2. July 16 1 The cardiac cycle

3. July 16 2 The cardiac cycle The cardiac events that occur from the beginning of one heartbeat to the beginning of the other. Each cycle is initiated by Spontaneous generation of AP in the SAN. There is delay of more than 1/10 second between passages of cardiac impulses from the atria into the ventricles. This delay allows the atria to contract ahead of the ventricles.

4. July 16 3 The cardiac cycle: Cardiac cycle consists of period of relaxation (diastole) during which the heart fills with blood, followed by a period of contraction (Systole) Blood normally flows continually from the veins into the atria. 75% before the atria contract. Atria contraction causes addition 25% of ventricular filling

5. July 16 4 Ventricular filling During ventricular systole large amount of Blood accumulate in the atria. Immediately after systole Ventricular pressures fall Moderately increase pressure's in the atria push the A-V valves open and allow blood to flow rapidly into the ventricles (period of rapid filling of ventricles).

6. July 16 5 Ventricular Filling This period lasts for about the first 1/3 of diastole During the middle 1/3 only small amount of blood flows from atria to ventricles. During the last 1/3 of diastole atria contract

7. July 16 6 Ventricular emptying Immediately after Ventricular contraction begins Ventricular pressure abruptly raises causing A-V valves to close. Additional 0.02 – 0.03Sec. Is required for the ventricles to build up sufficient pressure, to push semi lunar valves open. During this period contraction is occurring but no emptying. This period is called Isometric or Isovolumic contraction

8. July 16 7 Ventricular emptying When the Lt ventricular pressure rises slightly above 80mmHg, and Rt ventricular pressure slightly above 8mmHg. Semilunar valves open Blood begins to pour out of the ventricles 70% of emptying occur in the first third of ejection. 30% in the next two third.

9. July 16 8 Ventricular emptying At the end of systole, ventricular relaxation begins suddenly, allowing the intraventricular pressure to fall rapidly. Semilunar valves close For another 0.03 – 0.06Sec. The ventricular muscle continues to relax even though the volume does not change, giving rise to the period of Isovolumic or Isometric relaxation.

10. July 16 9 Ventricular emptying The intraventricular pressures fall rapidly back to their low diastolic level, then A- V valve open to begin a new cycle, of ventricular pumping. End diastolic volume 110 – 120mls Stroke volume ≈ 70mls End systolic volume, 40 – 50mls Ejection fraction, about 60%

11. July 16 10 ------ 120 60 20 50120 Ventricular volume (ml) Ventricular pressure (mmHg) Isovolumetric contraction Isovolumetric relaxation ejection

12. July 16 11 Heart Sound Two are normally heard through a stethoscope during each cardiac cycle. The first is a low, slightly prolonged “lub” fist sound caused by vibrations set up by the sudden closure of the mitral and tricuspid valves at the start of ventricula systole

13. July 16 12 Heart Sound The second is a shorter, high-pitched “dup” second sound caused by vibrations associated with the end of ventricular systole. A soft, low-pitched the end of ventricular systole. A soft, low-pitched third sound is heard about one-third of the way through diastole in many normal young individuals. It coincides with the period of rapid ventricular filling and probably due to vibrations set up by the inrush of blood.

14. July 16 13 Heart Sound A fourth sound can sometimes be heard immediately before the first sound when atrial pressure is high or the ventricle is stiff in conditions such as ventricular hypertrophy. It is due to ventricular filling rarely heard in normal adults.

15. July 16 14 Heart sounds Standard areas of auscultation Aortic area – second intercostal space Rt Pulmonary area – second intercostal space Lt Mitral area – apex Tricuspid area – fourth intercostal space Rt