Is it Safe for Asthmatics to Scuba Dive?

Are you asthmatic and concerned about whether it is safe to scuba dive? Traditionally doctors giving diving medicals took a very conservative approach. Mentioning "Asthma" had potential divers ejected from the surgery faster than you could say, "but it wasn't serious and it's gone away now". More recently, some dive physicians have begun to take a more liberal, informed consent approach in assessing previous or mild asthmatics for diving.

There are 3 main concerns:

First, asthma may make divers more likely to suffer a dive-related illness. We are all taught that the most important rule in diving is to breathe normally and to never hold your breath. If a diver ascends while holding his breath, the expanding air can damage delicate lung tissue, and air may be introduced directly into the blood, travel to the brain and cause an arterial gas embolism (AGE). There is concern that an asthmatic may suffer narrowing or blocking of small airways during a dive, and that expansion of any trapped air during ascent may lead to the same problem. There is also concern that use of reliever medication, such as Ventolin, prior to diving may cause the lungs to be less efficient at filtering out the venous nitrogen bubbles we all have after dives. These bubbles may then circulate through the lungs and reach arteries where they might, in theory, be more likely to contribute to the development of decompression illness.

Second, it is recognised that an asthma attack in the water may severely compromise the diver's safety by incapacitating him and causing an inability to function effectively. Indeed, it is hard to argue that difficulty breathing would not be a decided disadvantage if you were caught in a current that was sweeping you away from your boat.

Third, it is a plausible concern that diving itself could precipitate asthma. Asthma can be precipitated by the exercise associated with diving, or by the irritant effect of breathing a cold, dry gas. It is also recognised that regulators frequently leak a little salt water, and that some of this may be nebulised into a mist during breathing. This mist can irritate the airways and precipitate narrowing in vulnerable individuals.

The problem with all these very plausible concerns is that we have no idea how truly significant they are as there has been very little historic research. The data from retrospective surveys reveals that many asthmatics do dive, and that while their relative risk in diving may be more, their absolute risk remains reasonably low. For example 1 survey indicated that an asthmatic is twice as likely to suffer an AGE as a non-asthmatic. Sound bad? Maybe. But as the risk is low to start with, then not very much multiplied by 2 is still not very much. Continue

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