Assessment of fitness for recreational scuba diving in candidates with asthma: a pilot study

Characteristics of enrolled patients

All patients with asthma or possible asthma referred to Hvidovre University Hospital, Denmark, for assessment of fitness for recreational scuba diving over a 5-year period (2013–2017) were prospectively included in the present study.

Case history was obtained from all patients. Family disposition to asthma and allergy, that is, relatives with a diagnosis of asthma or allergies, and atopic disease and symptoms, including wheezing, dyspnoea, coughing, chest tightness, recurrent lower respiratory tract infections, exercise-induced wheezing, exercise-induced cough, night-time respiratory symptoms (coughing or wheezing during night-time) and symptoms of rhinitis, were recorded together with, if relevant, previous diagnosis of asthma and currently prescribed antiasthma therapy. Patients were categorised as smokers or never smokers, and lifetime tobacco exposure was calculated as pack-years (one pack-year=20 cigarettes a day for 1 year).

Methods

Spirometry, and if spirometry revealed signs of airflow limitation also bronchodilator reversibility test, measurement of fractional exhaled nitric oxide (F_ENO) and skin prick test were performed as part of the routine work-up for patients seen at the respiratory outpatient clinic for asthma.

Clinical algorithm for assessment of fitness to dive in patients with possible asthma

According to the national guideline, individuals with <10% decline in FEV₁ following administration of the highest dose in a bronchial challenge test with, for example, methacholine or mannitol can be regarded as having no medical contraindications to scuba diving.6–8 The present clinical algorithm applied mannitol challenge test. The mannitol test is an indirect bronchial provocation test which in general is more specific for identifying individuals with current airways inflammation because it causes release of mediators from inflammatory cells in the airways. The mannitol test is one of the more indirect tests (others include hypertonic saline, dry-air hyperpnoea and exercise) and is applied to this algorithm due to ease of use in everyday clinical practice. According to the algorithm, all individuals with a decline in FEV₁ ≥10% were offered rechallenge test with mannitol after stepping up their asthma therapy, primarily increasing the dose of inhaled corticosteroid (ICS) and/or add-on long-acting beta₂ agonist (LABA), after a minimum of 3 months. After the rechallenge, individuals with a decline in FEV₁ <10% were classified as having no medical contraindications to scuba diving.

Statistical analysis

Data were analysed using SPSS V.23. The results are expressed as mean±SD, exact number, percentages and OR with 95% CI, as appropriate. Further, when comparing the means of the divers having no medical contraindications to scuba diving versus those classified as having medical contraindications to scuba diving, independent samples t-test was used. A p value <0.05 was considered significant.

Baseline characteristics

A total of 41 participants were enrolled in the study (24 men), with a mean age of 33 years (range 10–69 years). Further characteristics are given in table 1.

All patients were assessed for fitness for recreational scuba diving, of whom 28 (68%) reported dyspnoea and 16 (38%) wheezing (figure 1). Levels of lung function and F_ENO are given in table 2.

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A total of 32 (78%) participants had a doctor-diagnosed asthma prior to referral for assessment of fitness to dive. Of the 41 participants, 29 were at the time of testing prescribed SABA, including 2 patients with no diagnosis of asthma, and 26 patients (63%) were prescribed maintenance therapy with ICS.

Assessment of fitness to dive using the clinical algorithm

First mannitol challenge test

All 41 enrolled participants who had a prior diagnosis of asthma or symptoms suggesting asthma had a mannitol challenge test. After the first mannitol challenge test, a total of 21 individuals had a decline of <10% in FEV₁ and were therefore classified as having no medical contraindications to scuba diving, according to the algorithm. Of these, 15 had a prior diagnosis of asthma. All patients with a fall of >10% in FEV₁ were offered step-up asthma therapy and a rechallenge test, but six patients did not wish to continue and were therefore assessed unfit to dive. Further details are given in table 3 and figure 2.

Table 3

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Results of initial mannitol challenge test according to current asthma therapy and outcome of the challenge test

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Figure 2

Flow chart showing the 41 candidates for recreational scuba diving tested with a mannitol challenge test and offered step-up asthma therapy and rechallenge test if there was a fall in FEV₁ >10% in the first mannitol challenge test. Candidates with a fall >10% in the retest were not fit for recreational scuba diving, along with candidates not interested in the retest. FEV₁, forced expiratory volume in 1 s.

Characteristics of individuals with no medical contraindications to scuba diving and individuals unfit to dive

Of the 41 patients, 28 (68%) had no medical contraindications to scuba diving, including 20 individuals with a prior diagnosis of asthma, leaving 13 individuals (32%) unfit to dive, including 1 patient with no prior diagnosis of asthma. This patient, however, had the highest level of F_ENO (115.5 ppb) of all participants and was afterwards diagnosed with asthma and prescribed asthma therapy. The flow of patients is shown in figure 2. When comparing individuals with no medical contraindications to scuba diving with individuals unfit to dive, no significant differences were found apart from the level of F_ENO; that is, in patients with no medical contraindications to scuba diving, the mean F_ENO was 22.8±12.4 ppb, compared with a mean of 55±36.5 ppb in individuals classified as being unfit to dive (p=0.01).

Comparing national guidelines

There are several published national guidelines around the world with different recommendations on how to assess diving candidates with asthma.

Strauss9 was the first in 1979 to suggest that contraindications to diving in subjects with asthma should include significant obstructive pulmonary disease with minimal values for FEV₁ and FVC and maximum voluntary ventilation of 75% of predicted; any asthma attack occurring within the past 2 years; the need for preventive therapy; or any episode of bronchospasm associated with exertion and/or inhalation of cold air. These contraindications are based on theoretical concerns rather than evidence, and most guidelines published since then have been based on this recommendation. Today, however, most diving experts or diving societies have more liberal approaches.

The British Thoracic Society Fitness to Dive Group (a subgroup of the British Thoracic Society Standards of Care Committee) and the Danish guidelines from the Danish Society of Respiratory Medicine share content from their respective guidelines and recommend that subjects with wheezing precipitated by exercise-induced, cold-induced or emotion-induced asthma should be excluded from diving, and that subjects with asthma should refrain from diving if they have symptoms requiring relief medication in the 48 hours preceding the dive and if they have reduced fall in peak expiratory flow (PEF) >10% from best values or increased peak flow variability >20% diurnal variation.8 10 Further, according to the Danish national guideline from the Flying and Diving Medical Society, individuals with >10% decline in FEV₁ following administration of the highest dose in a bronchial challenge test with, for example, methacholine or mannitol are classified as unfit for scuba diving.8

In the USA, the National Institutes of Health in 2016 published recommendations that allow subjects with well-controlled, mild-to-moderate asthma, that is, no current chest symptoms and with normal screening spirometry, to go scuba diving. The recommendation also states that patients with exercise-induced, emotion-induced and cold-induced asthma, along with patients with asthma requiring rescue medication within 48 hours, should not dive. Furthermore, the US recommendations point to other diving societies recommending that a patient with asthma should successfully pass a bronchial provocation challenge.11

In Australia and New Zealand, the South Pacific Underwater Medicine Society (SPUMS) recommends that candidates who indicate a history of asthma in the last 10 years and exhibit signs of wheezing or an unexplained cough, but have normal spirometry, should have bronchial provocation test, using indirect methods including dry-air hyperpnoea, exercise and hypertonic challenges (saline or mannitol). A positive response, that is, a reduction in FEV₁ of greater than 15%, should lead to a recommendation against diving, but does not preclude retest and reassessment after asthma control has been established. Those who ‘pass’ bronchial provocation tests and are taking antiasthma medication should be reassessed annually or sooner if they develop any symptoms. It is further recommended that ‘well-controlled’ individuals with asthma, that is, asymptomatic and show normal lung function on testing with spirometry and bronchial provocation, may be able to dive at an acceptable level of risk. All current divers with controlled asthma are strongly encouraged to monitor their peak flow twice daily during diving periods, with the recommendation to refrain from diving if PEF is more than 10% below their best value.12

There is no worldwide consensus on assessment, and this is primarily due to the limited evidence. National guidelines are mainly based on expert opinions, case reports of diving accidents, epidemiological data, anonymous questionnaires, experimental studies with real or simulated dives, and annual reports of diving fatalities, injuries and incidents,13–17 and none has generated direct evidence that diving with asthma increases the risk of misadventure. Future studies should therefore address the actual risk related to recreational scuba diving in individuals with asthma and the impact on the risk of level of asthma control, and larger studies using a clinical algorithm that assesses fitness to dive are necessary.

Impact of asthma triggers on fitness to dive

Most experts seem to agree that subjects with exercise-induced, cold-induced or emotion-induced asthma should be excluded from diving.2 7 18–20 The SPUMS guidelines on medical risk assessment for recreational diving do not, however, take this aspect into account.12 The present algorithm is not excluding divers with history of wheezing and/or other asthma symptoms triggered by exercise, cold or emotion, primarily due to the lack of evidence on an association between these symptoms and dive-related injuries.21 The concern is that the diving environment can be physically challenging and cold and trigger anxiety, and therefore cause an asthma attack. It is still worth noting that this concern is theoretical and that no evidence is indicating that candidates with exercise-induced, cold-induced or emotion-induced asthma with a negative mannitol challenge test and therefore no evidence of airway hyper-responsiveness should not be as fit to dive as other patients with asthma. Since there is no gold standard on how to assess fitness for recreational scuba diving in individuals with asthma or symptoms of asthma, this algorithm was developed for use in everyday clinical practice, but is limited on safety since it is not known whether or not diving with asthma is an actual risk factor for injuries.

Future investigations

To know more about potential risks when diving with asthma, more studies are needed. Due to ethical concerns about performing randomised clinical trials in this setting, the use of real-world experience, registry data and surveys is the only means to gain insight into the risks and recommendations when diving with asthma or symptoms of asthma.

Study limitations

The study is limited on safety since there is no evidence on how asthma affects recreational scuba diving and therefore no gold standard for assessment of fitness to dive with asthma.