The 1992 International Consensus Report on Diagnosis and Treatment of Asthma proposed the following definition for Asthma:
'Asthma is a chronic inflammatory disorder, in which many cells and cellular elements play a role, in particular mast cells, macrophages, neutrophils, and epithelial cells. In susceptible individuals, this inflammation causes recurrent episodes of wheezing, breathlessness, chest tightness and coughing, particularly at night or in the early morning. These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment. The inflammation also causes an associated increase in the existing bronchial hyperresponsiveness to a variety of stimuli.'
Persistent changes in lung function may occur over time as a result of sub-basement membrane fibrosis which can lead to airway remodelling.
Asthma represents a special problem for certification because it is a very common condition that has the potential to result in impairment or incapacitation.
Important factors in aeromedical decision making are:
A history of asthma requires careful consideration, so does a history of symptoms or clinical signs, including impaired lung function, suggesting the possibility of asthma.
The GD Examination Procedures [PDF 1.6 MB] prescribes the standard for spirometry completion. A single PEFR or spirometry reading 'within normal limits' is not sufficient to determine whether there is stability. PEFR diaries and serial spirometry may give some indication of asthma stability and an indirect measure of airways inflammation, but there are better tests available.
A spirometry before and after short acting bronchodilator should be performed at the time of examination on any one with a history of asthma, and anyone who has symptoms or clinical signs suggestive of asthma. The post bronchodilator spirometry should be performed even if the base line spirometry reading is entirely normal. This is because a normal spirometry (i.e. FEV1 100% of predicted) does not exclude significant reversibility. The normal values may also be optimistic.
The Global Lung Function Initiative (GLI), aims at establishing a mathematic formula (software) to predict normal values of spirometry for all ages and ethnic group. This is process in evolution. Ultimately it is expected that the GLI tool will become the universal tool for assessing spirometry results. See:
Until then the current NHANES 3 tables are acceptable, see:
People with a history of childhood asthma have a 40 % risk of recurrence in adulthood. Detailed inquiry and spirometry should also be performed in such applicants when they first apply and from time to time thereafter.
Spirometry must be interpreted as prescribed in the GD Examination Procedures [PDF 1.6 MB] and with consideration to the following:
Methacholine used to provoke bronchoconstriction is a repeatable method of assessing bronchiolar hyperresponsiveness (BHR). The table below demonstrates the interpretation of a Methacholine challenge. This test is however somewhat controversial and difficult to interpret.
Categorisation is based upon the concentration of Methacholine that results in a 20% reduction in FEV1. PC20 (mg/ml) - Bronchial Hyperresponsiveness (BHR).
|> 16||Normal bronchial responsiveness|
|4.0 – 16||Borderline BHR|
|1.0 – 4.0||Mild BHR - positive test|
|< 1.0||Moderate to severe BHR|
Before applying this interpretation, the following must be true:
(Reference: American Thoracic Society Guidelines, categorisation of Methacholine Challenge Test Results).
Other options include Hypertonic Saline as an indirect test or Eucapnic Voluntary Hyperventilation (which dries airway – so might better mimic cabin conditions).
Exhaled Nitric Oxide (FeNO) estimation is another indicator of airway inflammation. It has been shown to permit better control of asthma with reduced doses of corticosteroid inhalers but it does not predict well for exacerbations. Not all asthmatics have elevated FeNO.
Directing treatment at normalising the pulmonary eosinophilia has been shown to reduce exacerbations. Technically, however, it remains a labour intensive process and is not practical.
Severity is determined by the worst clinical features before treatment. This determination will give the ME an idea of how severe the condition may become if left untreated or if compliance is in question.
It is essential to document usual precipitants, frequency of asthma attacks, the rate of onset of asthma (precipitous asthma?), the need for acute therapy including nebulised bronchodilator, attendance to ED / GPs, hospitalisation including ICU admission and frequency of oral steroid use.
Generally speaking asthma control will be improved by preventative medications which usually include an inhaled cortico-steroid and LABA.
Ref: American Thoracic Society
|Symptoms||Night time symptoms||Lung function|
|Mild intermittent||Symptoms ≤2 times a week
Asymptomatic and normal PEF between exacerbations
Exacerbations brief (a few hours to a few days), variable intensity
|< 2 times a month||FEV1 of PEF >80 % predicted
PEF variability < 20 %
|Mild persistent||Symptoms > twice weekly but less than once a day
Exacerbation may affect activity
|> 2 times a month||FEV1 of PEF >80 % predicted
PEF variability 20 – 30 %
|Moderate persistent||Daily symptoms
Daily use of inhaled short- acting beta agonist
Exacerbation affect activity
Exacerbation > twice weekly
Exacerbation may last days
|> 1 time a week||FEV1 of PEF > 60%-< 80 %
PEF variability > 30 % predicted
|Severe persistent||Continual symptoms
Limited physical activity
|Frequent||FEV1 of PEF < 60% or predicted|
|Excellent control||Good control||Moderate control||Poor control|
|Prophylactic medication||May or not be used or needed||Yes||Yes||Yes|
|Night symptoms||No||No||More than 2 episodes per month||Occasional|
|Symptoms on exercise||No||No||More than 2 episodes per month||Occasional|
|Symptoms affecting work||No||No||More than 2 episodes per month||Occasional|
|Use of bronchodilator||No||No||Occasional||Frequent|
|Variation in FEV1 after Ventolin||No or less than 10%||No or less than 10%||10-15%||10-15%|
|Nitric oxide (while taking inhaled steroid treatment)||Less than 35 ppb
Only valid indicator in one who had elevated FeNO
|Less than 35 ppb
Only valid indicator in one who had elevated FeNO
|35-50 ppb if symptomatic||Greater than 50 ppb if symptomatic|
The ME should obtain sufficient information to assess the severity of the asthma and its stability.
Moderate and severe asthma require a high level or evidence that stability has been achieved to ensure a sufficiently low likelihood of incapacitation.
In case of doubt the ME should contact the CAA Aviation Medicine Team. The following guidance assumes correct assessment of the severity and stability of asthma. The ME should take a conservative approach to certification if unsure about the applicant’s asthma severity and err in favour of public safety, particularly when assessing Class 1 applicants.
Reminder: Severity is determined by the worse clinical features before treatment, i.e. the worse asthma episode an applicant may have experienced. ·