Systolic and diastolic blood pressure: what is recorded during the measurement

Anyone who measures their blood pressure always gets two values: systolic and diastolic blood pressure. Both are part of every blood pressure measurement and provide information about how high the pressure in the vessels is during different phases of the heartbeat. To interpret readings correctly, it is important to understand how these two values arise, what exactly is recorded during the measurement and why both values are important.

What do systolic and diastolic blood pressure mean?

The heart does not pump blood through the body evenly, but in surges. With every heartbeat, the left ventricle contracts and moves blood into the main artery. At that moment, the pressure in the vessels rises. This highest pressure during the heartbeat is called systolic blood pressure. It is the upper value of a blood pressure measurement.

This is followed by the relaxation phase of the heart. During this time, the heart chambers fill with blood again, and the pressure in the vessels drops. The lowest pressure during this phase is called diastolic blood pressure. It is the lower value of the measurement.

A blood pressure reading of 120 over 80 mmHg therefore means that the pressure in the vessels rises to 120 mmHg during the heartbeat and drops to 80 mmHg during the relaxation phase.

How is blood pressure measured?

Every blood pressure measurement records exactly these two pressure points: the highest pressure during the heart’s ejection phase and the lowest pressure during the relaxation phase. The values are given in mmHg, that is, in millimeters of mercury.

Blood pressure is usually measured with a cuff on the upper arm. At the doctor’s office this is done either manually with a cuff, stethoscope and pressure gauge, or with an electronic device. At home, electronic blood pressure devices are generally used as well.

The cuff is placed around the upper arm and filled with air. This temporarily compresses the artery in the arm. The device or the examiner then slowly releases the pressure again. In doing so, it is determined at which pressure the blood begins to flow again and when the blood flow is once more unimpeded. In this way the systolic and diastolic values are determined.

Why do measurements always produce two values?

Many people pay attention above all to the upper value. In reality, though, both values are important. The systolic value shows how strongly the pressure rises when the heart pumps blood into the circulation. The diastolic value shows how high the pressure in the vessels remains between two heartbeats.

Because blood pressure in the body is not constant but changes with every heartbeat, a blood pressure measurement always consists of these two figures. Only together do they give a meaningful picture.

Which values are considered unremarkable in a blood pressure measurement?

Blood pressure readings should always be considered in the context of the measurement situation. In general, values in the lower range are considered favorable. Elevated values should be observed and, if they occur repeatedly, clarified medically. At the latest with persistently elevated readings, a more detailed assessment is required.

What matters here is this: a single measurement is not enough to reliably diagnose high blood pressure. Blood pressure fluctuates over the course of the day and can be influenced, for example, by stress, excitement, exercise or pain. Readings should therefore always be taken several times and under conditions that are as calm as possible.

Why correct measuring is so important

For the systolic and diastolic values to be assessed reliably, the blood pressure measurement must be carried out correctly. Even small mistakes can lead to incorrect results. These include, for example:

• too little rest before the measurement
• speaking during the measurement
• crossed legs
• an incorrectly placed cuff
• an arm not positioned at heart level

Before the measurement you should therefore sit quietly for a few minutes. It is best to measure while seated, with a relaxed arm and a correctly placed cuff. It is often sensible to take two measurements in a row and to note down the readings.

What does it mean when only one value is elevated?

Both values are not always abnormal at the same time. Sometimes only the systolic — that is, the upper — value is elevated. This is especially common in older people. The cause is often that the large vessels lose elasticity with age. The pressure then rises more strongly during the heartbeat.

It can also happen, however, that the diastolic — that is, the lower — value in particular is elevated. This is seen more often in younger people. In such cases, it should be medically checked whether particular causes are behind it, such as hormonal disorders, kidney disease or other forms of secondary high blood pressure.

What is decisive, therefore, is not only that a measurement is taken, but also how the two values are assessed in relation to each other.

Is the upper or the lower value more important?

For assessing blood pressure, both values are fundamentally important. The systolic value and the diastolic value provide different information about the pressure in the vessels. Both can indicate an increased risk of cardiovascular disease.

That is why, with a blood pressure measurement, you should never look only at the upper or only at the lower value. Only the combination of both values makes a sensible interpretation possible.

Check blood pressure regularly

High blood pressure can persist for a long time without symptoms. That is precisely why it makes sense to check your own readings regularly. Especially from middle age onwards and with known risk factors, blood pressure should be measured again and again or checked at the doctor’s office.

Anyone who repeatedly measures elevated readings should have them clarified medically. Because only through a correct assessment of several measurements can it be reliably determined whether there is an increase in blood pressure that requires treatment.

Conclusion

Systolic and diastolic blood pressure are the two basic values of every blood pressure measurement. They show how high the pressure in the vessels is during the heartbeat and during the heart’s relaxation phase. For the values to be reliable, a correct measurement is essential. Those who measure their blood pressure correctly and regularly create the basis for detecting changes early and having them interpreted correctly from a medical standpoint.