It is defined as a common chronic disorder of the airways that is complex and characterize by:
- Variable and recurring symptoms
- Airflow obstruction
- Bronchial hyperresponsiveness
- An underlying inflammation
The interaction of these features of asthma determines the expression and severity of asthma. And also determine the response to treatment.
What ate the common symptoms of asthma?
- Cough (worse at night)
- Wheeze (high-pitched whistling sound) usually upon exhalation
- Shortness of breath
- Difficult breathing
- Severe airflow obstruction
- Tachycardia (increased heart rate)
- Tachypnea ( increased respiratory rate)
- The prolonged expiratory phase of respiration
- Use of accessory muscles of breathing during inspiration
- Pulsar's paradoxes which are greater than 10 mmHg and fall in systolic blood pressure during inspiration
The last two are usually present during severe asthmatic attacks.
Pathophysiology of asthma:
Asthma patients, experience increased smooth muscle along with increased mucus inside the airway. As a result, it causes the narrowing of the airway lumen. Thereby responsible for all the signs and symptoms of asthma.
When an allergen enters the trachea than the smooth muscle of the trachea contracts. So, on continued exposure of allergen to its walls it contracts further along with increased mucus production causing narrowing of the airway passage and ultimately leading to collapse.
Which cells are involved in allergic inflammation in bronchial asthma?
When an allergen enters into the body it initiates a cascade of reactions causing activation of Th2 cells and mast cells. So, Th2 cells release a family of cytokines like IL4, and IL5, which causes IgE production. So, these IgE antibodies get attach to muscles causing degranulation and release of mediators from muscles. However, It includes histamine leukotrienes and prostaglandins. It directly contracts the airways' smooth muscle causing bronchoconstriction.
What are the causes or trigger factors of asthma?
The etiology factors that can contribute to asthma or airway hyperactivity may include:
- Environmental allergens like house dust, mites
- Animal allergens especially cat and dog
- Environmental pollutants
- Tobacco smoke
- Aspirin or NSAIDs
- Viral respiratory tract infections
Diagnosis of asthma:
It is based on:
- The history
- Clinical features
- Laboratory investigation
- The laboratory evaluation of a patient with suspect asthma is predominantly focuse on pulmonary function testing most important of PFTs is spirometry in which a patient is ask to breathe in and breathe out through a mouthpiece and the amount of air inhaled and exhaled is recorded. So, it also includes the measurement of force expiratory volume in one second which is FEV1 and forced vital capacity FVC, which is the volume of air that can be forcibly blown out after the full inspiration. So, when the ratio of FEV1 by FVC is less than 0.7 it indicates obstructed disease like asthma.
- Bronchodilator response
- Another thing that helps in diagnosis is bronchodilator response. Acute reversibility of airway obstruction is test by administering two to four puffs of quick-acting bronchodilators like Albuterol and repeating spirometry for 10 to 15 minutes. Later on, an increase in FEV1 of 12 or more accompanied by an absolute increase in the fever of at least 200 ml can attribute to bronchodilator responsiveness with 95 certainties of asthma.
- Other tests that help in diagnosis are peak expiratory flow, exhaled nitric oxide, and eosinophilia in the blood test.
Treatment of asthma:
This is guide by GINA which is a global initiative for asthma routine assessment of symptoms and lung function. It is done by:
- Patient education preference
- Controlling environmental factors or trigger factors
- Comorbid conditions that contribute to asthma severity
- Pharmacological and non-pharmacological therapy
Adjust the treatment review response in form of symptoms, exacerbation side effects, patient satisfaction, and lung function.
Pharmacological therapy is the main stray of management in most patients with asthma. This is also guide by the stepwise approach given by GINA. There are five steps which are based on the frequency of asthma symptoms or frequency of short-acting beta-agonist use with or without these risk factors for exacerbation.
- One is symptoms less than twice a month without a risk factor
- Step two can be twice a month but without risk factors or less than twice a month having a risk factor
- The three steps are twice a month and having a risk factor
- Step four troublesome asthma symptoms most days along with a risk factor
- Step five is an initial presentation of severely uncontrol asthma or an asthma exacerbation with the risk factor present
Now if the patient is on step one then the reliever medication in the form of SABA or short-acting beta agonist is the preferred option and there is no need for any controller medication.
In step 2 low dose ICS or inhaled corticosteroid is the preferred controller choice. However, other options include leukotriene receptor antagonists with low-dose theophylline.
In steps, 3-5 reliever medication can either SABA or low-dose ICS. Whereas LABAs which is a long-acting beta-agonist can be use as a controller choice in both step three as well as in step four. So, in step five add-on treatments like tiotropium anti-IgE anti-iIL5 can use as the preferred controller choice and low-dose oral corticosteroids can tried.
New modalities in treatment of asthma:
New modalities for patients whose asthma inadequately control high-dose inhaled glucocorticoids and LABAs the anti-IgE therapy that is omalizumab may be considered if there is objective evidence of sensitivity to a perennial allergen. and if the serum IgE level is within the established target range.
Monoclonal antibodies like mepolizumab against IL5 are potent chemoattractants for eosinophils. They are indicate for treatment with severe eosinophilic asthma poorly control with conventional therapy.
A new modality is bronchial thermoplasty. It is a device-base intervention available to treat severe asthma utilizing a special catheter introduce via fiber optic bronchoscope. Moreover, to impair bronchial smooth muscle contractility thermal energy is apply to the bronchial walls.