DETERMINANTS AND FACTORS AFFECTING CARDIAC OUTPUT

DETERMINANTS AND FACTORS AFFECTING CARDIAC OUTPUT DETAILED SLIDE

1. DETERMINANTS AND FACTORS AFFECTING CARDIAC OUTPUT DEEPAK CHOUDHARY ROLL NO-21 BATCH-2017-18

2. CONTENTS CARDIAC OUTPUT EJECTION FRACTION CARDIAC INDEX VARIATIONS IN CARDIAC OUTPUT FACTORS MAINTAING CARDIAC OUTPUT VENOUS PRESSURE FORCE OF CONTRACTION HEART RATE PERIPHERAL RESISTANCE BIBLIOGRAPHY

3. Cardiac Output Cardiac Output is the volume of blood pumped into the aorta each minute by the heart , and is expressed by the following equation: CO = SV x HR Where: CO is cardiac output expressed in L/min (normal ~5 L/min) SV is stroke volume per beat HR is the number of beats per minute

4. Cardiac output is frequently stated in terms of cardiac index Cardiac Index= Cardiac output/body surface area It is the cardiac output per square meter of body surface area Normal average cardiac index for adult is about 3 L/min/m Cardiac Index

5. EJECTION FRACTION Fraction of end diastolic volume that is ejected out by each ventricle Normal-60-65%

6. Variations in cardiac output PHYSIOLOGICAL CAUSES Age- ↑ ses with age Sex- less in females more in males Body build- ↑ ses with body build Exercise- ↑ ses with exercise High altitude- ↑ ses Pregnancy- ↑ ses Sleep-↓ ses

7. PATHOLOGICAL CAUSES INCREASE Fever Anemia Hyperthyroidism DECREASE Hypothyroidsm Shock Hemorrhage Congestive cardiac failure

8. Factors maintaining cardiac output Cardiac output is maintained by four factors- Venous return Force of contraction Heart rate Peripheral resistance

9. VENOUS RETURN Amount of blood which is returned to heart from different parts of the body. The cardiac output is directly proportional to venous return providing other three factors remain the same. Venous return in turn, depends on following factors Respiratory pump Muscle pump Gravity Venous pressure

10. Respiratory pump

11. Muscle pump Muscle pump is the muscular activity that helps in return of blood to heart Veins have valves which help in movement of blood towards heart. When muscle contract , vein located in between muscles is compressed ,blood is propelled towards the heart. Valves are closed by back flow. During relaxation the muscles, the valves close and prevents back flow of blood. Valves distal to muscles opens and allows blood to flow upwards.

12. GRAVITY Gravitational force reduces the venous return When a person stands for a long period, gravity causes pooling of blood in the legs , which is called venous pooling. Because of venous pooling, the amount of blood returning to heart decreases.

13. VENOUS PRESSURE Venous pressure affects venous return. Pressure in venules is 12-18mm Hg while in superior vena cava it falls about 5.5 mm Hg. In the smaller and larger veins,the pressure gradually decreases. The pressure gradient at every part of venous tree helps as a driving force for venous return.

14. Rol e Of Fran k - Starling Mechani s m I ncre as e d Veno u s R e tur n Card iac muscles stre t che s t o g r ea t e r l ength Ven t r icular muscle co n tract s wi t h g r ea t e r force I ncre as e d Card iac O utput Frank - Starling law of the heart states that when there is increased quantities of blood flow into the heart, the cardiac muscle contracts with increased force, and this empties the extra blood that has entered from the systemic circulation. And so there is increased cardiac output. 2 . FORCE OF CONTRACTION

15. PRELOAD It is streaching of cardiac muscle fibre at the end of diastole, just before contraction Cardiac output is directly proportional to preload AFTERLOAD it is the force against which ventricles must contract and eject the blood. Force of contraction and cardiac output is inversely proportional to afterload

16. 3 .HEART RATE Cardiac output is directly proportional to heart rate. If there is marked decrease in heart rate ,cardiac output decreases.

17. 4. PERIPHERAL RESISTANCE Peripheral resistance is the resistance offered to blood flow at the peripheral blood vessels. Peripheral resistance is the resistance or load against which the heart has to pump the blood. Cardiac output is inversely proportional to peripheral resistance.

18. BIBLIOGRAPHY Guyton and Hall Textbook of Medical Physiology E-Book (Guyton Physiology) Essentials of Medical Physiology by k.sembulingum Google TEXTBOOK OF PHYSIOLOGY BY AK JAIN 5. Ganongs Review Of Medical Physiology 25th Edition