The Respiratory System: An SLP’s Understanding

The respiratory system is not an area we learned a lot about in grad school (or any other time for that matter). We may have read an article or two on the important factors of lung health to consider when managing dysphagia and the risks for aspiration pneumonia, but have we ever truly studied the respiratory system itself? Probably not. But if yes? I applaud you because it’s an extremely important area for us not only to be aware of, but to understand well. Why? Because our role as speech pathologists is to manage the aerodigestive system. Emphasis on aero in case you missed that. The oropharynx is one tube for both swallowing and breathing (I know, not sure what our creator was thinking with that one, but nobody’s perfect). Then we have the larynx as this bizarre-looking valve separating the two (probably meant more to protect the airway and expel aspiration more than for talking, but we are a creative bunch). So problems in breathing can cause problems in swallowing and vice versa. Let’s get into the basics of breathing and find out what we should know in order to apply this knowledge to our patients with dysphagia.

The Basics of Breathing

The primary purpose of the respiratory system is pretty simple. We move our lungs in and out (ventilation) in order to take in oxygen and release carbon dioxide (respiration). If I’m riding an inhaled air wave I travel through the oropharynx, get sucked down into the trachea through the larynx and down into a series of descending and progressively narrow tubes (from the main stem bronchi to the end of the bronchioles) into tiny clusters of sacs called alveoli (man, it’s crowded in here). Once you land in these warm, moist sacs (ugh, sticky) you get absorbed into the blood stream towards the heart where it pumps oxygen to your entire body and returns CO2 back through the heart and into the lungs (whoa, what a ride). We then exhale air through the reverse route in order to release CO2 back into the air.

The lungs are incredibly elastic from top to bottom (including the alveoli themselves). They’re like stretchy balloons allowing air to easily fill them up when the diaphragm below the lungs and the intercostal muscles in your ribs contract to expand your chest and open up your lungs. It works like a vacuum, creating negative air pressure inside the lungs so that positive pressure can be pulled in from outside the body. Exhalation is normally just the relaxation of these muscles to close the space in your lungs, creating positive pressure which pushes air back out into the...well, air. I say normally because we can create forced exhalation through our abdominal and intercostal muscles (i.e. sneezing, coughing, yelling, exercising, or even sighing like when you close your eyes to go to sleep and you just remembered you forgot to take out the garbage).

We do this process about 10-20 times a minute (average respiratory rate) and, similar to swallowing, it can be done voluntarily (i.e. meditating) or involuntarily (thanks nervous system!). Unless something goes wrong, this process actually works seamlessly, which is why we pretty much never think about it. But unfortunately things can go wrong and that 10-20 times a minute may increase to 30-40 times a minute. Then we have a problem (which we will discuss in the second part of this post covering disease processes).

Keeping Clean

The lungs are also fantastic at staying clean. First, think about the air we breathe. Air is actually only 21% oxygen. The rest is mostly nitrogen, but also includes some nonsense: pollutants, pollen, and dust. Live in a city? You don’t even want to know what you’re breathing in. Through a complex interplay between mucus, cilia, alveoli absorption, and macrophages, we can clean up, clear out, and absorb pretty much any outside contents that don’t belong there (I discuss this process in more detail in my blog on ARDS with Dr. Coyle and Kelsey Day, which you can find here). As you can imagine, keeping the lungs clear is what keeps them running smoothly.

Healthy lungs work wonderfully well. They ventilate without a hitch and respirate to keep our oxygen flowing and our body functioning. But of course things do go wrong occasionally. Problems occur and one problem often leads to the next. Poor ventilation may result in poor respiration and vice versa. Extra contents in the lungs may result in both poor ventilation and poor respiration leading to a functional decline which only leaves the opportunity for more contents to enter the lungs (i.e. aspiration).

Understanding the Whole System

The respiratory system is amazing. It’s only when things go wrong that we notice it at all. In the next part of this blog series I’ll do an overview of the major respiratory disease processes, how they work, and how it affects our breathing. Then we will tie everything back to swallowing: what we are all really interested in. The body cannot be seamlessly separated into parts and functions because everything is tied together in a complex system: The human system. To understand swallowing we need to understand breathing and to understand dysphagia we must understand respiratory disease. If we step away from the microscope where we examine each part of the system in a silo we can instead get into our educational helicopters so we can see these systems from a bird’s-eye view and comprehend them as a whole. Then we’ll know how they all work together successfully (and what happens when they don’t).

Stay tuned. More in this series next week :)

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