Dyspnoea

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Dyspnoea is the medical term for feeling short of breath - also referred to as "shortness of breath", "breathlessness" (or simply "being breathless"), or occasionally as "Air hunger". It is a feeling of excess effort in breathing, or of being short of air.

The sensation is common, and not pathological in exercise, however undue shortness of breath on exertion (SOBOE) or at rest is distressing and remarkable.

It can be a distressing symptom of disease. To understand why, one needs to understand how breathing is regulated.

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dys- +‎ -pnoea, from Latin dyspnoea, derived from Greek δύσπνοια (dúspnoia, “bad breathing”), compound of δυσ- (dus-, “bad, unfortunate”) and πνοή (pnoḗ, “breeze”).)

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Regulation of breathing

We are all very familiar with the way that at rest - particularly during sleep, the breathing is relatively slow and shallow, whereas during vigorous exercise, when oxygen requirements increase, the rate and depth of breathing increases.

We do not have to think about this - we do it subconsciously, driven by the respiratory centre in the brain. The drive to breathe uses a feedback loop, which automatically regulates our breathing.

One might imagine that the driver would be oxygen levels. Normally, however - in healthy people - the main driver is actually carbon dioxide levels. When we exercise, we metabolise oxygen - it combines with carbon and hydrogen atoms to form water and carbon dioxide - just as when organic matter is burned, but in a much more controlled way. The carbon dioxide is in solution in the blood stream, as carbonic acid, so it reduces the pH of the bloodstream; and this is detected by chemoreceptors which feed back to the respiratory centre. Reduced oxygen levels ("hypoxia" are more commonly a significant driver for respiration in people with respiratory illness who have persistently raised carbon dioxide levels ("hypercapnia"). Psychology also affects breathing via the autonomic nervous system; this can result in hyperventilation.

Things which increase the respiratory drive

Anything that increases the respiratory drive will increase the respiratory rate and, if the respiratory rate cannot be increased sufficiently, can cause dyspnoea.

Broadly, these things can be categorised as follows:

  • Things which increase the demand for oxygen, such as exercise, increased body temperature, increased metabolic rate.
  • Decreased ability to oxygenate the blood as it passes through the lungs - which can relate to
  • decreased efficacy of each alveolus;
  • having part or parts of the lungs which air cannot reach, but which are being perfused with deoxygenated blood. When this blood returns via the pulmonary artery, it mixes with oxygenated blood, and decreases the overall oxygen saturation of the arterial bloodstream. (See also Oxygen saturation, Oxygen delivery.
Decreased ability to provide oxygenated blood to the tissues (especially the brain), often a consequence of heart failure (inability to pump hard enough).

Medical causes of dyspnoea

  • insidious breathlessness and monophonic wheeze if there is lobe collapse; or
  • an enlarging pleural effusion.

Dyspnoea and end of life care

Towards the end of life, dyspnoea can be a very distressing symptom. While there may be underlying pathological or physiological causes of the symptom, there can also be a strong psychological component; and, regardless of the cause, reducing symptoms and distress is an important part of medical care, particularly when no treatment of the underlying condition can be offered.[1][2]

References