Change in heart rate upon inspiration and expiration?

[DrOwnage]

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Can someone please clarify this subject for me. I have had mixed results reading different sources concerning how heart rate increases and decreases with the respiratory cycle.

I have read articles saying that respiratory sinus arrhythmia is a normal condition where heart rate increases upon inspiration and decreases upon expiration (which I'm pretty sure is correct).

But I have read other sources stating differently (Lange):

Filling of the right side of the heart is transiently increased during inspiration and, by Starling's law, stroke volume and thus cardiac output are transiently increased. Since changes in output of the right side of the heart induce changes in output of the left side of the heart, the net effect of inspiration will be a transient increase in stroke volume and cardiac output from the left ventricle. This will lead to a transient increase in arterial pressure and a transient increase in firing of the arterial baroreceptors. In addition, because of the inspiration-induced decrease in intrathoracic pressure, the cardiopulmonary baroreceptors in the vascular and cardiac walls will be stretched and will increase their firing rate. These baroreceptor inputs will act on the medullary cardiovascular centers to produce reflex adjustments to lower arterial pressure: that is, increase cardiac parasympathetic nerve activity and decrease sympathetic nerve activity --> therefore decreasing heart rate.

Can someone explain solidly which is right and why? Thank you.

 

[ChrisGriffen]

Inspiration=increase in HR

 

[Kahreek]

Can someone please clarify this subject for me. I have had mixed results reading different sources concerning how heart rate increases and decreases with the respiratory cycle.

I have read articles saying that respiratory sinus arrhythmia is a normal condition where heart rate increases upon inspiration and decreases upon expiration (which I'm pretty sure is correct).

But I have read other sources stating differently (Lange):

Filling of the right side of the heart is transiently increased during inspiration and, by Starling's law, stroke volume and thus cardiac output are transiently increased. Since changes in output of the right side of the heart induce changes in output of the left side of the heart, the net effect of inspiration will be a transient increase in stroke volume and cardiac output from the left ventricle. This will lead to a transient increase in arterial pressure and a transient increase in firing of the arterial baroreceptors. In addition, because of the inspiration-induced decrease in intrathoracic pressure, the cardiopulmonary baroreceptors in the vascular and cardiac walls will be stretched and will increase their firing rate. These baroreceptor inputs will act on the medullary cardiovascular centers to produce reflex adjustments to lower arterial pressure: that is, increase cardiac parasympathetic nerve activity and decrease sympathetic nerve activity --> therefore decreasing heart rate.

Can someone explain solidly which is right and why? Thank you.

this is very good reasoning, great research projects start with very far less bright ideas.
Although, In medicine you will learn that if A leads to B, doing the inverse path from B doesnt necessarily lead to A.

 

[GadRads]

"Normally during inspiration, systolic blood pressure decreases ≤10 mmHg.,[1] and pulse rate goes up slightly. This is because the intrathoracic pressure becomes more negative relative to atmospheric pressure. This increases systemic venous return, so more blood flows into the right side of the heart. However, the decrease in intrathoracic pressure also expands the compliant pulmonary vasculature. This increase in pulmonary blood capacity pools the blood in the lungs, and decreases pulmonary venous return, so flow is reduced to the left side of the heart. Also the increased systemic venous return to the right side of the heart expands the right heart and directly compromises filling of the left side of the heart. Reduced left-heart filling leads to a reduced stroke volume which manifests as a decrease in systolic blood pressure. The decrease in systolic blood pressure leads to a faster heart rate due to the baroreceptor reflex, which stimulates sympathetic outflow to the heart."

http://en.wikipedia.org/wiki/Pulsus_paradoxus

Can someone please clarify this subject for me. I have had mixed results reading different sources concerning how heart rate increases and decreases with the respiratory cycle.

I have read articles saying that respiratory sinus arrhythmia is a normal condition where heart rate increases upon inspiration and decreases upon expiration (which I'm pretty sure is correct).

But I have read other sources stating differently (Lange):

Filling of the right side of the heart is transiently increased during inspiration and, by Starling's law, stroke volume and thus cardiac output are transiently increased. Since changes in output of the right side of the heart induce changes in output of the left side of the heart, the net effect of inspiration will be a transient increase in stroke volume and cardiac output from the left ventricle. This will lead to a transient increase in arterial pressure and a transient increase in firing of the arterial baroreceptors. In addition, because of the inspiration-induced decrease in intrathoracic pressure, the cardiopulmonary baroreceptors in the vascular and cardiac walls will be stretched and will increase their firing rate. These baroreceptor inputs will act on the medullary cardiovascular centers to produce reflex adjustments to lower arterial pressure: that is, increase cardiac parasympathetic nerve activity and decrease sympathetic nerve activity --> therefore decreasing heart rate.

Can someone explain solidly which is right and why? Thank you.

 

[yehhhboiii]

the negative intrathoracic pressure increases the capacity of the intrathoracic pulmonary veins so venous return to the left atrium and left ventricle temporarily decreases. reduced filling leads to a reduced stroke volume. less stroke volume means that the heart requires less time to empty the left ventricle.

 

[Charles_Carmichael]

The way I think about it:

Inspiration --> decreased pulmonary venous return to the left heart (because more blood is "stored" in the pulmonary vessels) --> drop in SV and CO --> drop in MAP --> baroreceptors kick in --> increased sympathetic tone to increase MAP --> increased HR, SV, CO to make the baroreceptors happy.

It all has to do with the decreased intrathoracic pressure also stretching out pulmonary vessels and allowing more blood to be stored there instead of returning to the left heart. The subsequent events result from the increased sympathetic tone due to baroreceptors sensing a drop in BP.

 

[SpecterGT260]

the negative intrathoracic pressure increases the capacity of the intrathoracic pulmonary veins so venous return to the left atrium and left ventricle temporarily decreases. reduced filling leads to a reduced stroke volume. less stroke volume means that the heart requires less time to empty the left ventricle.

"Time required" doesn't really play a role. But the baroreceptors will see the pressure drop and increase HR via reflex loop.