Definition, duration, and stages of cardiac cycle

1. BY;
Y.V.VANAJA
LECTURER
VIJAY MARIE COLLEGE OF NSG
CARDIAC CYCLE

2. INTRODUCTION
 The heart as a pump.
 2 separate pump in series.
 Systole – contraction
 Diastole – relaxation.

3.  Cardiac cycle – both electrical &
mechanical events associated
with one heart beat is called
cardiac cycle.
• Cycle includes the contraction or
systole of the atria and ventricles
and the relaxation or diastole of
the ventricle

4. DURATION OF CARDIAC CYCLE
 the normal number of
cardiac cycles per minute
ranges from 60-80.
 IF Normal Heart rate is 75
beats /min
= 0.8 sec.

5. STAGES OR EVENTS OF CARDIAC CYCLE
 Atrial systole (0.1)
 Ventricluar systole (0.3)
 Cardiac Diastole
• Atrial diastole (0.7)
• Ventricular diastole ( 0.5)

6.  During the atrial systole, which lasts
about 0.1 sec, the atria are contract forcing
the blood into ventricles at the same time,
the ventricles are relaxed.
 Depolarization of the SA node causes
atrial depolarization, marked by p wave in the ECG
 Atrial depolarization causes atrial systole
 as the atria contract, they exert pressure on the
blood within which forces blood through the
open AV valves io the ventricles.
 Atrial systole contributes a final 25 ml of blood
to the volume already in each ventricle ( about 105ml)
ATRIAL SYSTOLE

7.  The end of the atrial systole is also the end of the ventricular diastole
 thus the ventricle contains about 130 ml at the end of its relaxation
period.
 this blood volume is called as the end- diastolic volume ( EDV)
 the QRX complex in the ECG marks the onset of ventricular
depolarization

8. VENTRICULAR SYSTOLE
 Ventricluar systole is the contraction
of the left and right ventricles

 ventricular depolarization causes
ventricular systole
 as the ventricular systole begins
pressure rises inside the ventricles
and pushes blood up against AV
valves( forcing them to shut for
about 0.5 sec ,
 both the SL and AV valves are closed
( isovolumetric contraction )

9.  continued contraction of the ventricles causes pressure inside the chambers
to rise sharply
 when left ventricular pressure surpasses aortic pressure at about 80mmhg
and right ventricular pressure rises above the pressure in the pulmonary
trunk about 20 mmhg, both the SL valves open - ( ventricular ejection lasts
about 0.25 sec)
 The pressure in the left ventricle continues to rise to about 120 mmHg
 the presure in the right ventricle continues to rise to about 25 to 30mmHg
 the left ventricle ejects 70ml of blood into the aorta
 the right ventricle ejects the same volume of blood into the pulmonary
trunk
 the volume remaining in each ventricle at the end of systole about 60ml is
the end systolic volume

10. Stroke volume
 The volume ejected per beat from each ventricle, equals end diastolic
volume minus end systolic volume
SV = EDV-ESV
 The T wave in ECG marks the onset of ventricular repolarization
SV = 130 - 60 = 70mL

11. CARDIAC DIASTOLE
ventricular diastole is when the ventricles are relaxing, atrial diastole is when the
atria are relaxing. Together they are known as complete cardiac diastole.
Cardiac diastole
• Atrial diastole
• Ventricular diastole

12. ATRIAL DIASTOLE (0.7)
 Coincide with Ventricular
Systole & most of the
ventricular diastole.
 Atria Relax – gradual filling
of atria – pressure slowly
increases.

13. VENTRICULAR DIASTOLE
As the ventricles relax
pressure with in chambers falls
Blood in the aorta and pulmonary trunk
begins to flow backward to the regions of
lower pressure in ventricles
Closes SL Valves
The aortic valve close at a presuure of
about 100mmhg
x

14.  when the ventricular blood volume does not change because all
four valves are closes this is the period of isovolumetric relaxation.
 at the end of the relaxation period the ventricles are about 3/4 full
.
 the p wave appears in ECG signaling the start of another cardiac
cycle.