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Cardiovascular Physiology

Cardiovascular Physiology. Wu Minfan Department of Physiology, Shenyang Medical College. Introduction. The cardiovascular system consists of the heart and the blood vessels. The right ventricle pumps blood through the pulmonary circulation to the left atrium.

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Cardiovascular Physiology

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  1. Cardiovascular Physiology Wu Minfan Department of Physiology, Shenyang Medical College

  2. Introduction The cardiovascular system consists of the heart and the blood vessels. The right ventricle pumps blood through the pulmonary circulation to the left atrium. The left ventricle ejects blood through the systemic circulation to the right atrium. The function of blood circulation is to transport substances in human body. (F)

  3. Systemic and Pulmonary Circulation

  4. 1. Right Heart • a. receives venous blood from systemic circulation via superior and inferior vena cava into right atrium. b. pumps blood to pulmonary circulation, and then to left heart. 2. Left Heart • a. receives oxygenated blood from pulmonary circulation via pulmonary vein into left atrium. • b. pumps blood into systemic circulation, and then to right heart.

  5. Heart Valves 1. Atrioventricular V a. mitral--between LA and LV; two leaflets b. tricuspid--between RA and RV; three leaflets 2. Semilunar V a. aortic--three leaflets b. pulmonary--three leaflets

  6. Function of Heart Valves Prevent backward flow Provide low resistance to forward flow

  7. Section one Pump function of the heart The busy and hard working heart!

  8. I. Cardiac Cycle 1.Concept: The period of one contraction and one relaxation of the heart. 2.Relationship of the cardiac cycle and Heart rate 60s Cardiac cycle= ———— Heart rate Heart rate:75 beats/min 60s Cardiac cycle = —— =0.8sec 75

  9. A cardiac cycle consists • of a systole and a diastole. • Atrial cycle equals to • ventricular cycle. • Diastole is longer than • systole. • When heartbeat becomes more rapid, the cardiac cycle is shorter, and the diastole is much shorter than normal.Tachycardia is unfavourable for the heart.

  10. Whole heart relaxation phase means this period of the first 0.4s of the ventricular relaxation in which atrium is also in relaxation state. 0.7s 0.1s Atrium Ventricle 0.3s 0.5s Relaxation Contraction

  11. II. Mechanical events of the cardiac cycle 1. For example: Processess of blood ejection and filling in the left ventricle Ventricular Systole （1）Period of isovolumic contraction 0.05s（2）Period of rapid ejection 0.1s（3）Period of slow ejection 0.15s

  12. Atria S D D D D D D D Ventricles D S S S D D D D .1 .2 .3 .4 .5 .6 .7 .8 Ventricular Diastole （4）period of isovolumic relaxation 0.07s（5）Period of rapid filling 0.11s（6）Period of slow filling 0.22s（7）Atrial systole 0.1s

  13. 2. The Phases of the Cardiac Cycle • Period of isovolumic contraction Events: ventricular contraction ventricular pressure rise  atrioventricular valve close the ventricular pressure increase sharply Period: 0.05 sec atrioventricular valve close  S1- first heart sound Importance: enable the ventricular pressure to rise from 0 to the level of aortic pressure

  14. (2) Period of ejection • Events: ventricular contraction continuously • the ventricular pressure rise above the arterial pressure • semilunar valves open  blood pours out of the ventricles

  15. Rapid ejection period (0.10s, 66% of the total ejected blood volume, stroke volume) • Reduced ejection period (0.15s, 34% of the total ejected blood volume , stroke volume) • The aortic pressure actually exceeds the ventricular pressure, but momentum keeps the blood moving forward.

  16. (3) Period of isovolumic relaxation • Events: • ventricular muscle relax • the ventricular pressure fall • lower than the aortic pressure • aortic valve close • the ventricular pressure fall sharply

  17. S2- second heart sound ←closure of aortic and pulmonary semilunar valves at beginning of ventricular diastole • Period: 0.06-0.08 s • Importance: Enable the ventricular pressure to fall to the level near the atrial pressure

  18. (4) Period of filling of the ventricles Events: Ventricular muscle relax continuously  the ventricular pressure is equal or lower than the atrial pressure atrioventricular valve open • blood accumulated in the atria rushes into the ventricle • blood flow quickly from the atrium to the ventricle.

  19. Period of rapid filling. • (0.11s, amount of filling, 2/3 of total filling blood volume) • 2) Period of reduced filling • (0.22s, little blood fills into the ventricle)

  20. (5) Atrial systole Significance, 25% of total filling blood volume During high output states or in the failing heart, the amount added by atrial contraction may be of major importance in determining the final cardiac output.

  21. Correlation of events in the left side of the heart in each cardiac cycle Rapid Ventricular Filling Atrial Systole Reduced Ejection Rapid Ejection Isovolumic Relax. Reduced Ventricular Filling Atrial Systole Isovolumic contract. Aortic opens :>O Aortic closes Mitral opens Mitral Closes S1 :>D S2

  22. Heart sounds Action of the heart produces mechanical vibrations which are audible at the chest wall as the heart sounds. The first heart sound iscaused by closure of the atrioventricular valves and so marks the beginning of ventricular systole. The second heart sound iscaused by closure of the aortic and pulmonary valves and so marks the beginning of ventricular diastole.

  23. The third heart sound iscaused by sudden stretch of the ventricular wall and papillary muscle, and sudden deceleration of filling flow at the end of rapid filling period. The fourth heart sound iscaused by unusually strong atrial contraction at the end of ventricular diastole.

  24. III. Cardiac Output 1.Stroke volume The amount of blood pumped out of each ventricle per beat is called the stroke volume, about 70mL in a resting adult. Stroke volume= end diastolic volume – end systolic volume

  25. 125 the normal range is: 55-65% 70 55 2.Ejection fraction stroke volume × 100% = ejection fraction End diastolic volume 70×100% —— =56% 125

  26. 3.Cardiac output The output of each ventricle per minute is called the cardiac output. Cardiac Output = Stroke Volume× Heart Rate CO=SV×HR =70 × 75 =5250（ml） It varies with sex, age, and exercise

  27. 4.Cardiac index There is a correlation between resting cardiac output and body surface area. The cardiac output per square meter of body surface area is known as the cardiac index. It averages 3.2L/ min·m2 5-6L/min the normal range is: 3.0 – 3.5 L/min·m2 1.6-1.7m2

  28. 5.Cardiac work Like any machine, the heart does work in moving the blood through the circulatory system.

  29. 5.Cardiac work Stroke work (J)= stroke volume(L) ×gravity of blood (mean arterial pressure-mean left atrial pressure) (mmHg) ×13.6 ×9.807 ×(1/1000) Minute work (J)= stroke work(J) ×Heart rate Minute work of the right heart = 1/6 of minute work of the left heart

  30. IV. Factors Affecting Cardiac Output Contractility Preload Stroke Volume Afterload Heart Rate Cardiac Output

  31. Definitions • Preload • amount of stretch on the ventricular myocardium prior to contraction • Ventricular end-diastolic volume or pressure • Afterload • the arterial pressure that a ventricle must overcome while it contracts during ejection • impedance to ventricular ejection

  32. Definitions • Contractility • myocardium’s intrinsic ability to efficiently contract and empty the ventricle • (independent of preload & afterload)

  33. Preload(Initial length in Cardiac muscle ) Define：Regulation of contractilityand cardiacoutput as a result of changes in cardiac muscle fiber initial length is called heterometric autoregulation, or Starling’s law of the heart. Stroke volume Frank-Starling curve Ventricular end-diastolic volume

  34. the Frank - Starling mechanism • Frank - Starling curve (1914): • Normal range of the LVEDP, 5-6 mmHg; Optimal initial preload, 12-15 mmHg ( 2.0 – 2.2 µm ) • When the LVEDP is 15-20 mmHg, LV work is maintained at almost the same level. • When the LVEDP > 20 mmHg,LV workdoes not change or slightly decreases. Left ventricle (LV) function curve

  35. Starling Mechanism : The heart can automatically regulate and balance the relation between stroke volume and volume of venous return : Volume of venous return ↑=> the end-diastolic volume ↑ (preload↑)=> ventricular contraction ↑→ stroke volume ↑

  36. Factors determining the preload (LVEDP) • 1. Blood volume of venous return. • Period of the ventricle diastole (filling) – heart rate • Speed of the venous return (difference between the venous pressure and atrial pressure) • 3) pericardial fluid • 4) ventricular compliance =ΔV/ΔP • --denotes the ease or difficulty with which something can be stretched. myocardial fibrosis • 2. Ventricular residual blood volume after contraction

  37. Importance of the heterometric regulation • In general, heterometric regulation plays only a short-time role, such as during the body posture change, artery pressure increase, and unbalance between the left and the right ventricular outputs. • In other conditions, such as exercise, cardiac output is mainly regulated by homometric regulation.

  38. Cardiac output 5 3 1 200 mmHg 100 Aortic pressure (mmHg) 2.Afterload（Aortic pressure）

  39. Short time change of the arterial pressure • Arterial pressure rises : • isovolumetric contraction phase becomes longer • period of ejection becomes shorter • stroke volume less • more blood left in the left ventricle • LVEDP increase • through heterometric regulation • stroke volume return to normal in next beat.

  40. Long time high arterial pressure • through neural and humoral regulation • the stroke volume is maintained at normal level • pathogenesis of the cardiovascular system hypertension myocardial hypertrophy heart failure

  41. 3.Myocardial Contractility （homometric regulation） the regulation due to changes in contractility independent of initial length. numbers of activated cross bridge Ca2+ concentration ATPase activity

  42. Heart rate (beat/min) Cardiac cycle (sec) Systole (sec) Diastole (sec) • 40 1.5 • 0.8 0.3 0.5 • 120 0.5 0.25 0.25 • 200 0.3 0.16 0.14 Cardiac output 40 180 Heart rate (beat/min) 4.Heart rate

  43. (1). heart rate ↑→cardiac output ↑ (40—180beats/min) (2). heart rate > 160—180beats/min heart rate <40beats/min =>cardiac output ↓

  44. V. Cardiac reserve • The capacity of the heart to increase cardiac output to satisfyhuman metabolic needs is called cardiac reserve. • The maximal cardiac output subtracts the normal value. • It reflects the ability of the heart to adapt the change of environment (internal or external)

  45. During muscular exercise, there is increased cardiac output. Myocardial contractility Heart rate Diastolic inflow Stroke volume

  46. Rest Exercise CO SV HR EDV ESV LVW (L/min) (mL/beat) (beat/min) (mL) (mL) (J/min) 5 60~80 70~80 120~160 60~80 60 35 120~140 180~210 130~170 10~20 195 30 60~80 130~140 10~20 40~50 135 Reserve volume

  47. 1 Heart rate rises：2-2.5 times 200 beats/min 140 ( ml ) 2 Reserve of stroke volume ： 15 End-diastolic volume 15 ml 125 70 55 End-systolic volume 35-40 35-40 ml 15-20

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