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Transcript
The cardiac cycle May 17 1 The cardiac cycle The cardiac events that occur Each cycle is initiated by Spontaneous generation of AP in the SAN. There is delay of more than 1/10 second from the beginning of one heartbeat to the beginning of the other. between passages of cardiac impulses from the atria into the ventricles. This delay allows the atria May 17 to contract ahead of the ventricles. 2 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 May 17 continually from the veins into the atria. 75% before the atria contract. Atria contraction causes addition 25% of ventricular filling 3 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 May 17 and allow blood to flow rapidly into the ventricles (period of rapid filling of ventricles). 4 Ventricular Filling This period lasts During the middle 1/3 for about the first 1/3 of diastole only small amount of blood flows from atria to ventricles. During the last 1/3 of diastole atria contract May 17 5 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 May 17 to push semi lunar valves open. During this period contraction is occurring to build up sufficient pressure, but no emptying. This period is called Isometric or Isovolumic contraction 6 Ventricular emptying When the Lt ventricular pressure rises 70% of emptying slightly above 80mmHg, and Rt ventricular pressure slightly above 8mmHg. Semilunar valves open Blood begins to pour out of the ventricles occur in the first third of ejection. 30% in the next two third. May 17 7 Ventricular emptying At the end of systole, For another 0.03 – 0.06Sec. May 17 ventricular relaxation begins suddenly, allowing the intraventricular pressure to fall rapidly. Semilunar valves close The ventricular muscle continues to relax even though the volume does not change, giving rise to the period of Isovolumic or Isometric relaxation. 8 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% May 17 9 Ventricular pressure (mmHg) 60 - 20 - Isovolumetric contraction Isovolumetric relaxation May 17 120- 50 120 Ventricular volume (ml) 10 Heart Sound Two are normally heard through a stethoscope during each cardiac cycle. The first is a low, slightly prolonged “lub” May 17 fist sound caused by vibrations set up by the sudden closure of the mitral and tricuspid valves at the start of ventricula systole 11 Heart Sound The second is a shorter, high-pitched “dup” A soft, low-pitched the end of ventricular systole. A soft, low-pitched third sound is heard second sound caused by vibrations associated with the end of ventricular systole. about one-third of the way through diastole in many normal young individuals. It coincides with the period of rapid ventricular filling May 17 and probably due to vibrations set up by the inrush of blood. 12 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 May 17 rarely heard in normal adults. 13 Heart sounds Standard areas of auscultation May 17 Aortic area – second intercostal space Rt Pulmonary area – second intercostal space Lt Mitral area – apex Tricuspid area – fourth intercostal space Rt 14