Lecture 6_Cardiac cycle. ppsx Cardiac cycle
- 1. Pressure changes in the heart and cardiac cycle Dr Akanksha Department of Physiology, AIIMS, New Delhi email: drakanksha111@gmail.com
- 2. Cardiac Cycle The events includes: 1. ECG changes 2. Changes in the pressures in different chambers of the heart 3. Changes in the volume in different chambers of the heart 4. Changes in the aortic, pulmonary arteries 5. Heart sounds Events that occurs from the beginning of one heart beat to the beginning of the next are called cardiac cycle. The sequence of electrical and mechanical events that repeats with every heart beat is called cardiac cycle.
- 3. Atrial systole 0.1s Atrial diastole 0.7s Ventricular diastole 0.5s Ventricular diastole 0.3s Complete cycle ~0.8 s
- 4. At High HR Diastole Systole Heart rate (beats/minute) Seconds • Length of cardiac cycle ↓ • Systole more fixed • Diastole shortens to a greater extent • Blood supply to sub-endocardial portions and vent filling compromised beyond 180/min
- 10. Joint diastole • The atria and the ventricles are both in diastole. • Both atrio-ventricular valves are open. • The blood received in the atria is passively transferred to ventricles during this period.
- 11. Atrial systole • The p wave causes atrial contraction. • ↑ intra atrial pressures from 0 to: 4-6mmHg Right Atrium 7-8 mmHg Left Atrium • Ventricular filling 70% passive, 30% atrial contraction At high heart rates 40% of ventricular filling by "atrial kick."
- 12. Isovolumetric contraction • The QRS wave causes ventricular contraction. • Pressure rises without change in volume of the ventricles Left ventricle rises from 10 to 80 mm of Hg Right ventricle rises to 15 mm of Hg • Closure of AV valves. First heart sound S1 • End diastolic Volume (EDV): 150ml (Preload)
- 13. Isovolumetric contraction Electrically, ventricular systole is defined as the interval between the QRS complex and the end of the T wave (the Q-T interval). Mechanically, ventricular systole is defined as the interval between the closing of the AV valves and the opening of the semilunar valves (aortic and pulmonary valves).
- 14. Ventricular ejection • Rising pressure in ventricles exceeds the aortic/pulmonary pressure and the semilunar valves open • Ventricular pressure ↑ Peak LV pressure ~120 mm Hg, Peak RV pressure ~ 25 mm Hg. • 70% of ejection takes place in 1/3rd of the total ejection time.(Rapid ejection phase) • Stroke volume: ~70 ml
- 15. Isovolumetric relaxation • T wave causes ventricular relaxation. • Blood continues to eject till the pressure in the ventricles falls below the aorta/pulm art and the semilunar valves close. • Second heart sound S2 • End systolic relaxation = ~50 ml
- 16. Pressure volume loop of left ventricle • A : Diastolic filling • A –B: Vent passive distension • B-C : Vent compliance • C : Atrial systole • C-D : Isovolumetric contraction • D-E : Rapid ejection • E-F : Slow ejection • F-A : Isovolumetric relaxation
- 17. Ventricular volumes • Stroke volume: volume of blood ejected by each ventricle per stroke/ systole at rest is 70-90 mL. • End-diastolic ventricular volume: 130 mL. • End-systolic ventricular volume: 50 mL • Ejection fraction: the percent of the end-diastolic ventricular volume that is ejected with each stroke, is about 65%. – The ejection fraction is a valuable index of ventricular function.
- 18. JUGULAR VENOUS PULSE ( JVP ) Rt Internal jugular vein • The right internal jugular vein is in a direct line with right atrium hence pressure changes in the Rt atrium are transmitted to it. • JVP can not be palpated because of very low pressure in the veins. • JVP can be inspected and recorded. • JVP > 10 cm H2O usually indicates volume overload; • JVP <5 cm H2O usually indicates hypovolemia
- 19. JVP measurement • Position: Semi-reclining position with 45° angle with neck muscles relaxed. • Identify Jugular venous pulsation: Use tangential beam of light through torch & note the upper level of pulsation. • Measurement: Locate the sternal angle (Angle of louis). Measure the vertical distance (in cm) between the horizontal lines drawn from the upper level of venous pulsation and the sternal angle. • Calculate the right atrial pressure: Normally, the center of right atrium is 5 cm below the sternal angle. Hence, Add +5 cm to the above measurement to obtain the right atrial pressure.
- 20. a peak: contraction of the right atrium. c peak reflects the pressure rise in the right ventricle early during systole and the resultant bulging of the tricuspid valve—which has just closed—into the right atrium. x minimum occurs as the ventricle contracts and shortens during the ejection phase, later in systole. v peak venous filling by venous return (tricuspid closed) y minimum reflects a fall in right atrial pressure atrial emptying, (tricuspid open) Clinical significance of JVP: Raised JVP value indicates right heart failure. Giant “a” wave: Heart block. Giant “c” wave: tricuspid insufficiency.
- 21. Carotid Pressure and Radial pressure Pulse: The palpable expansion of the artery due to pressure wave transmitted with each ventricular systole Dicrotic notch: Aortic valve closure
- 25. Wigger’s diagram ----JVP LV Pressure ---- Aortic pressure
- 26. Questions?