Normal breathing is a mechanical process in which chest muscles around the lungs and the diaphragm pull air into the lungs and force it back out of the lungs. Breathing is a critical component of respiration, a process in which oxygen from the air is taken into the body and carbon dioxide is removed from the body and released into the air.

Common trouble breathing includes:

• Crackles, a bubbling, crackling or clicking sound made in the lower airways of the lungs.
• Crackles can be caused by pneumonia, pulmonary edema, pulmonary fibrosis, and acute bronchitis.
• Shortness of breath or trouble catching your breath with or without exertion
• Stridor, a high-pitched sound made during breathing, often caused by some kind of blockage in the throat. Stridor can be caused by epiglottitis, smoke inhalation, swelling of the throat, tonsils or adenoids, or choking on a foreign object, such as a bone.
• Wheezing, a whistling sound made by narrowing of the air passages in the lungs. Wheezing can be caused by asthma, anaphylactic reaction, chronic obstructive pulmonary disease (COPD), acute bronchitis, bronchiolitis, heart failure, or pneumonia.

Depending on the cause, breathing difficulties can be brief and disappear quickly, such as with hyperventilation. Breathing difficulties can occur in sudden, severe Asthma episodes, such as breathing difficulties that occur during sleep apnea or asthma. Breathing difficulties can also be chronic and ongoing over a long period of time, such as with Asthma, COPD or lung cancer. 

Breathing difficulties can occur as a symptom of diseases, disorders and conditions of the respiratory system, as well as other body systems. Breathing difficulties can also be caused by diseases and conditions of body systems other than the respiratory system. For example, in the cardiovascular system, breathing difficulties can be a symptom of congestive heart failure or heart attack.

Complications of breathing difficulties include:

• Hypoxia (low oxygen levels).
• acidosis.
• arrest and cardiopulmonary arrest in sudden Asthma attack.
• failure due to severe Asthma attacks.