Monday, 18 March 2019

Is it of benefit to know our Blood Pressure?

I read the following BBC news article concerning blood pressure and cholesterol.  It says:
People are being encouraged to know their cholesterol and blood pressure numbers as well as they know their bank Pin code - because it could save their life.
In respect to blood pressure this advice conflicts with a study* cited by a BMJ paper.  It states:
[I]f you are a hypertensive man you would minimise your chances of overall as well as CV-related mortality if you do not find out about it. If you find out, your chances of dying increases but according to this study, you should still not treat your [hypertension].
So according to this study it's best if we never have our BP checked in our lives, but if we do and our BP is high, we should not take any medication for it.  This is quite radical!

In addition the BMJ paper mentions that we do not know if high blood pressure (HBP) causes major coronary heart disease (CHD) rather than being a mere correlation. It may be, for example, that it is stress that causes major coronary heart disease.  Since stress also causes high blood pressure, it only appears that high blood pressure causes CHD.  The paper also mentions:

[I]t may be that with age some organ or body part malfunctions and that HBP is required to minimise the negative consequences of such malfunction, the same way that fever helps fight disease. Indeed, patients with CHD may have greater HBP to properly perfuse vital organs and a drop in BP could even precipitate myocardial ischaemia and a subsequent CHD event.

So high blood pressure might be your body's response to things going wrong in your body, in which case artificially decreasing BP without addressing the original cause could be deleterious to one's health.

If we have high blood pressure should we be concerned?  The following figure from the BMJ paper is of interest:

 


Regarding this figure the paper says:

[O]verall deaths related to HBP hardly increase until an SBP of around 175 is reached. But even if SBP increases to about 185, the number of deaths rises from around 15 to 28, an increase of 13/1000 or 1.3%. Only when SBP exceeds the 185 mark does the number of deaths start to increase steeply. In this case, the difference between normal SBP and that over 190 is 27 (15–42) extra deaths/1000, or 2.7%.
SBP standing for systolic blood pressure (the higher figure in a BP reading). It's the dashed line we're interested in as this tracks cardiovascular deaths. We can see that deaths don't start to significantly increase until one's SBP is over 180.

Incidentally, my average blood pressure using my own home monitor over thousands of readings is 131/90.  The lower figure, the diastolic, is slightly too high (it needs to be less than 90).  However, my average diastolic reading when I see my doctor tends to be 5-10 less than what my own blood pressure monitor typically gives.

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* Barengo NC, Kastarinen M, Antikainen R, et al. The effects of awareness, treatment and control of hypertension on cardiovascular and all-cause mortality in a community-based population control of hypertension. J Hum Hypertens 2009;23:808–16.




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