ASTHMA

Asthma is a syndrome characterized by airflow obstruction that varies markedly, both spontaneously and with treatment. It is a major non-communicable disease, affecting both children and adults. It affected an estimated 262 million people in 2019 and caused 461000 deaths. It is the most common chronic disease among children. 

CAUSES AND RISK FACTORS:

Asthma develops due to interaction between various host and environmental factors. 

The host factors are:

Atopy (Type-1 hypersensitivity): Atopy is the major risk factor for asthma, and nonatopic individuals have a very low risk of developing asthma. Atopy is due to the genetically determined production of specific IgE antibodies, with many patients showing a family history of allergic diseases.

The environmental factors include:

1) Allergens (Airborne) 

2) Chemical 

3) Irritants

4) Viral Upper Respiratory Infections

5) Physical Stress

6) Emotional Stress

7) Air pollution

8) Occupational Asthma

9) Tobacco

The risk factors include - 

1) Improper diet:. Observational studies have shown that diets low in antioxidants such as vitamin C and vitamin A, magnesium, selenium, and omega-3 polyunsaturated fats (fish oil) or high in sodium and omega-6 polyunsaturated fats are associated with an increased risk of asthma.

2) Obesity: Asthma occurs more frequently in obese people (body mass index >30 kg/m2 ) and is often more difficult to control. Although mechanical factors may contribute, they may also be linked to the pro-inflammatory adipokines and reduced anti-inflammatory adipokines that are released from fat stores. 

CLASSIFICATION OF ASTHMA:

Asthma is of 2 types - extrinsic (immune) and intrinsic (non-immune).

Extrinsic asthma:

It is IgE mediated (Type -1 ) Hypersensitivity and usually begins in childhood. The most common causes are environmental allergens - dust, pollen, food, etc. Patients often have a family history of allergy or associated allergies.

Intrinsic Asthma:

It is a non-immune mechanism and usually occurs in adults. The most common causes are - respiratory tract infections and viruses. The family history of allergy or associated allergies is significant.

PATHOGENESIS:

In acute asthma, type-1 hypersensitivity reaction is evident. Due to atopy, by exposure to allergens, there is mast-cell degranulation, which leads to the release of histamine, leukotrienes, and PGD2. Also, the stimulation of CD4+TH2 subset cells, leads to the release of IL - 13, causing an increase in IgE, and also the increased secretion of mucus. 

In chronic asthma, type-4 hypersensitivity reaction is evident. Persistent airway inflammation leads to airway remodeling and continuous, non-responsive airway obstruction. It involves CD4+TH2, macrophages, and eosinophils, which stimulate the release of leukotrienes and these leukotrienes cause bronchoconstriction, epithelial damage, and chronic, irreversible airway disease.

DIAGNOSIS:

The diagnosis of asthma is usually apparent from the symptoms of variable and intermittent airways obstruction but must be confirmed by objective measurements of lung function.

LUNG FUNCTION TEST:

Simple spirometry confirms airflow limitation with a reduced FEV1, FEV1 /FVC ratio, and PEF.

whole-body plethysmography shows increased airway resistance and may show increased total lung capacity and residual volume. Gas diffusion is usually normal, but there may be a small increase in gas transfer in some patients.

AIRWAY RESPONSIVENESS:

The increased AHR is normally measured by methacholine or histamine challenge with the calculation of the provocative concentration that reduces FEV1 by 20% (PC20). Allergen challenge is rarely necessary and should only be undertaken by a specialist if specific occupational agents are to be identified.

HEMATOLOGIC TESTS:

Blood tests are not usually helpful. Total serum IgE and specific IgE to inhaled allergens (radioallergosorbent test [RAST]) may be measured in some patients.

IMAGING:

Chest roentgenography is usually normal but in more severe patients may show hyperinflated lungs. In exacerbations, there may be evidence of a pneumothorax. High-resolution computed tomography (CT) may show areas of bronchiectasis in patients with severe asthma, and there may be thickening of the bronchial walls, but these changes are not diagnostic of asthma.

SKIN TESTS:

Skin prick tests to common inhalant allergens (house dust mite, cat fur, grass pollen) are positive in allergic asthma and negative in intrinsic asthma but are not helpful in diagnosis.

 

Exhaled Nitric Oxide:

FENO is now being used as a noninvasive test to measure airway inflammation. The typically elevated levels in asthma are reduced by ICS, so this may be a test of compliance with therapy. 

TREATMENT:

The treatment of asthma includes both pharmacologic and non-pharmacologic methods. 

The pharmacologic method includes, bronchodialtors and controllers.

BRONCHODILATOR THERAPY:

Bronchodilators help relax the bronchial smooth muscles and give a rapid relief to the patient, but they do not provide an etiotropic treatment. Bronchodilators include Beta-2 agonists, anticholinergics and theophylline.

CONTROLLERS:

Controllers include inhaled and systemic, corticosteroids, antileukotrienes, Steroid sparing therapies, anti-IgE, and immunotherapy. 

The non-pharmacological methods to contol asthma include maintaing a healthy diet, avoidance of tobacco smoke, physical exercise, and avoidance of medications that exacerbate asthma. 

PREVENTION:

Asthma is included in the WHO Global Action Plan for the Prevention and Control of NCDs and the United Nations 2030 Agenda for Sustainable Development.

REFERENCES:

1) ASTHMA. (n.d.). [PHOTOGRAPH]. https://i0.wp.com/images-prod.healthline.com/hlcmsresource/images/topic_centers/2019-7/Mom-giving-nebulizer-breathing-treatment-to-sickbaby-girl-1296x728-header.jpg?w=1155&h=1528

2) Asthma. (2021, May 3). WHO.INT. https://www.who.int/news-room/fact-sheets/detail/asthma

3) ASTHMA RISK FACTORS. (n.d.). [PHOTOGRAPH]. https://symptomsofasthma.org/wp-content/uploads/2019/09/109997576-risk-factors-for-asthma-infographics-of-the-disease-illustration-of-a-cute-girl-with-an-inhaler-temp.jpg

4) Bronchial Asthma. (2019, September 7). [Video]. YouTube. https://www.youtube.com/watch?v=VDOJF2YqQnw

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6) Fauci, A. S., MD, Hauser, S. L., MD, Longo, D. L., MD, Jameson, L. J., MD, & Kasper, D. L., MD. (2015). Harrison’s Principles of Internal Medicine (19th ed.). McGraw-Hill Professional Pub.

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8) SIDE EFFECTS OF ASTHMA MEDICATIONS. (n.d.). [PHOTOGRAPH]. https://www.verywellhealth.com/thmb/-uMDjB13UYlR8GJd7m1kAR4LdSM=/614x0/filters:no_upscale():max_bytes(150000):strip_icc():format(webp)/asthma-medication-side-effects-200593.FINAL-ecb38c7028d349228c888e1f67b82509.jpg

9) TREATMENT OF ASTHMA. (n.d.). [PHOTOGRAPH]. https://www.verywellhealth.com/thmb/T8WOfqTG4I0Ea7NYfNomK-jdH6I=/614x0/filters:no_upscale():max_bytes(150000):strip_icc():format(webp)/what-is-the-best-medicine-for-asthma-82807_FINAL-adf48d6c4b5c4a95981e3e0201198583.png