Asthma and Diving: What to Expect at Your Diving Medical
Oct 4
7 min read
If you have asthma and want to scuba dive, you may be asked to have a medical assessment before you are cleared to dive. This can understandably sound a little daunting, particularly if you have had asthma since childhood, rarely use your inhaler, or feel that your asthma is very well controlled.
The good news is that having asthma does not automatically mean that you cannot scuba dive. The UK Diving Medical Committee (UKDMC) guidance recognises that carefully selected divers with asthma can probably dive safely, provided their asthma is well controlled and their lung function is acceptable on their usual medication.
So, what is the doctor actually looking for — and what can you expect when you attend an asthma diving assessment?
Why can asthma be a problem for divers?
There are good reasons why asthma could increase the risk of problems while scuba diving.
Asthma causes inflammation and narrowing of the airways. During an asthma attack, bronchospasm and mucus can narrow the airways further. This can make it difficult for air to move freely in and out of the lungs.
That matters particularly during ascent.
As a diver ascends, the gas in the lungs expands. Normally, this expanding gas can simply be breathed out. If part of the airway becomes obstructed, however, air can potentially become trapped in the lungs. This creates the risk of pulmonary barotrauma — essentially an over-expansion injury to the lung — and, in severe cases, a pneumothorax (collapsed lung) or arterial gas embolism.
An asthma attack underwater could also create a different problem. Cold air, exercise and emotional stress can all contribute to triggering asthma. These are all things that can occur during diving.
And breathing underwater is already more demanding than breathing on the surface. As depth increases, the gas being breathed becomes denser and breathing requires more effort. During a difficult dive, a diver may therefore be working hard physically while also having to cope with increasingly difficult breathing.
An attack underwater could potentially result in severe breathlessness, panic, loss of control and, in the worst case, drowning.
The purpose of the diving medical assessment is therefore not simply to ask, “Does this person have asthma?” Instead, it is to identify divers whose airways may be unstable or who may be particularly prone to exercise-induced bronchospasm.
What does the assessment involve?
For a diver with a history of asthma, the assessment may include spirometry before and after exercise.
Spirometry is a breathing test that measures how much air you can move and how quickly you can breathe it out. We use it to establish your baseline lung function and then look for evidence that your airways narrow following exercise.
This is important because some people can have relatively normal breathing at rest but develop exercise-induced bronchoconstriction when they exercise.
The exercise component of the assessment is intended to identify divers whose asthma may not be adequately controlled during strenuous activity.
Why does that matter to a diver?
Imagine being underwater and having to fin hard against a current, assist a buddy, deal with a problem, or make a controlled ascent following an unexpected event. These situations can substantially increase your breathing rate and physical workload.
If exercise triggers significant narrowing of the airways, this could cause symptoms at exactly the time when you most need to be able to breathe effectively.
There is a concern that airway narrowing during a dive could contribute to air trapping during ascent and therefore increase the risk of pulmonary barotrauma.
The UKDMC's published exercise-testing material describes exercise followed by repeat spirometry at 5, 10, 15 and 30 minutes.
Before your appointment: should you take your inhalers?
Yes — take your regular asthma medication as you normally would that morning.
The purpose of the assessment is to establish how well your lungs function under the conditions in which you would actually be diving.
For example, if you normally use a preventer inhaler every morning, take it as usual on the morning of your appointment.
You should not deliberately stop your medication in an attempt to produce a different result unless your doctor has specifically instructed you to do so.
We are interested in how well controlled your asthma is on your usual treatment, because that is the situation in which you will normally be diving.
What should you bring?
There are a few simple things that are useful to bring to your appointment:
Photo ID
Your reliever inhaler (eg. Salbutamol)
Comfortable clothing
Trainers or other suitable footwear for exercise
You will be doing some exercise, so you may wish to dress comfortably for this.
What happens during the appointment?
1. We start with your medical and diving history
We will first talk about your asthma and your general health.
This may include questions about:
When you were diagnosed with asthma
Your usual symptoms
How often you need your reliever inhaler
Your preventer and other asthma medication
Previous asthma attacks
Hospital or emergency department attendances
Symptoms triggered by exercise, cold air or other factors
Your recent asthma control
Your diving experience
The type and depth of diving you undertake
Any previous problems while diving
We are particularly interested in whether your asthma is stable and well controlled.
2. Height and weight
We will record your height and weight as part of the medical assessment.
3. Baseline spirometry
We then perform your initial spirometry.
This gives us a measurement of your lung function before exercise.
You will be asked to take a full breath in and then breathe out as hard and as fast as you can through the spirometer (a plastic tube connected to a laptop and software). It takes a little technique, and we repeat the manoeuvre three times to make sure we have a reliable result.
4.The exercise test
This is usually the part of the appointment that divers are most curious about.
The exercise component involves stepping up and down from a 30 cm step to a set beat.
It can feel surprisingly fast!
The aim is not to see how fit you are or whether you can complete a fitness test. The purpose is to raise your heart rate and, importantly, increase your breathing rate to reproduce the sort of physiological demand that can occur during strenuous exercise.
Think of a situation such as finning hard against a current or dealing with a difficult situation underwater.
5.Spirometry after exercise
Once you have finished exercising, we repeat your spirometry at intervals — typically at approximately:
5 minutes
10 minutes
15 minutes
30 minutes
We are looking for evidence that your airways have narrowed following exercise.
A significant fall in lung function would suggest exercise-induced bronchoconstriction that may not be adequately controlled.
That is important for diving because we want to minimise the possibility of a diver developing significant airway narrowing during a strenuous dive.
What happens if I pass?
If your assessment is satisfactory, you can usually be issued your diving medical certificate on the day.
That means you can get on with planning your diving rather than waiting for additional investigations.
It is worth remembering, however, that passing an exercise test does not mean that asthma can never cause you problems. It tells us that your asthma and lung function are satisfactory under the conditions tested.
Asthma can change.
What if I don't pass the exercise test?
If your lung function falls significantly following exercise, that does not necessarily mean that you can never dive again.
Instead, it may indicate that your asthma is not sufficiently controlled for diving at that point in time.
A sensible next step is usually to see your GP or asthma clinician to review and optimise your asthma treatment.
Once your treatment has been optimised, you may be able to repeat the diving assessment after an appropriate period — commonly at least four weeks of stable treatment before retesting.
The aim is not to prevent people with asthma from diving unnecessarily. It is to make sure that the asthma is sufficiently well controlled to make diving as safe as reasonably possible.
Passing the test doesn't mean “asthma can never flare up”
This is an important distinction.
The exercise assessment tells us about your airway response on the day of testing. It cannot predict every future asthma flare-up.
For example, you might pass your assessment but then develop a chest infection or a cold while on a diving holiday.
That is why monitoring your asthma remains important even after you have been cleared to dive….
Monitoring your asthma before and during diving
If you have asthma, it can be useful to monitor your peak flow (PF) around periods of diving.
UKDMC guidance recommends:
Measure your peak flow twice a day for at least three days before diving and during the diving period.
If your peak flow falls 15% below your normal best, do not dive until it has returned to normal for 48 hours.
If you have needed to use your reliever inhaler, do not dive until your peak flow has been normal for 48 hours.
If you become short of breath or wheezy on the surface or underwater, abandon the dive.
Because of the theoretical risk of pulmonary barotrauma, ascents should be controlled and within the recommended computer ascent rate, with particular care taken during the last 5 metres.
If there is any change in your overall asthma control, seek advice from your GP and then your diving physician before returning to diving.
What if I have a cold?
This is where common sense matters.
If you have a cold or respiratory infection and your asthma is worse than usual, don't dive just because you have a valid diving medical certificate.
A certificate is not a guarantee that you are fit to dive every single day of the year.
If your breathing is different from normal, your peak flow has fallen, you are wheezy, or you are needing your reliever inhaler more than usual, it is sensible to stay out of the water until your asthma has returned to its normal level of control.
When in doubt, don't dive and seek advice.
The bottom line
For many divers, an asthma diving assessment is much less intimidating than they expect.
The process is essentially:
History → height and weight → baseline spirometry → exercise → repeat spirometry → assessment of the results.
The exercise test is there for a very specific reason: to identify people whose airways narrow significantly when they exercise, despite having acceptable lung function at rest.
For a diver, that information matters. A difficult dive can involve significant physical exertion, increased ventilation and stress. If asthma becomes poorly controlled under those conditions, there may be consequences both during the dive and during ascent.
The goal of the assessment is therefore not simply to find reasons to stop people diving. It is to identify those divers whose asthma is sufficiently well controlled to allow them to dive while minimising the potential risks associated with unstable airways.
If you have asthma and are considering scuba diving, or you have previously been told that you cannot dive because of your asthma, a diving physician can assess your individual circumstances and advise you on what is appropriate for you.
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