Sign up ×
Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. It's 100% free, no registration required.

I wanted to understand what is the difference between systolic and diastolic readings of blood pressure. I understand 120-80 to about 100-60 is considered normal but does the difference in the two values in the reading hold any significance?

I have read some text here and here.

share|improve this question

2 Answers 2

up vote 13 down vote accepted

The difference between systolic (the upper number) and diastolic (the lower number) pressures is known as the pulse pressure:

Systemic pulse pressure = Psystolic - Pdiastolic

For a typical blood pressure reading of 120/80 mmHg the pulse pressure is therefore 40 mmHg.

It is proportional to stroke volume, the amount of blood pumped from the heart in one beat, and inversely proportional to the compliance or flexibility of the blood vessels, mainly the aorta.

A low (also called narrow) pulse pressure means that not much blood is being expelled from the heart, and can be caused by a number of factors, including severe blood loss due to trauma, congestive heart failure, shock, a narrowing of the valve leading from the heart to the aorta (stenosis), and fluid accumulating around the heart (tamponade).

High (or wide) pulse pressures occur during exercise, as stroke volume increases and the overall resistance to blood flow decreases. It can also occur for many reasons, such as hardening of the arteries (which can have numerous causes), various deficiencies in the aorta (mainly) or other arteries, including leaks, fistulas, and a usually-congenital condition known as AVM, pain/anxiety, fever, anemia, pregnancy, and more. Certain medications for high blood pressure can widen pulse pressure, while others narrow it. A chronic increase in pulse pressure is a risk factor for heart disease, and can lead to the type of arrhythmia called atrial fibrillation or A-Fib.

share|improve this answer

The pulse pressure,being the differential pressure is an indication of how hard the heart is working,the higher this is the more load on heart,remenber the heart is a pump,it has an inlet (low pressure) and an outlet (high pressure) if your blood flow is good and not restricted the ratio will be low,the heart will not work so hard. I have found good readings seem to be around 30 and bad readings 50 or more. ie 120/80 will be 40

share|improve this answer
Welcome to the site. Please provide referenced scientific sources, or a scientific explanation based upon solid reasoning when answering a question. Right now, your answer is based solely upon personal opinions, and is incomplete. – Raoul Jan 28 at 11:36
RaoulThis is so easy to understand,basic mechanics,there are many references to this, – user13242 Jan 29 at 4:18

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.