What is blood pressure? Blood pressure is the force imposed by the circulating blood on the wall of blood vessels i.e. arteries. Each heart cycle (heart beat) consists of a contraction of the muscles of the heart, resulting in the pumping out of blood, with the highest pressure in the cycle called “Systolic”. This part of the cycle is followed by a short period in which the heart muscles (myocardium) are relaxing and the heart is filled up with blood. This period consists of the lowest blood pressure called “diastolic”. Therefore systolic (contraction) and diastolic (dilation) are used to describe the highest and lowest blood pressure in each heart beat.

Where is blood pressure measured? As the blood flows through arteries and away from the heart the resistance to the flow and the blood pressure decreases in the small arteries, capillaries and veins before returning to the heart. Consequently blood pressure is measured at the upper arm of an individual, which is closest to the heart for a more reliable reading. The blood pressure is recorded as Systolic over Diastolic pressure in mmHG. The optimal blood pressure in healthy adults should not be greater than 120: 80mmHg.

Does an individual’s blood pressure vary? Arterial blood pressure is constantly changing during the course of the heart’s cycle and is affected by numerous factors including anxiety. Furthermore, the pattern of blood pressure fluctuates during the day with the lowest levels in the morning and the highest in the afternoon and evening. It is also slightly lower in the summer than in the winter.

What is Hypertension? Hypertension is a clinical condition of the heart and blood vessles, where systolic blood pressure is increased above 140mmHg or diastolic pressure above 90 mmHg (please see the table). Persistent hypertension is proven to be a risk factor for heart attack, stroke, heart and kidney failure. Excessive body weight, high salt intake diets, smoking, high levels of alcohol consumption and stress are all linked with high blood pressure. Conversely, an increased intake of oily fish (which has a high concentration of omega 3 fatty acids), relaxation, exercise, increased K+ (potassium) intake to counteract/counter balance Na+(salt), and abstinence from tobacco and alcohol have proved to help control blood pressure and even ameliorate an already established hypertension.

NB Hypotension is the opposite of hypertension ie where blood pressure is below 90: 60 mmHg.

Adult’s classification of Blood Pressure/mmHg





< 90

< 60


90 - 119

60 - 79


120 – 139

or 80 – 89

Hypertension (Stage 1)

140 – 159

or 90 – 99

Hypertension (Stage 2)

160 - 179

or 100 - 109

Critical Hypertension

≥ 180

or ≥ 110

Published 05/06/2011, Review date May 2015