Asthma pathophysiology and types

Asthma is a chronic inflammatory disorder causes due to immune responses leads to swelling and narrowing of airways causes wheezing, shortness of breath, chest tightness and coughing particularly at night or in early morning. It can be classified according to sign and symptoms, severity, forced expiration volume in 1 second (FEV1) and peak expiration flow rate.

Pathogenesis of Asthma

It is an immunological disorder causes reversible air flow obstruction. Pathogenesis of this disorder can be divided into three steps.
1. Stimuli from external stimulus: Stimuli can be given by the following types-
a) Allergens (dust)
b) Medication: aspirin, penicillin
c) Exercise
d) Hormonal changes
All these are the stimulus which starts the immune responses leads to the development of Th-2 lymphocytes predominant immune response associated with atrophy lead to IgE-mediated inflammation. T-helper cells like cytokines participate to contribute inflammation of airways lead to hyperactive responses of IgE.
2. Bronchoconstriction: During asthma airways tract react with allergens produces mucus in large amount leads to difficulty in breath
3. Bronchial inflammation: After the immune response occurs mucus producing cells grow large and produces more mucus as cell mediated arm of immune system is activated and airways become highly inflamed.
Acetylcholine is the parasympathetic immunomodulator present in the smooth muscles of airways control the bronchoconstriction and production of mucus when this process get highly activated lead to asthma. Vagal tone is increased in the airways inflammation associated with asthma leads to exaggerated acetylcholine release. Acetylcholine controls this whole process by acting on muscrinic receptors m2 and m3. When parasympathetic activity increased in airways lead to inflammation so anticholinegic therapy is used which acts as bronchodilators.

Types of Asthma

We can classify asthma in different order which keep you in different category which helps the doctors to prescribe you different treatment depending on the category type.

1) Depending on the participation of allergens, asthma is divided into following types-
A. Atropic (Extrinsic) asthma
B. Non-atropic (intrinsic) A.

Atropic asthma

This type of asthma is also known as allergic asthma may be due to the continues exposure to allergens like smoke, dust mites, mold, animal dander and is mainly occur due to the immune responses.

Non-atropic asthma

In this type of asthma there is not any involvement of allergens but may be due to other reasons. Depending on this it is of various types:
a) Cough variant asthma: In this type of asthma there is involvement of cough allergens with other symptoms of asthma.
b) Occupational asthma: This kind of asthma affects the people working in the area of high pollution due to the shortness of breath.
c) Exercise induced asthma: It is due to the condition of bronchoconstriction during the exercise.
d) Nocturnal asthma: amount of breath inhaled by a person is measured in FEV1Which is decreased by at least 15% from bed time includes the other symptoms of asthma which may disrupt the sleep and may wake up you from sleep.
e) Steroid resistant asthma: Peoples who regularly inhaled glcocorticoids may become unresponsive to that normal dose include other symptoms.
f) Health condition mimic asthma: Asthma may leads to other problems included cardiac arrhythmia, vocal cord dysfunction.
g) Child hood asthma: It is occur in children due to the hormonal changes.
h) Adult orient asthma: it is occur after the age of 20 more in women as compare to men due to plastic, pollution, mites.
i) Bronchial asthma: difficulty in breathing and wheezing, mucus of airways become narrow, thick mucus produced which causes irritation.

2. Classification of asthma based on severity:
A. Intermittent( moderate asthma)
B. Mild persistent( acute asthma)
C. Severe persistent( life threatening)

Mast cell stabilizers used in the treatment of asthma

Mast cell stabilizers are also becoming popular in the treatment of asthma. They act by inhibiting the release of mediators such as histamine from the mast cells and hence prevent the asthma attack. This over secretion of mediators from the mast cells is one of the chief reasons of asthma.

Individual mast cell stabilisers for asthma

1. Sodium Cromoglycate (Cromolyn Sodium) - Sodium cromoglycate is the first drug used in this class. Cromolyn sodium is synthetic derivative of chromone. It acts by preventing the release of asthmatic mediators like histamine, leukotrienes, interleukins, PAF etc. from mast cells.

Sodium cromoglycate does not affect the antigen-antibody reaction and hence it has no effect if used at the time of asthmatic attack. Sodium cromoglycate is effective in the prevention of bronchospasm caused by any reason. However, long term use of Sodium cromoglycate decreases the response of inflammatory cells.

Sodium cromoglycate is orally ineffective drug and so most preferably it is administered as aerosol preparation. Sodium cromoglycate is used in the treatment of bronchial asthma, allergic rhinitis and allergic conjunctivitis.

The main adverse effects of Sodium cromoglycate include bronchospasm, throat irritation and cough can occur in some patients. Rare side effects are nasal congestion, headache, dizziness, arthralgia, rashes and dysuria.

2. Nedocromil Sodium – Nedocromil Sodium is another chromone derivative which is almost similar in action to the cromoglycate. The only difference with the Sodium cromoglycate is that it is more potent than the same and hence requires lesser dose.

3. Ketotifen – This is the only orally active mast cell stabilizer. Primarily this drug is antihistaminic (H1) and slightly cromoglycate type activity. Ketotifen chemically is non chromone derivative and primarily used for the prophylaxis of asthma.
The main side effects of ketotifen include sedation, dry mouth, dizziness, nausea, weight gain etc.

Note- This article is written for the purpose of providing you the basic knowledge of the topic and should not be taken as for prescription.

Other suggested readings for the treatment of asthma-
1. Treatment of asthma by sympathomimetic drugs.

2.Herbal drugs used for the treatment asthma