Why We Cough

This article is from the blog of Dr. Jeff Swigris of National Jewish Hospital in Denver. It explains the many causes of our cough, the pulmonary fibrosis cough. Mine is usually from not having enough prednisone or if my O2 is too low. It is a fascinating article. Please take the time to read it:

Cough in Pulmonary Fibrosis

Hi gang! I hope everyone is settling nicely into 2014. In this blog, I’m going to discuss cough—what it is, why it occurs in patients with PF and what we might be able to do about cough in those PF patients plagued by this annoying symptom.

What is cough?

Let’s start with a description of cough. (Full disclosure: I went back and read a chapter in one of our general pulmonary texts just to remind myself of all the stuff I’ve forgotten about cough since first learning about it…and to make sure what I was about to type had some validity to it.)

We, in the PF world, know cough as a potentially endlessly frustrating, forceful exhalation of air from the lungs, most often (but not always) with little or no mucus, accompanied by a sound that can be equal parts annoying (to the cougher and those around him) and embarrassing, and instigated by any number of feelings/triggers. Others know cough as a normal, primitive defense mechanism of the human body that attempts to protect the windpipe by expelling ANYTHING (except air) that gets close to its opening (the larynx…a.k.a. voice box).

Here’s another look at the larynx, including a view from above (on the RIGHT). Remember that little guy with the blue visual field that I used in one of my previous blogs when discussing how we view CAT scans? Well, he’s back.

Imagine you’re sitting above the voice box (just like that little guy down there), looking down on the structures of the voice box; what you would see is shown in the circular image on the right.

The whitish things that make an UPSIDE DOWN “v” inside the circle are the vocal cords. They sit like a little door (more like a double sliding glass door) at the top of the windpipe (trachea). The opening between the vocal cords is called the glottis. If you go through the glottis, you’re inside the windpipe (trachea). When we breathe (IN or OUT), the vocal cords are open to allow air to pass. Our voices come from air flowing up out of the lungs, through the windpipe, and between the vocal cords (i.e., through the open glottis). The pitch and tone of our voice depends on, and varies with, the length and tension of the vocal cords, which alters the size and shape of the glottis.

All of this is important to understanding cough. Here’s what happens in a normal cough; there are four events:
1) deep inspiration (glottis is open to allow air in the lungs). This deep
inspiration serves 3 purposes:
a) it dilates the airways
b) it stretches the muscles used in exhalation
c) it fills the lungs with air
2) glottis closes (that is, the vocal cords come together to close the
opening to the windpipe) and expiration begins (against the closed
vocal cords). This causes pressure to build inside the chest.
3) the glottis is exploded open and air is expelled as the inflated lungs
and stretched expiratory muscles RECOIL from their
stretched/expanded status.
4) a recovery phase marked by another deep inspiration.

It seems like I say “this is really complex” whenever I’m talking about things related to the human body…and I’m going to have to say it again: cough is a really complex thing. There are receptors for cough all over the place, including in and around the larynx (voice box), the windpipe and other large airways and even the EARDRUM and EAR CANAL (have you ever triggered a cough when cleaning your ear canal with a Q-tip?…don’t do it now…you should never put anything smaller than your elbow in your ear canal). Anyway, these various receptors can trigger cough when exposed to any number of mechanical or chemical stimuli (i.e., when they are touched by anything or when certain chemicals come in contact with them).

When triggered, the receptors start complex circuits in motion that involve various nerve pathways and body chemicals that ultimately result in cough. This is not well understood (there I go again), but in disease states, the cough receptors are OVER-sensitive, so things that might not normally cause cough, suddenly do.

Why do patients with PF cough?

Do you know the #1 reason why patients with PF cough? Like the rest of us, the #1 reason why patients with PF cough is postnasal drip. How so? Mucus from the nasal passages and/or sinuses drips down onto the soft palate then down the back of the throat toward the voice box. Remember, the body wants to protect the windpipe by expelling anything other than air that gets close…so, when the mucus gets down there close to the voice box (or on it in many cases), a cough is triggered. See the green mucus I’ve added to the image?

Another reason why patients with PF might cough is GERD or the reflux of gas/acid/other liquid (alkaline)/food into the esophagus from the stomach. Because of a feedback loop (from esophagus to airways), all that is needed to trigger a cough is stuff coming up out of the stomach and hitting the lower esophagus…that’s it. Most people don’t even know this is going on…it can be entirely asymptomatic (except for the cough). Here’s how it is believed to work…

…the stuff in the stomach (red) is supposed to stay down in the stomach, but it sloshes up into the esophagus. The esophagus is not made to withstand being bathed in that stuff, and it knows it, so it sounds the alarm (lightning bolt). The alarm is picked up by the (no one is sure but maybe the) brain or spinal cord, which then sends a message to the windpipe and airway to MAKE A COUGH. This seems like an odd reflex, since the cough doesn’t clear the stuff out of the esophagus…it likely has to do with the fact that in human embryonic development, the lungs come from the same tissue that gives rise to the esophagus, stomach and first part of the small intestine…so the nerve pathways are likely the same for both.

Whatever the case, the cough can occur when the stuff comes only a little way out of the stomach. But, in some people, the stuff does come all the way up to the top of the esophagus and even out of the esophagus and over into the voice box…that will trigger a cough, big time…and people will often get a really bitter, sour, burning taste along with it…but again, some people can be asymptomatic (except cough) even when that happens. Here’s a picture of this…

We know GERD is very common in patients with PF. In fact, there are some pretty compelling data to suggest silent aspiration (reflux all the way up the esophagus and then down the windpipe into the lungs) actually causes PF…but the jury is still way out on that theory.

So people with PF can cough because of postnasal drip, GERD and a host of other things…of course, the cough might also arise from PF itself. Like everything else here, this is pretty poorly understood. What is known is that patients with PF have increased sensitivity to cough-inducing substances. That is, when a cough-inducing substance (e.g., capsaicin – the stuff that makes hot peppers hot) is inhaled, it takes less of it to induce a cough in a person with PF than in a person without PF. This is true for other substances often used in cough research (things like substance P and bradykinin).

Do you remember when we talked about traction bronchiectasis? That is, the airways getting tugged open as the lung around the airway retracts with scar? This is a very common finding in patients with PF; in fact, it’s one of the hallmarks of fibrosis on HRCT. Here’s a picture of it…

It turns out that this distortion of the airways increases their cough sensitivity…makes them more likely to trigger a cough than a normal airway exposed to the same thing. So, as I mentioned above, airways in PF are overly sensitive to begin with; those airways with traction bronchiectasis are ULTRA-sensitive.

Also, (this is incredibly interesting), researchers have discovered that chest wall vibration can induce cough in some patients with PF. So, talking for any length of time (do you cough after talking on the phone for a while?) or as crazy as it seems, the cough itself—things that can cause vibrations in the chest—can bring on (or beget) cough.

What I hear from PF patients in clinic

What I hear from my PF patients is that many cough when they breathe hard and/or fast, like when they’re hurrying to do something. They tell me they cough when they talk for extended periods (e.g., on the phone is a common one). One that I’ve really come to appreciate is that many patients will tell me they cough whenever their oxygen saturation is low.

What can be done?

So, if you have PF and you cough, what can be done? Well, the first order of business is to rule out causes of cough other than PF itself. I mentioned two up there…there are others, so make sure you and your practitioner have worked through the possibilities before attributing your cough entirely to PF.

If you’ve arrived at the conclusion that your cough is from PF, there are some things to try. There are data to suggest prednisone improves cough in patients with PF. Please don’t take this as a blanket endorsement for chronic prednisone use in patients with IPF (or PF from any cause for that matter); whether to even try prednisone to specifically target cough from PF is a decision you and your practitioner should make together.

Believe it or not, I have had some patients sing the praises of the following things for decreasing the frequency and/or severity of their cough: benzonatate, N-acetyl cysteine (NAC), horehound cough drops, and Fisherman’s Friend cough drops. I’ve used all of these to treat cough in my PF patients: narcotics, nebulized lidocaine, amitriptyline, gabapentin, and baclofen. I’ve had some success with hypnosis in a couple patients. Which, if any is “right” for you is a decision you need to make you’re your practitioner.

You’ve probably read, there are emerging and potentially promising data on thalidomide’s ability to decrease cough frequency and severity, and to improve cough-related quality of life, in patients with PF. If you haven’t, you can find the article HERE. Thalidomide has some side effects, but it seems like people with terrible PF-related cough are willing to put up with them to get some relief. The good news is that there are newer, apparently less-toxic derivatives (i.e., cousins) of thalidomide out there…and more on the way. We’ll have to test those to see what they can do for our patients.

Now, you should know that, in any person, cough can be caused by more than one thing…in fact, many of my PF patients talk about their “PF cough” and their “other cough.” Treating cough, regardless of cause, can be a real challenge. I like to set the stage up front: I tell my patients this is going to be a process of trial and error; there may be—but probably won’t be—a “magic bullet” that magically takes the cough away. Often, there is some benefit from one intervention, but then another thing needs to be added/tried. Try not to get frustrated, and don’t give up hope. As you can see from the paragraphs above, there are a bunch of things to try. Work with your practitioner, and let him/her know what is working (or not) and how.