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Cardiac Cycle
Cardiac Cycle
? Cardiac cycle is the mechanical sequence of
events as blood enters the atria and leaves the
ventricles
? The events includes
1. Changes in the pressures in different chambers of the heart
2. Changes in the volume in different chambers of the heart
3. Changes in the aortic, pulmonary arteries
4. Heart sounds
5. ECG changes
Cardiac Cycle
0.5 sec
0.1 sec
0.7 sec
0.3 sec
Phases of Cardiac Cycle
Ventricular Systole
? Isovolumetric contraction
? Rapid ejection
? Slow ejection
Phases of Cardiac Cycle
Ventricular Systole
? Isovolumetric contraction
? Rapid ejection
? Slow ejection
Ventricular Diastole
? Isovolumetric relaxation
? Rapid filling
? Slow filling (Diastasis)
? Filling d/t Atrial Systole
Phases of Cardiac Cycle
Ventricular Systole
? Isovolumetric contraction
? Rapid ejection
? Slow ejection
Ventricular Diastole
? Isovolumetric relaxation
? Rapid filling
? Slow filling (Diastasis)
Start
? Filling d/t Atrial Systole
Cardiac Cycle
Phases
Cardiac Cycle
Phases
Cardiac Cycle
Phases
Cardiac Cycle
Phases
Cardiac Cycle
Phases
Phases of Cardiac Cycle
Ventricular Systole
? Isovolumetric contraction
? Rapid ejection
? Slow ejection
Ventricular Diastole
? Isovolumetric relaxation
? Rapid filling
? Slow filling (Diastasis)
? Filling d/t Atrial Systole
Ventricular Systole
? Isovolumetric contraction phase
? Rising ventricular pressure results in closing of AV valves (1st
heart sound ? "lubb")
? Ventricles are contracting but no blood is leaving
? Ventricular pressure not great enough to open semilunar valves
? Ventricular ejection phase opens semilunar valves
? Ventricular ejection phase
? Semilunar valves opens
? Rapid Ejection (70% blood)
? Slow ejection (30% blood)
Ventricular Diastole
? Isovolumetric relaxation
? volume does not change as ventricles relax, pressure
drops and AV valves open
? Ventricular fil ing
? Rapid ventricular filling:as blood flows from full atria
? diastasis: as blood flows from atria in smaller volume
? atrial systole pushes final 20-25 ml blood
Phases of Cardiac Cycle
Ventricular Systole
Duration (approximate)
? Isovolumetric contraction
0.05 sec
? Rapid ejection
0.10 sec
? Slow ejection
0.15 sec
Ventricular Diastole
? Isovolumetric relaxation
0.10 sec
? Rapid filling
0.10 sec
? Slow filling (Diastasis)
0.20 sec
? Filling d/t Atrial Systole
0.10 sec
Normal Volume of Blood in Ventricles
? Atrial systole pushes final 20-25 ml blood (20%)
? After atrial contraction, 110-120 ml in each ventricle
(end-diastolic volume)
? Contraction ejects ~70 ml (stroke volume output)
? Thus, 40-50 ml remain in each ventricle (End
systolic volume)
? The fraction ejected is then ~60% (ejection fraction)
A Simple Model of Stroke Volume
Ventricular Pressures
? Blood pressure in aorta is 120 ? 80 mm Hg
? Blood pressure in pulmonary trunk is 25 ? 8 mm Hg
? Ventricular pressure usually not increases during diastole
? Right Atrial pressure changes reflected in Jugular vein
Jugular venous pulse waves
Jugular venous pulse waves
? a-wave is due to atrial systole which causes increase in
the intra-atrial pressure
? C-wave occurs during the isometric contraction of the
ventricles due to bulging of the tricuspid valve
? V-wave is due to accumulation of blood during late part
of the ventricular systole or protodiastolic phase and
isometric relaxation of the ventricles
Jugular venous pulse waves
? X-wave is due to downward displacement of the A-V
valve (tricuspid valve) and the AV ring during maximum
ejection phase of ventricular contraction
? Y-wave is due to opening of the AV valve (tricuspid
valve) during maximal ventricular filling phase
Jugular venous pulse waves
? "a-c" interval measures the time of conduction of the cardiac impulse
from the right atrium to the ventricles
? The a-c interval corresponds to the P-R interval of the ECG
? The "a-c" interval is prolonged in cases of delayed conductivity in the
AV bundle which is an early sign of heart block
? In partial heart block, the number of "a" waves is greater than the
number of the "c" or "v" waves.
? In atrial fibril ation, the "a" wave is absent.
Putting it all together!
Putting it all together!
Thank You
This post was last modified on 08 April 2022