Cardiovascular | Cardiac Cycle

Summary

This video explores the cardiac cycle, detailing the mechanical events of blood flow through the heart's chambers. It covers atrial and ventricular pressure differences, valve actions, and how these events correlate with EKG readings, providing insights into the heart's function over an average cycle time of 0.8 seconds.

Takeaways

• 💓 The cardiac cycle refers to the sequence of mechanical events involving blood flow through the heart chambers, averaging 0.8 seconds in duration.
• 📈 The atrial and ventricular pressures are critical in the opening and closing of heart valves; higher atrial pressure opens the atrioventricular (AV) valves, while higher ventricular pressure closes them.
• 🚫 The semilunar valves (SLV), including the pulmonary and aortic valves, open only when the ventricular pressure exceeds the arterial pressure, preventing backflow of blood.
• 🌊 Blood flow into the heart is primarily passive during mid to late ventricular diastole, filling the ventricles with 70-80% of the incoming blood by gravity.
• 🔄 The isovolumetric contraction phase marks the beginning of ventricular squeezing without any change in volume, as the pressure rises to surpass the arterial pressure.
• 🗨 The first heart sound, 'Lub' or S1, is produced when the AV valves snap shut during isovolumetric contraction.
• 💉 The ventricular ejection phase, or mid to late ventricular systole, is when the ventricles forcefully expel blood into the pulmonary artery and aorta, opening the semilunar valves.
• 📊 The EKG's QRS complex corresponds to the ventricular depolarization and contraction during both isovolumetric contraction and ejection phases.
• 🛑 The second heart sound, 'Dub' or S2, occurs when the semilunar valves close after the ventricles have ejected blood, during the isovolumetric relaxation phase.
• 🔙 The dicrotic notch represents a brief rise in aortic pressure when the semilunar valves close, contributing to the second heart sound.
• 🔁 The cardiac cycle repeats every 0.8 seconds, with the ventricles relaxing and filling up again before the next cycle of contraction and ejection.

Q & A

What is the cardiac cycle?

The cardiac cycle refers to the series of mechanical events that occur as blood flows through the different chambers of the heart, taking approximately 0.8 seconds on average.

What are the two main types of valves in the heart mentioned in the script?

The two main types of valves mentioned are the atrioventricular (AV) valves, which include the tricuspid and mitral valves, and the semilunar valves, which include the pulmonary and aortic semilunar valves.

What happens during mid to late ventricular diastole?

During mid to late ventricular diastole, blood from the systemic and pulmonary veins accumulates in the atria, causing the atrial pressure to be slightly greater than the ventricular pressure, which opens the AV valves and allows blood to passively flow into the ventricles.

What is the significance of the P wave on the EKG?

The P wave on the EKG signifies the depolarization and contraction of the atria, which occurs towards the end of ventricular diastole and helps to push the remaining 20% of blood into the ventricles.

What is isovolumetric contraction?

Isovolumetric contraction is a phase in the cardiac cycle where the ventricles begin to contract, but the pressure within the ventricles has not yet risen enough to open the semilunar valves, so no blood is being ejected from the heart.

What is the first heart sound, and what causes it?

The first heart sound, also known as 'Lub' or S1, is produced when the AV valves snap shut during isovolumetric contraction, marking the transition from diastole to systole.

What is the difference between the atrial pressure and ventricular pressure during ventricular ejection?

During ventricular ejection, the ventricular pressure is greater than the atrial pressure, which keeps the AV valves closed. The ventricles are actively contracting to eject blood into the pulmonary trunk and aorta, causing the semilunar valves to open.

What is the second heart sound, and what causes it?

The second heart sound, referred to as 'Dub' or S2, is produced when the semilunar valves snap shut after the ventricles have ejected their blood, marking the end of systole and the beginning of diastole.

What is the dicrotic notch, and when does it occur?

The dicrotic notch is a brief rise in aortic pressure that occurs when the aortic semilunar valve closes, which happens after the ventricles have ejected their blood and the pressure in the aorta becomes greater than the pressure in the ventricles.

What phase of the cardiac cycle is characterized by the relaxation of the ventricles and the closing of all valves?

The phase characterized by ventricular relaxation and the closing of all valves is called isovolumetric relaxation, which occurs just before the ventricles begin to refill with blood from the atria.