HOW WELL DO WE UNDERSTAND THE SIGNIFICANCE OF SYSTOLIC BLOOD PRESSURE READINGS?

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Having been diagnosed with high blood pressure (BP) at the age of 70, I was often puzzled by the considerable variations between systolic values produced by different types of monitors (all claimed to be calibrated). The same monitors consistently produced only marginal differences between diastolic values.

This led me to question the meaning of the systolic readings and how well are they understood.

Since pressure is force per unit area, and force is defined as the change of momentum (a product of mass and velocity) with time, the shorter the pumping impulse produced by the heart, the higher the peak pressure. In fact, the theoretical pressure at the very start of the pumping action, when the blood just starts to flow, is infinite!

What is measured at the upper arm or wrist is also greatly influenced by the state of the arteries. The stiffer these are the higher the pressure will be. This is due to the fact that stiff artery walls will absorb much less energy than supple ones.

And then there is the third major factor – the sensitivity / response time of the measuring instrument.. This can probably explain why, using a number of different makes / types of BP monitors, within a short period and under the same conditions, significantly different systolic BP readings can be produced.

However, what matters most is the doubt over the interpretation of systolic BP readings. How many of us are given powerful drugs aimed at lowering pressures produced by nothing more than well functioning hearts.

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  • Posted

    I've never used more than one monitor apart from the one in the surgery, which is a non digital hand held pump type so cannot comment on numerous different machines. My own is an Omron and 2 readings taken 2 minutes apart give wildly differing readings. the systolic reading can be as much as 20 or 30 points lower the second reading, that's with using the same machine. The diastolic figure hardly changes. That's normal I think. However the surgery reading is quite off the page so I am thankful that I can take my own otherwise I would be highly over medicated.

    Interesting to hear you say that hypertension is nothing more than a well functioning heart. When they discovered my hypertension I was really upset at the thought of lost health and medication for the rest of life. I was quite angry really when the nurse told me that after all I was 70 - as though I really ought to be in an old folks home; for myself I hadn't really noticed my 70th birthday !. She frightened me with stories of heart attacks and strokes etc so that I wished I'd never had the check up in the first place.

    I now take a fairly low dose of Losartan and wonder if that is too high as I often feel dizzy or spaced out some hours after taking the pill, especially after a walk..

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  • Posted

    I have been telling people force was mass times acceleration f = ma. Is that what you are saying? I don't understand why the force would be theoretically infinite. Forgotten a lot since school for sure. At 120 mm Hg systolic, your heart is producing the equivalent of a column of blood about 5.05 feet high assuming a blood density 1.06 gm/ml. Central line pressures are reported to be 5 to 15 mm Hg higher than this. Anyway, you do have to be careful to have the point where the cuff center is located at the phlebostatic axis (same gravitationally as centers of the atria) - 4 ICS mid chest laterally or you are taking BP at a column height that is wrong. For instance, if you have your wrist on a low desktop, it may be a foot lower than the axis, resulting in pressures reported as 1 foot / 5 feet or 20% higher than standard reference point down the "column".

    There is such a thing as "labile" blood pressure in which individuals have serious, idiopathic fluctuations. The gold standard for calibration and accuracy remains a mercury sphygmomanometer.

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  • Posted

    Quantum Physics !!!!
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  • Posted

    Since acceleration equals change of velocity divided by time, force being mass times acceleration is the same as change of momentum divided by time. As for the theoretical 'infinite' pressure, this comes from the division by time - the shorter the time it takes for the mass to 'move', the greater the acceleration (and force/pressure). This is not Quantum Physics. In fact we all know that, in order to achieve the best results when using a hammer, we use it to delivery a sharp blow. The sharper the blow, the more force it delivers.

    There is no doubt that high blood pressure is, in many cases, linked to clogging and hardening of the arteries. However, in my opinion, all those on BP medications should look very seriously at their life style. This is particularly true for older people who could benefit greatly from eliminating foods which may no longer agree with them. I would also highly recommend getting the current copy (March 2014) of What Doctors Don't Tell You (WDDTY) which contains an eye opening article titled 'Change of Heart' (page 18).

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  • Posted

    The whole of Jane's first paragraph applies exactly to my experience. And one rheumatologist has suggested that my blood pressure is "labile". In fact Jane's second paragraph applies too. I was also warned y more than one GP/consultant that if I didn't take medication I could have a stroke or heart attack - my pharmacist was aghast to hear that. You did make me laugh though, Jane, about being in an old folk's home - not much hope for me then at a couple of years older than you!

    My two medications seem to be controlling my BP for most of the day but it rises in the evening - does anyone take some of their medication at night?

    What's upsetting me most about the medication is that I've always had a daily brisk walk in the belief that it will help to control my blood pressure, but since being on the medication I am running out of energy and puff if I walk fast, so wonder what the medication is doing to my heart.....worse still don't know which of the meds is responsible!!

    As for "The gold standard for calibration and accuracy remains a mercury sphygmomanometer", this doesn't proe "accurate" for me, because s soon as I'm at the surgery/hospital my BP goes up to 200!

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