About Dyspnea - Definition, Pathophysiology and Types of Dyspnea

Dyspnea is an upleasant subjective complaint involving the patient's perception of breathing difficulty or discomfort. Dyspnea :Breathlessness; shortness of breath; the sensation of difficult, labored, or uncomfortable breathing.

Dyspnea may refer to a single sensation caused by a single mechanism or to several sensations combined in the one term. The following are probably different sensations:
  • The profound hyperpnea that occurs during and after severe exercise.
  • The sensation arising from bronchial or bronchiolar obstruction in patients with asthma and bronchitis.
  • The breathlessness that may occur with inappropriately slight exertion in patients with heart disease or severe anemia
  • The sensation that compels breathing after breath holding
The amount of ventilation and the sensation of dyspnea are influenced by the affect of arterial hypoxia on the carotid and aortic bodies and of CO2 on the respiratory centers in the medulla (visceral, neural and emotional stimuli may also involved). No single mechanism explains all instances of dyspnea, but some useful relationships have emerged. Dyspnea depends on the amount of ventilation required by the individual's physiologic state (resting, exercising, hypercapnic) and on the capacity of his lungs and thorax to deliver this ventilation efficiently. The amount of ventilation required may be less than 5 L/min at rest and more than 100 L/min after severe exercise, a trained athlete may be able to exceed 200 L/min.

Types of Dyspnea
  • Nocturnal Dyspnea, occurs only at night and may be paroxysmal as in patients with heart failure.
  • Orthopnea, occurs when a patient liesdown as in cases with heart failure, asthma and chronic obstructive disease of the lungs.
  • Trepopnea, breathlessness only in the left or right lateral lying position. This does not occur When a patient is In the supine position. This occurs in patients with heart disease.
  • Platypnea, occurs only in the upright position.

Assessment of dyspnea
The treatment of shortness of breath depends upon the cause, so there are some necessary tests. A chest X-ray to look for fluid, infection, tumor, or collapse of the lung will always be done. 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 by checking the oxygen saturation in the venous blood with a clothes-peg-like apparatus worn on the finger.

If an accurate measure of oxygen in the arterial blood is needed, (for example, if a blood clot in the lung, called pulmonary embolus, is suspected) then 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 radioactive 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 tumors in the lung, infection, collections of fluid secondary to tumors, or chronic lung or heart damage, the cause of the shortness of breath is often known and exhaustive tests are not necessary.


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