Facebook Twitter RSS Reset

Asthma, Definition, incidence, etiology, risk factors, pathophysiology, clinical manifestations

‘Asthma’ is a Greek word which means ‘breathless’ or ‘to breathe with open mouth’.

DEFINITION

The Global Strategy for Asthma Management and Prevention Guidelines define asthma as ‘a chronic inflammatory disorder of the airways associated with increased airway hyper-responsiveness, recurrent episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night/early morning’. Asthma is often called Reactive Airway disease.

INCIDENCE AND PREVALENCE

There is a marked variability in the global prevalence rates. It is reported to involve from about 1% to over 20% individuals in different populations. An overall global asthma burden of about 300 million patients had been estimated previously.

Prevalence rates from India and several other Asian countries have been reported to lie between 2% to 5% in most countries. The Indian estimates, based on the average, 2.05% prevalence of current asthma was 21 million for all age groups.

There is a huge economic burden of asthma on both the individual and the society. The estimated total annual cost of about Rs. 32 billion for patients with chronic asthma with additional cost of about Rs. 5 billion for acute asthma (for the year 2011) is an enormous burden for the healthcare infrastructure of a developing country.

ETIOLOGY AND RISK FACTORS

  1. Host factors
    • Age and sex
    • Racial and ethnic factors
    • Genetic polymorphisms
    • Other Atopic Conditions
    • Obesity
  2. Environmental factors
    • Aeroallergens
    • Exercise
    • Infections (? Protective role)
    • Occupational exposures
    • Environmental pollutants
      • Outdoor pollution
      • Indoor pollution
      • Environmental tobacco smoke/In utero exposure to smoke
      • Solid fuel combustion
    • Diet: Processed foods
      • Breastfeeding (Protective role)

Host factors

  • Age and sex – On an average, asthma occurs with equal frequency in both sexes. There is a male predominance in children, being twice as common in boys as in girls before 14 yrs of age. The sex difference disappears as the age advances, to a higher incidence in women in adults.
  • Racial and ethnic factors – Asthma is known to differ in prevalence in different racial and ethnic populations. Some of these differences could be due to different genetic polymorphisms.
  • Genetic polymorphisms – There is a strong genetic pre-disposition of asthma. The presence of a family history of asthma and other allergies in the first degree relatives of patients indicates the role of genetic factors.
  • Other atopic conditions – Presence of nasal (allergic rhinitis) and skin atopis (atopic dermatitis), sinusitis and nasal polyposis is frequently associated with asthma.
  • Obesity – Presence of obesity is also a recognized risk factor. Obesity is partly genetic and partly environmental in origin. In obesity, asthma is supposedly mediated through the release of leptins.

Environmental factors

  • Aeroallergens – Approximately 40% of all cases of asthma are related to an allergic response. Many airborne pollens, fungal spores, home dust mite, insect debris, cat and dog dander, have been implicated as independent risk factors for asthma.
  • Exercise – Asthma that is induced or exacerbated during physical exertion is called exercise – induced asthma(EIA). Typically, EIA occurs after vigorous exercise, not during it. Symptoms of EIA are pronounced during activities where there is exposure to cold air.
  • Infections – Infections are important triggers of asthma symptoms. Respiratory Syncytial Virus (RSV) and parainfleunza virus infections are known to cause asthma in children. On the other hand, early childhood infections are reported to protect from asthma. The “hygiene hypothesis” is based on the concept that exposure to airway infections and allergens early in life causes maturation of T-helper 1 (Th 1) lymphocytes over Th-2 lymphocytes, thereby decreasing the risk of allergies.
  • Occupational Exposures – Exposure to chemical vapors, irritant gases, metal fumes and other exhausts amongst persons engaged in different occupations may cause airway sensitization and increased production of IgE, which commonly manifest as occupational asthma.
  • Environmental Pollutants – Exposure to outdoor and indoor pollutants is an important cause of respiratory morbidity and asthma exacerbations. Domestic combustion of solid fuel for cooking and heating is an important cause of indoor air pollution in India as well as in several third-world countries. Passive exposure to tobacco smoking, an important source of indoor air pollution. Environmental Tobacco Smoke (ETS), is another important cause of increased asthma morbidity amongst both children and adults. In utero exposure of the foetus to smoking from a smoker mother is reported to influence the lung development.
  • Diet – Foods are commonly blamed to aggravate asthma in India but scientific evidence is inadequate. Some data suggest the role of processed foods contributing to the increased incidence of asthma. Food additives like sulfiting agents are widely used in the food and pharmaceutical industries as preservatives and sanitizing agents. Breast milk-fed infants have lower incidence than those fed with formula milk or soya proteins.

Pathophysiology of asthmatic attack

pathophysiology asthama

CLINICAL MANIFESTATIONS

The characteristic clinical manifestations of asthma are dyspnea, wheezing, cough and chest tightness after exposure to a precipitating factor. Expiration may be prolonged. Instead of a normal inspiratory –expiratory ratio of 1:2, it may be prolonged to 1:3 or 1:4.During asthma attack clients are dyspneic and have marked respiratory effort. Manifestations of marked respiratory effort include nasal flaring, pursed-lip breathing, and use of accessory muscles. Respiratory rate is significantly increased.
Auscultation of breath sounds usually reveals wheezing, especially during expiration. As asthma progresses, the patient may wheeze during inspiration & expiration both. The inability to auscultate wheezing in an asthmatic client with acute respiratory distress may be an ominous sign. It may indicate that the small airways are too constricted to allow any air flow. The client may require immediate, aggressive medical intervention.

In addition, bronchospasm may lead to almost continuous coughing in an attempt to exhale and clear the airway. Percussion of lungs indicate hyper resonance.

Person has a feeling of suffocation and signs of hypoxemia, which include restlessness, increased anxiety, inappropriate behaviour, increased pulse and BP, and pulsus paradoxus (a drop in systolic pressure during the inspiratory cycle greater than 10 mmhg ).

Part 1 | Part 2 | Part 3