Pneumothorax is when air accumulates between the lung and chest wall, causing the lung to collapse. This can be caused by trauma or underlying medical conditions such as COPD and can also occur spontaneously without any underlying disease. Increased air inside the chest cavity can cause an increase in pressure that pushes against the heart and lungs, reducing blood flow throughout your body. This is a sign of tension pneumothorax. It typically requires immediate medical attention as it can be life-threatening if left untreated.