1. Cardiovascular Physiology
Dr. Noha Elsayed

3. Objectives
Describe Blood flow from the heart (Pulmonary and systemic).
Define cardiac output (CO) and list its determinants.
Describe the events that comprise one cardiac cycle.

5. The heart
The heart is the central pump of the cardiovascular system that drives blood through the blood vessels.
Diastole Systole
A heart beat consists of a systole plus a diastole of cardiac chambers.
The heart of a normal adult male beats automatically and regularly at a rate of 75 beats/minute during rest. The normal range of heart rate is between 60 – 100.
Tachycardia.
Bradycardia.

6. The heart as a pump:
The heart is two pumps in series (i.e., the right and left sides) that are connected by the pulmonary and systemic circulations.

7. Blood flow from the heart
During ventricular systole, blood is pumped into the circulation.
During diastole, the pumping of blood stops and the ventricles get filled with blood.
In this way, the flow of blood from the ventricles into the systemic and pulmonary circulations is an intermittent pulsatile flow.

8. Systemic and pulmonary circulations

9. Cardiac output
* Cardiac output is the blood flow generated by each ventricle per minute. * The cardiac output is equal; to the volume of blood pumped by one ventricle per beat times the number of beats per minute: COP = SV . HR Where COP = cardiac output, SV = stroke volume, and HR = heart rate.

10. The stroke volume for each ventricle averages 70 ml of blood, and a normal heart rate is approximately beats/minute; therefore, the cardiac output at rest is approximately 5 L/min. The heart rate is under neural control. Cardiac sympathetic efferent activity increases the heart rate, whereas parasympathetic (vagal) efferent impulses decreases heart rate. The stroke volume varies with the volume of blood in the ventricle at the onset of contraction, changes in the force of ventricular contraction, and the arterial pressure.

11. Cardiac Cycle Electrical Conduction Pathway
Initiated by the Sino-Atrial node (SA node) which is myogenic at action potentials/minute
Depolarization is spread through the atria via gap junctions and internodal pathways to the Atrio-Ventricular node (AV node)
The fibrous connective tissue matrix of the heart prevents further spread of APs to the ventricles
A slight delay at the AV node occurs
Due to slower formation of action potentials
Allows further emptying of the atria
Action potentials travel down the Atrioventricular bundle (Bundle of His) which splits into left and right atrioventricular bundles (bundle branches) and then into the conduction myofibers (Purkinje cells)
Purkinje cells are larger in diameter & conduct impulse very rapidly
Causes the cells at the apex to contract nearly simultaneously
Good for ventricular ejection

13. Cardiac Cycle Phases of the cardiac cycle
Cardiac Cycle is alternating periods of systole and diastole
Systole = period of contraction
Diastole = period of relaxation
Phases of the cardiac cycle
1.Isovolumetric Ventricular Contraction phase:(beginning of systole)
After the ventricles have filled by a trial contraction ,AV valves close as the ventricles begin their contraction and intraventricualar pressure increases.
The semi lunar valves remain closed and this makes ventricle a closed cavity.
The volume in the ventricles remains unchanged throughout the contraction ,hence the name isovolumetric.
Closure of the AV valves in this phase causes the first heart sound.

14. Cardiac Cycle Phases 2. Rapid Ventricular Ejection
Intraventricular pressure overcomes aortic pressure
Semilunar valves open
Blood is ejected
3. Reduced ejection
The continued contraction of the ventricles pushes the remaining blood into the blood vessels (aorta and pulmonary artery)slowly.
At the end of this phase the ventricles begin to relax.
4 .protodiastolic phase
When ventricles begin to relax ,the AV valves close and the semilunar valves remain open.
As the intra ventricular pressure decreases below the pressure in the aorta and pulmonary artery ,the blood tries to come back into the ventricles,
This is prevented by closure of semilunar valve which produces the second heart sound.
5 . Isovolumetric Ventricular Relaxation(beginning of diastole)
Intraventricular pressure drops below aortic pressure
Semilunar valves close = second heart sound (dup)
Pressure still hasn’t dropped enough to open AV valves so volume remains same (isovolumetric)

15. 6 .first rapid ventricular filling :
Since there is reduced intraventricualar pressure in this phase causing the semilunar valves to close .
The AV valves open and there is sudden rush of blood into the ventricles from the atria.
7 .reduced ventricular filling :
During this phase both atria and ventricles are relaxing ,the blood entering the atria ,fill the ventricles passively.
8 .last rapid filling phase:
This phase coincides with a trial contraction.
The atria are in systole forcing blood into the ventricles which are relaxed.

16. Cardiac Cycle Phases

17. Task for home
Student 1 define cardiac output (CO) and list its determinants.
Student 2 Describe the events that comprise one cardiac cycle with diagram.
Student 3 coronary artery disease.

18. Reference