Diastolic pressure is the lower number in the record of blood pressure. It is the pressure at the moment the heart is relaxed and filling with blood between beats.
It reflects above all the tone (resistance) of the small vessels. In young people a rise in the lower pressure is an important early sign of hypertension, whereas in older adults systolic comes to the fore.
Reference ranges
Diastolic BP (mmHg), by pressure category:
| Normal | < 80 |
| Hypertension stage 1 (ACC/AHA) | 80 – 89 |
| Hypertension stage 2 | ≥ 90 |
| Low | < 60 (assess by symptoms) |
What an elevated level means
Elevated diastolic pressure means the small vessels are in constant tone (spasm) and the heart finds it harder to "rest" between beats. In young people this is often the first sign of developing hypertension.
A persistently high lower pressure, like a high upper one, damages the vessels and raises cardiovascular risk, accelerating atherosclerosis.
What a low level means
Low diastolic pressure (< 60) can be a normal variant, but it deserves attention in two situations: with symptoms (weakness, dizziness) and in older adults with high upper pressure.
The point is that the heart receives blood precisely in diastole: if the lower pressure is too low, coronary blood flow can suffer. Causes also include dehydration, blood loss and an overdose of antihypertensives.
How the test is done
Diastolic is measured with a monitor at the same time as systolic by the standard rules (at rest, seated, the cuff at heart level, 2–3 readings).
It is always assessed together with the upper number and in the light of age: the same value means different things in a young and an older person.
What affects the value
- Small-vessel tone and stress — raise the lower pressure.
- Salt, excess weight, alcohol — raise it.
- Age — in older adults diastolic can fall.
- Physical activity, weight loss — lower it.
- Dehydration, blood loss — lower it.
- Antihypertensive medications — lower it.
Assess blood pressure and risk
Determine your blood-pressure category and the risk of hidden hypertension:
Frequently asked questions
What does high lower pressure with a normal upper one mean?
An isolated rise in diastolic is more common in young and middle-aged people and usually reflects increased tone of the small vessels. It is an early sign of hypertension that should not be ignored even with a normal upper number.
Is low diastolic pressure dangerous in older adults?
It can be. The heart is supplied with blood in diastole, so a too-low lower pressure (especially < 60) against a high upper one can impair coronary blood flow. Such a situation is assessed together with a doctor.
Why is the lower pressure more important in young people?
In young people the vessels are elastic, and a rise in pressure shows up earlier as a rise in diastolic (the tone of the small vessels). With age the arteries become stiffer, and systolic pressure becomes the leading risk marker.
Related terms
Sources
- American Heart Association — Understanding Blood Pressure Readings
- 2017 ACC/AHA BP classification (review). NCBI/PMC
- MedlinePlus (NIH) — Low Blood Pressure