Restrictive (as Pulmonary Fibrosis) vs.Obstructive Disease (COPD)
Although there are hundreds of diseases that can affect the lungs, we do broadly describe almost all lung disease as either restrictive or obstructive. The obstructive group of diseases, primarily emphysema and chronic bronchitis, are also known as Chronic Obstructive Pulmonary Disease or COPD. It wasn’t that long ago that asthma was included in COPD, but since asthma is really episodic and reversible, it has come out from under the COPD umbrella.
There are over 200 known causes of restrictive disease. For years it was just called Pulmonary Fibrosis, and since the cause is unknown in the majority of patients (60 percent), it is formally identified as Idiopathic Pulmonary Fibrosis or IPF. IPF was first described by two doctors in 1944 and for many years we called IPF the “Hammon-Rich Syndrome” after these two doctors. It wasn’t really defined and classified until 1975, and in recent years it has also been referred to as a UIP (Usual Interstitial Pneumonia).
So while the vast majority of obstructive disease is made up of a handful of diseases, restrictive disease comes in hundreds of entities. It is interesting to note that there are an estimated 128,000 people afflicted with IPF in the United States. Contrast that with more than 15 million patients with COPD, and you can begin to see why and how the allocation of resources has been decidedly in favor of research to treat COPD over IPF. IPF can develop after exposure to dusts caused by breathing in cotton fibers during mill work, or exposure to beryllium as seen in some workers in the fluorescent light bulb industry, or to those who have been exposed to asbestos and silica particles. The list is very long.
Let’s look at a new patient through the eyes of the pulmonologist. Our male patient is already on nasal oxygen, has had some pulmonary function testing and complains of:
- Shortness of breath, especially with exertion
- Significant drops in O2 saturations with activity
- Mild to moderate Pulmonary Hypertension
- Bluish nail beds
- Unexplained weight loss
- Poor 6-minute walk results
- Decreased diffusion of oxygen (DLCO) into the lung
- Muscle aches
- It would be hard to tell whether our man has COPD or IPF based on the above in- formation. We need a bit more history. He does have a dry harsh cough, was a smoker in the past, but quit over 25 years ago. His work history is not significant for inhaling hazardous particles. We need the rest of the pulmonary function testing results which measure both flow rates and the volume of air in the various compartments of the lungs. The patient’s expiratory flow rate (FEV1) is 115 percent of his predicted normal. (Usually this is 75 percent to 80 percent.) He can really blast out that air on command. How- ever, the amount (volume) of air he blows out (his forced vital capacity [FVC]) is only 55 percent of his predicted. Remember normal values for pulmonary function studies are based on a person’s height and age. The clinical picture becomes a little clearer for your physician. With COPD we see reduced expiratory flow rates. The DLCO is almost always reduced in both conditions, so while helpful, it is not diagnostic by itself.