Any physical activity increases the body’s metabolic rate. There is a greater demand for oxygenation and when the existing depth and rate of breathing is insufficient for the body’s needs, it will subsequently rise to compensate accordingly. It is normal to be out of breath after a strenuous activity, like running or swimming. However, the level of activity should correlate with the degree of breathlessness. Within minutes the body’s mechanisms to restore oxygen and carbon dioxide levels are sufficient and the breathlessness eases with a short rest.
People who are less active are more likely to be short of breath with even mild activity. Despite this, the body rapidly compensates and the breathlessness resolves. However, in some cases there is breathlessness that does not correlate to the level of activity. Even simple activities like walking, picking up an object or sometimes just standing for a short periods leads to breathlessness. This is known as exertional dyspnea.
In these cases, not only is there breathlessness but the ability to compensate is often delayed and a person finds difficulty in breathing as the oxygen and carbon dioxide levels are not returned to normal at a fast enough rate. The shortage of oxygen and excess of carbon dioxide leads to a sensation of air hunger. Dizziness and sometimes even blurry vision may be evident as the brain cannot tolerate this prolonged period of diminished oxygen levels and function normally.
What is chronic exertional dyspnea?
Chronic exertional dyspnea is breathlessness even with moderate activity. As explained above, it does not correlate with the level of activity and the oxygen and carbon dioxide levels take longer than normal to return to pre-activity levels. Regulating the blood gas levels is not the function of the lungs alone. Gas exchange occurs in the lungs but several other systems play as well. The heart and blood vessels (cardiovascular system) are responsible for carrying deoxygenated blood to the heart and circulating oxygenated blood throughout the body. The nervous system as a whole regulates the breathing rate and depth, heart rate and even the diameter of the blood vessels in response to changing gas levels. Even the kidneys, bone marrow and nutritional state can all contribute to the oxygen-carrying capacity of the blood and therefore impacts on breathing.
Oxygen utilization and carbon dioxide production may increase as much as 20-fold during strenuous exercise. As the oxygen is utilized the respiratory rate increases in proportion in a healthy person. The respiration rate actually starts increasing the moment exercise commences even before the oxygen levels fall and carbon dioxide levels increase. This response ensures that there is a constant and increased oxygen supply during activity which is controlled by the respiratory center in the brain. Even in moderate exercise where a person has not reached their activity threshold and discontinued activity due to choice, the ventilation rate remains elevated for a short while afterwards. It is still unclear whether the respiratory centers response to exercise even before the oxygen levels drop is a learned response or due to some neurogenic or hormonal stimulus that arises with increased muscle activity. However, in a person with chronic exertional dyspnea, these ventilatory responses are not as synchronized.
Causes of Chronic Exertional Dyspnea
Most of the causes of chronic exertional dyspnes are related to pathology in the lungs and/or heart and blood vessels. However, it may occur with obesity and in a very sedentary person. It it important to note whether the dyspnea has remained constant over a period of time, is gradually progressing or rapidly progressing. Some of the main causes of chronic exertional dyspnea are discussed below.
Chronic Heart Failure
Chronic heart failure is the inability of the heart to pump sufficient blood to meet the needs of the body. It may be associated with a heart attack (myocardial infarction), heart valve defects, high blood pressure (hypertension), heart muscle disease (cardiomyopathy), irregular heart rhythm and thyroid problems.
Ischemic heart disease
Ischemic heart disease (IHD) is when there is an inadequate blood suppy to the heart muscle leading to injury of the muscle. Coronary artery disease is one of the most common causes of ischemic heart disease. It may initially present as angine (ischemic cardiac pain) and eventually progress to heart failure or even lead to a heart attack.
Chronic obstructive pulmonary disease
Chronic obstructive pulmonary disease (COPD) is a progressive disease of the terminal airways and/or air sacs of the lungs. Air flow and oxygenation of the blood is impaired. COPD is most commonly seen with tobacco smoking and environmental or occupational exposure to dust and gases.
Asthma is a condition associated with hyper-responsive airways that leads to attacks of airway narrowing which is reversible. It is one of the most common causes of chronic exertional dyspnea. Asthma usually starts from childhood and most cases are allergic in nature.
Interstitial lung disease
Interstitial lung diseases are a broad group of lung disease usually associated with chronic inflammation that eventually leads to progressive scarring of the lung tissue. This may include sarcoidosis, fibrosing alveolitis, extrinsic allergic alveolitis and pneumoconiosis.
A pleural effusion is the accumulation of fluid around the lungs in the pleural spaces. Small effusions are unlikely to cause prominent dyspnea. A pleural effusion may be due to a number of different causes without actual pathology of the lung.
- Bronchial carcinoma
- Severe anemia
- Pulmonary embolism