The Pocketbook Guide to Airway Physiology

Take a deep breath. Now let it out slowly. Do you ever stop to think about the amazing physiological processes that take place within our bodies, each time we take a breath? Breathing is one of many bodily functions we take for granted—that is, until we are unable to breath. Something to think about the next time you treat an asthmatic or choking victim.

Breathing is the culmination of a complex dance between several systems within the body:

  • Pulmonary – where gas exchange takes place
  • Neurologic – which houses the main triggers for respiration
  • Cardiac – which provides a backup system to initiate respiration

And although these systems work in tandem to regulate the acid–base balance of the body through respiration, the true “brains” of the process are aptly found within our brain stem: specifically, within the medulla and pons.

Normally, we are driven to take a breath when the CO2 levels in our bodies rise, which is monitored by the respiratory centers within the brain. We also have a backup mechanism, controlled by chemoreceptors in the aortic arch and carotid arteries, which are triggered by changes in oxygen levels (hypoxic drive).

The diaphragm, which provides the pressure changes that allow the lungs to inflate and deflate, is innervated from the phrenic nerve and branches from the spinal cord between C3 and C5. A spinal injury in this region can transect the phrenic nerve, cutting off communication between the brain and diaphragm, making respiration impossible.

Gas exchange within the body takes place through five actions within the respiratory system:

  1. Ventilation – the movement of air into and out of the lungs
  2. Distribution – the delivery of air into the lungs for gas exchange to take place
  3. Diffusion – tissues within the lungs engaging in gas exchange
  4. Perfusion – blood flow through the pulmonary vasculature to allow diffusion
  5. Circulation – the heart distributing blood throughout the body so that the other processes can take place

Disruption of any of these processes, or impairment of one of the regulatory systems of the body, can produce abnormal breathing patterns, which are apparent during your physical assessment. These patterns affect the regularity of breathing, its rate, or its depth. They include:

  • Kussmaul’s respirations: characterized by fast and deep labored breathing, often punctuated by sighs, and associated with metabolic acidosis
  • Cheyne–Stokes: a cyclic pattern of progressively increasing rate and depth of respirations followed by periods of apnea; often seen in overdose, acidosis, and increased intracranial pressure
  • Apneustic breathing: prolonged periods of gasping followed by brief, ineffective expiration
  • Hyperventilation: an increased rate and depth of respirations often seen with anxiety, fever, exertion, acid–base imbalance, or damage to the midbrain
  • Bradypnea: abnormally slow rate of respiration seen in drug or alcohol ingestion, central nervous system lesions, metabolic disorders, and fatigued patients
  • Apnea: the absence of respirations
  • Agonal respirations: an abnormal pattern of slow, shallow, deep, or gasping respirations

When functioning normally, the respiratory system provides the necessary oxygen for our existence. When things go wrong, the body can compensate to a point, but without immediate intervention, the patient will die. By understanding the underlying principles of the system and identifying the warning signs when things are malfunctioning, you can better treat those patients suffering from respiratory insufficiency.


2011, Pollak, A., Ed.

Critical Care Transport, American College of Emergency Physicians, Jones and Bartlett.