Systolic and diastolicSystole · Diastole

Systolic and diastolic are the two numbers in a blood pressure reading. Systolic, the higher figure, is the peak pressure in your arteries as the heart contracts. Diastolic, the lower one, is the trough as the heart relaxes and refills between beats.

Both carry information and their relative importance changes with age. Diastolic pressure predicts risk more strongly in younger adults, while systolic pressure becomes the dominant predictor from middle age onwards as arteries stiffen.

That stiffening is why isolated systolic hypertension, a high top number with a normal bottom one, is the commonest pattern in older people. Stiff arteries cannot absorb the pulse of each beat, so the peak rises while the trough does not.

The gap between them, pulse pressure, is therefore a rough marker of arterial stiffness, and a wide gap in an older person is a recognised risk signal rather than a curiosity.

Both numbers move constantly. They dip during sleep, rise on waking, climb with stress, caffeine, cold, a full bladder and the act of being measured in a clinic, which is why diagnosis rests on repeated readings, usually at home or over 24 hours, rather than on one visit.

Technique changes the answer substantially: sitting, back supported, feet flat, arm at heart height, correct cuff size, several minutes of quiet, no talking.

In practice, record both numbers rather than only the top one, average several readings across days, and take a persistently raised average to a GP. Our heart age calculator uses systolic pressure alongside your other numbers.