Asthma: a very basic introduction?
- It affects over 10% of children and around 5-10% of adults, with the prevalence of asthma increasing.
- Not only does asthma account for a significant morbidity burden it should be remembered that around 1,000 people die in year from asthma in the UK, 30-40 of whom are children.
What is asthma?
- Defined as a chronic inflammatory disorder of the airways secondary to hypersensitivity.
- The symptoms are variable and recurring and manifest as reversible bronchospam resulting in airway obstruction.
Risk factors and aetiology?
A number of factors can increase the risk of a person developing asthma:
- personal or family history of atopy
- antenatal factors: maternal smoking, viral infection during pregnancy (especially RSV)
- low birth weight
- not being breastfed
- maternal smoking around child
- exposure to high concentrations of allergens (e.g. house dust mite)
- air pollution
- 'hygiene hypothesis': studies show an increased risk of asthma and other allergic conditions in developed countries.
- Reduced exposure to infectious agents in childhood prevents normal development of the immune system resulting in a Th2 predominant response
Focusing on atopy, patients with asthma also suffer from other IgE-mediated atopic conditions such as?
- atopic dermatitis (eczema)
- allergic rhinitis (hay fever)
A number of patients with asthma are sensitive to aspirin.
- Patients who are most sensitive to asthma often suffer from nasal polyps.
- Remember the nose is part of the respiratory tract from a histological point of view.
Finally around 10-15% of adult asthma cases are related to allergens in the workplace.
- Occupational asthma is usually diagnosed by observing reduced peak flows during the working week with normal readings when not at work.
- Examples of common occupational allergens include isocyanates and flour.
Symptoms and signs?
- cough: often worse at night
- 'wheeze', 'chest tightness'
- expiratory wheeze on auscultation
- reduced peak expiratory flow rate (PEFR)
- Spirometry is a test which measures the amount (volume) and speed (flow) of air during exhalation and inhalation.
- It is helpful in categorising respiratory disorders as either obstructive (conditions where there is obstruction to airflow,
- for example due to bronchoconstriction in asthma) or restrictive (where there is restriction to the lungs,
- for example lung fibrosis). Key metrics include:
FEV1: forced expiratory volume - volume that has been exhaled at the end of the first second of forced expiration
FVC: forced vital capacity - volume that has been exhaled after a maximal expiration following a full inspiration
Typical results in asthma?
Other investigations to consider
chest x-ray: particular in older patients or those with a history of smoking