Chapter 17: Function of the Heart

Copyright © 2007 by Saunders, an imprint of Elsevier Inc. Lesson 17.1 Objectives Define cardiac cycle with respect to systole and diastole. Describe the autonomic innervation of the heart. Define cardiac output and explain how changes in heart rate and/or stroke volume change cardiac output. Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Lesson 17.1 Objectives (cont’d.) Describe the effect of Starling’s law of the heart on myocardial contraction. Define preload and explain how it affects cardiac output. Define afterload and identify the major factors that determine afterload. Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Lesson 17.1 Objectives (cont’d.) Describe the inotropic effect on myocardial contraction. Define the special clinical vocabulary used to describe cardiac function. Define heart failure and differentiate between right-sided and left-sided heart failure. Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Copyright © 2007 by Saunders, an imprint of Elsevier Inc. Cardiac Cycle Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Cardiac Cycle (cont’d.) Cardiac cycle: sequence of events that occurs during one heartbeat Three stages: Atrial systole Ventricular systole Diastole Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Autonomic Control of the Heart Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Autonomic Control of the Heart (cont’d.) Autonomic wiring: Sympathetic nerves innervate: SA node AV node Ventricular myocardium Parasympathetic nerves innervate: Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Autonomic Control of the Heart (cont’d.) Autonomic firing: Sympathetic stimulation increases: SA node activity and heart rate Speed of cardiac impulse traveling from SA node throughout His-Purkinje system Force of myocardial contraction Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Autonomic Control of the Heart (cont’d.) Autonomic firing (cont’d.): Parasympathetic stimulation: Decreases SA node activity and heart rate Decreases speed of cardiac impulse traveling from SA node to AV node Does not affect the strength of myocardial contraction Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Copyright © 2007 by Saunders, an imprint of Elsevier Inc. Cardiac Output Cardiac output: amount of blood pumped by each ventricle in one minute Two factors: Heart rate Stroke volume Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Cardiac Output (cont’d.) Heart rate: number of times the heart beats each minute due to the rhythmic firing of the SA node Resting heart rates differ due to: Size Gender Age Stroke volume: amount of blood pumped by the ventricle per beat Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

How to Change Stroke Volume Starling’s law of the heart. Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

How to Change Stroke Volume (cont’d.) Altering stroke volume: Starling’s law of the heart: allows the heart to pump out the same amount of blood it receives due to stretch of the myocardial fibers Inotropic effect Positive (+) inotropic effect: increases stroke volume by strengthening the force of myocardial contraction Negative (−) inotropic effect: decreases the force of the contraction resulting in a weaker myocardial contraction Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Heart Talk: Clinical Terms End-diastolic volume (EDV): amount of blood in the ventricle at the end of diastole Preload: amount of blood in the ventricle at the end of diastole (same as EDV) Ejection fraction: percentage of the EDV that is pumped out of the ventricle Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Heart Talk: Clinical Terms (cont’d.) Afterload: resistance or opposition Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Heart Talk: Clinical Terms (cont’d.) Inotropic effect: change in myocardial contraction that is not due to stretch Chronotropic effect: change in heart rate Dromotropic effect: change in the speed at which the cardiac impulse travels from the SA node through the AV node and the His-Purkinje system Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Heart Talk: Clinical Terms (cont’d.) Receptor Language: Beta1-adrenergic receptor activation Beta1-adrenergic receptor blockade Muscarinic (cholinergic) receptor activation Muscarinic (cholinergic) receptor blockade Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Copyright © 2007 by Saunders, an imprint of Elsevier Inc. Heart Failure Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Heart Failure (cont’d.) Left-heart failure: Backward failure: blood backs up into the lungs Forward failure: heart is unable to pump sufficient amount of blood to systemic circulation Common causes: Myocardial infarction (MI) Chronic hypertension Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Heart Failure (cont’d.) Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Heart Failure (cont’d.) Right-heart failure: blood backs up into the veins that return blood to the right heart Common causes: Consequence of left-sided failure Chronic lung disease Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Heart Failure (cont’d.) Goals of treatment of heart failure: Strengthen myocardial contractile force Remove excess water Decrease the work of the heart Protect the heart from excess sympathetic nerve activity Copyright © 2007 by Saunders, an imprint of Elsevier Inc. All rights reserved.