Pulse Pressure, age, and vessel compliance

[MudPhud20XX]

Kaplan physio says:

"A compliant artery has a small pulse pressure (PP) and that a stiff artery has a large pulse pressure. Also, pulse pressure increases with age b/c compliance is decreasing."

1. Now compliance is opposite to elasticity and don't we lose elasticity of our vessel as we get older? Thus, as we age, shouldn't our vessel compliance increase?

I get that we get stiffer arteries as we age, so are you saying stiffer the artery there is more elasticity? I thought babies have elastic vessel and as we get older we lose elasticity thus gain compliance, what am I missing here?

2. Can anyone explain why stiff artery gives you higher PP? If you imagine stiffer the blood vessel, I would think both systolic and diastolic will rise thus gives no change in PP. Kaplan guy says PP increases as we go distally, but his explanation does not make any sense to me.

Many thanks in advance.

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[cbrons]

Think of it like this... as you age, the arterial compliance decreases. Saying an artery is "stiff" is a roundabout way of saying it has low compliance (i.e. the vessel doesn't "comply" with distention - it requires more energy). Compliance is the inverse of elastance. Elastance is basically a measure of how much the vessel wants to return to its original conformation (transmural pressure) following distention.

A stiffer aorta (a less compliant aorta OR a more elastic aorta) will produce a higher systolic pressure (given the same stroke volume). Since pulse pressure is systolic - diastolic, you can see why an lower compliant vessel produces a higher pulse pressure.

By the way, this is the main reason why blood pressure tends to increase with age (decreased arterial compliance). But be careful, because this increase due to a decrease in compliance does not result in an increase in mean arterial pressure. If there is an increase in MAP, it is due to an increase in TPR. Just a side note.

 

[cbrons]

 

[MudPhud20XX]

Wow thanks so much! What book is this?

 

[MudPhud20XX]

Think of it like this... as you age, the arterial compliance decreases. Saying an artery is "stiff" is a roundabout way of saying it has low compliance (i.e. the vessel doesn't "comply" with distention - it requires more energy). Compliance is the inverse of elastance. Elastance is basically a measure of how much the vessel wants to return to its original conformation (transmural pressure) following distention.

A stiffer aorta (a less compliant aorta OR a more elastic aorta) will produce a higher systolic pressure (given the same stroke volume). Since pulse pressure is systolic - diastolic, you can see why an lower compliant vessel produces a higher pulse pressure.

By the way, this is the main reason why blood pressure tends to increase with age (decreased arterial compliance). But be careful, because this increase due to a decrease in compliance does not result in an increase in mean arterial pressure. If there is an increase in MAP, it is due to an increase in TPR. Just a side note.

Thanks so much, I really appreciate it. So are you saying that the arterial elasticity increases as we age? I just feel like that's counter-intuitive, so being stiffer = more elasticity ???

 

[cbrons]

Thanks so much, I really appreciate it. So are you saying that the arterial elasticity increases as we age? I just feel like that's counter-intuitive, so being stiffer = more elasticity ???

Yes... think about it. What is something that is highly elastic? A rubberband. What happens when you stretch (distend) a rubberband and then release? It quickly snaps back to its original conformation. The degree to which the rubberband "wants to snap back" is elasticity.

Apply that thinking to blood vessels. If you stretch an elastic blood vessel, it will want to "snap" back to its original diameter (transmural pressure). It will resist your effort to stretch it.

Wow thanks so much! What book is this?

Not sure, I dug this diagram up from a powerpoint on our schools web database.

 

[voicesinmyhead]

Sorry, why is there a pulse pressure increase as you move across the circulatory tree distally?

 

[iamgonnaeat]

Sorry, why is there a pulse pressure increase as you move across the circulatory tree distally?

I believe it has to be because of decreased compliance

 

[Transposony]

The aorta contains elastic fibers that stretch during systole expanding the aorta. Just like a stretched rubber band, this stretching of elastic fibers stores energy (and volume) within the confines of aorta and also keeps the systolic blood pressure down (thereby reducing stress on the aortic wall).
During diastole this stored energy (and therefore volume) is released as the aorta recoils which keeps pressure high as the aorta empties. This facilitates delivery of blood to the periphery during diastole.
Pulse pressure is affected by the compliance of the arterial wall since a compliant artery stretches with systole (thereby reducing systolic blood pressure) and recoils in diastole (thereby keeping diastolic pressure up) to maintain tissue perfusion.
Therefore, compliant arteries have smaller pulse pressure (relatively lower systolic pressure & higher diastolic pressure). Stiff arteries have larger pulse pressures (relatively higher systolic pressure & lower diastolic pressure).
Aging reduces elasticity and therefore aortic compliance which translates to decreased stretch during systole (relatively increased systolic blood pressure) & decreased recoil during diastole ((relatively decreased blood pressure during diastole) thereby increasing the Pulse pressure.
The aorta is the most compliant artery since it has most elastic fibers as compared to peripheral arteries which are stiffer since they have less and less elastic fibers as you go distally.
The reason why the pulse pressure increases as you move across the circulatory tree distally is simply due to decreased compliance as explained above.

 

[FindMeOnTheLinks]

Branch points also transmit a bit of pressure backwards, thus contributing to the increased pulse pressure as you move distally in the arterial tree. (From BRS/Costanzo)