This chapter is based upon Ultimate Pulmonary Wellness Webinar 18: “Interstitial Lung Diseases” and “Pulmonary Fibrosis and ILD’s: Early Diagnosis and Best Treatments” both with my friend, Robert Kaner, MD; the person who I consider to be one of, if not the tippy-top super guru in Pulmonary Fibrosis (PF), Idiopathic Pulmonary Fibrosis (IPF), and other Interstitial Lung Diseases (ILD’s).

The subject of Interstitial Lung Diseases (ILD’s) is an extremely complex topic, often even for clinicians, even for physicians, and even for many pulmonary specialists. So, it is no surprise that it is equally if not more difficult for patients and other laypeople. 

When it comes to ILD’s, there is a lot of misunderstanding, misinformation, and confusion out there; so much so, that before we even get into the material, I want to highlight three key points right here from the get-go, because failing to appreciate these concepts can literally mean the difference between life and death. 

If you take nothing else away from or don’t understand anything else in this chapter, please understand the following three points:

1. Early diagnosis and treatment are critical; especially since some of the ILD’s are noted to have a 3-5-year life expectancy from time of onset, although please don’t get hung up on those specific numbers since one, there is variability in these numbers and two, new treatments are being worked on all the time.

1. Getting a definitive diagnosis is critical to your care. One of the reasons for this is that some of the treatments used to treat some ILD’s have not only been proven ineffective; but they can be harmful in the case of other ILD’s, meaning that they can make the disease worse by speeding up its progression.

1. Having the right team, especially, a pulmonologist who specializes in ILD’s is also critical. ILD’s are serious and cannot afford to be handled by anything less than an expert. I would say “as serious as cancer”, but in many cases, ILD can be more serious in some cases, so only the best and the brightest will do. 

If you do not have access to physicians and other health care professionals that specialize in ILD’s then you need to find one, even if it means travelling to an academic medical center or Center of Excellence in another location. In doing so, you can be properly diagnosed and started on the right treatment regimen. Then, after getting a definitive diagnosis and initial treatment plan, you can be managed along with your local pulmonologist. Again, this can literally be the difference between life and death. 

Please understand that I am not telling you these things to scare the bejesus out of you. Chances are, that’s already been done. I am telling you these things to impress upon you the fact that ILD is nothing to play with, nothing to sleep on, and not something to dabble with. You cannot afford not to take this seriously. And if you choose to stop reading here, “get thee to an ILD specialist, go.” -William Shakespeare (partially)

When people talk about obstructive lung diseases like Asthma, Emphysema, or Chronic Bronchitis, which are diseases that affect the airways, most people have at least a general idea of what we’re talking about. But…when you say the words “interstitial lung disease” or “ILD,” people generally have no idea what you’re talking about (again, including many clinicians). So, in the interest of getting us off on the right foot, let’s talk about what ILD’s are, what they aren’t; and why they are so difficult to diagnose and treat. 

To be clear, ILD is not one specific disease or diagnosis. Rather, ILD’s are a large group of disorders; or more specifically, a category or classification of diseases, that are grouped together because they have similar clinical, radiographic (X-ray or CT scan), and pathological mechanisms. 

Anatomy and Physiology 

Interstitial lung diseases occur in the alveoli, or alveolar spaces, where gas exchange occurs. Deep within this gas-exchanging part of the lungs, there is an interface between the capillaries, where red blood cells take on oxygen from outside to be used by the body and release carbon dioxide to the atmosphere. The alveolus is surrounded by a very thin structure, called the alveolar wall, which contains epithelial cells that line the air space; and pulmonary capillaries that are only wide enough to accommodate one red blood cell at a time. There is also a connective tissue “scaffolding” that holds that structure together. Interstitial lung diseases are centered on those alveolar walls and the structures that hold the gas exchanging part of the lung together. 

Often, people will compare the alveoli to a bunch of grapes. So, if you think of a cluster of alveoli as a bunch of grapes, the alveolar wall would be analogous to the skin of the grape, and that’s what gives it its tensile strength and the ability to maintain its structure. So, the simple explanation is that when you have an interstitial lung disease, the skin of the grape gets thicker, and you end up with smaller grapes with less air in each grape.

But it turns out that the physiology is a little bit more complicated. In a normal lung, you have this very thin membrane that allows oxygen to go from the airspace of the lung into the pulmonary capillary. In a normal lung, the distance that the oxygen must travel to cross that membrane is very short. In the case of ILD, this membrane gets thicker and the distance for diffusion is longer, so the process is going to be less efficient, but it turns out to be even more complex than that. I told you it’s complex!

Think of your pulmonary circulation as a series of parallel pipes. Your entire cardiac output, i.e., the volume of blood pumped by your heart, must travel through these pipes, aka the pulmonary circulation and when we exercise, this cardiac output increases dramatically. In a person with normal, healthy lungs, there is enough capacity in these pipes to allow for this increased cardiac output to travel through the pulmonary circulation effectively. 

However, when you have a progressive interstitial lung disease, there’s inflammation and scarring in the gas exchanging part of the lung, and over time, you lose more and more of those pipes. In this situation, the only way you can maintain cardiac output is for the velocity of the red cells to increase, so they start speeding through the remaining pulmonary capillaries faster and faster.

Again, in a person with normal, healthy lungs, the red blood cell is in the pulmonary capillary for about a quarter of a second, and by the time it goes from the beginning of the capillary to the end, it’s completely saturated with oxygen. However, if you lose enough of your pulmonary circulation, the red blood cells may have to go so fast during either exercise or activity, that they are unable to become fully saturated with oxygen by the time they get to the end. This is known as exercise-induced oxygen desaturation, and the more capillaries you lose, the worse it gets, as interstitial lung disease progresses.

Therefore, in people that have interstitial lung disease, their oxygen saturation at rest may be perfectly normal or near normal, but when they exercise, their oxygen saturation drops, sometimes very dramatically and that’s why you may need large amounts of supplemental oxygen when you exercise to compensate for that impaired physiology.