Initial CO increase during exercise

[brucecanbeatyou]

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I'm watching DIT and reading FA. Dr. Jenkins uses some lectures from last year, dubbing over the new FA page numbers. This hasn't been an issue until this morning -

On page 254 (FA 2011), it says, "During exercise, CO increases initially as a result of an increase in HR." Dr. Jenkins, using a lecture from last year, says that "During exercise, CO increases initially as a result of an increase in SV, and after prolonged exercise, the CO increases as a result of an increase in HR."

I'm thinking that it's just one of FA's many type-o's, and that they meant to include that last part/it got messed up in this years' printing, but it's not on the errata.

Anyway, does anybody know what it is? Does HR increase first or EF?

 

[SirGecko]

To be fair, the increase in CO is due to both an increase in SV and HR. BRS phys says that "Cardiac output is increased, primarily as a result of the increased heart rate and, to a lesser extent, the increased stroke volume." So I'd lean toward First aid being right here.

My Guyton and Hall Medical Physiology text also confirms this. (that heart rate is a much bigger part of the increase in CO than SV) I think maybe what DIT was going for is that your SV increases then plateaus a lot earlier than HR. (but HR is still the major determinant in CO during exercise)

 

[RapplixGmed]

I think you can figure this out from first principles and common sense.

At the beginning of exercise, your heart rate can easily increase 2x or more. Can you imagine your heart expanding to double its size to increase CO by 2x?

 

[mastamark]

I think you can figure this out from first principles and common sense.

At the beginning of exercise, your heart rate can easily increase 2x or more. Can you imagine your heart expanding to double its size to increase CO by 2x?

👍 Very nice, summed it.

When you play it out, the CO will increase initially due to the increased HR, as it may take slightly longer for the increase in SV from the combined increased preload and decreased afterload. That doesn't take too long however.

An increased HR overtime has to be matched by either an equal increase of preload or decrease in afterload, or it isn't efficient. So these factors are 1:1 when it really needs to.

Dont forget low dose epi(early workout) will go strait to work on B1 receptors to increase HR and contractility, with the latter not being a big issue until there is an increased return.

It takes a high dose epi to hit those B2s(vasodilate:more out-more return), which I'm thinking takes a little bit of continuous exercise to get out, think of the runner's high kicking in late.

I'm just guessing this how it works so take it will a grain of salt and forgive me if I'm wrong. I thought thinking it out would help me study a bit. Good luck all.