General Medicine
High Blood Pressure (Hypertension)
Blood pressure that stays above 140/90 damages the heart, brain and kidneys silently. What the numbers mean, and what actually brings them down.
19 Aug 202612 min read
Diastolic
Pronounced dy-uh-STOL-ik
Also known as Diastolic pressure, The lower number, Diastole
Diastolic pressure is the lower of the two blood pressure numbers: the pressure remaining in the arteries while the heart relaxes and refills between beats. In a reading of 130 over 85, the diastolic pressure is 85.
In Cardiology
Every heartbeat has two phases. In systole the heart contracts and pushes blood out, producing the higher figure. In diastole it relaxes, the valves close, and the chambers fill again for the next beat — but the arteries stay under pressure throughout, because they are elastic and hold the blood back like a squeezed hose. That residual pressure is the diastolic number, and it never falls to zero in a living person.
What the numbers mean
A diastolic pressure below 80 mmHg is optimal; 80 to 84 is normal, 85 to 89 is high-normal, and 90 or above measured properly and repeatedly on separate occasions meets the definition of . The category is set by whichever of the two numbers is worse, so 150 over 78 is hypertension just as 128 over 96 is. Diastolic pressure also has a practical importance beyond classification: the coronary arteries fill during diastole, so it is the diastolic pressure that supplies the heart muscle itself.
Two patterns are worth recognising. In younger adults raised more often shows up in the diastolic number, and it should not be dismissed as unimportant because the top figure looks acceptable. After about the age of sixty the arteries stiffen, systolic pressure climbs and diastolic pressure often falls, widening the gap between them; that widening pulse pressure is itself a marker of arterial stiffness rather than a reassuring sign. A diastolic pressure under about 60 in someone on treatment is worth reporting, since over-treating can leave the heart's own supply short.
Where this comes up
Related terms
- SystolicSystolic is the top number in a blood pressure reading — the pressure in the arteries at the moment the heart contracts. It is the higher of the two figures.
- Blood pressureBP, Arterial pressureBlood pressure is the force of blood against the artery walls, written as two numbers in millimetres of mercury: the higher one is the pressure as the heart squeezes, the lower one the pressure as it refills. It varies through the day, so a diagnosis is never made on one reading.
- HypertensionHigh blood pressure, Blood pressure ka marzHypertension is blood pressure that stays high enough, over repeated proper measurements, to damage the arteries over time. It almost never causes symptoms, which is why it is found by measuring rather than by feeling unwell.
- AtherosclerosisHardening of the arteries, Arterial plaqueAtherosclerosis is the build-up of fatty, fibrous plaque inside artery walls, which stiffens them and narrows the channel blood flows through. It develops silently over decades and is the process behind most heart attacks and strokes.