The term dyspnoea describes the feeling of difficulty with breathing, often described  as feeling short of breath.

There are various types of dyspnoea, described by the situation that led to it:

• Exertional dyspnoea refers to shortness of breath when doing a physical activity, such as walking or running
• Paroxysmal nocturnal dyspnoea refers to shortness of breath waking people up at night in sudden episodes
• Orthopnoea refers to shortness of breath that is worse on lying flat
• Trepopnoea refers to shortness of breath that is worse on one side compared with the other

There are many causes of dyspnoea, most commonly related to how the body gets oxygen:

1. The lungs, which oxygenate the blood
2. The heart, which lumps oxygenated blood around the body
3. The blood, which carries the oxygen itself

To investigate these causes, doctors order several tests:

• A chest X-ray
• A CT scan
• An echocardiogram
• An arterial blood gas
• An ECG
• Lung function tests (also called respiratory function tests)
• A right heart catheter (sometimes with exercise)
• A stress test