Quick question about sympathetic discharge to the heart?

In summary: It's one of my favorite subjects. Btw, I forgot to mention that SV can be affected indirectly by sympathetic activity in another way. As HR increases, left ventricular filling time (LVFT) decreases which can result in lower EDV (depending on filling rate, a function of total pulmonary resistance) and thereby lower SV unless the ejection fraction is increased. So there's no simple correlation between sympathetic activity and SV.
  • #1
662
3
Hello everyone,

Vasomotor centre for example, increases heart rate and increases blood vessel constriction and raises total peripheral resistance. The end result is increase in stroke volume. My question is if blood pressure is raised too much by constricting blood vessels, wouldn't that make it hard for the ventricles to pump blood and decrease stroke volume. Thanks :smile:
 
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  • #2
sameeralord said:
Hello everyone,

Vasomotor centre for example, increases heart rate and increases blood vessel constriction and raises total peripheral resistance. The end result is increase in stroke volume. My question is if blood pressure is raised too much by constricting blood vessels, wouldn't that make it hard for the ventricles to pump blood and decrease stroke volume. Thanks :smile:

Correct except that the end result is increased cardiac output, but not necessarily increased stroke volume. Increased total peripheral resistance (TPR) due to sympathetic vasomotor action will increase mean arterial pressure (MAP) and tend to reduce stroke volume (SV) particularly if there is aortic disease resulting in stiffening (atherosclerosis). Cardiac output (Q) can be maintained by the corresponding increase in heart rate (HR) which also results from sympathetic activity (Q=HR x SV). Other factors are also involved such as end diastolic volume(EDV) and ejection fraction which is SV/EDV. In healthy persons this ratio is large, but with heart failure (due to myocardial disease and/or increased TPR) it can drop to 50% or lower.

Reliance on sympathetic activity to deal with physical demands is not the most efficient or healthiest physiological mode. With regular vigorous exercise, resting EDV and SV increase allowing good tissue perfusion at rest with low MAP and low HR. With physical stress, increase in HR alone can often meet the tissue demand and increased MAP is due mostly to increased Q, not increased TPR.

EDIT: The situation with SV and sympathetic activity can be complicated by increased venous return and increased EDV, so SV can increase even if TPR is increased. It just depends on how much and the general state of cardiovascular health.
 
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  • #3
SW VandeCarr said:
Correct except that the end result is increased cardiac output, but not necessarily increased stroke volume. Increased total peripheral resistance (TPR) due to sympathetic vasomotor action will increase mean arterial pressure (MAP) and tend to reduce stroke volume (SV) particularly if there is aortic disease resulting in stiffening (atherosclerosis). Cardiac output (Q) can be maintained by the corresponding increase in heart rate (HR) which also results from sympathetic activity (Q=HR x SV). Other factors are also involved such as end diastolic volume(EDV) and ejection fraction which is SV/EDV. In healthy persons this ratio is large, but with heart failure (due to myocardial disease and/or increased TPR) it can drop to 50% or lower.

Reliance on sympathetic activity to deal with physical demands is not the most efficient or healthiest physiological mode. With regular vigorous exercise, resting EDV and SV increase allowing good tissue perfusion at rest with low MAP and low HR. With physical stress, increase in HR alone can often meet the tissue demand and increased MAP is due mostly to increased Q, not increased TPR.

EDIT: The situation with SV and sympathetic activity can be complicated by increased venous return and increased EDV, so SV can increase even if TPR is increased. It just depends on how much and the general state of cardiovascular health.

Thanks. Nice detailed answer :smile:
 
  • #4
sameeralord said:
Thanks. Nice detailed answer :smile:

It's one of my favorite subjects. Btw, I forgot to mention that SV can be affected indirectly by sympathetic activity in another way. As HR increases, left ventricular filling time (LVFT) decreases which can result in lower EDV (depending on filling rate, a function of total pulmonary resistance) and thereby lower SV unless the ejection fraction is increased. So there's no simple correlation between sympathetic activity and SV.
 
  • #5


Hello,

That is a great question. While it is true that excessive vasoconstriction can lead to an increase in blood pressure, the body has mechanisms in place to prevent this from causing issues with heart function. The autonomic nervous system, specifically the parasympathetic branch, works to counteract the effects of sympathetic discharge on the heart. It slows down heart rate and decreases blood vessel constriction, allowing for proper filling of the ventricles and maintaining stroke volume. Additionally, the body also has mechanisms to regulate blood pressure, such as the renin-angiotensin-aldosterone system, which can decrease peripheral resistance and maintain blood flow to the heart. Overall, the body has intricate systems in place to maintain balance and prevent excessive sympathetic discharge from negatively impacting heart function. I hope this helps answer your question.
 

1. What is sympathetic discharge to the heart?

Sympathetic discharge to the heart refers to the activation of the sympathetic nervous system, which leads to an increase in heart rate and force of contraction. This is also known as the "fight or flight" response, as it prepares the body for physical activity or stress.

2. How does sympathetic discharge affect the heart?

Sympathetic discharge increases the heart rate and force of contraction through the release of the hormone epinephrine (adrenaline) from the adrenal glands. This results in increased blood flow to the muscles and organs, allowing the body to respond to a perceived threat or need for physical activity.

3. What triggers sympathetic discharge to the heart?

Sympathetic discharge can be triggered by various factors, including physical or emotional stress, exercise, pain, fear, and low blood pressure. The sympathetic nervous system responds to these stimuli by releasing epinephrine, which activates the body's "fight or flight" response.

4. How is sympathetic discharge to the heart controlled?

The sympathetic nervous system is controlled by the hypothalamus in the brain, which receives signals from other areas of the brain and the body. It can be further regulated by other hormones, such as cortisol and norepinephrine, which modulate the effects of sympathetic discharge on the heart.

5. Can sympathetic discharge to the heart be harmful?

In some cases, excessive sympathetic discharge can be harmful to the heart and the body. Chronic stress and high levels of sympathetic activity have been linked to cardiovascular diseases such as hypertension and heart failure. However, in most cases, sympathetic discharge is a normal and necessary response to maintain the body's physiological balance.

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