Chapter 3. The Heart Pump

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 identifies the factors that influence myocardial oxygen consumption.

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.

Left Pump

The mechanical function of the heart can be described by the pressure, volume, and flow changes that occur within it during a single cardiac cycle. A cardiac cycle is defined as one complete sequence of contraction and relaxation. The normal mechanical events of a cycle of the left heart pump are correlated in Figure 3–1. This important figure summarizes a great deal of information and should be studied carefully.

Ventricular Diastole

The diastolic phase1 of the cardiac cycle begins with the opening of the atrioventricular (AV) valves. As shown in Figure 3–1, the mitral valve passively opens when left ventricular pressure falls below left atrial pressure and the period of ventricle filling begins. Blood that ...