Asthma
Key Points
- Asthma is a common chronic inflammatory disorder of the airways.
- The common symptoms of asthma are breathlessness, wheeze and cough.
- Reversible airflow obstruction is the main physiological measure used in the diagnosis of asthma.
- Asthma triggers should be identified and avoided where possible.
- Poorly controlled asthma remains a significant health burden despite effective therapy.
- The keystone of pharmacological therapy in people with asthma is the delivery of effective anti-inflammatory drugs.
- Well-established national and international guidelines should be used to direct therapy.
- Asthma therapy should be titrated to the lowest effective dose to ensure control with minimal side effects.
- Inhaler technique is crucial to ensure that drug delivery is effective.
- People with asthma should be offered asthma education and self-management plans.
Pathophysiology
Asthma is an inflammatory disorder of the airways, and various inflammatory cells and mediators have been identified as playing an important role in the pathophysiology of asthma. Bronchial hyper-reactivity is recognised as a key feature of asthma pathophysiology. This results in the airways of people with asthma responding to exposure to particular triggers, which vary from person to person.
Exposure to triggers causes constriction of the airway smooth muscle, resulting in bronchoconstriction. Bronchoconstriction is a result of activation of the parasympathetic pathways of the autonomic nervous system. The release of acetylcholine by the postganglionic nerve fibres activates the M3 muscarinic receptors within the airway smooth muscle. Activation of these receptors results in contraction of the smooth muscle and, consequently, constriction of the diameter of the airway.
Result: AIRWAY NARROWING
Symptoms: Breathlessness, Wheeze, and Cough.
Some people with asthma have brittle asthma, which is classified into two types. Type I brittle asthma is defined by periods of prolonged peak flow variability, whereas type II is characterised by sudden deteriorations on a background of good control and relatively normal lung function.
Over the last few years there has been a paradigm shift in the understanding of asthma pathophysiology. This has led to asthma no longer describing a single disease but a collection of multiple subgroups referred to as phenotypes (Wenzel, 2012).
The majority of people with asthma have an inflammatory process driven by TH2 processes that tend to be associated with atopy, allergy, type I hypersensitivity and eosinophilic inflammation. Asthma associated with eosinophilic inflammation has long been recognised to be responsive to treatment with corticosteroids (Brown, 1958). Conversely, non-TH2-driven asthma is associated with a later age of onset, obesity and neutrophilic inflammation; these patients tend to demonstrate a lack of response to corticosteroid treatment.
Clinical signs and symptoms
Asthma classically presents with cough, wheeze and breathlessness, often induced by exposure to trigger factors. The frequency and severity of these symptoms is highly variable between individuals. Asthma tends to demonstrate diurnal variation, generally with increased symptoms at night and early in the morning.
Potential Triggers
| Type of potential trigger | Triggers |
|---|---|
| Allergens | House dust mite, Animal dander, Moulds, Pollens |
| Infectious agents | Influenza, Rhinovirus |
| Drugs | NSAIDs, Beta blockers, Prostaglandins |
| Occupational | Isocyanates, Wheat flour, Latex, Formaldehydes, Hair colourants |
| Other | Exercise, Cold air, Stress, Sulphites, Nitrogen oxides |
Signs of acute asthma include tachypnoea (increased rate of respiration), wheeze on expiration and use of accessory muscles of respiration. In children, there may also be indrawing of the intercostal muscles.
Investigations
The diagnosis of asthma is primarily a clinical one; there is no single standardised definition of symptoms or investigation findings (BTS/SIGN, 2016). A key part of the process is identifying characteristic symptoms from the patient history. However, due to the long-term nature of the condition, history alone is insufficient, and it is important to use diagnostic tests to provide objective evidence of reversible airflow obstruction.