Associated Prof. of physiology Cardiac cycle By Dr. Enas Albendary. References Guton& Hall 11th ed. Ganong. Several Websites Associated Prof. of physiology Dr. Enas (2009)

Objectives Cardiac Cycle Definition Phases Events, their names & duration Pressure changes Atria Ventricles Aorta Volume changes ECG & Cardiac Cycle Heart Sounds & Cardiac Cycle Dr. Enas (2009)

Cardiac Cycle It is the cardiac events that occur from the beginning of one heart beat to the beginning of the next one. Dr. Enas (2009)

Heart acts as a dual pump The cardiac cycle consists of one systole-diastole sequence of the heart,& it lasts about 0.8 sec. It starts by atrial systole (contraction). Followed by ventricular systole then diastole (relaxation) of the whole heart. Dr. Enas (2009)

‘Heart’ Dual Pump Dr. Enas (2009)

What is the meaning of Systole and Diastole Dr. Enas (2009)

Phases of Cardiac Cycle There are seven (7) phases of cardiac cycle: 1- Atrial systole.(0.1 second). Ventricular Systole: divided into 3 phases:- 2- Isovolumetric ventricular contraction.(0.05 sec.). 3- Rapid ventricular ejection.(0.15 sec.). 4- Reduced ventricular ejection.(0.1 sec.). Ventricular Diastole: divided into 3 phases:- 5- Isovolumetric ventricular relaxation.(0.06 sec.). 6- Rapid ventricular filling. (0.1 sec.). 7- Reduced ventricular filling (diastasis) (0.2 sec.). Dr. Enas (2009)

Phases of Cardiac Cycle Dr. Enas (2009)

1- Atrial Systole In this phase , both atria contract leading to blood evacuation into the ventricles. 1- Atrial pressure:- This initially increases (due to reduction of arterial volume,then decrease again due to evacuation of blood into corresponding ventricle. 2- Ventricular pressure:- This initially increase slightly (due to entry of blood) then drop due to ventricular dilation. 3- Ventricular volume:- Increase slightly due to ventricular dilation. 4- Valves: A-V valves are open while seilunar valves are closed. 5- Aortic Pressure:-Decrease gradually due to continuous blood flow from the aorta to the periphery. 6- Heart sounds: 4th heart sound is recorded in this phase. 7- ECG :- P wave start about 0.02 before this phase . While main P wave,P-R segment & Q wave occure during it. Dr. Enas (2009)

2- Isometric (Isovolumetric) ventricular contraction phase This is the early phase of vent. systole in which the ventricle contract but not ejection occurs. Its events include the following :- Ventricular pressure & volume: The ventricles contract isometrically i.e. without shortening of the cardiac muscle .So vent. pressure rises sharply while vent. Volume remain constant Valves: Vent. Press. Become greater than atrial press. Causes closure of A-V valves producing 1st heart sound while semi lunar valves are still closed. Sound: 1st heart sound due to sudden closure of A-V valves Atrial pressure: slightly increased due to bulging of A-V cusps into the atria. Aortic pressure: this decrease to a minimum of about 80 mmHg at the end of this phase (diastolic blood pressure). ECG: The Q wave starts about 0.02 second before this phase, while the R &S waves occur during it. Dr. Enas (2009)

3- Rapid ventricular ejection phase: In this phase, the semilunar valves open &blood is ejected into the great arteries. Its events include : Ventricular volume & pressure : vent. Contract isotonically (i.e cardiac musc. Fibers are shortened) .So vent. Volume is rapidly decreased while its pressure is markedly increased to maximum 120 mmHg. Valves: A-V valve are still closed while semilunar valve. Will open b/c vent. Press. Will exceed aortic press. Sound: continuation of 1st heart sound. Atrial pressure: decreased b/c its widening of its cavity then increase due to its filling by venous return. Aortic pressure: is markedly increased due to ejection of blood to it & reach maxim.120mmHg.(systolic blood pressure) ECG: The S-T segment is present in this phase and T wave start in its late part. Dr. Enas (2009)

4- Reduced ventricular ejection phase: The event in this phase are a continuation of those occurring in the preceding phase: Ventricular volume:- this is further decreased. Ventricular pressure:- This is slightly decreased due to ejection of most blood in preceding phase Aortic pressure:- is slightly decreased. Valves: still the semilunar valve are open &the AV valves closed. Sound: there are no sound in this phase. Atrial pressure: this is still increasing due to venous return. ECG: this show most of the ascending limb and the top of the T wave. Dr. Enas (2009)

5- Isovolumetric ventricular relaxation phase: This is the early phase of ventricular distole in W’ventricles relax but no filling occurs. Its events include : Ventricular volume:- remains unchanged Ventricular pressure:- falls sharply (to 0- 5mmHg.) Aortic pressure:- is initially increase (due to elastic recoil of aorta ) then gradually decrease due to continuous flow of blood to peripheral arteries. Valves:- Semilunar valves are suddenly closed & A-V valve is still closed. Sound: the 2nd heart sound Atrial pressure: this is still increasing due to continuous venous return. ECG: most of the descending limb of the T wave is present in this phase. Dr. Enas (2009)

6- Rapid ventricular filling phase:- In this is phase, the atrial pressure exceeds the ventricular pressure, so the AV valve open and rapid filling of the ventricles. Its events include : Ventricular volume & pressure: there is initial decrease in pressure due to vent. Relaxation then increase markedly while volume is increased gradually Atrial pressure: initial increase due to rush of blood into ventricles then increase due to venous return. Aortic pressure: still decrease due to continuous flow of blood to the periphery. Valves: the Sound: the 3rd heart sound. ECG: the early of the T-P segment and the U wave are present in this phase. Dr. Enas (2009)

7- slow ventricular filling phase: In this is phase, Its events include : Ventricular volume & pressure: these still gradually increase but at a slower rate. Atrial pressure: this is still increasing due to venous return. Aortic pressure: this is still decreasing due to continuouse blood flow from the aortic to the peripheral arteries. Valves: the AV valves are open while the semilunar valve are closed. Sound: there are no sound in this phase. ECG: the late part of the T-P segment and the start of the P wave are present in this phase. Dr. Enas (2009)

Changes in ventricular pressure& volume in systole& diastole Dr. Enas (2009)

Dr. Enas (2009)