What is the medical term for high blood pressure?

Hypertension, and it is called the silent killer for an accurate reason: it produces essentially no symptoms while doing cumulative damage to arteries, heart, kidneys, eyes and brain. Most people who have it do not know, and a substantial share of those who do are not adequately treated.

The two numbers measure different moments. The upper figure is the pressure while the heart contracts, the lower while it relaxes and fills, and both are quoted in millimetres of mercury - a unit that survives from the original instrument, a column of mercury the pressure could physically hold up. Modern devices contain no mercury and the unit has stuck anyway.

It is also the condition that produced one of medicine's most useful accidents. Sildenafil was developed as a treatment for angina and hypertension, performed unimpressively in trials, and the researchers noticed an unexpected effect that trial participants were reluctant to return their unused tablets. Several classes of blood pressure drug have similar origins - the first ACE inhibitor came from the venom of a Brazilian pit viper, whose bite drops the blood pressure of its prey.