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Blood pressure: what it is and how to measure it

By Cristiano Antonino On Jan 1, 2023

Blood pressure is the pressure that blood exerts on the walls of the arteries of the cardiovascular system. It depends on both the amount of blood pumped by the heart and the resistance to blood flow

Pressure rises and falls according to the contractions of the heart: it is highest when the heart contracts (systole) to push blood into the circulation (systolic pressure) and lowest when the heart relaxes (diastole) to fill with blood (diastolic pressure).

Blood pressure, normal values

The unit of measurement of blood pressure is the millimetre of mercury (mmHg). Values recognised as normal in the healthy population range between 110-130 mmHg systolic.

One speaks of hypertension (high blood pressure) when the usual blood pressure values are at or above 90 mmHg minimum and/or 140 mmHg maximum.

The higher the blood pressure, the greater the risk of damage to the heart and blood vessels in organs such as the brain and kidneys.

Most hypertensives have no symptoms, which is why hypertension is called the ‘silent killer’.

The only way to know if you are hypertensive is, therefore, to have your blood pressure measured periodically.

If uncontrolled, hypertension can lead to serious cardiovascular problems such as heart attack, increased heart volume and heart failure. Against high blood pressure, the World Health Organisation recommends to:

promote a healthy lifestyle and a healthy diet
avoid alcohol consumption
exercise regularly and maintain a normal body weight
stop smoking and exposure to second-hand smoke
learn to manage stress

Low blood pressure or hypotension, on the other hand, is found in a person whose maximum arterial blood pressure is below 100 mmHg.

How blood pressure is measured

Blood pressure is commonly measured at the level of the artery in the arm (humeral artery).

The measurement is taken on the patient in a sitting position, with the arm resting on a horizontal plane at heart level.

The instrument used to measure pressure is the sphygmomanometer, a device consisting of a cloth cuff fitted with an air chamber, a pump with a valve to inflate and deflate the air chamber, and a mercury graduated column (0 to 300 millimetres) where the pressure values are read.

Automatic electronic devices also exist, but the mercury sphygmomanometer is still considered the most accurate and reliable instrument and remains the one generally used by doctors.

Digital blood pressure monitors, which are more convenient to use, are suitable for home self-measurement by the patient himself.

When measuring blood pressure, one must

allow the patient to sit and relax for a few minutes in a quiet room;
take at least two measurements, with an interval of 1 or 2 minutes between each;
the first time measure the blood pressure in both arms to identify possible differences due to peripheral vascular disease;
in the elderly, in diabetics and in all cases where orthostatic hypotension is suspected, measure blood pressure 1 and 5 minutes after the patient has assumed the upright position;
patients who have eaten, drunk coffee or tea, smoked or undergone physical exertion must wait at least one hour before measurement.
Blood pressure is subject to fluctuations.

This is why the diagnosis of hypertension or hypotension requires numerous measurements during several medical examinations.

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