Blood pressure, balloons and hot water bottles
Channel: York Cardiology
Date: 23/10/2022

The whole subject of blood pressure is poorly understood, poorly taught and poorly managed. Today I wanted to try and simplify the subject using the analogy of balloons and hot water bottles.

What is high blood pressure?

I was once upon a time giving a lecture and there were clinicians present from Europe as well as America and I asked the question ‘What is high blood pressure?’  - the Americans in the audience said anything higher than 120/80 is high. The europeans said anything above 140/90 is high. So my response was that why don’t we pay for all the American ‘hypertensives’ (ie who have BPs of upto 139/89) get a one way ticket to Europe and encourage them to settle there. This would cure their hypertension without subjecting them to a lifetime of medications! How ludicrous is it that a chronic condition could be ‘cured’ by simply moving a patient to a different continent.

 The definition of high blood pressure is not a number. The definition of high blood pressure should be ‘that blood pressure that does that individual some form of harm - if it is not doing you any harm then it is not high for you’ and if we think about it this way we can start to understand how ridiculous the whole notion of taking the whole population and calibrating them against a single set of numbers - which, ironically, changes every few years because the so called experts change their mind every few years.

Another point to mention is that high blood pressure is important for 2 reasons:

The high blood pressure is a symptoms of something else going on in the body in which case you want to treat and identify the thing that is underlying the high BP readings (in some way if you don’t do this you are doing the patient a disservice because you have simply silenced a scream for help)

The blood pressure numbers themselves are causing you harm - in which case, treating and lowering the numbers does make sense. Most of modern day management of blood pressure concerns itself with simply lowering the number and not identifying and tackling the underlying causes and this is perhaps why despite all this emphasis on hitting the numbers hard with pills has not made a huge difference to the incidence of complications such as heart attacks, strokes and kidney failure.Whilst I am confident that some people do benefit from having their numbers reduced to the cut-offs defined by the ‘experts’, I am also very confident that a tonne of patients end up being overmedicated unnecessarily and have to endure the indignity of carrying an incorrect label of hypertension, suffer the extra costs of medications and insurance and worst of all put up with possible side effects of a shed-load of pills.

This is perhaps why the Americans keep reducing the thresholds for treatment - because they are not identifying the root cause of the problem - such as sugar, obesity and stress. As it is too difficult and perhaps unprofitable to reduce sugar and stress, lets just hit the blood pressure more - that is actually profitable to do and the best thing is that if the patient doesnt have a heart attack or a stroke then we will say it is because of our excellent tablets and if they did then we would say that it was because they had hypertension and they need even more meds. Either way its a win for us!


What is blood pressure?


Ultimately the whole concept of blood pressure is that when the heart pumps blood out it has  to generate enough pressure within our circulatory system to be able to perfuse our vital organs with oxygen rich blood.

If the pressure is too low, the blood doesn’t get to our vital organs and this results in suffocation and death of important cells in our vital organs.

If the pressure is too high, then there is a risk of damaging our most fragile blood vessels by causing them to burst. This then leads them to heal by clotting off which means that again that our vital organs are deprived of blood and get damaged. If your pressure is not doing you any damage then it is not high for you. 


Physiologically, the formula to calculate pressure is force/area.

So if the force that is exerted over a constant area is doubled then the the pressure is doubled. If the force stays the same but the area is halved, the pressure will also double.

When we measure the blood pressure, we usually measure two values. So typically we get a measurement of 130/80. 130 is the systolic pressure. 80 is the diastolic pressure.

The Systolic blood pressure. 
This is when the heart is pumping and ejecting blood into the vascular system and therefore is the highest pressure that the circulation is exposed to

And the diastolic blood pressure.
This is when the heart is relaxing and filling with blood and therefore the lowest pressure within our circulation.

I want to explain this by using a balloon