Chapter 9: Circulatory Responses to Exercise

OBJECTIVES

By studying this chapter, you should be able to do the following:

1. Provide an overview of the design and function of the circulatory system.

2. Describe the cardiac cycle and the associated electrical activity recorded via the electrocardiogram.

3. Discuss the pattern of redistribution of blood flow during exercise.

4. Outline the circulatory responses to various types of exercise.

5. Identify the factors that regulate local blood flow during exercise.

6. List and discuss those factors responsible for regulation of stroke volume during exercise.

7. Discuss the regulation of cardiac output during exercise.

OUTLINE

• Organization of the Circulatory System 194

  • Structure of the Heart 194

  • Pulmonary and Systemic Circuits 195

• Heart: Myocardium and Cardiac Cycle 195

  • Myocardium 196

  • Cardiac Cycle 197

  • Arterial Blood Pressure 199

  • Factors That Influence Arterial Blood Pressure 201

  • Electrical Activity of the Heart 202

• Cardiac Output 204

  • Regulation of Heart Rate 204

  • Heart Rate Variability 207

  • Regulation of Stroke Volume 208

• Hemodynamics 210

  • Physical Characteristics of Blood 210

  • Relationships among Pressure, Resistance, and Flow 210

  • Sources of Vascular Resistance 211

• Changes in Oxygen Delivery to Muscle during Exercise 212

  • Changes in Cardiac Output during Exercise 212

  • Changes in Arterial-Mixed Venous O₂ Content during Exercise 214

  • Redistribution of Blood Flow during Exercise 214

  • Regulation of Local Blood Flow during Exercise 215

• Circulatory Responses to Exercise 216

  • Emotional Influence 217

  • Transition from Rest to Exercise 217

  • Recovery from Exercise 217

  • Incremental Exercise 217

  • Arm Versus Leg Exercise 218

  • Intermittent Exercise 219

  • Prolonged Exercise 219

• Regulation of Cardiovascular Adjustments to Exercise 220

KEY TERMS

arteries

arterioles

atrioventricular node (AV node)

autoregulation

capillaries

cardiac accelerator nerves

cardiac output

cardiovascular control center

central command

diastole

diastolic blood pressure

double product

electrocardiogram (ECG or EKG)

heart rate variability

intercalated discs

mixed venous blood

myocardium

pulmonary circuit

sinoatrial node (SA node)

stroke volume

systole

systolic blood pressure

vagus nerve

veins

venules

INTRODUCTION

One of the major challenges to homeostasis posed by exercise is the increased muscular demand for oxygen; during heavy exercise, the demand may be 15 to 25 times greater than at rest. The primary purpose of the cardiorespiratory system is to deliver adequate amounts of oxygen and remove wastes from body tissues. Further, the circulatory system also transports nutrients and aids in temperature regulation. It is important to remember that the respiratory system and the circulatory system function together as a “coupled unit”; the respiratory system adds oxygen and removes carbon dioxide ...