Hangout interval – Mechanism, significance

• The pulmonary valve remains open for some time even after the right ventricular pressure becomes equal to pulmonary artery pressure at end of systole
• This time interval is known as hangout interval

Why does pulmonary valve remain open even after pressure equilisation?

• According to Newton’s first law of motion, every body continues to move at constant speed unless acted upon by an external force
• In this case, the blood continues to flow from the right ventricle even after the the pressure in the right ventricle and the pulmonary artery becomes equal
• Just like a rolling ball is stopped by the friction offered by the ground, the ejection of blood is stopped by the resistance offered by the pulmonary vasculature
• Since the pulmonary vascular resistance is low compared to the systemic vascular resistance, it takes some time for the blood flow from the right ventricle to stop
• This corresponds to the hangout interval

Significance of hangout interval

• Hangout interval is shortened in cases of increased pulmonary vascular resistance such as pulmonary vasospasm, obliteration of pulmonary vessels etc

Does the aortic valve have a hangout interval?

• Due to high systemic vascular resistance, the aortic valve closes almost immediately
• Hence hangout interval is negligible