The heart itself, of course, needs its own blood supply in order for it to keep working. This is known as the coronary circulation, with the coronary artery delivering oxygenated blood to the heart itself, and the coronary vein taking deoxygenated blood away. If the coronary artery becomes narrowed or, worse still, blocked – for example, by a fat deposit – the amount of oxygen reaching the heart is reduced and can result in an angina or heart attack. The latter is also known as a myocardial infarction; myocardial refers to the heart muscle, and an infarction means a breach in the blood supply.

Another potential issue is if the blood isn’t being pumped at the right force around the body. This is what the term blood pressure refers to, and it varies according to how hard the heart is pumping and how much resistance there is in the arteries. The resistance can go up if the arteries are narrowed, not just by fat deposits on the walls, but also because of the nervous system telling the muscles inside them to contract, perhaps because of trying to retain body heat when the environment is cold, or as a reaction to a medicine. Blood pressure can also alter if the blood volume changes, for example, if someone is dehydrated, their blood pressure may drop.

Measuring blood pressure

The two figures that comprise a blood pressure measurement are the systolic and diastolic pressures – the former being the higher number because it shows how strongly the ventricles are contracting in order to send blood around the body, and the latter the lower number during which the ventricles are relaxed because they are filling with blood.

Measuring blood pressure involves fixing a cuff around the upper arm – usually at around the same level as the heart – and then inflating it until the blood flow through the brachial artery is obstructed. By gradually deflating the cuff, the point at which the heart beat returns gives the systolic pressure, with the diastolic measurement taken when the pulse apparently disappears again as air continues to be let out of the inflated cuff.