It is suggested you make yourself familiar with how the lungs are constructed and work

We understand the NTM bacteria inflame the cell wall of the small airways in your lung. The lung reacts by producing mucus. Over time the inflammation causes changes in the airway cell structure. These changes make the cell wall stiffer and the airways gets bigger. The muscles that inflate your lungs and allow you to inhale air, then need more force to work.  If there is a lot of mucus in the airways, breathing becomes even more difficult.

The mechanism used to pass Oxygen in the air you breath into your blood and exhale the waste Carbon Dioxide is largely unaffected by the bacteria. Even though you may find breathing difficult. It is unusual for the blood oxygen level measured from your finger (Oximeter) to show a level below 90% when supplementary oxygen is desirable. Using supplementary Oxygen when the Oxygen concentration is above 90% may cause other problems in the body.

If you find you are close to not breathing at all, but your Oxygen concentration is above 90 %, try to relax as much as you can, and go to hospital immediately.  Sometimes  Emergency doctors can think you have an Asthma attack. This is unlikely to be true, it is more likely that your main airways are blocked with mucus. In extreme cases, you will need very urgent help.

Click on How the Lungs work to learn more.

More information about the respiratory system  can be found in the text book”Human Anatomy & Physiology., by Marieb & Hoenn. This text is very easy to read in a language most of us can understand. Second hand copies are readily available on Gum Tree