I thought Id do something a little different with today’s post and teach some Respiratory Therapy 101 to my fellow asthmatics . A mini series if you will, on topics that I think every asthmatic should be familiar with.
Things like.. Dyspnea, what exactly is it? Or, Air-trapping? Or how about, Obstructive lung disease..what is it? I’m sure most of you have probably heard of these terms before, but do you really know what they mean? I think the more you know about your disease and how your lungs work in general, the better you’ll be at treating your asthma and the better you’ll be at communicating with your medical provider… and maybe even teach them a thing or two.
Before we get into any of these lessons, I think it’s really important that we review some breathing basics. We already know(at least I hope we do), that the reason we breath in the first place, is so that we can get oxygen into our body and carbon dioxide out. For the purpose of this review however, let’s focus on the the mechanics of breathing itself. In other words..the act of taking a breath in and then blowing it out… how does it all work? It’s pretty amazing actually Let’s call today’s episode, the “Breathing Cycle”.
Most people think that the act of breathing is simply a matter of taking a breath in, and then blowing it back out. Actually, there are 4 distinct phases to the breathing cycle; There’s the Inspiratory phase , the Inspiratory pause , the expiratory phase and the expiratory pause phase. When everything is working right, the process is effortless and we’re not aware of it. Add asthma to the mix, it’s a different story. For now though, lets see what happens during normal breathing.
To help you visualize what I’m talking about, I found this really cool video (courtesy of the nice folks at Interact Medical), that illustrates beautifully,the mechanics of normal breathing. They do a great job of depicting the diaphragm’s role in breathing (shown in yellow).
Here’s what’s happening:
1) Inspiration(the act of inhaling or taking a breath in), is an active process. By active, I mean that it requires muscle power to do it. In this case, it’s the diaphragm that’s doing the work. A signal from the brain tells the diaphragm muscle to contract. As the diaphragm contracts and pulls down, it creates a vacuum inside the chest cavity (kinda like drawing back on a syringe) and by doing so, enlarges of the abdominal cavity. This in turn causes the lungs to be pulled down open, which allows fresh air to rush into them. When you take a breath in, you are literally sucking the air into your lungs. (During normal breathing, this is not noticeable.)
2 Inspiratory pause As air is drawn into the lungs, tiny stretch receptors tell the brain when the lungs are full enough. The contraction of the breathing muscles then seizes and the air is held in the lungs. This is part of the breath cycle that we call the “inspiratory pause”. It only lasts a fraction of a second, but it’s there.
3) Next we have the expiratory phase( the act of exhaling). Assuming that you have healthy lungs, expiration should be totally passive. The diaphragm and the other breathing muscles simply relax to their resting postion and the air is expelled from the lungs.
4) Finally, we have the expiratory pause, which is just the pause between exhaling and taking the next breath in. This phase can last several seconds depending on the body’s need to start the cycle over again. Pretty cool eh.
Now that we know how this all works, let me throw some numbers at you just for fun.
If an adult person with healthy lungs takes 12 breaths ( breath cycles) per minute, this means that it takes appx 5 seconds to complete each breath cycle (12 breaths x 5 seconds=60 seconds or 1 minute). Within that 5 second period, appx 1.5 sec will be spent in the insp. phase, 0.5 secs in the insp pause phase and 2-2.5 sec in the exhalation phase. In a person with healthy lungs, the expiratory phase is usually 1.5 to 2 times longer than the inspiratory phase ( what we call the I:E ratio). In a person with chronic asthma or COPD, the expiratory phase can be many times longer than that. With my own asthma, when I get really tight or I’m trapping a lot of air , it can take me a full 15-20 seconds to exhale a single breath. If it was taking me 20 seconds to exhale a single breath, I would only be able to take 3 or 4 breaths per minute, right? Well, if that were the case I wouldn’t stay conscience for very long. Actually, when asthmatics get really tight like that, we’re forced to terminate the exhalation early, so that we can make room for the next breath. Because we’re continually terminating each breath early , we end up having an abnormal amount of air that stays trapped in our lungs. ie…air trapping! (More about air trapping in a future lesson).
Here’s another RT tidbit for you: Did you know that no matter how hard you try, you can never exhale all of the air out of your lungs? If that were the case, your lungs would totally collapse and you would not be able to overcome the resistance that it would take to re inflate them again. In the Respiratory field, we call this residual lung volume.