Why is LV filling less during inspiration?

[donkeykong1]

I'm trying to understand why left ventricular filling actually decreases during inspiration. If during inspiration, expansion of the lungs and pulmonary tissues causes pulmonary blood volume to increase [right side has a greater preload=hence greater stroke volume], shouldn't this increase drive volume into the left atrium and subsequently into the left ventricle?

I'm sure I'm missing a clear point on this one

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[Suncrusher]

the fact that pulmonary vascular volume increases during inspiration is precisely why less blood returns to the left side of the heart. In contrast, during expiration, lung deflation causes flow to increase from the lungs to the left atrium, which increases left ventricular filling.

 

[Charles_Carmichael]

During inspiration, blood gets "stored" in the pulmonary vasculature, since the capacity for storing blood in the pulmonary veins increases due to the negative pressure. So, instead of blood flowing down into the left atrium, it's retained in the pulmonary veins. That's why you get decreased LV filling.

Edit: Suncrusher beat me to it. Damn you! =P

 

[Suncrusher]

Edit: Suncrusher beat me to it. Damn you! =P

: ] you did a better job of explaining it, anyway!

 

[donkeykong1]

During inspiration, blood gets "stored" in the pulmonary vasculature, since the capacity for storing blood in the pulmonary veins increases due to the negative pressure. So, instead of blood flowing down into the left atrium, it's retained in the pulmonary veins. That's why you get decreased LV filling.

Edit: Suncrusher beat me to it. Damn you! =P

thanks. so the blood is retained in the pulm veins since the pressure in the left atrium is higher during inspiration?

 

[Zzmed]

During inspiration there is a drop in the intrathoracic pressure which increases blood flow out of the vena cava into the right side of the heart. As you said, increased preload ---> increased stroke volume of the right ventricle ---> increase in pulmonary blood flow. So pulmonic valve closes later to accomodate more blood entering the lungs.
Blood ''wants to" stay more in the lungs because negative intrathoracic pressure diminishes the pressure diffference between lungs and left ventricle when in diastole. (Lungs pull blood in inpiration. LV in diastole pulls blood. BUT LUNGS WIN). So aortic valve closes earlier because of decreased return of blood to left heart.

 

[donkeykong1]

During inspiration there is a drop in the intrathoracic pressure which increases blood flow out of the vena cava into the right side of the heart. As you said, increased preload ---> increased stroke volume of the right ventricle ---> increase in pulmonary blood flow. So pulmonic valve closes later to accomodate more blood entering the lungs.
Blood ''wants to" stay more in the lungs because negative intrathoracic pressure diminishes the pressure diffference between lungs and left ventricle when in diastole. (Lungs pull blood in inpiration. LV in diastole pulls blood. BUT LUNGS WIN). So aortic valve closes earlier because of decreased return of blood to left heart.

ok. thus its b/c the pressure gradient between the lungs and left side of the heart is non-existent. its not that the pressure in the lungs is so much lower than the LA, otherwise more blood would flow back into the PV since there aren't any valves preceding the LA.

thanks this was confusing b/c i'm in cardio block, but haven't had respiratory yet