How to measure blood pressure correctly: how it works and what matters

What is actually measured during a blood pressure measurement?

With every heartbeat, the heart pumps blood into the body. This creates pressure on the vessel walls. This pressure is called blood pressure.

Every blood pressure measurement always records two values:

• the systolic value: it indicates the pressure when the heart contracts and pumps blood into the circulation
• the diastolic value: it indicates the pressure when the heart relaxes again between two heartbeats

Why is correct measuring so important?

Blood pressure fluctuates quite naturally over the course of the day. Physical activity, stress, excitement, heat or cold can all influence the readings. That is why a single measurement often does not say much. Only repeated and correctly performed measurements show whether blood pressure is in fact persistently elevated.

Precisely for that reason, it is not only the result that matters, but also how it was measured.

When are blood pressure readings considered elevated?

Under the US guideline, high blood pressure in adults starts at 130/80 mmHg: it is present when at least one of the two values is persistently at or above this level. Readings of 120 to 129 systolic with a diastolic value below 80 count as elevated.

To assess this reliably, the values are measured not just once but several times, either at the doctor’s office, via a 24-hour measurement or through regular self-measurement at home.

How is blood pressure measured at the doctor’s office?

At the doctor’s office, the measurement is usually taken on the upper arm with a cuff. The classic approach uses a blood pressure device with a cuff, a pressure gauge and a stethoscope.

The cuff is placed around the bare upper arm and first inflated enough to briefly interrupt blood flow in the artery. The air is then slowly released. As soon as the blood flows again, sounds of flow become audible. The first audible sound marks the systolic value. When the sounds disappear again, the diastolic value is read.

Why is blood pressure measured several times at the doctor’s office?

An elevated value in a single measurement does not automatically mean high blood pressure. Many people are tense during a doctor’s visit, so blood pressure can temporarily rise. That is why, in practice, it is usually not measured just once.

For a careful measurement, it is important to:

• sit quietly for a few minutes before measuring
• measure blood pressure several times in a row
• keep short intervals between measurements
• measure on both arms at the start if possible

What is a long-term blood pressure measurement?

When it is unclear whether blood pressure is really persistently elevated, a 24-hour long-term measurement can be useful. For this, you wear a blood pressure cuff with a small portable device for a day. It measures automatically at regular intervals — during the day and at night as well.

The advantage: this makes it possible to see how blood pressure behaves in everyday life, whether it fluctuates strongly and whether it drops sufficiently at night. Nighttime elevated readings in particular can be medically important.

During the long-term measurement, you should continue everyday life as normally as possible. Particular exertion or anything unusual can be noted, so that the readings can be interpreted better afterwards.

Measuring blood pressure at home: why it makes sense

Self-measurement at home is particularly helpful because it provides readings under normal everyday conditions. It complements the measurement at the doctor’s office and can help detect persistently elevated blood pressure or monitor a treatment.

Instead of a long-term measurement, blood pressure can also be measured and documented at home in the morning and evening over several days. An average can then be formed from these readings.

Which devices are suitable for home use?

For self-measurement, electronic blood pressure devices are usually used. Upper-arm devices are generally the most reliable. There are also wrist devices, but these are more prone to error if the position is not exactly right. With wrist devices it is especially important that the device is held exactly at heart level during the measurement.

Not every device measures equally reliably. That is why a tested, good-quality device should be used whenever possible.

How to measure blood pressure correctly at home

For the readings to be meaningful, the measurement should always be carried out under conditions that are as identical as possible.

This is how to measure blood pressure on the upper arm correctly:

First, sit up straight and place both feet relaxed side by side on the floor. The arm should be free of clothing. The cuff is placed directly on the upper arm, about two to three centimeters above the crook of the elbow. It should fit firmly but not constrict, with room for two fingers underneath.

Then rest the arm relaxed on a table so that the cuff is roughly at heart level. Before starting, sit quietly for about five minutes.

During the measurement it is important to stay calm, breathe normally and not speak. After the first measurement, wait one to two minutes and then measure a second time. The results should be noted down.

It is best to measure in the morning and in the evening.

What can distort the measurement?

Even small mistakes can affect the readings. Unfavorable, for example, are:

• speaking during the measurement
• an incorrect sitting posture
• crossed legs
• an arm not positioned at heart level
• too little rest before the measurement
• exercise, smoking or caffeine in the 30 minutes before, or great excitement

How often should you measure?

How often you should measure depends on the situation. When blood pressure is being newly assessed or a therapy has been changed, more frequent measurements make sense. If blood pressure has been stable for a longer period, less frequent checks are often enough.

It is especially useful to measure regularly over several days before a doctor’s appointment and to bring the readings along. This allows the blood pressure situation to be assessed much better than on the basis of a single value.

Conclusion

Measuring blood pressure is far more than a quick glance at two numbers. What is decisive is measuring correctly, calmly and regularly. Only in this way can reliable readings be obtained and abnormalities detected early.

Those who measure their blood pressure correctly create the basis for spotting changes in time and deciding together with their doctor whether further action is needed.