Lung Anatomy 101: Why does asthma cause chest pain?
Anyone who's ever had an asthma attack knows about the chest tightness and why it occurs. Yet what about the chest soreness that occurs the next day? Why does asthma causes chest pain?
The interesting thing to note here is there are no pain receptors in your lungs!!! The reason asthma causes pain is because asthma causes you to breathe the wrong way.
Confused? Allow me to explain with a pithy lesson on how we breathe. (To learn why we breathe click here)
Breathing is the process of moving air into and out of the lungs. Breathing is one of the few bodily functions that can be done either consciously (you control it) or unconsciously (without thinking of it).
Unconscious breathing: Most of the time you don't think about breathing, yet you continue to do it. This is an important safety net for life, because if we had to think about breathing 24-7 we'd accomplish little and most life would cease to exist.
Air goes into your lungs because a negative pressure is created that sucks air in, kind of like a vacuum. Normal exhalation is passive. Normal unconscious breathing is generally called quiet breathing.
There are basically two forces that create a breath:
1. Muscles of respiration
2. Negative recoil of the lungs
How do we inhale during normal breathing?
Diaphragm: The main muscle of respiration is this large muscle that contracts during inspiration. When it contracts it moves downward making more room in the lungs and creates a negative pressure, causing air to be drawn in.
External Intercostal Muscles: These are positioned between the ribs and contract during normal breathing, pulling the ribcage outward. These assists the diaphragm in lifting the rib cage and creating negative pressure in the lungs. They also assist with expiration.
Scalene: This might assist the diaphram.
Since these muscles are used with every breath you take, they are well conditioned and do not cause pain when you use them.
How do we exhale during normal breathing?
Exhalation is normally passive. It occurs when the muscles of respiration relax. When this occurs the rib cage is drawn in, and the lungs are compressed. This increases the pressure in the lungs, and air is pushed out. This is also referred to as normal elastic recoil of the lungs.
Abdominal muscles and internal intercostals contract and have a minor role in exhalation.
Conscious breathing: Sometimes you take in a breath by thinking about it. For normal conscious breathing the mechanisms are the same as above.
What I just described is normal breathing for a healthy individual. The way we breathe changes somewhat when the lungs are diseased. If you have a disease like asthma, where the air passages are narrowed -- at least during an acute episode, you may have to make an extra effort to get air in and out.
When this occurs, the accessory muscles of breathing are used.
What are accessory muscles of breathing?
Accessory muscles are supplemental, and this basically means they are muscles that are not used for normal breathing. However, when you are having an asthma attack, these muscles contract to help pull the ribcage out.
The main accessory muscles are:
1. Sternocleidomastoid (neck)
2. Scalene (neck)
The minor accessory muscles are:
3. Serratus Anterior (minor role, side of chest)
4. Pectoralis Major (minor role, chest)
5. Pectoralis Minor (minor role, chest)
6. Upper Trapezius (back, shoulder and neck)
7. Latissimus Dorsi (side of chest and abdomen)
8. Erector Spinae (deep back)
9. Iliocostalis Lumborum (deep back)
10. Serratus Posterior (mid back)
11. Serratus Inferior (mid back)
12. Serratus Superior (mid back)
13. Levatores Costarum (chest)
14. Tranversus Thoracis (chest)
15. Subclavius (chest)
Since these muscles are not used normally, the day after an asthma attack they may hurt. It's the same principle that applies after you work out for the first time in a long time. There are no pain receptors in the lungs, so it is for this reason asthma can cause chest pain or soreness.
I don't expect you guys to remember all these muscle groups, yet if you check out the links above, or use this diagram, you'll see why you hurt where you do after an asthma attack. Most of the muscles used are in the neck, chest, back and abdominal regions.
And use of these muscles can cause cause chest pain or discomfort.
With some diseases states that are chronic in nature, or where the lungs are permanantly scarred (such as COPD, severe asthma, cystic fibrosis, etc), these muscles can be overused and can even become enlarged. The same that occurs after chronic weight training.
If the lungs lose their elasticity (if they become stiff and unable to recoil), your body will have to use all the above mentioned muscles to force air out of your lungs. This is generally called active forced breathing or forced exhalation. It is generally active or conscious, and is often referred to as labored breathing. Other examples of this are emphysema and pulmonary fibrosis.
Muscles that assist with forced exhalation include:
1. Abdominal Muscles
2. Internal Intercostals
3. Innermost Intercostals
When you are breathing normally you are using your diaphragm. This allows you to get the most out of each breath. When this occurs, your stomach moves out, and your chest does not move.
When you are having trouble breathing, it's good to focus on breathing by this method. It is healthier and easier, and helps you breathe better.
When your lungs are sick and you are using your accessory muscles to breath, your chest wall moves inward and your stomach is sucked in to help you force air in. This is not a very effective method of breathing. Since you're using your accessory muscles, it leads to chest soreness -- just like when you work out in the gym.
Every study I've ever seen on this subject shows that good asthma control and breathing exercises can help prevent asthma, and thus prevent the need to work out your accessory muscles, and ultimately prevent the chest discomfort that comes with it.
In my next post I'll review some breathing exercises that should make breathing easier during an asthma attack, and also help you prevent asthma altogether.