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- What causes coughing and breathlessness?
Having a cough is a very common symptom of the frequent colds and upper respiratory infections that we are all prone to. It is also normal to feel breathless when running or climbing stairs. But coughing and breathlessness that occur without explanation, or that persist for weeks or months, may indicate a more serious lung problem that requires investigation and treatment.
Whatever the cause of coughing and breathlessness, the actual mechanisms that bring about these potentially distressing symptoms are quite well understood.
What is a cough?
A cough is a complex reflex action that is a response to an irritation in the airways. This irritation can occur anywhere from the pharynx (throat) to deep within the lungs. This then sets off a sequence of events that ends with a cough:
- The sensations of irritation are picked up by receptors in the airways and relayed to the ‘cough centre’ in the brain stem
- From here, nerve impulses pass to the intercostal muscles, diaphragm and throat, which all contract in a coordinated sequence
- First there is an inhalation followed by a powerful exhalation against a closed glottis (throat valve)
- The cough reflex then expels air from the lungs with such force that any mucus within the airways is forced out at the same time.
Types of cough
There are many different types of cough, depending on the underlying cause. A dry cough usually accompanies an upper respiratory tract viral infection. A deeper productive cough, often described as a hacking cough, may indicate a lung infection, and mucus will be coughed up into the mouth. If this mucus, then called sputum, is clear or white, it is likely that the infection is viral. Green sputum or dark yellow sputum is usually a sign of a bacterial lung infection.
Coughing can also be classified according to time span:
- An acute cough is one that lasts anything up to three weeks
- A sub-acute cough lasts longer than three weeks but clears up before eight weeks
- A chronic cough is one that persists for more than eight weeks.
Generally, acute and sub-acute coughs are caused by short-term conditions such as viral lung infections while a chronic cough may occur with chronic lung diseases such as emphysema, chronic obstructive pulmonary disease (COPD) and chronic bronchitis.
Common causes of coughing
Coughing is usually caused by irritated and therefore inflamed airways, which can develop for many different reasons:
- Postnasal drip: when excessive mucus produced by the nasal passages drips down the back of the throat.This often happens during a common cold or as a result of an allergic reaction such as hay fever
- Asthma: narrowing and inflammation of the airways in response to allergens or other environmental factors, collectively known as triggers
- Bronchitis: a chronic inflammation of the airways, usually due to smoking
- Pneumonia: a condition caused by infection in which the airways become inflamed and the air sacs begin to accumulate fluid (known as consolidation)
- Lung infection: bacterial infections cause a characteristic yellow/grey/green sputum to be coughed up
- Chronic obstructive pulmonary disease (COPD): a combination of bronchitis and emphysema
- Gastroesophageal reflux syndrome (GERD): this is severe heartburn due to stomach acid escaping up into the oesophagus and rising to the throat, causing enough irritation to stimulate the cough reflex
- Environmental pollution: breathing in dust particles less than ten microns across (one hundredth of a millimetre) can cause coughing. Smoke inhalation is a good example.
Other causes of coughing include whooping cough, tuberculosis, cystic fibrosis, inhaled foreign bodies (pieces of food, children’s toys), lung cancer and sarcoidosis; coughing is also a side effect of some medications such as ACE inhibitors.
What is breathlessness?
A feeling of being ‘short of breath’ is known medically as dyspnea. It occurs when not enough oxygen is delivered from the alveoli into the blood. Chemoreceptors in the body detect this and send signals to the brain to stimulate a faster breathing rate and also deeper breaths.
Most of us experience this after some degree of exertion, such as climbing a flight of stairs or running for a bus, and certainly during exercise. But when someone feels short of breath even when just walking gently, or when sitting down, it is a clear sign that the airways are not functioning as efficiently as possible and that some underlying condition is causing the problem.
Common causes of breathlessness
The underlying cause of breathlessness is always a lack of oxygen in the blood. This may be because the lungs have become less efficient at gas exchange, or because the circulation has become less efficient at moving blood between the lungs and the tissues. Conditions that impair gas exchange include:
- Emphysema: a long-term degeneration of the lung tissue in which the delicate alveolar walls break down and are replaced by tougher scar tissue. The lungs become much less efficient at gas exchange
- Bronchitis: inflammation of the bronchi, the larger airways that lead into each lung
- Asthma: irritation of the airways caused by an oversensitivity to common triggers
- COPD: chronic damage to the lungs that leaves less capacity for gas exchange
- Pneumonia: the alveoli become filled with fluid
- Pulmonary embolism: a blood clot in the lungs
- Pneumothorax: a collapsed lung due to blunt or sharp trauma (car accident, stab wound)
- Lung fibrosis: lung damage that can occur due to chronic disease, chemotherapy or radiation damage
- An upper respiratory tract infection: caused most often by a virus, but secondary infection with bacteria is then possible. When severe, this can lead to breathlessness
- Heart disease: irregular heartbeats or a heart attack can lead to sudden attacks of breathlessness. Heart failure also causes fluid to accumulate in the lungs, leading to chronic breathing problems
- Lung problems: tumours in the lungs and lymph nodes can seriously affect lung function.
Other causes include anaphylaxis (severe allergic reaction), cardiac tamponade (blood in the membrane that surrounds the heart) and even the simple panic attack.
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