A Conversation for Measuring Blood Pressure

Diastole, and UK technique

Post 1

James the Techie

A well-written article, and a good lay explanation - well done! As another medical student, I'd have to quibble one point, though.

You describe the phases of the heart's contraction, including diastole - the period when the ventricle is dilating and filling with blood. You later claim that this is "the source of diastolic blood pressure." It isn't. Diastolic BP is the BP at this *time*, but the pressure in the arteries (with the aortic valve shut, and hence isolated from the heart) is caused by the elasticity of the arterial walls.

For those who I've just confused, think about pumping up a bicycle tyre (or tire, if you're American.) You're pumping into a stretchy tube via a one-way valve. While you draw air into the pump (diastole), the pressure inside the tyre comes from the elastic walls squeezing inwards. While you pump into the tyre (systole), you add pressure from the force of the pump to this wall pressure, giving a higher pressure.

Of course, it's not a perfect analogy, because fortunately the blood can circulate back to the pump (otherwise you'd burst!) But I hope you see what I mean.

Incidentally, usual practice in the UK is to measure BP by listening over the brachial artery (at the elbow) rather than the radial (at the wrist), though we would still feel there to start with (though many experienced doctors don't bother!) This gives very similar results.

Diastole, and UK technique

Post 2


Of course, you are 100% correct about the source of pressure during diastole. I was trying to describe the heart's state during diastole more than the source of pressure.
However, the position of auscultation i believe is the same (at or below the anterior fossa). There is a huge variation of anatomy here where the distal brachial and the proxiaml radial meet. As a practical matter, I typically auscultate lower on the fossa than others who listen right below the cuff higher up on the arm. Personally I find this gives less artifact-sounds (from rubbing against the nearby cuff). Both positions do exactly the same thing, and are entirely correct (or incorrect if you are working beneath a supervisor who insists that one postion is correct rather than another) The point is minor, but I think we're talking about the same technique.
Thanks for your feedback!
by the way, if you have time, take a look at my metabolic syndrome article. I'm doing a particlulary gruesome surgery rotation right now and cannot really work on the article as I would like, but I would love to get some advice on how it's going.

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Diastole, and UK technique

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