What mechanism are responsible for the PR interval decresing during exercise?
I understand that the heart needs to beat faster and consequently the interval will decrease but what exactly causes this?
Answers:
The P-R interval is mainly determined by the time taken to surpass through the AV node, so what you're looking for is something that will change AP velocity in this region. This is under the control of both sympathetic (increasing conduction velocity) and parasympathetic (decreasing conduction velocity) nerves (which both couple intracellularly to cAMP, increasing and decreasing this, respectively). During exercise at hand is an increase of sympathetic nerve firing (so, noradrenaline onto beta1 receptors) and a decrease in parasympathetic (ACh onto M2 receptors) firing, which both head to an increase in conduction velocity and hence the change in PR interval.
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Answers:
The P-R interval is mainly determined by the time taken to surpass through the AV node, so what you're looking for is something that will change AP velocity in this region. This is under the control of both sympathetic (increasing conduction velocity) and parasympathetic (decreasing conduction velocity) nerves (which both couple intracellularly to cAMP, increasing and decreasing this, respectively). During exercise at hand is an increase of sympathetic nerve firing (so, noradrenaline onto beta1 receptors) and a decrease in parasympathetic (ACh onto M2 receptors) firing, which both head to an increase in conduction velocity and hence the change in PR interval.
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