Chapter 1 | How the Human Body Breathes


In order to understand mechanical ventilation, you must first have a basic understanding of how the human body is designed to breathe. Oxygen is the food of the human body. Every cell requires it to create energy and carry out its various functions. On the other hand, carbon dioxide (CO2) is the garbage of the human body that every cell creates as a byproduct of its functions. It is commonly known that the lungs are the organ that take the oxygen from the air and bring it into the body, and that they expel (exhale) CO2 at the same time. But what is the mechanism that triggers this to happen and how exactly does this exchange occur?

This chapter describes the process by which the human body takes in and expels air in a straightforward and understandable way. As the saying goes, “it’s as natural as breathing,” so we’ll try to avoid overcomplicating things. You’ll learn about breathing with the aid of simple, everyday analogies and object lessons. Consider trying these object lessons yourself as you wrap your head around the concepts you are learning.


How and when will you apply the concepts you are learning in this chapter? The mechanism of breathing is fundamental to the real-world use of ventilators. The health care professional will benefit greatly from understanding the natural process that the mechanical ventilator is intending to replicate (or imitate as closely as possible) to better aid them in using a ventilator effectively in practice.

Learning Objectives

At the end of this chapter, you will be able to:

  1. Explain the body mechanics of inspiration and expiration.
  2. Identify key parts of the body involved in breathing.
  3. Define FRC and Intrinsic PEEP and the importance to the alveoli.
  4. Understand the basic pressure changes that occur in the lungs during the respiration process.

Key Terms

In this chapter, you will learn about all of the following key terms. These terms will be used throughout this book, so it is important to take the time to master them and practice your recall often.

  • respiratory system
  • lungs
  • lobes
  • alveoli, alveolus
  • oxygen (O2)
  • carbon dioxide (CO2)
  • inspiration
  • expiration
  • chemoreceptors
  • diaphragm
  • negative pressure
  • positive pressure
  • Functional Residual Capacity (FRC)
  • Positive End-Expiratory Pressure (PEEP)
  • surfactant
  • cm H2O
  • Palveoli
  • Ppleural
  • Pmo
  • pleural space

Whenever these terms are first introduced in this chapter, they are bolded. However, if you need additional information about a term than what is provided here, you can research it in The Free Dictionary: Medical Dictionary.


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