Like most automatic processes in the body, we usually don’t give our respiratory system much thought until something goes wrong. Feeling out of breath after a tough workout is one thing, but you should seek medical attention if you experience lasting breathing troubles or sudden, severe shortness of breath. The average human can live around three weeks without food and three days without water, but just three minutes without air can lead to brain damage and death. Serious lung diseases like chronic obstructive pulmonary disease (COPD) or pulmonary arterial hypertension (PAH) often lead to respiratory problems, but the lungs aren’t always to blame. The immune system, the heart and the brain can also contribute to breathing difficulties. Here are some conditions that can impede the ability to breath freely.