Asthma

Considerations

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:

• Adequacy of respiratory function;
• Severity of asthma;
• Stability of asthma;
• Medication requirements.

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.

Symptoms & signs suggestive of asthma

• Cough, worse at night, recurrent wheeze, recurrent breathlessness or chest tightness;
• Peak expiratory flow (PEF) variation of 20 % or more from PEF measured in the morning (prior to any bronchodilator) to PEF taking in the afternoon or evening (can be after bronchodilator). This is best documented by diary that includes exposure to symptoms precipitants.
• FEV1 variation of > 200 ml;
• FEV1 variation of 12%; or more;
• Hyperexpansion of the thorax (un-reliable on plain chest x-ray);
• Expiratory wheezing during normal breathing, noting that sounds during forced exhalation may originate in the glottis;
• Nasal symptoms or polyps;
• Allergic skin manifestations in the presence of the above symptoms.

Investigations

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:

lungfunction.org(external link)

Until then the current NHANES 3 tables are acceptable, see:

Spirometry NHANES III Reference Values(external link)

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.

Interpretation of spirometry

Spirometry must be interpreted as prescribed in the GD Examination Procedures [PDF 1.6 MB] and with consideration to the following:

• Loop spirometry (showing inspiratory and expiratory flow volume loops) gives more information than measurement of FEV1 and FVC alone;
• Spirometric examination is best undertaken by an accredited Lung Function laboratory and reported by a Respiratory Physician, but may be undertaken by a competent ME, in accordance with the GD requirements;
• According to the American Thoracic Society a variability of 12 % or 200 ml in FEV1 is significant. An FEV1/FVC ratio of less than 70 % indicates obstruction;
• Lung function varies with age and ethnicity. The FEV1/ FVC ratio declines with age;
• A reduced FVC with maintenance of the FEV1/FVC ratio suggests a restrictive pattern. There are a number of causes for this, including a variety of lung diseases and obesity.

Bronchial challenge using Methacholine (or Histamine)

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:

1. baseline airway obstruction is absent;
2. spirometry quality is good;
3. there is substantial post-challenge FEV1 recovery.

(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.

Classification of asthma severity

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 exacerbation	Frequent	FEV1 of PEF < 60% or predicted

Indications of control / stability

	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

Information to be provided

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.

History of childhood asthma

• Respiratory questionnaire at the first application;
• GP notes at the first application if the ME is uncertain about the history;
• Spirometry pre and post bronchodilator on first application;
• Inquiry at each subsequent examination about symptoms suggesting recurrence of asthma – if any positive answers, refer to ‘current asthma’ below. The consideration must be documented.

History of asthma in adulthood, or current asthma

• Respiratory questionnaire at each examination;
• PEF series on first application, and consider at subsequent examinations;
• Spirometry pre and post bronchodilator at each examination, unless there is well established stability. In this case slightly less frequent spirometry testing is permissible;
• Copy of GP notes for the past 24 months at the first Class 1 application;
• Copy of GP notes for the past 24 months at the first Class 2, or 3 application if the asthma is suspected to be mild persistent or worse;
• Copy of GP notes for the past 12 months at subsequent Class 1, 2 and 3 if there is any doubt regarding the recent asthma history, i.e. if the asthma is known or suspected not to be under good control, or if an exacerbation has occurred;
• A respiratory physician report at the first Class 1 application if the asthma is suspected to be 'mild persistent', or worse. Subsequent reports may be required on a case by case basis or if the control is suspected to be moderate or poor;
• A respiratory physician report at the first Class 2 or 3 application if the asthma appears to be moderately severe or worse, or if the control is moderate or poor. Subsequent reports may be required on a case by case basis;
• Other reports as the ME may find reasonably necessary.

Disposition

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. ·

• Moderate or poor control of asthma: The applicant may not be assessed as meeting the Part 67 medical standards and should be assessed via the flexibility process;
• Past childhood asthma - Class 1, 2 or 3 adult applicants with a history of childhood asthma but none since childhood: May be assessed as meeting the Part 67 medical standards if no current asthma is demonstrated;
• Mild intermittent asthma - Class 1, 2, or 3 – Excellent or Good control achieved. The applicant may be assessed as meeting the Part 67 medical standards provided the certificate is endorsed with the requirement to have a short acting bronchodilator readily available at all time when flying and not to fly while experiencing symptoms of asthma. Applicant to comply with any prophylactic treatment.
• Mild persistent asthma - Class 1: Excellent or Good control achieved. The applicant may be assessed as meeting the Part 67 medical standards provided that the applicant is successfully treated with inhaled steroids, compliant with treatment, and stability has been reliably demonstrated following a respiratory physician report. The certificate should be endorsed with the requirement to have a short acting bronchodilator readily available at all time when flying and not to fly while having symptoms of asthma. The applicant should be informed to ground self and report to CAA in case of discontinuation of prophylactic medication;
• Mild persistent asthma - Class 2 & 3: Excellent or Good control achieved. The applicant may be assessed as meeting the Part 67 medical standards providing that the applicant is successfully treated with inhaled steroids, compliant, and stability has been reliably demonstrated. In doubt a respiratory physician report should be requested, but is not routinely required. The certificate should be endorsed with the requirement to have a short acting bronchodilator readily available at all time and not to fly or operate as an ATC while experiencing any symptoms of asthma. The applicant should be informed to ground self and report CAA in case of discontinuation of prophylactic medication.
• Moderate asthma - Class 1: The applicant may not be assessed as meeting the Part 67 medical standards and should be assessed via the flexibility process;
• Moderate asthma - Class 2 & 3: Excellent or Good control achieved. The applicant may be assessed as meeting the Part 67 medical standards provided that the applicant is successfully treated with inhaled steroids, compliant, and stability has been reliably demonstrated following a respiratory physician report. The certificate should be endorsed with the requirement to have a short acting bronchodilator readily available at all time when flying and not to fly or operate while experiencing any symptoms of asthma. The applicant should be informed to ground self and report to CAA in case of discontinuation of prophylactic medication;
• Severe asthma – All classes: The applicant may not be assessed as meeting the Part 67 medical standards and should be assessed via the flexibility process.