Shortness of breath, known also by its medical term "dyspnea," is described as an uncomfortable awareness of breathing. It is a common symptom in advanced cancer, especially if the cancer involves the lung. It is also the major symptom of chronic lung disease and congestive heart failure (a chronic heart condition).

Dyspnea can cause a lot of discomfort and suffering. However, shortness of breath, like pain, is a subjective symptom, meaning it cannot be measured like a fever or high blood pressure. It is possible to measure how fast someone is breathing, with normal breathing considered to be 14 to 16 breaths per minute. But even if a person is found to be breathing very rapidly, they may not feel short of breath. Similarly, a person with lung cancer may be breathing at a normal rate, but when asked, they could feel very short of breath. A useful way to measure shortness of breath is to use a visual analog scale just as you can do for pain, where a "1" equals no shortness of breath and a "10" represents the most severe shortness of breath.

If your doctor or health care team does not ask you about shortness of breath, be sure to tell them. It is also useful for the doctor to know if your dyspnea has come on gradually or suddenly and what makes it worse. Any other symptoms that are associated with the dyspnea such as cough, mucus production, or pain should also be reported.

Shortness of breath, like pain, is a complex symptom affected by physical, psychological, and social factors. Environment, for example, can affect the perception of shortness of breath. Being in a small room with many people and no obvious air circulation will intensify the feeling of dyspnea. Anxiety is a natural reaction to breathlessness. If there is preexisting anxiety, even if it's not related to the shortness of breath, it will make the perception of breathlessness worse.

Shortness of breath has a dramatic effect on quality of life. With severe dyspnea, a person will become completely out of breath by walking a few feet to the bathroom. Eating a meal becomes a chore, dressing is an exhausting experience, housework is impossible, and going out of the house is an experience of the past. The worst shortness of breath occurs when every breath is uncomfortable and a full sentence cannot be spoken.

The causes of dyspnea are mainly physical and fall into 3 categories.

The first category is when lung tissue is damaged by smoking, recurrent infection, cancer, or other diseases, and cannot exchange oxygen and carbon dioxide with the blood as well as it should. In consequence, breathing becomes more work. Causes for this included:

  • cancer in the lung
  • infection (e.g., pneumonia)
  • fluid between lung and its lining (pleural effusion)
  • chronic lung damage (chronic bronchitis, emphysema)
  • asthma
  • collapse of lung
  • blood clot (pulmonary embolism)
  • damage from radiation treatment for cancer
  • damage from chemotherapy treatment for cancer

The second category involves breathlessness due to weak breathing muscles, which occurs as a result of diseases like ALS (Lou Gehrig's disease) or advanced cancer. In these instances the lung cannot expand properly. Causes include:

  • long-term illness and fatigue
  • neuromuscular diseases such as ALS

The third category is when abnormal processes in the body, such as anemia or a failing heart, cause the lungs to work harder in an effort to supply enough oxygen to the body. Hyperventilation, secondary to anxiety and panic, is also a cause of dyspnea.

Assessment of dyspnea

Your doctor will perform a complete physical examination and will ask you questions about your shortness of breath. Taking into account your medical history, your doctor may suspect certain causes of shortness of breath and will perform tests to narrow down and find the cause. You may have a chest X-ray to look for fluid, infection, tumour, or collapse of the lung. Often the blood is checked for anemia or infection. If the heart is suspected of being a contributing cause, an electrocardiogram may be done.

Measuring the level of oxygen in the blood is a way of determining how effectively the lungs are working. This can be done simply using a clothes-peg-like device worn on the finger. If a more accurate measure of oxygen in the arterial blood is needed, a sample of blood is taken from the artery in the wrist.

If the cause of the dyspnea is not obvious from these tests, breathing assessment tests, called pulmonary function tests, or special scans looking for blood clots in the lung may need to be done. If a collection of fluid between the lung and the ribcage (pleural effusion) is seen, a sample of the fluid may be useful in looking for the reason why the fluid has collected. In palliative care, where the common causes of shortness of breath are tumours in the lung, infection, collections of fluid due to tumours, or chronic lung or heart damage, the cause of the shortness of breath is often known and exhaustive tests are not necessary.

Romayne Gallagher, MD 
in association with the MediResource Clinical Team