Lecture 1A. Part 1 The HEART and Cardiac Cycle Holdorf RVT

Contents The Anatomy of the Heart The Cardiac Cycle: Diagrams 1-14 Wiggers Diagram Heart Sounds

The Anatomy of the Heart

The Cardiac Cycle The mechanical events which occur in one cardiac cycle = I systole and one diastole. 1 cardiac cycle = one systole (Contraction) and Diastole (relaxation) Events start at the left heart, in the atria and left ventricle. It needs to be noted that similar events happen in the right heart simultaneously.

4 chambers We will be looking at only 2

Say hello to the King, the Prince, and their humble servant

Left atrium left ventricle and aorta. Left atrium contracts Phase of cardiac cycle when left atrium contracts In this first phase… What is happening in the atrium? What is happening in the ventricle? What is happening in the aorta?

Atrial Contraction

Phase of atrial contraction, the mitral valve most be OPEN, and the Aortic valve must be CLOSED. During atrial contraction, there is communication between the left atrium and the left ventricle But there is no communication between the left ventricle and aorta It means for the left ventricle, the input system is working but the output system is not working Before atrial contraction starts, about 80% of ventricular filling is already done. It means atrial contraction just adds about 20% of ventricular filling 80% of ventricular filling is passive

If someone has a problem with atrial contraction, still most of the ventricle can obtain blood. Hence, the patient will not suffer significantly. This last 20% of ventricular filing becomes more important in human beings when they become physically active (during exercise) Pressure: When left atrium contracts, the pressure in the left atrium goes up Pressure in the left atrium slightly increases.

A wave is produced when there is an increased pressure in the left atrium Due to atrial contraction wave is called the “A” wave or pressure wave “A” wave is pressure wave: produced by the atrial contraction.

Mitral valve must now be open and whatever pressure that is in the left atrium must now be communicated into the left ventricle. So, just before the contraction of the left atrium, we can say that the pressure in the left ventricle is 0 (zero). It was a relaxed chamber. But now, blood is being pushed into the left ventricle, and now pressure increases slightly. This is done by the electrical activity of the AV node (Atrial-Ventricular node) It is now time for the left ventricle to contract. So this phase has ended. We will call this first phase the phase of ATRIAL CONTRACTION Review: Left atrium contracts, pressure wave increases in the left atrium Mitral valve is open, and pressure and blood volume is transferred into the left ventricle. The aortic valve is closed, become the pressure in the aorta is more than the pressure of the left ventricle

Now the next phase can be called VENTRICULAR CONTRACTION Depolarization will come to the left ventricle which will lead to the contraction of the left ventricle The atrial contraction has become completed and we are entering into the phase of atrial relaxation and ventricular contraction. The onset of the next phase, Ventricular contraction, the Aortic valve starts as being closed. Pressure is about 80 mmHg within the aorta. When the ventricle starts to contact, the pressure in the ventricle starts to increase. Now the ventricular pressure becomes more than the atrial pressure

At the beginning of ventricular contraction, the pressure rises to about 5 mmHg. As soon as blood in the ventricular is slightly higher than that of the left atrium, blood will try to move back into the left atrium. Mitral now has to close. Ventricle will continue to contract (squeezing the blood) But the point that is important, is when the ventricle will contract as a closed chamber. Why? The mitral valve will be closed and the aortic valve is still closed.

Pressure Points: AT 5 mmHg, the closure of the mitral valve. The closure of the mitral valve produces a sound: THE FIRST HEART SOUND S1 = closure of the mitral valve during the closed chamber contraction phase of the Ventricular contraction phase Which corresponds with the closure of the tricuspid valve on the right side of the heart. After that the closed chamber contraction of the left ventricle pressure increases The pressure goes up to 80 mmHg

This phase of closed Ventricular contraction is called ISOVOLUMETRIC CONTRACTION where the mitral valve is closed and the aortic valve is closed. This is early Ventricular systole During this phase no blood is entering or leaving the ventricle The same amount of blood is in the ventricle for this phase. During this phase: Pressure in the ventricle increases

The atrium: What happens there The atrium: What happens there? The closing of the mitral valve causes a slight bulge in pressure in the left ventricle which can be measured as a C wave. C wave = a slight increase in pressure in the left atrium via ventricular contraction. Now venous blood from the lungs is coming to the left atrium. At this time, the mitral valve is closed, so the atrium is now acting as a tank. The atrium will accumulate the blood returning from the lungs and will slightly increase the atrial pressure Now: Ventricle contracts and closes the mitral valve The pressure increases but does not increase enough to open the mitral valve No blood change or size change in the left ventricle so we call this Isovolumetric contraction phase. Early part of ventricle systole

As soon as the Pressure in the left ventricle reaches 81 mmHg, the aortic valve opens. And when the aortic valve opens, blood will start ejecting rapidly from the left ventricle. The aorta is elastic and will stretch out when receiving the blood. The left ventricle blood pressure can reach as high as 120 mmHg   Now the Ventricle chamber and the aortic chamber are acting like a single chamber.

Lecture 1A. The Cardiac Cycle 2017 Part 1 FIN