Definition of high blood pressure
What to do in case of hypertension?
For a better understanding of blood pressure The follow-up of a high blood pressure
High blood pressure damage High blood pressure and special cases
Why does high blood pressure exist? The self-measurement of blood pressure
How to measure high blood pressure? About Us
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II – For a better understanding of blood pressure

Description of the arteries and the blood pressure
2.1 - Working of the blood circulation: the vessel and the heart
2.2 - Definition of the blood pressure
Who is concerned with high blood pressure?
2.3 - Epidemiological data
2.4 - Influence of sex
2.5 - Race
The risk is raised by the existence of other diseases
2.6 - Cholesterol
2.7 - Diabetes
2.8 - Tobacco
2.9 - The age

2.2 - Definition of the blood pressure

The purpose of the blood pressure is to push blood and the red corpuscles to the tissues of the organism so that they can perform their function: to oxygenate organs. At the tissue level, blood pressure is very low and the speed of the blood has been slowed down so that oxygen can pass to the organs more efficiently.

The blood pressure is defined as the product between the multiplication of the resistance of the vessel in which there is the blood and the cardiac output.

Blood pressure = Resistance of the vessels x cardiac output


The resistance of the vessel corresponds to the rigidity of the wall of the artery, which can vary in many circumstances.

The cardiac output corresponds to the capacity of the heart to pump blood at each contraction (or systole), thus corresponding to a volume of blood pumped per minute (approximately 5 litres per minute).

The resistance of the vessel may rise for instance when the nervous system increases its tonicity or when age causes a thickening of the wall.

In the same way, when the heart beats in a more energetic way, the cardiac output raises thus making the blood pressure increase.

- Fluctuation of the blood pressure

- According to the localization

The more the blood moves away from the heart in the arteries the less significant the blood pressure will be. The reason is that the oxygen carried along by the blood must have enough time to oxygenate the organs.

In practice, it was noted that the blood pressure measured at the arm is close to the one measured in the aorta. But the blood pressure measured at the wrist seems to be less reliable.

- According to time

The blood pressure fluctuates in the short, middle or long-term.

In fact, there is a cycle of blood pressure over the life span. It is higher for older subjects than for young subjects. Thus, the age is a significant factor of the blood pressure variation.

But the blood pressure also varies according to seasons, since it is lower in summer than in winter.

Variation of the systolic blood pressure during the year

The blood pressure also varies over 24 hours; it is higher in working life, i.e. the day, than in period of sleep. A recording of the blood pressure during 24 hours, with an ambulatory blood pressure monitor, provides this data.

Lastly, the blood pressure fluctuates in the short-term according to our emotions, the respiratory rate and our nervous commands, which automatically control the blood pressure.

File last reviewed on : 18 dec 2011
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