1. 1 1 Cardiac output and Venous Return Faisal I. Mohammed, MD, PhD

2. 2 2 Objectives Define cardiac output and venous return Describe the methods of measurement of CO Outline the factors that regulate cardiac output Follow up the cardiac output curves at different physiological states Define venous return and describe venous return curve Outline the factors that regulate venous return curve at different physiological states Inter-relate Cardiac output and venous return curves

3. 3 3 Cardiac Output is the sum of all tissue flows and is affected by their regulation (CO = 5L/min, cardiac index = 3L/min/m 2 ). CO is proportional to tissue O 2. use. CO is proportional to 1/TPR when AP is constant. CO = (MAP - RAP) / TPR MAP= CO x TPR Important Concepts About Cardiac Output (CO) Control

4. 4 Mean Arterial Pressure (MAP) 0.0 0.3 0.8 t1t1 t2t2 MAP= 1/3 systolic pressure + 2/3 Diastolic pressure MAP= Diastolic Pressure +1/3 Pulse Pressure

5. 5 5 Electromagnetic flowmeter Indicator dilution (dye such as cardiogreen) Thermal dilution Oxygen Fick Method CO = (O 2 consumption / (A-V O 2 difference) Measurement of Cardiac Output

6. 6 6 Electromagnetic flowmeter

7. q 1 =CO*C VO2 q 2 =amount of Oxygen uptake by the lungs q 3 = CO* C AO2 and equals = CO*C VO2 + O 2 uptake Oxygen uptake = CO{C AO2 -C VO2 } CO=Oxygen uptake/{C AO2 -C V O2 }

8. 8 8 Spirometer

9. 9

10. 10 Swan-Ganz catheter

11. 11 O 2 Fick Problem If pulmonary vein O 2 content = 200 ml O 2/ L blood Pulmonary artery O 2 content = 160 ml O 2 /L blood Lungs add 400 ml O 2 /min What is cardiac output? Answer: 400/(200-160) =10 L/min

12. Area = t2t2 t1t1 Area = C* (t 2 -t 1 ) (Rectangular) C =Area /( t 2 - t 1 ) Cardiac output =

13. 13

14. Thermodilution Method Curve AREA = t1t2

15. 0 200 400 600 800 1000 1200 1400 1600 35 30 25 20 15 10 5 0 5 4 3 2 1 0 CARDIAC OUTPUT (L/min/m) CARDIAC OUTPUT OXYGEN CONSUMPTION (L/min) O 2 CONSUMPTION WORK OUTPUT DURING EXERCISE (kg*m/min) OLYMPIC ATHLETE COUCH POTATO Copyright © 2006 by Elsevier, Inc.

16. 16 Magnitude & Distribution of CO at Rest & During Moderate Exercise

17. 17 Variations in Tissue Blood Flow Brain14 70050 Heart 4 20070 Bronchi 2 100 25 Kidneys22 1100 360 Liver 27 1350 95 Portal (21) (1050) Arterial (6) (300) Muscle (inactive state)15 750 4 Bone 5 250 3 Skin (cool weather) 6 300 3 Thyroid gland 1 50 160 Adrenal glands 0.5 25 300 Other tissues 3.5 175 1.3 Total 100.0 5000 --- Per cent ml/min ml/min/ 100 gm

18. 18 Control of Cardiac Output

19. 19 Factors that affect the Cardiac Output

20. NORMAL HYPEREFFECTIVE -4 0 +4 +8 25 20 15 10 5 0 CARDIAC OUTPUT (L/min) RIGHT ATRIAL PRESSURE (mmHg) HYPOEFFECTIVE CARDIAC OUTPUT CURVES

21. 21 Cardiac Output (CO) and Reserve CO is the amount of blood pumped by each ventricle in one minute CO is the product of heart rate (HR) and stroke volume (SV) HR is the number of heart beats per minute SV is the amount of blood pumped out by a ventricle with each beat Cardiac reserve is the difference between resting and maximal CO

22. 22 Plateau of CO curve determined by heart strength (contractility +  HR)  Sympathetics  plateau  Parasympathetics (HR  )  plateau)  Plateau Heart hypertrophy  ’s plateau Myocardial infarction  plateau)  Plateau The Cardiac Output Curve

23. 23 Valvular disease   plateau (stenosis or regurgitation) Myocarditis   plateau Cardiac tamponade  plateau)  Plateau Metabolic damage   plateau The Cardiac Output Curve (cont’d)

24. 24 Frank-Starling Mechanism  Within physiological limits the heart pumps all the blood that comes to it without excessive damming in the veins.  Extra stretch on cardiac myocytes makes actin and myosin filaments interdigitate to a more optimal degree for force generation.

25. 25 20 15 10 5 0 -4 0 +4 +8 Cardiac Output (L/min) Right Atrial Pressure (mmHg) (Parasympathetic stimulation) Zero sympathetic stimulation Normal sympathetic stimulation Maximum sympathetic stimulation Effect of Sympathetic and Parasympathetic Stimulation on Cardiac Output

26. NORMAL HYPEREFFECTIVE -4 0 +4 +8 25 20 15 10 5 0 CARDIAC OUTPUT (L/min) RIGHT ATRIAL PRESSURE (mmHg) HYPOEFFECTIVE CARDIAC OUTPUT CURVES

27. Cardiac Output curve (Plateau curve)

28. 10 5 0 CARDIAC OUTPUT (L/min) RIGHT ATRIAL PRESSURE (mmHg) -4 0 4 8 12 15 IPP= -4mmHg IPP= -2mmHg IPP = INTRAPLEURAL PRESSURE IPP= -5.5mmHg IPP= 2mmHg CARDIAC TAMPONADE

29. Factors Affecting Cardiac Output

30. Factors Affecting Stroke Volume Contractility of Muscle cells Cont = ESV

31. A Summary of the Factors Affecting Cardiac Output

32. 32 REGULATION OF STROKE VOLUME: PRELOAD decreased heart rate increased length of diastole increased ventricular filling increased venous pressure increased venous return increased ventricular filling increased preload increased ventricular stretch Frank-Starling mechanism increased force of contraction increased stroke volume increased cardiac output

33. 33 REGULATION OF STROKE VOLUME: CONTRACTILITY increased sympathetic activity increased epinephrine other factors increased contractility increased force of contraction increased stroke volume increased cardiac output

34. 34 REGULATION OF STROKE VOLUME: AFTERLOAD increased arterial pressure increased afterload decreased blood volume ejected into artery decreased stroke volume decreased cardiac output

35. 35 Effect of Venous Valves

36. 36 Effect Of Gravity on Venous Pressure

37. 37 Venous Pressure in the Body Compressional factors tend to cause resistance to flow in large peripheral veins. Increases in right atrial pressure causes blood to back up into the venous system thereby increasing venous pressures. Abdominal pressures tend to increase venous pressures in the legs.

38. 38 Central Venous Pressure  Pressure in the right atrium is called central venous pressure.  Right atrial pressure is determined by the balance of the heart pumping blood out of the right atrium and flow of blood from the large veins into the right atrium.  Central venous pressure is normally 0 mmHg, but can be as high as 20-30 mmHg.

39. 39 Factors affecting Central Venous Pressure  Right atrial pressure (RAP) is regulated by a balance between the ability of the heart to pump blood out of the atrium and the rate of blood flowing into the atrium from peripheral veins.  Factors that increase RAP:  -increased blood volume  -increased venous tone  - dilation of arterioles  -decreased cardiac function

40. 40 Effect of Venous Valves

41. 41 Venous Valves Valve Deep vein Perforating vein Superficial vein

42. 42 Factors that Facilitate Venous Return

43. RIGHT ATRIAL PRESSURE (mmHg) -4 0 4 8 12 VENOUS RETURN (L/MIN) 0 5 10 MSFP= 7 MSFP= 14 MSFP= 4.2 MSFP = Mean Systemic Filling Pressure The Venous Return Curve

44. 20 15 10 5 0 VENOUS RETURN (L/min/m) RIGHT ATRIAL PRESSURE (mmHg) -4 0 4 8 MSFP = 7 NORMAL RESISTANCE 1/2 RESISTANCE2 X RESISTANCE

45. 45 Beriberi - thiamine deficiency  arteriolar dilatation   RVR because VR = (MSFP - RAP) /RVR (good for positive RAP’s) A-V fistula  (? RVR)  RVR C. Hyperthyroidism  (? RVR)  RVR Venous Return (VR)

46. 46 Anemia   RVR (why?)  Sympathetics   MSFP  Blood volume   MSFP + small  in RVR  Venous compliance (muscle contraction or venous constriction)  SFP)  MSFP Venous Return (VR) (cont’d)

47. 47  Blood volume   MSFP  Sympathetics  (? v. comp. and MSFP)  Venous compliance and  MSFP Obstruction of veins  (? RVR)  RVR Factors Causing  Venous Return

48. 25 20 15 10 5 0 CARDIAC OUTPUT AND VENOUS RETURN (L/min/m) RIGHT ATRIAL PRESSURE (mmHg) -4 0 4 8 12 16 NORMAL CARDIAC VR CURVE NORMAL SPINAL ANESTHESIA SPINAL ANESTHESIA MAXIMAL SYMPATHETIC STIMULATION SYMPATHETIC STIMULATION MAX

49. Thank You