Silly question--air in heart?

[HereWeGo21]

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So, obviously there's no air in the heart. This would produce a fatal air embolus.

But, then what is there?
Say that systole has just finished, and diastole begins. At the beginning of diastole, the ventricles are empty. They start filling from zero. So, what occupies the ventricle before blood has filled it?

Taking this further, what about severe mitral stenosis? What if the ventricle is unable to fill all the way? Then a half-full ventricle contracts into the aorta. But how is there no air?

The ventricle couldn't be a complete vacuum could it? Because then it would collapse on itself.

 

[AxiomaticTruth]

... think of a water balloon. It gets squeezed so water escapes (end of systole). The balloon is empty. "So, what occupies the balloon before water has filled it?"

IE nothing. The ventricle collapses so it's always filled with something. End of systole, there's only end systolic blood volume left. There's never air or vaccuum. Like you said, can't be a vacuum, so it DOES collapse on itself. In other words, the volume occupied by the ventricle (and the whole heart) at the end of systole is smaller than the volume at the end of diastole.

I think you're confusing the heart with something that has rigid walls. There, if you drain something without replacing that same volume, it's going to "fill" with a vaccuum (unless there's a gas inside).

 

[QualityProcess]

So, obviously there's no air in the heart. This would produce a fatal air embolus.

But, then what is there?
Say that systole has just finished, and diastole begins. At the beginning of diastole, the ventricles are empty. They start filling from zero. So, what occupies the ventricle before blood has filled it?

Taking this further, what about severe mitral stenosis? What if the ventricle is unable to fill all the way? Then a half-full ventricle contracts into the aorta. But how is there no air?

The ventricle couldn't be a complete vacuum could it? Because then it would collapse on itself.

the ventricles aren't empty at the end of systole, there is blood in them. In normal systole, the LV ejects about 55-70% of the total end diastolic volume.

 

[HereWeGo21]

the ventricles aren't empty at the end of systole, there is blood in them. In normal systole, the LV ejects about 55-70% of the total end diastolic volume.

Oh, right.

But then even so? What fills up the rest of the 45-30% of the ventricle after the stroke?

 

[HereWeGo21]

... think of a water balloon. It gets squeezed so water escapes (end of systole). The balloon is empty. "So, what occupies the balloon before water has filled it?"

IE nothing. The ventricle collapses so it's always filled with something. End of systole, there's only end systolic blood volume left. There's never air or vaccuum. Like you said, can't be a vacuum, so it DOES collapse on itself. In other words, the volume occupied by the ventricle (and the whole heart) at the end of systole is smaller than the volume at the end of diastole.

I think you're confusing the heart with something that has rigid walls. There, if you drain something without replacing that same volume, it's going to "fill" with a vaccuum (unless there's a gas inside).

Hmm. But then why do we have an "isovolumetric expansion"? The whole meaning of this is that the heart expands, but the amount of volume in the ventricle doesn't change. So the heart couldn't just be collapsed on the remaining blood in the ventricle the whole time. We know it's expanding.

Edit:
Maybe, once the negative pressure becomes "unbearable", the mitral valve opens and ventricular filling begins. Yeah, that makes sense. Thank you everyone!

 

[AxiomaticTruth]

Exactly. I see why you're confused. The "isovolumetric" refers to how the ventricles don't change volume, and the "expansion" refers not really to the ventricles, but to the heart as a whole. That's why isovolumetric expansion is followed by "volumetric" expansion with the opening of the mitral valve. Your edit is 100% correct. Same with "isovolumetric" contraction needs to build UP the pressure in the ventricles to overcome the native resistance of the pulm/aortic valves.

 

[Instatewaiter]

Hmm. But then why do we have an "isovolumetric expansion"? The whole meaning of this is that the heart expands, but the amount of volume in the ventricle doesn't change. So the heart couldn't just be collapsed on the remaining blood in the ventricle the whole time. We know it's expanding.

Edit:
Maybe, once the negative pressure becomes "unbearable", the mitral valve opens and ventricular filling begins. Yeah, that makes sense. Thank you everyone!

A few points:
There is no "air".

I think you mean isovolumettric relaxation and contraction. This means the volume stays the same but the pressure changes by the ventricle contracting or relaxing. .

There is slight vacuum forces in the LV which helps with LV filling during diastole

Just before systole, the LV is completely filled and the volume is large (i.e. Your end diastolic volume).
So after systole and the fraction of blood is ejected (i.e. The ejection fraction), the volume of the LV is reduced (end systolic volume). The LV still remains filled with blood and not with air.