BOOK – Chapter 2: The Respiratory System

Chapter 2: The Respiratory System

“Breathe! You are alive.” – Thich Nhat Hanh, Zen Buddhist Monk


Know Thyself!


It never ceases to amaze me how many people I meet, who are living with a chronic illness, often for years, who have little or no knowledge about the biological system involved, let alone the disease itself and its impact on their bodies and their lives. Please understand that it is not my intention to present you with a doctoral-level dissertation on the respiratory system (and I’m pretty sure you don’t want one).


However, when it comes to dealing with a chronic illness, a basic understanding of the anatomy (structure), physiology (function) and pathophysiology (disease) will go a long way. My hope is that this information will help you better understand your condition, as well as provide you with the necessary vocabulary and context for more meaningful communication with your doctor and other health care professionals. Throughout this book, I will explain how various factors affect your breathing and what you can do to improve not just your breathing, but also your life.


Breathing is “Multi-Factorial”


I tell people over and over again: “breathing is a multi-factorial process.” What I mean by that is that on any given day, there are a whole host of factors, both internal and external to our bodies that can affect how well (or how poorly) we breathe. Besides just our lungs and the respiratory system, these can include things like proper medication use, activity versus inactivity, the foods we eat (or don’t eat), maintaining a healthy weight as compared to being overweight or underweight and managing stress and anxiety effectively; not to mention the possible effects of weather; and other environmental factors that can have either a positive or negative impact on our breathing.


As an example, think about how your body reacts when you step outside on a cold winter day as opposed to when it’s hot and humid; or how you feel after indulging in a big meal or having a few too many cocktails. Using temperature as an example, we know that our body functions best at a temperature of 98.6 degrees Fahrenheit. This is why we sweat in the summer and shiver in the winter as our body attempts to cool and warm itself, respectively.


Breathing is Multi-Systemic


Breathing is also multi-systemic. Contrary to what many people believe, breathing is not just a function of the lungs and the respiratory system alone. In fact, multiple systems contribute to the act of breathing including the following:


  • Neurologic system (brain, spinal cord, and nerves)
  • Cardiovascular system (heart and circulation)
  • Musculoskeletal system (muscles, bones, joints)
  • Endocrine system (glands and hormones)
  • Gastrointestinal system (digestion and the digestive tract)


While each system is specialized to perform a different function or set of functions, they are also interconnected, working together; constantly monitoring and adapting to changes in the internal and external environment in an effort to establish a physiologic state of balance known as equilibrium.


The net impact of each system will vary depending on the individual and their particular conditions and co-morbidities; i.e. other medical issues. Other systems can and will be involved on an individual, case-by-case basis. Therefore, it is essential that you, along with your doctor, investigate and explore all of the factors that could potentially be contributing to your shortness of breath.


The Respiratory System


The primary functions of the respiratory system are to deliver oxygen (O2) to the body and remove carbon dioxide (CO2) and other waste products of metabolism. At the most basic level, when you take a breath, O2 molecules enter the lungs and cross into the bloodstream. This “oxygenated” blood is then transported to the heart, where it is pumped to every cell and organ of the body for use as fuel during metabolism.


CO2 and other metabolic waste products cross from the cells and organs of the body into the bloodstream. This “deoxygenated” blood is then transported back to the heart, where it is pumped to the lungs and expelled during exhalation.


Pulmonary Anatomy and Physiology


Air can enter the body through either the nose or the mouth. When you breathe in through your nose, three important functions are performed. First, the air is filtered by tiny hair-like structures; called cilia, trapping particles of dust and debris in the mucus membranes. Second and third, the air is also warmed and humidified by tiny blood vessels called capillaries.


From the nose, air continues into the nasopharynx, the uppermost part of the throat. When you breathe in through your mouth, air passes through the oropharynx, the middle part of the throat. The nasopharynx and oropharynx meet in the back of the throat, or pharynx, and continue down through the laryngopharynx, the lowest part of your throat and the larynx (also known as the voice box).


From the larynx, air enters the trachea, or windpipe, through the epiglottis, a cartilaginous flap that opens during breathing and closes during swallowing to prevent solids and liquids from entering the trachea, airways and lungs.


The trachea splits into the right and left mainstem bronchi, going to the right and left lung, respectively. The bronchi then continue to divide, getting smaller and smaller, branching into secondary and tertiary bronchi and even smaller bronchioles. After approximately 20 to 23 divisions, the air finally reaches the alveoli, the tiny air sacs in the lungs where gas exchange occurs.




Inhalation is an active process, meaning that it requires the active muscular contraction of the diaphragm, the primary muscle of inspiration (and the intercostal muscles) for it to occur. In order for us to take a breath, the brain sends a signal down the spinal cord to the phrenic nerve. When the phrenic nerve innervates (i.e. sends an impulse to) the diaphragm, it contracts downward, creating a negative pressure in the thoracic cavity. It is this negative pressure that causes the lungs to inflate, filling up with air.


When breathing demands increase—as in the case of physical activity or exertion, or in the context of respiratory disease, your body can call on the accessory muscles, which include the muscles of the neck, back, and chest, among others, to assist with ventilation.


People with restrictive lung diseases, such as Pulmonary Fibrosis or Scleroderma, have a difficult time with the inhalation phase of breathing due to increased stiffness of the lungs. As a result, they have to generate significantly greater force in the respiratory muscles in order to overcome the increased lung resistance.


People with restrictive lung disease often take shallow breaths with less air in each inhalation. As a result, they are forced to breathe more rapidly in order to keep up with the body’s ventilation and respiration demands. This is in contrast to people who have obstructive lung diseases, who have difficulty in expelling air out of the lungs, which I will discuss next.




During quiet breathing, exhalation is a mostly passive process, relying on relaxation of the respiratory muscles, and the natural elastic recoil of the lungs, which causes them to deflate and expel air. Exhalation can also become an active process when the expiratory muscles, particularly the abdominals, contract to actively force air out of the lungs. This forced exhalation can be done voluntarily or involuntarily and can occur during strenuous (or not so strenuous) activity, particularly in cases of impaired lung function.


People with obstructive lung diseases, such as COPD do not have difficulty getting air into the lungs. Instead, they have a difficult time getting air out of the lungs during exhalation. This can be caused by several factors including airway inflammation, mucus or spasm in the airways, a decrease in the natural recoil in the lungs or the destruction of the small airways and alveoli.


Air trapping can also lead to larger (hyperinflated) lungs. The more air that is left in the lungs, the less efficient each breath will be in diluting the stale air and sufficiently reducing CO2. Over time, this can potentially lead to CO2-retention as COPD worsens. This is in contrast to people with restrictive disease, which can lead to smaller (hypoinflated) lungs.


In some cases, people can have a combination of both restrictive and obstructive disease, meaning that they have difficulty with both inhalation and exhalation.


Efficiency, Effectiveness and Miles Per Gallon


If you think of your body like an automobile, the efficiency with which your body utilizes oxygen is similar to how many miles you get per gallon of gas (mpg). If your engine is run-down or your oil badly needs changing or your tires don’t have the proper amount of air in them, your car will be less efficient and get fewer miles per gallon. The same is true when it comes to your body.


Ventilation and Respiration


The mechanical act of moving air in and out of the lungs; i.e. inhalation and exhalation is called ventilation. Ventilation is an active process, meaning that it requires the contraction and relaxation of the respiratory muscles, for it to occur.


The chemical exchange of oxygen (O2) and carbon dioxide (CO2) between the external environment and the cells of the body is called respiration or gas exchange. Respiration is a passive process and occurs constantly, regardless of muscle activity or phase of ventilation. In other words, it occurs at the cellular level, during both inhalation and exhalation, as well as during any pauses in between.


While there are many factors involved in how well your body uses oxygen, its overall efficiency is based upon three main factors:


  1. How effectively your lungs move air in and out?
  2. How effectively your heart pumps blood?
  3. How efficiently your muscles utilize oxygen?


If there is a problem in any one of these areas, your body will not be as efficient at using oxygen and you will be more short of breath. For example, if you have a chronic respiratory disease, your lungs will not move air in and out as effectively. If you’ve had a myocardial infarction (heart attack), your heart will not pump blood as effectively. If you lead a sedentary lifestyle, then your muscles will not utilize oxygen as effectively.


If you have problems in more than one area (which is not uncommon), your breathing (and other issues) can multiply. As an example, if you have both heart and lung disease, you will likely have significantly more difficulty than if you had either one alone.


Here is the good news, though, and again, I am completely biased.  But…in our experience, we have found that the right combination and type of exercise and breathing techniques can significantly improve the effectiveness of the respiratory, cardiovascular and muscular systems, thereby improving your body’s overall efficiency at using oxygen.


In addition, despite a large body of scientific literature stating the opposite, we firmly believe that under the right conditions, your pulmonary function can also improve. In the chapter on exercise, I will explain what makes our training methods so different, so effective and what we believe is the key to improving pulmonary function. This will hopefully allow you, the patient, as well as other rehabilitation professionals and programs to benefit from what we at PWRC know to be true.