Skip to Main Content

++

OBJECTIVES

++

The student knows the basic electrical and mechanical events of the cardiac cycle:

  • Correlates the electrocardiographic events with the mechanical events during the cardiac cycle.

  • Lists the major distinct phases of the cardiac cycle as delineated by valve opening and closure.

  • Describes the pressure and volume changes in the atria, the ventricles, and the aorta during each phase of the cardiac cycle.

  • Defines and states normal values for (1) ventricular end-diastolic volume, end-systolic volume, stroke volume, diastolic pressure, and peak systolic pressure, and (2) aortic diastolic pressure, systolic pressure, and pulse pressure.

  • States similarities and differences between mechanical events in the left and right heart pumps.

  • States the origin of the heart sounds.

  • Diagrams the relationship between left ventricular pressure and volume during the cardiac cycle.

    The student understands the factors that determine cardiac output:

  • Defines cardiac output.

  • States the relationship between cardiac output, the heart rate, and stroke volume.

  • Identifies the major determinants of stroke volume.

    • States the Frank–Starling law of the heart.

    • Predicts the effect of altered ventricular preload on stroke volume and the ventricular pressure–volume relationship.

    • Predicts the effect of altered ventricular afterload on stroke volume and the ventricular pressure–volume relationship.

    • Predicts the effect of altered ventricular contractility (inotropic state) on stroke volume, ejection fraction, and the ventricular pressure–volume relationship.

  • Draws a family of cardiac function curves describing the relationship between filling pressure and cardiac output under various levels of sympathetic tone.

    The student understands the sources of energy and the energy costs of cardiac work:

  • Identifies the cardiac substrates and metabolic pathways for ATP production.

  • Lists the factors that influence myocardial oxygen consumption.

++

INTRODUCTION

++

The repetitive, synchronized contraction and relaxation of the cardiac muscle cells provide the forces necessary to pump blood through the systemic and pulmonary circulations. In this chapter, we describe (1) basic mechanical features of this cardiac pump, (2) factors that influence and/or regulate the cardiac output, and (3) sources of energy and energy costs required for myocardial activity.

++

CARDIAC CYCLE

++

Left Pump

++

Image not available.A cardiac cycle is defined as one complete sequence of cardiac filling, cardiac muscle excitation and contraction with ejection of blood and then muscle relaxation (diastole and systole). Graphs of several normal events of a single cycle of the left heart pump are plotted on the same time line in Figure 3–1. Changes in electrical activity, muscle contractions, pressures, volume, valve position, heart sounds, and aortic flow are shown so that events that are occurring simultaneously in different parts of the cycle can be assessed. This important figure summarizes a great deal of information and should be studied carefully.

++
Figure 3–1.

Cardiac cycle—left heart pump. Cardiac cycle phases: A, diastole; B, systole that is divided into 3 periods; C, isovolumetric contraction; D, ejection; and E, isovolumetric relaxation.

Graphic Jump Location

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.