Explaining the differences in pathophysiology between various lung diseases to new medic students can be a daunting task. Fluid and bronchoconstriction and sputum—oh my! How do we describe all the idiosyncrasies between cardiac and non-cardiac causes?
To differentiate the causes of each, a visual aid may help. What’s easily accessible, cost effective, looks like alveoli and can be your snack after class? Popcorn!
Let that pop around in your head while we review the role of the lungs in the circulatory process. In a normal lung, air enters through the trachea, to the bronchi, then to the bronchiole and finally to the alveoli, which are wrapped in capillaries. Healthy circulation occurs when a sufficient amount of oxygen comes in and is converted to carbon dioxide.
What happens when something goes wrong with one or more of these structures? Which disease process affects which structures and what happens as a result?
Here’s where the popcorn comes in. Get six quart-sized Ziploc bags. Label them: normal, asthma, pneumonia, chronic bronchitis, emphysema and congestive heart failure. Pop some popcorn. Fill the “normal” bag with popcorn and you’re done. You can add a normal-sized straw inside to indicate the trachea (a big, green Starbucks straw works perfectly).
Asthma creates a narrowing of the airways as a result of constriction to the surrounding smooth muscles and inflammation of the airway walls. A patient with asthma also has increased mucous production, which leads to further obstruction. So, fill the “asthma” bag with popcorn, but leave a little room and add a smaller straw (a coffee stirrer works nicely). Now the fun part: Seal the top with a small space left open, suck the air out and quickly seal it up. It should give the idea of the tightness and constriction associated with asthma.
Pneumonia happens when microscopic organisms such as viruses or bacteria invade alveoli, causing them to inflame and produce nasty sputum. What looks like nasty sputum? Peanut butter! Take your “pneumonia” bag filled with popcorn and add chunks of peanut butter. Try to create them in large globs to simulate a pulmonary consolidation. Add a normal-sized straw to finish.
Smoking and environmental factors can cause chronic bronchitis, which destroys the cilia. This allows a clear pathway for bacteria and viruses to create infection. The mucous linings then inflame and the goblet cells overproduce mucous. The result is blockage to the bronchioles.
To simulate this type of mucous production, take your filled “chronic bronchitis” bag and drip honey or syrup all around the inside edges. Add a normal-sized straw. This gives the impression of the mucous coming from many different locations.
Now for the yucky one—emphysema. We all know smoking is a main cause of emphysema; however, it can also be caused by environmental contaminates or genetic issues. Emphysema destroys the terminal bronchioles and alveoli. This weakening causes the alveoli to form large blebs, which aren’t as efficient and can easily collapse. Emphysema can best be represented using burnt popcorn. Stuff it in the labeled bag, add a normal-sized straw and seal it up so you don't have to smell it.
Although other chronic obstructive pulmonary diseases can result in cor pulmonale, congestive heart failure (CHF) is the main respiratory distress of cardiac etiology. CHF results from the heart’s inability to pump properly due to a myocardial infarction, chronic high blood pressure or any other issue that would decrease the force of contractions or cause increased pressure to pump against. This causes backed-up blood into the pulmonary circuit (left-sided heart failure specifically) and the serum to be pushed out of the vessels into the lungs. It then mixes with the air, and causes pulmonary edema.
So, add water to the CHF bag. Hold it upright to demonstrate a patient in a seated position with the fluid at the bottom of the bag. Then take the bag and lay it horizontally to show how much alveolar space is taken when a patient with CHF lies supine. This helps explain the tripod position as well as why these patients need multiple pillows at night to breathe.
I’ve always learned better with visual and tactile tasks. I find that passing these “lungs” around the room helps cement the concepts for my students, and I hope it works for you too.