The sequence of events in a cough reflex:
Inhalation to a high lung volume -> closure of the glottis -> contraction of the expiratory muscles (generating high positive intrathoracic pressure) -> opening of the glottis -> high velocity expulsion of air through the airways -> continued contraction of the expiratory muscles.
The diagram below shows the 4 stages in a cough reflex.
It is noteworthy to bare in mind that any conditions such as those causing weakness of the expiratory muscles, vocal cord pathology or tracheostomies causes impairment in the ability of the body to clear their airways effectively.
An occasional cough is normal as it helps clear foreign substances and secretions from the lungs and helps prevent infections.
Based on the type of we can generally classify cough into:
1.Dry cough - cough that does not bring up any sputum during expulsion
2.Productive cough - cough that brings up sputum or mucus during expulsion
Based on the duration of the cough it is generally accepted that a cough that lasts more than 3 weeks can be considered as chronic cough, although there are some quarters who feel that not every prolonged cough that last more than 3 weeks can be considered as chronic. I will not dig any deeper into it's technicalities in this post (Google it!). Let's try to see the possible causes of chronic cough as there has been a rise in such cases in our primary health care centers.
Among the common causes of chronic cough:
1. Postnasal drip caused by chronic rhinitis and sinusitis
Glands in your nose and throat produce a quart or two of mucus, which cleans and moisturizes our nasal passages. Normally, we swallow the fluid without knowing it, but in rhinitis, the cells lining the nasal passages becomes inflammed and swollen. It then start producing mucus in extensive amounts. The excess mucus then accumulates behind the nose and descend down the throat. This is called postnasal drip and can cause irritation and inflammation that triggers your cough reflex.
Patients with cough due to this condition will typically have frequent clearing of their throat during the day, will complain of cough when talking for prolonged periods of time or when laughing, and will often have worse cough when they first lie down at night.
If the postnasal drip is chronic, your cough is likely to become chronic, too. Though postnasal drip is often obvious, it's possible to have the condition without ever having symptoms.
Sinuses are air filled spaces situated in our skull. The main sinuses are :
Frontal sinus in the forehead, Ethmoid sinus between our eyes, Maxillary sinus in our cheek bones and Sphenoid sinus at the back of the nose.
Sinusitis, similar to rhinitis, is a condition where the cells lining the sinus gets inflammed, swollen and starts producing excessive mucus, which in turn descends down behind the throat, leading to post nasal drip.
There is also a condition called rhino sinusitis which is the combination of both the conditions above.
Common triggers of rhinitis sinusitis:
- Inhaled irritants such as dust, smog, smoke.
- Food allergies. Common food that causes allergy are nuts, eggs, wheat, milk and dairy products, soy products, seeds, sea food with shell, etc.
- Illnesses; Such as flu, colds, bronchitis, ear infections, tonsillitis and asthma
N.B: In asthma, not only does the excess mucus lead to an asthma attack, but it also causes a sufferer to start breathing through the mouth taking in non-filtered, non humidified and cold air. This in turn can trigger and worsens the asthma attack.
This is a common cause of chronic cough in adults and in children. The cough commonly occurs with wheezing and shortness of breath. The absence of wheezing on the other hand does not mean that the person is not having an asthma attack. There is a type of asthma, sometimes referred to as cough variant asthma, where cough is the only symptom. An asthma-related cough may be seasonal or caused by an upper respiratory tract infection, or exposure to cold air, chemicals or fragrances.
3. Gastroesophageal reflux disease (GERD)
Here there is a back flow of the stomach acid upwards along the esophagus that constantly causes irritation in the esophagus, throat and even the lungs that leads to chronic coughing, heartburn and sour taste behind the tongue. There is also cough that is caused by asymptomatic GERD.
Reflux of acid to the posterior pharynx may cause inflammation and edema of the vocal cords. In some cases, patients will have recurrent aspiration with a consequent low-grade chemical pneumonitis (inflammation of the lung tissue) in the lungs.Finally, GERD may lead to cough by provoking bronchospasm (narrowing of the bonchus, the main airway tube). Acid in the esophagus can induce bronchospasm in patients with asthma via reflex mechanism mediated by the vagus nerve.
4. Respiratory tract infection
A respiratory tract infection almost always cause inflammation of the cells that line the airways. This does to a certain extent make it sensitive to irritants, which in turn triggers a cough reflex.
Other not so common causes of chronic cough:
1. Blood pressure drugs
Chronic cough is a notorious side effect of a group of anti-hypertensive drugs (blood pressure drugs) known as Angiotensin-Converting Enzyme (ACE) inhibitors. This side effect is more apparent among the Asian population and can begin from within a week to even more than six months after starting therapy.
2. Chronic bronchitis
This is long-standing inflammation of the major airways (bronchial tubes) which can cause congestion, breathlessness, wheezing and a cough. This can be caused by infection or in chronic smokers who's airways have been damaged.
This is a serious, chronic lung condition in which abnormal widening of your bronchus affects their ability to clear mucus from your lungs. Signs and symptoms include a cough that may bring up discolored sputum or blood, shortness of breath and fatigue. In bronchiectasis, areas of the bronchial wall are destroyed and become chronically inflamed, ciliated cells are damaged or destroyed, and secretions (mucus) accumulate. Also, the bronchial wall becomes less elastic—the affected airways become wider and flabby and may develop outpouchings or sacs that resemble tiny balloons.
The most common cause of this condition is severe respiratory infections. Also can be caused by immune deficiency disorders, hereditary disorders (such as cystic fibrosis), mechanical factors (such as bronchial obstruction caused by an inhaled object, a lung tumor, or other disorders) and from inhaling toxic substances that injure the bronchi, such as noxious fumes, gases, smoke (including tobacco smoke), and injurious dust (silica, coal dust).
4. Lung cancer
This is relatively uncommon. Only a small percentage of people with a chronic cough have lung cancer, and most are current or former smokers. If you smoke now, smoked at one time or your sputum contains blood, see your doctor.