It is important to understand how breathing is “supposed” to work in healthy lungs in order to appreciate how it affects people with COPD.
People usually breathe without thinking about it. When you breathe in, air goes in via your nose or mouth, down the back of your throat, down the windpipe (trachea), splits into the two large airways (bronchi), into the smaller airways to the air sacs (alveoli) where oxygen in the air is passed into the bloodstream. Carbon dioxide is passed from the bloodstream into the air in your lungs. The air then travels the reverse pathway as you breathe out.
This video explains how breathing works:
Muscles Used In Breathing
Air doesn’t pass in and out on its own; muscles in the chest ensure this happens. The main muscles of breathing are the diaphragm and the intercostal muscles. The other muscles which can play a part are known as the accessory muscles.
This muscle is responsible for approximately 60 – 80 % of the air that enters the lungs during quiet (resting) breathing.
The diaphragm is a dome shaped layer of muscle that separates the chest cavity from the abdominal cavity. The diaphragm is a bit like the heart muscle in that it does not tire, contracting and relaxing without ‘effort’.
Here is a video showing the diaphragm at work:
The Intercostal Muscles
This group of muscles are found between the ribs and form the chest wall. They help to lift the rib cage up and out during breathing in to allow the lungs to expand. They work harder when we need to exert ourselves to help allow more air into the lungs.
On exertion, when extra oxygen is required, other muscles of the neck, spine and abdomen are also used. They are only used when we are exercising quite hard or during fight / flight responses and they tire quickly.
What Happens When You Breathe In (Inhalation)
As you breathe in, or inhale, the diaphragm tightens (contracts) and moves downward. The intercostal muscles also contract pulling your rib cage upwards and outwards. Both of these muscle activities cause an increase in the space in your chest cavity (thorax). This results in a lower air pressure and the lungs expand to fill the space. As your lungs expand, air is pulled in through your nose or mouth to equalise the pressure.
What Happens When You Breathe Out (Exhalation)
Exhaling is, obviously, the opposite: The diaphragm relaxes, moves upwards to its relaxed curved state, and the air pressure in the chest cavity (thorax) therefore increases (because there is now less air space). The lungs deflate and air passes out of your mouth and nose. It is important to remember that there are no muscles working when we breathe out normally. Exhalation is a completely passive action.
How Breathing Changes with COPD
Due to the physical changes to the lungs with COPD (as discussed in the earlier chapter), the mechanics of breathing (how breathing works) can change quite dramatically.
Airflow obstruction and inflammation causes increased resistance to the movement of air in and out of the lungs. This means it is harder to breathe in and out. People without COPD can get an understanding of what this feels like by breathing through a straw for a while. It is not pleasant!
Over-inflation (hyperinflation) is another major cause of breathlessness. Air becomes ‘trapped’ in the lungs (not expelled fully with each breath out). When you are unable to breathe out fully, it makes it much harder to take the next breath in. This can lead to a shortened, ‘flattened’ diaphragm which is then at a mechanical disadvantage, and is unable to work as efficiently as normal. To compensate the intercostal muscles (those between the ribs) have to work harder and they use much more energy than the diaphragm. Breathing out is no longer a passive process and thus uses a lot more energy.
Accessory Muscles need to assist with the breath in in some situations, and this uses even more energy.
Clearing Sputum from their lungs is also a problem that some people experience, or they just produce huge volumes of sputum which makes it difficult to clear. This can also cause more difficulty with breathing. We talk about methods for Clearing Sputum on page 39. LINK NEEDED HERE
All of the above means that people with COPD tend to adopt a shallow ‘upper chest’ breathing pattern, and they are unable to fully expel all the air with each breath out. The intercostal muscles and accessory muscles work overtime and demand a lot of oxygen to do so and the end result leaves you feeling tired and breathless.
As people with COPD tend to use more energy just to breathe it can mean that other previously simple tasks can become extremely difficult due to breathlessness and tiredness. They can then begin to start avoiding doing exercise or heavy tasks because the feeling of breathlessness is unpleasant or frightening. In turn this leads to a reduction in fitness, and then further breathlessness on exertion.All this can seem quite depressing; it may feel that there is no way back. However with the help of healthcare professionals within a pulmonary rehabilitation programme, improvements can be gained in breathing whilst at rest and with exertion. If you have recognised the symptoms in the diagram above ensure you discuss with your doctor or nurse about attending pulmonary rehabilitation.
Adapted from Global Initiative for Chronic Obstructive Lung Disease (GOLD). Global Strategy for the Diagnosis,
Management and Prevention of COPD, 2010. Available at: http://www.goldcopd.org.