The document discusses the cardiac cycle and its four stages: atrial diastole, atrial systole, ventricular systole, and ventricular diastole. It describes the opening and closing of valves between the atria and ventricles that allow blood to flow in and be pumped out. Key waves in an ECG like the P, QRS, and T waves correspond to electrical signals during contraction and relaxation of the heart chambers. The cardiac output and factors that can increase or decrease it are also covered, along with the Frank-Starling law and conditions of hypoeffective and hypereffective heart function.

3.  Definition:
“ The events that occur from the begining
of one heart beat to the begining next one is called
cardiac cycle.”
 Systole:
Period of ventricular contraction.
 Diastole:
Period of ventricular relaxation.
 Note: Normally diastole is longer than systole.

4.  During systole there is conttraction of the cardiac
muscle and pumping of blood from ventricles.
 During diastole, there is relaxation of cardiac muscle
and filing of blood.
 These changes are repeated during every heart beat in
a cyclic manner.

6.  P,QRS and T waves are electrical voltages generated by
the heart and recorded by E.C.G from the body
surface.
 P wave is caused by spread of depolarization through
atria and this is followed by atrial contraction, which
causes a slight rise in atrial pressure.
 About 0.16 sec after onset of p wave, QRS wave appears
as a result of electrical depolarization of ventricles.
 T wave represent stage of repolarization of ventricles,
therefore T wave occurs slightly before the end of
ventricular contraction.

8.  About 80% of blood flows directly through
atria into ventricles even before atrial
contraction.
 Then atrial contraction usually causes an
additional 20% ventricular filling.
 Therefore atria simply functions as a primer
pump.

11. 4 Stages of Cardiac cycle

12. Stage 1- Atrial diastole
 Biscuspid and tricuspid valves are closed.
 Muscles in the atria relaxes and the pressure decreases
while volume increases inside.
 Blood returns to the heart under low pressure in the
veins and enters the two atria
 The vena cava carry deoxygenated blood to the right
atrium.
 The pulmonary veinns carry oxygenated blood to the
left atrium.

13. Stage 2- Atrial systole
 It is the time when the heart is filled with blood .
 The muscle in the atrial walls contracts with the help
of SAN.
 The pressure increases and the atrio-ventricular valves
open so the blood found in atria is forced into the
ventricles.
 Blood from atria does not go back into the pulmonary
veins or the vena cava because of the semilunar valves
which prevent backflow.

14. Stage 3- Ventricular Systole
 0.1 second after the contraction of the atria, the
ventricles also contract.
 Thick muscular walls of the ventricles squeeze inwards
on the blood, increasing pressure and pushing it out of
the heart.
 As pressure in ventricles become greater than that in
atria, the atria-ventricular valves shut, preventing
backflow to the atria.
 Instead, blood rushes upwards into aorta and the
pulmonary atery, pushing open the semilunar valves.

15. Stage 4- Ventricular diastole
 Here, the muscles relaxes
 As this happens, pressure in ventricles drops
 The high pressure blood which has just been pushed
into the arteries would flow back in the ventricles.
 But, this is prevented by the presence of the semilunar
valves which snap shut as the blood fills their cusps.

16. Cardiac output
 “Volume of blood being pump by ventricles
per unit time is called cardiac output.”
 5L/min in aged male person
 5.6L/min male in young healthy person
 4.9L/min in females

18. Franklin Starling Law
“The ability of heart to pump
automatically whatever amount
of blood flows into right atrium
from the veins.”

19. Two Conditions
Hypereffective heart Hypoeffective heart
 It cause nervous
disorder.
 It also caused hypertrophy
(increase in muscle size)
 It cause heart failure.
 It also caused
Myocordial Infraction.

20. Defict of High Cardiac output
 Due to high cardiac output; some abnormalities
1. Beriberi:
 Weakness
 It is caused by deficiency of vitamin B1 (thiamine).
2. Hyperthyroidism:
Due to dilation of blood vessels.
3. Anemia:
A condition in which there is a deficiency of
red cells or haemoglobin in the blood.

21. Defict of Low Cardiac output
 A) Cardiac reason-
Myocardial Infraction
Coronary Heart disease
 B) Non-cardiac reason-
Fainting
Decrease in blood volume (hemorrhage)

22. Isometric/Isovolemic contraction
 Isovolemic mean “the same volume”.
 At the beginning of systol, ventricular
contraction occur. The AV Valve close and
pressure begin to build up in the ventricle.
No out of flow of blood occur during the
first 0.2-0.3 sec of ventricle contraction. This
period is known as isovolemic contraction.

23. BaroReceptor Reflex
 They are also called pressure buffers.
 They maintain Arterial Pressure.
 Location:
1. In small amount
A) Thoraic artery b) neck region
2. In large amount
A) Carotid artery b)Aortic artery

28. References: