Arteries & Diastolic Blood Pressure

[SaintJude]

During systole, blood is pumped from the left ventricles into the aorta. The elasticity of the walls of the receiving large arteries, which stretch out to receive the volume of blood from the ventricles, allows the vessels to maintain sufficient pressure while the ventricular muscles are relaxed.

I have a question about this statement in my Kaplan review book says: "If it weren't for the elasticity of the large arteries, your diastolic blood pressure would plummet to zero." Why?

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[MT Headed]

When you heart relaxes, it ain't squeezin but the blood is still flowing. How is that? It's those balloon-like arteries that are still squeezin and since the heart has a one way valve the squeezed blood is pushed in the forward direction.

If your arteries were made of steel pipe, then you would lose the buffering/averaging capability of your pliable arteries. Your systolic would rocket up as your heart pushed new blood in an unexpandable container, and when the heart stops squeezin there wouldn't be anything squeezin anywhere and the diastolic would drop off a lot. This is basically what happens when people get old and their arterial walls get calcified.

 

[dranet]

Some definitions of Diastolic BP are a pain. The Diastolic BP is the pressure that already exists in the arteries. If the heart just stopped and there was blood in the Aorta you'd still find pressure (and I am not talking about dead people/animals). The defn that it is the pressure in the arteries near the heart when the left ventricle relaxes is misleading.
You have two types of arteries Elastic and muscular. The AORTA (and other large arteries near the heart) is thick with elastic tissue in its tunica media and elastic tissue when stretched like a spring will return with a restoring force. So volume and then pressure from the left ventricle are what the Aorta is responding to with its elasticity. A volume of blood is always there so some restoring force is always there. I was an ICU nurse and I saw this many times. When people haemorrhage with huge losses of blood you will see the diastolic BP drop despite the ventricles making a strong effort to pump hard (ANS-Symp helps out), the lack of blood in the Aorta prevents the elastic fibres from doing their job, they aren't stretched! And down goes the diastolic BP. When this occurs the patient is in dire straits. A drop in Systolic BP is a concern, the ANS-Symp will kick in, but when it gets to Diatolic BP drop the patient better get some fluid volume into them

 

[dranet]

In Non essential Hypertension e.g the result of hardening of the arteries, the Diastolic BP goes up, not down!

 

[MT Headed]

In Non essential Hypertension e.g the result of hardening of the arteries, the Diastolic BP goes up, not down!

I am certainly no expert in this matter (though I do hope to be in a couple of years!) but I distinctly remember using physics principles in an A&P class to figure out that hardening of the arteries ought to cause systolic to rise and diastolic to lower, since the flexible aorta would not be so flexible and therefore more sensitive to volume changes. I remember getting the question right when most of the class got it wrong.

I found this item in "Circulation", the journal of the American Heart Association: "Over the last few years, a paradigm shift has occurred, away from the prior concern over an elevation of diastolic pressure to our current awareness that an elevation of systolic pressure and, to an even greater extent, the combination of higher systolic and lowered diastolic pressures (ie, a widening of the pulse pressure) are the major determinants of cardiovascular risk in the elderly.3 This should come as no surprise because the widening pulse pressure reflects atherosclerotic stiffening of the aorta and large capacitance vessels.4 This provides a smaller, rigid reservoir wherein systolic inflow raises pressure and diastolic emptying lowers pressure to a greater degree than occurs with more compliant, elastic vessels. In addition, pulse-wave velocity is faster through stiff vessels, so that the usual reflection of the pressure wave back from the periphery occurs in midsystole rather than diastole, augmenting the already elevated systolic pressure and removing a major support of diastolic pressure. Therefore, the widened pulse pressure so typically found in the elderly reflects both a rise in systolic levels and a fall in diastolic levels."
http://circ.ahajournals.org/content/102/10/1079.full

 

[SaintJude]

Thanks for the responses. Recap:

So as left ventricles contract and pushes blood into the aorta, the aorta stretches its elastic walls causing the aortic pressure to reach it peak--this pressure peak is aka systolic arterial pressure and averages 120 mmHg.

Then comes diastole. Ventricular relaxation will cause the arterial pressure to decrease as less blood is filling the aorta. Because the walls of the aorta are elastic, the walls will recoil to maintain a continuous pressure on the reduced blood volume. So it's really the ability for the walls of large arteries to recoil that prevents a complete drastic drop to 0 as Kaplan noted.

On to the next thread! Thanks--I hope we all ace this exam!

 

[Erythropoietin]

I am certainly no expert in this matter (though I do hope to be in a couple of years!) but I distinctly remember using physics principles in an A&P class to figure out that hardening of the arteries ought to cause systolic to rise and diastolic to lower, since the flexible aorta would not be so flexible and therefore more sensitive to volume changes. I remember getting the question right when most of the class got it wrong.

I found this item in "Circulation", the journal of the American Heart Association: "Over the last few years, a paradigm shift has occurred, away from the prior concern over an elevation of diastolic pressure to our current awareness that an elevation of systolic pressure and, to an even greater extent, the combination of higher systolic and lowered diastolic pressures (ie, a widening of the pulse pressure) are the major determinants of cardiovascular risk in the elderly.3 This should come as no surprise because the widening pulse pressure reflects atherosclerotic stiffening of the aorta and large capacitance vessels.4 This provides a smaller, rigid reservoir wherein systolic inflow raises pressure and diastolic emptying lowers pressure to a greater degree than occurs with more compliant, elastic vessels. In addition, pulse-wave velocity is faster through stiff vessels, so that the usual reflection of the pressure wave back from the periphery occurs in midsystole rather than diastole, augmenting the already elevated systolic pressure and removing a major support of diastolic pressure. Therefore, the widened pulse pressure so typically found in the elderly reflects both a rise in systolic levels and a fall in diastolic levels."
http://circ.ahajournals.org/content/102/10/1079.full

Nice article . We also have to keep in mind that older ppl need a higher pulse to balance his/her cardiac output volume because their hearts are weaker compared to a middle-aged person. Also, aortic elasticity is reduced mostly with the obese and the elderly.

 

[dranet]

Interesting article but narrows into just one circumstance for the many BPs you see in older people. It focuses on changing awareness of the risk group they have worried about and brought to drs awareness that the risk group looks different to what it had in the past. Atherosclerotic vessels do eventually lose their elasticity and lumenal diameter because they scar and get stiff. Now see if that explains this BP... 220/180. We have a pulse pressure and it looks pretty good. Patient is disorientated most of the time though! Any way diastolic BP is still the pressure attributed to arterial anat and phys whilst Systolic is still to do with blood volumes ejected and flowing thru arteries. The article doesn't really change that just the timing of when things happen.