In high blood pressure, usually both the systolic and the diastolic pressures are elevated. Isolated systolic hypertension is increasingly common with advancing age. In almost everyone, blood pressure increases with age, with systolic pressure increasing until at least age 80 and diastolic pressure increasing until age 55 to 60, then leveling off or even falling. Malignant hypertension is a particularly severe form of high blood pressure that, if left untreated, usually leads to death in 3 to 6 months. It's fairly rare, occurring in only about 1 in every 200 people who have high blood pressure, but it's several times more common in blacks than in whites, in men than in women, and in people of lower socioeconomic status than in those of higher socioeconomic status.
Malignant hypertension is a medical emergency.
The pressure in the arteries can be increased in various ways. For one, the heart can pump with more force, putting out more fluid each second. Another possibility is that the large arteries can lose their normal flexibility and become stiff, so that they can't expand when the heart pumps blood through them. Thus, the blood from each heartbeat is forced through less space than normal, and the pressure increases. That's what happens in elderly people whose arterial walls become thickened and stiff because of arteriosclerosis.