of short-term regulation bring about an adjustment of the arterial pressure within seconds. The most important mechanism is the baroreceptor reflex. If there is higher pressure in the vascular system, the arterial walls are stretched more. This is registered by the baroreceptors in the vessel walls and the information is passed on to the sympathetic nervous system via the medulla oblongata in the spinal cord. There is a stretching of the vessels and a decrease in the ejection volume from the heart, as a result of which the pressure decreases again somewhat. If, on the other hand, the pressure in the vessels is too low, the sympathetic nervous system reacts by narrowing the vessels and increasing the volume of blood ejected. The blood pressure rises.
If the blood pressure is to be adjusted in the medium term, the renin-angiotensin-aldosterone system reacts in particular. This is made up of various hormones that are released in the kidney and heart. If the body registers too little kidney blood flow, then renin is released from the kidneys. This leads to the activation of angiotensin 2 and aldosterone and thus to a narrowing of the vessels. The blood pressure rises. If the pressure in the kidneys is too high, the release of renin is inhibited and the aldosterone effect cannot take place.
Blood pressure can also be regulated in the long term. The kidneys also play an important role in this. If the mean arterial pressure increases too much, increased excretion from the kidneys (pressure diuresis) reduces the volume in the vascular system and thus the pressure. If the increased blood pressure puts too much strain on the auricles, the ANP is released from the heart. This also causes an increased excretion of fluid from the kidneys. If the blood pressure drops too much, the neurohypophysis releases the antidiuretic hormone (ADH). This leads to increased water reabsorption from the collecting ducts and distal tubules of the kidneys and thus to an increase in volume in the vascular system. In addition, the ADH itself has a vasoconstricting effect via special V1 receptors (vasoconstrictor). The renin-angiotensin-aldosterone system also comes into effect with long-term regulation, which, in addition to the vasoconstricting effect, also causes increased retention of water and sodium in the kidneys and thus in turn reduces the volume in the vascular system.
You can find information on low blood pressure here: low blood pressure
Blood pressure during pregnancy
Blood pressure should be closely monitored during pregnancy, as both permanently low blood pressure and permanently high blood pressure (pregnancy high blood pressure) can have negative effects on mother and child. At the beginning of pregnancy the blood pressure drops because the body produces more progesterone and estrogens, which relax the blood vessels in order to optimally supply the uterus and the embryo with oxygen and nutrients.
The result is low blood pressure, especially in the first trimester of pregnancy.
In principle, this low blood pressure is harmless, but should not fall below values of 100/60 mmHg for a long time, as otherwise the uterine blood flow is insufficient to supply the child with enough oxygen and nutrients.
Blood pressure should not be too high during pregnancy. Values of over 140/90 mmHg are considered to be elevated and there is a risk of pregnancy hypertension
If high blood pressure occurs before the 20th week of pregnancy, it probably already existed before the pregnancy. This suspicion is confirmed if the blood pressure remains high even after pregnancy.
About 15% of all pregnancies develop a hypertensive pregnancy disease. Pregnant women older than 40 years or with a multiple pregnancy are particularly at risk. Persistently high blood pressure during pregnancy must be treated, as the risk of preeclampsia in women with gestational hypertension is 25%. In preeclampsia, in addition to the pathologically increased blood pressure, there is a loss of protein via the urine and water retention in the tissue. Preeclampsia is problematic because it can lead to severe complications such as eclampsia or HELLP syndrome in up to 0.5% of pregnant women.
High blood pressure during pregnancy should therefore always be treated by a doctor and in the vast majority of cases it can be adjusted with high blood pressure medication so that there is no danger to mother or child.
Read more under the topic:
- Pregnancy Hypertension - How Dangerous Is It?
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Blood pressure in children
The blood pressure in children is dependent on age, gender and height, but also other factors such as disposition or body weight play a role. Even in children, blood pressure is a Cuff on the upper arm measured. In order not to falsify the results of the blood pressure measurement due to the cuff that is too large for adults, there are special blood pressure cuffs for children.
Newborn have an average blood pressure of 80/45 mmHg, in the course of development the blood pressure continues to rise with age and reaches the at around 16-18 years of age Optimal values for an adult, which at approx 120/80 mmHg lie. An average five-year-old child has a blood pressure of around 95/55 mmHg, whereas a ten-year-old child already has values of 100/60 mmHg. In twelve-year-olds, the blood pressure is around 115/60 mmHg, 16-year-old teenagers achieve almost the optimal values of adults with a blood pressure of 120/60 mmHg.
The values given for children are of course only Averages and can deviate up or down by up to 15 mmHg even without disease value, depending on Stage of development, size and weight of the child. It is noticeable that especially young teenage girls often have rather low blood pressure, which, however, does no disease value Has.