The Physiology of Respiration

This CE activity is approved by EMS World Magazine, an organization accredited by the Continuing Education Coordinating Board for Emergency Medical Services (CECBEMS), for 1.5 CEUs. There are two ways to take the CE test that accompanies this article and receive 1.5 hours of CE credit accredited by CECBEMS: 1. Click here to download a PDF of the test. The PDF has instructions for completing the test. 2. Or go to www.rapidce.com to take the test and immediately receive your CE credit. Questions? E-mail editor@EMSWorld.com.

Objectives

• Discuss the physiology of the respiratory system
• Review causes of impairment of effective respirations
• Discuss prehospital assessment tools for the patient with difficulty breathing

EMS providers are often summoned to assist patients in respiratory distress. The subjective sensation of difficulty breathing—known as dyspnea—experienced by these patients can be caused by myriad conditions.¹ The causes range from non-life-threatening conditions (e.g., a muscle strain causing pain on inspiration) to complex mixed medical conditions that lead to confusing patient presentations (e.g., acute cardiogenic pulmonary edema and pneumonia).

It can sometimes be difficult to discern the root cause of a patient’s condition with the limited diagnostic resources available to EMS. Some providers may focus on differentiating between specific diagnoses, while others may offer the same treatment to all patients who verbalize a complaint of difficulty breathing. As EMS providers, we need to be better prepared to isolate the specific difficulty a patient is experiencing when they complain of difficulty breathing (e.g., getting air in vs. getting air out and inadequate gas exchange). Hopefully, with a broader knowledge of respiratory physiology, you will be able to recognize the specific area of compromise, which will guide you to the appropriate intervention.

Overview of Respiration

Taber’s Cyclopedic Medical Dictionary defines respiration as the “interchange of gases between an organism and the medium in which it lives.”² In the human body, we can further classify respiration by external and internal processes.³ The external process of respiration involves the transfer of oxygen (O₂) and carbon dioxide (CO₂) that occurs in the lungs between the atmosphere and the pulmonary circulation. The internal process of respiration is the similar process that occurs at the cellular level. While both aspects of respiration are essential to life, this article focuses on external respiration and its three primary components: ventilation, perfusion and diffusion. A thorough understanding of each of these components and their potential impairments can guide EMS providers in their efforts to manage patients who complain of difficulty breathing.

The Respiratory System (Physiology)

The ultimate function of the respiratory system is gas exchange.⁴ This gas exchange consists of obtaining O₂ from the atmosphere and removing CO₂ from the blood. It is important to consider that O₂ is necessary for normal metabolism and CO₂ is a waste product of this metabolism. CO₂ is only inhaled in negligible quantity and thus the CO₂ we exhale is created within the body. While CO₂ plays a role in acid-base balance, it must be cleared from the body in appropriate levels through ventilation.

Neural Control of Respiration

Although gas exchange takes place in the lungs, the respiratory system is controlled by the central nervous system (CNS).⁴ While we do have some voluntary control of breathing, it is regulated automatically and functions whether we think about it or not. Breathing can, however, be suppressed at the neurological level due to narcotic or sedative overdose, as well as brainstem injury.⁴