Cardiac output is defined as the volume of blood pumped by the heart each minute and is regulated intrinsically by factors affecting preload and afterload as well as extrinsically by the autonomic nervous system and hormones. Venous return is a primary extrinsic regulator of cardiac output, increasing stretch of cardiac muscles and stimulating an increase in heart rate. A combination of preload, contractility, afterload and heart rate determine cardiac output under normal resting conditions and during physical activity.

1. Addis Ababa University Collage of Health Science Department of Physiology By : Robel Abay September 19 09/30/11 Regulation of cardiac out put

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19. Increase in preload 09/30/11

20. Increased after load 09/30/11

23. Factors Affecting End-diastolic Volume Ventricular EVD Ventricular performance Total blood volume Body position Intrathoracic pressure Atrial contrib. to vent. filling Pumping action to skeletal muscle Venous tone Intrapericardial pressure ventricular compliance STRETCHING OF MYOCARDIUM 09/30/11

24. Preload vs Afterload Venules / veins Arterioles Capacitance vessels Resistance vessels Affect preload Affect afterload 09/30/11

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31. Effect of Bainbridge and Baroreceptor Reflex on HR Intravenous infusion Increased right atrial pressure Stimulate atrial receptors Bainbridge reflex Increased cardiac output Increased arterial pressure Baroreceptor reflex Heart rate 09/30/11

32. C. Humoral regulation HR/CO INSULIN THYROID GLUCAGON CATECHOLAMINES STEROIDS POTENTIATION

33. CARDIAC OUTPUT HEART RATE MYOCARDIAL CONTRACTILITY PRELOAD AFTERLOAD CARDIAC FACTORS COUPLING FACTORS 09/30/11

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36. Thank you