Mechanism of physiological split in second heart sound

During inspiration the aortic component of the second heart sound is heard about 0.02 to 0.08 seconds before the pulmonary component. The reason is as follows:

  • During inspiration, a negative intrathoracic pressure is created to inhale air into the lungs
  • This creates a vaccum effect which results in increased venous return to the right side of the heart
  • Hence the right ventricle takes a longer time to eject the blood into the pulmonary system
  • Also since pulmonary vasculature expands in capacity, lower amount of blood flows into the left atrium
  • Hence the left ventricle takes a shorter time to eject blood into the aorta
  • Because of these 2 factors, the aortic valve closes before that of the pulmonary valve and we can appreciate the split during inspiration

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