Asthma definition : Asthma is generally a respiratory condition characterized by reversible bronchospasm and chronic inflammation of the airway passages. The incidence of asthma has been increasing in the recent years.
Ashtma causes : Asthma is thought to be due to the genetic predisposition in the individuals due to the hyper reactivity in the airways.
This respiratory disorder is due to the exposure of susceptible individuals to certain substances (allergens/triggers), which induces marked bronchospasm and airway inflammation.
Individuals with asthma produce large amount of the antibody IgE. These IgE antibodies attach to the mast cells present in the tissues.
If an individual is exposed to a trigger like pollen, the result is allergen-binding mast cell-bound IgE. This, in turn, causes the release of certain inflammatory mediators like histamines, leukotrienes and eosinophilic chemotactic factor.
The response of the patient to these triggers can be divided into two phases like early phase and late phase.
Asthma Triggers List
- Allergens like pollen, fungi, pet dander, dust mites
- Cold air
- Strong emotions
- Cigarette smoke
- Respiratory tract infections
Clinical Classification of Asthma
Asthma can be classified clinically on the basis of the asthma attack to the patient.
- Mild intermittent: In this case, the patient is attacked by asthma twice a week or less.
- Mild persistent: In this case, asthma attack occurs more than twice a week.
- Moderate persistent: Asthma attack occurs almost daily and is severe that it affects the activity of a person.
- Severe persistent: In this case, asthma attacks are very frequent and persist for a long period of time. These attacks severely limit the activity of the patients.
Asthma is divided into two phases on the basis of response of the patient to the triggers. The two phases are:
- Early phase
- Late phase
Early Phase of Asthma
The early phase of the asthma is characterized by the
- Marked constriction of the bronchial airways
- Edema of the airways
- Excessive mucus production
The bronchospasm is due to the increased release of the inflammatory mediators like histamine, prostaglandins and bradykinins. In the early stages of the asthmatic response, inflammatory mediators promote bronchoconstriction rather than inflammation.
Late Phase of Asthma
The late phase of asthma occurs several hours after the initial onset of the symptoms and it manifests mainly as an inflammatory response.
Eosinophils are the white blood cells, which are the primary mediators of the inflammation during the asthmatic response which stimulate the degranulation of the mast cells and release the substances that attract other white blood cells to that area.
Subsequent infiltration of the airway tissues with white blood cells like lymphocytes and neutrophils contribute to the overall inflammatory response of the late phase of asthma.
- Difficulty in breathing
- Rapid and shallow breathing
- Increased respiratory rate
- Excess production of the mucus
- Barrel chest due to air trapping in the lungs
- Significant anxiety
The possible asthma complications may include the occurrence of Status asthamaticus which is a life threatening condition of prolonged bronchospasm that is not responsive to the drug therapy.
Pneumothorax is another possible consequence as a result of increase in lung pressure, which can result from extreme difficulty involved in expiration during a prolonged asthma attack.
The other complications of asthma like hypoxemia and acidosis may also occur and can result in overall respiratory failure.
Stages of an Acute Asthma Attack
There are four stages in the asthma attack:
Stage I: It is a mild attack and the patient feels mild dyspnea, diffuse wheezing and there will be adequate air exchange.
Stage II: It is a moderate stage and the symptoms will be respiratory distress while taking rest and marked wheezing.
Stage III: It is a severe stage and the patient suffers from marked respiratory distress and cyanosis. The asthma patient experiences marked wheezing and absence of breath sounds.
Stage IV: It is the stage of respiratory failure. The patient suffers from severe respiratory distress, lethargy, confusion and prominent pulsus paradoxus, which is an abnormally large reduction in stroke volume, pulse wave amplitude and systolic blood pressure during inspiration.
Asthma treatment is based on the frequency and severity of the asthma attacks: It includes the following:
- The person, who is susceptible to asthma, should avoid allergens and triggers and should be away from them. The patient should improve the ventilation of the living areas and can use air conditioning.
- Bronchodilators: Short acting beta-adrenergic receptor activators act as bronchodilators which can be administered as required in the form of a nebuliser solution by using a metered dispenser. Alternatively, they can be injected subcutaneously. Bronchodilators dilate the bronchioles and prevent the bronchoconstriction. They do not prevent the inflammatory response. Examples of bronchodilators are Albuterol and Terbutaline.
- Xanthine drugs: Xanthine drugs cause bronchodilation and inhibit the late phase of asthma. These drugs are administered orally as second line drugs in combination with other therapies like with steroids. An example of this is Theophylline which has significant central nervous system, cardiovascular and gastrointestinal side effects, thereby limiting the overall usefulness of the theophylline.
- Anti-inflammatory drugs: Corticosteroids are the anti-inflammatory drugs. These steroids are administered orally or by inhalation to blunt the inflammatory response of the asthma. The long term oral use of corticosteroids may produce significantly adverse effects that include immunosuppression, increased susceptibility to infections, osteoporosis while also showing effects on other hormones like glucocorticoids.
- Cromolyn sodium: Cromolyn sodium is an anti-inflammatory agent that inhibits both the early and late stages of the asthma. Its mechanism of action involves the mast cell function or its response to allergens.
- Leukotriene modifiers: These are the new class of agents that block the synthesis of inflammatory mediators named as leukotrienes. An examples of leukotrienes is Zafirlukast.
Regulation of Respiration
Respiration is regulated by the rhythmic discharges from the respiratory center in the medulla. The discharges are modulated by input from pontine and higher central nervous system (CNS) centers and vagal afferents from the lungs.
Various chemical factors affect the respiratory center, including the partial pressure of carbon dioxide in the arterial blood by an action on medullary chemoreceptors, and of oxygen by an action on the chemoreceptors in the carotid bodies.
Some voluntary control can be superimposed on the autonomic regulation of breathing, by implying connections between the cortex and the motor neurons, innervating the muscles of respiration.
Bulbar poliomyelitis and lesions in the brain stem result in loss of the autonomic regulation of respiration without loss of voluntary regulation.
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