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The cardiac cycle

The cardiac cycle. Pressure and volume changes and associated valve movements during the cardiac cycle. Describing the sequence of events in one heart beat. Definitions. Systole = period of ventricular contraction. Diastole = period of ventricular relaxation.

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The cardiac cycle

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  1. The cardiac cycle Pressure and volume changes and associated valve movements during the cardiaccycle. Describing the sequence of events in one heart beat

  2. Definitions • Systole = period of ventricular contraction. • Diastole = period of ventricular relaxation. • NOTE:  Normally diastole is longer than systole.

  3. Cardiac cycle • General Principles. • Contraction of the myocardium generates pressure changes which result in the orderly movement of blood. • Blood flows from an area of high pressure to an area of low pressure, unless flow is blocked by a valve. • Events on the right and left sides of the heart are the same, but pressures are lower on the right.

  4. Atrial systole • The heart is full of blood and the ventricles are relaxed • Both the atria contract and blood passes down to the ventricles • The atrio-ventricular valves open due to blood pressure • 70% of the blood flows passively down to the ventricles so the atria do not have to contract a great amount.

  5. Ventricular systole • The atria relax. • The ventricle walls contract, forcing the blood out • The pressure of the blood forces the atrio-ventricular valves to shut (producing the heart sound ‘lub’)

  6. Ventricular systole • The pressure of blood opens the semi-lunar valves. • Blood passes into the aorta and pulmonary arteries.

  7. Diastole • The ventricles relax • Pressure in the ventricles falls below that in the arteries • Blood under high pressure in the arteries causes the semi lunar valves to shut. This produces the second heart sound, ‘dub’. • During diastole, all the muscle in the heart relaxes.

  8. Blood from the vena cava and pulmonary veins enter the atria. • The whole cycle starts again.

  9. Cardiac cycle Match the letter on the graph to the following events • Semi-lunar valves open • Atrio-ventricular valves close, • Semi-lunar valves close • Atrio-ventricular valves open

  10. atrio-ventricular valves open

  11. atrio-ventricular valves close atrio-ventricular valves open

  12. semi-lunar valves open atrio-ventricular valves close atrio-ventricular valves open

  13. semi-lunar valves open semi-lunar valves close atrio-ventricular valves close atrio-ventricular valves open

  14. Calculate heart rate (pulse). • One full heart beat takes 0.8s in this example. • What is the pulse rate of this person?

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