Asthma is one of the chronic respiratory conditions that is characterized by the narrowing and swelling of airways and the production of extra mucous.  It is the most common Chronic respiratory disorder in childhood.(1)Asthma is believed to be localized to the lungs but current evidence demonstrates that it affects the entire respiratory tract. This condition mainly affects the respiratory system of the victim, especially the smaller airways e.g. the bronchi and bronchioles. Mucosa is the inner lining in the aforementioned airways and it is surrounded by a layer of smooth muscle. Asthma severely affects the airways by inflaming them which ultimately results in them becoming hyper-responsive to specific triggers. Despite noticeable improvements in the management and diagnosis of asthma as well as the availability of widely accepted clinical practice guidelines, estimate control remains suboptimal.

Causes

Asthma triggers are both allergic and non-allergic.

  • Allergic triggers include cockroach residue, dust mites, animal dander, pollens, mould, powders, and perfumes.
  • Non-allergic triggers are cold air, strenuous exercise, tobacco smoke exposure, viral infections.

Some evidence demonstrates that there may be genetic mutations behind the development of asthma. Different regions of chromosomes that are linked with asthma susceptibility have been recognized. Those chromosomal regions are associated with the expression of respiratory tract hyperresponsiveness, synthesis of IgE-antibodies, and inflammatory mediators. (2)

Pathophysiology

Allergic and non-allergic triggers cause chronic inflammation in the airway. It elevates the level of Th2 cells. Elevated TH2 levels, release cytokines such as interleukin 4, interleukin 5, interleukin 9, interleukin 3, and Promote the production of immunoglobulin E and eosinophilic inflammation. Production of IgE stimulates the synthesis of inflammatory mediators such as cysteinyl leukotrienes and histamine.

These mediators lead to bronchospasm, increased mucus secretion, and edema.

If left uncontrolled, cytokines and mediators enhance the inflammatory response that causes progressive bronchial hyperactivity and airway inflammation.Over time this inflammation declines the lung functionand causes more complicated airway obstruction. (3)It brings up the importance of regular assessment of asthma.

Signs and symptoms.

In asthma there are three important changes;

  1. smooth muscle contraction
  2. Smooth muscle hypertrophy
  3. and mucus hypersecretion

All of these contribute to the narrowing of the airways. These three features result in the silence symptoms of asthma which include persistent cough, Dyspnoea or shortness of breath, and Wheezing.

Some patients also feel chest tightness or chest pain in asthma.

Phenotypes of asthma

Asthma had been considered a single respiratory disorder, but current studies have concentrated on its heterogeneity. According to these studies, asthma is consists of several phenotypes. These phenotypes differ in the age of asthma, duration of asthma, lung function, sex, and atopy.

Three wheeze phenotypes of asthma have been recognized in children.

  1. Transient early wheezing
  2. IgE-mediated wheezing (atopic)
  3. non-atopic wheezing (4)
  • The transient wheezing phenotype is linked with the symptoms that last for the first five years of life and it is not linked with allergic sensitization or family history. Its risk factors include impaired lung function, exposure to the infected children, and maternal smoking during pregnancy.
  • Children with non-atopic wheezing phenotype experience wheezing up to their adolescence.This type is not associated with allergic factors, rather children experience wheezing due to viral infections.
  • IgE-mediated wheezing is also known as a classic asthma phenotype. In this type, children suffer persistent wheezing due to allergic triggers, airway hyperresponsiveness, and dysfunctioning of the lungs at an early age.

Risk factors.

There are several factors thought to increase the risks of developing asthma.They include the following:

  1. Family history; if one of the parents has asthma then the risk of developing asthma increases.
  2. Gender and age; asthma is more common in children than adults. Boys are more likely to develop asthma than girls.
  3. Asthma allergies; sensitivity to allergens is often an accurate predictor to develop asthma.
  4. Smokers have a higher risk of asthma.
  5. Air pollution; this is the main component of smog. Constant exposure to air pollution raises the risk for asthma those who grew up in urban areas have a higher risk for asthma.

Diagnosis

The diagnosis of asthma includes a physical examination, medical history, and assessment of lung functions such as spirometry.

  • Physical examination includes
  1. Examination of wheezing on auscultation
  2. Examination of the upper respiratory tract
  3. Examination of skin for signs and symptoms of other allergic conditions.
  • In medical history, the classical symptoms of asthma are assessed such as
  1. Wheezing
  2. Chest Tightness
  3. Breathlessness
  4. Cough
  • Along with these symptomatic patterns of asthma are also assessed in medical history. Such as
  1. Episodic/recurrent
  2. Occurs in the early morning or at night
  3. Occurs on the exposure to irritants
  • Objective assessment of lung functioning includes spirometry.

Spirometry checks how well the lungs are working.It measures the following parameters;

  1. Forced vital capacity (FVC) which is the maximum volume of the air that one can exhale
  2. Forced expiratory volume in 1 s (FEV1)

In Normal conditions, the FEV1/FVC ratio is greater than 0.90 in children and 0.75 to 0.80 in adults. These values are less in asthmatic patients.

Treatment.

The main aim of managing asthma is to have complete control over the disease to prevent exacerbations and reduce the risk of mortality and morbidity. Other goals are to reduce the need for medication, to minimize the severity and frequency of asthma symptoms, to improve the impaired functioning of lungs.

  • Inhaled medications

These medications come in various forms including dry powder inhalers (DPIs) and pressurized metered-dose inhalers (pMDIs).

  • Reliever medications

Inhaled Beta 2 agonists are the most commonly used reliever medications to treat acute symptoms of asthma. E.g., salbutamol, terbutaline.

 

  • Inhaled corticosteroids (ICs)

These are highly effective anti-inflammatory medications to treat asthma. Their regular use reduces the symptoms, improves lung function, and minimizes exacerbation.However, ICs do not cure asthma completely and symptoms can occur within a few weeks after discontinuation.

  • Leukotriene receptor antagonists. LTRAs

LTRAs, Such as Montelukast is considered to be the well-tolerated and safe treatment of Asthma

  • Theophylline

It is an oral bronchodilator and has anti-inflammatory effects. Due to a narrow therapeutic window and more adverse events, it is given to patients over 12 years who are intolerant to other therapies.

 

References

  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4426892/
  2. https://pubmed.ncbi.nlm.nih.gov/20176271/
  3. https://erj.ersjournals.com/content/erj/30/3/452.full.pdf
  4. https://www.sciencedirect.com/science/article/abs/pii/S1526054204000211
  5. https://pubmed.ncbi.nlm.nih.gov/30275843/