Cardiovascular Physio Question

[Polar101]

---

Members do not see this ad.

I was reading Costanzo for physiology and am really confused about compliance/elastance. She says that the greater the amount of elastic tissue there is in a blood vessel, the higher the elastance is and the lower the compliance. But, when we age don't the number of elastic fibers decrease? I was under the impression that as we age compliance decreases and elastance increases (since its the inverse of compliance). Is she implying that elastic fibers increase as we age?
I don't know, I'm really confused. If someone can clear this up for me I would really appreciate it!!

 

[MrBeauregard]

You are correct that elastance and compliance are inversely related; if elastance increases, compliance will decrease. You can think of this in the exact same way you think about an emphysematous lung compared to a lung with any restrictive disease. In emphysema, you have a loss of elastic tissue, thus an increase in compliance. In a restrictive lung disease, you have an increase in elastic tissue and thus compliance will decrease. This is just another example so that you understand the relationship.

You asked the following question: "But, when we age don't the number of elastic fibers decrease?" You then proceeded to say that: "I was under the impression that as we age compliance increases and elastance decreases..." Your question and the statement that followed are saying the exact same thing, so I'm not sure where you're confused. You didn't give us any of her text so that we can see what exactly she said concerning elastic fibers and aging, so it's tough to interpret what she is saying. Maybe include some of the text and we'll go from there.

 

[Polar101]

Thanks for the response. You're right, I did state the same thing. I actually meant to say that "as we age compliance actually decreases (not increases) and elastance increases (arteries become stiffer)". On the next page Costanzo writes that as we age compliance decreases and I agree with that. I'm just having trouble understanding how elastic fibers would increase as we age (since elastance would increase).

I hope it's clear now and sorry for the mistake in my question!

 

[phltz]

Thanks for the response. You're right, I did state the same thing. I actually meant to say that "as we age compliance actually decreases (not increases) and elastance increases (arteries become stiffer)". On the next page Costanzo writes that as we age compliance decreases and I agree with that. I'm just having trouble understanding how elastic fibers would increase as we age (since elastance would increase).

I hope it's clear now and sorry for the mistake in my question!

If you hold everything else constant and just cram more elastic fibers into a given vessel, yes, compliance will decrease, and if you hold everything else constant while removing elastic fibers, compliance will increase. As people age, the elastic fiber content is not the only thing changing, so this analysis doesn't capture the whole picture.

As elastic fiber content drops, the overall strength of the vessels would drop if nothing else changed, probably increasing the risk of dissection and the like. I imagine (although am not 100% sure of this) that to compensate, the content of other types of load-bearing fibers is increased. The result of a net swap of elastin for collagen would result in a decrease in compliance.

 

[Polar101]

Yeah, that totally makes sense! I actually now remember reading somewhere that collagen cross-linking increases as we age, so I think that is what is contributing to the increase in elastance.

Thanks a lot!!