Author's Note: I am not a doctor, but I find the physiological side of scuba diving fascinating. The following is merely a summary of some basic research I have done regarding scuba diving and asthma. Remember to consult with a doctor before diving with asthma.
Diving with asthma is a controversial topic. In the past, any history of asthma was considered a definitive contraindication for diving. Recently, the accepted opinion has begun to change. Many diving doctors now accept that asthma is not an absolute contraindication for scuba diving. Potential divers with asthma should be evaluated individually to determine their fitness to dive. Doctors will consider the type and severity of asthma, a person's history of attacks, and what triggers asthma when deciding whether to clear an individual for diving. Potential divers with a history of asthma must see a diving doctor and undergo routine lung evaluation before taking to water.
What is Asthma?:
Asthma is a disease that causes a person's airways to constrict in response to some stimuli. People with asthma may experience an asthmatic episode (or attack) when exposed to allergens or cold, as a response to exercise, or when under extreme stress.
Asthma is a common disease. Studies estimate that up to 7% of the population of the United States has been diagnosed with asthma at some point in their lives. Some people have asthma during childhood, but grow out of it, while others develop asthma later in life.
Why Can Asthma Be Dangerous When Diving?:
During an asthma attack, a person's airways contract. If we imagine the airways leading to the lungs as pipes, the diameter of the pipe decreases during an asthmatic episode. The result is that air can not move efficiently in and out of the lungs. This leads to an increase in breathing resistance, or the amount of effort it takes for a person to inhale and exhale.
The air that divers breathe is compressed by the pressure of the water. Compressed air is denser than air on the surface and therefore has an increased breathing resistance (takes more effort to inhale and exhale). If breathing air on the surface is like sucking air through a pipe, then breathing air at depth is like sucking honey through a pipe. The deeper a diver, the denser (or thicker) the air he breathes is, and the more his breathing resistance increases. Add the increased breathing resistance underwater to the already increased breathing resistance during an asthma attack, and it is possible that a diver experiencing as asthma attack underwater will not be able to get a sufficient amount to air.
As a diver ascends, the air in his lungs expands in response to the decrease in water pressure. This is not a problem for a non-asthmatic diver because the expanding air escapes out his airways as he exhales. However, a diver having even a mild asthma attack will not be able to release air from is lungs at a normal rate because his airways are contracted. The expanding air may become trapped in the lungs. Even small amounts of trapped expanding air can cause decompression illness which may have severe, and sometimes fatal, effects.
Diving with asthma is more dangerous than normal exercise with asthma because of the logistics of diving. Underwater, divers can not immediately cease exercise or access asthma medication.
Is Asthma an Absolute Contraindication for Diving?:
No. Some people with asthma may be cleared for diving. This depends upon the type of asthma and an individual's history. A potential diver should consult with a diving doctor, undergo routine lung health tests, and fully understand the risks of diving with asthma before making his final decision.
What Do Doctors Consider When Determining an Asthmatic's Fitness to Dive?:
Some of the considerations when evaluating an individual's fitness to dive are his type of asthma, the frequency of asthma attacks, medication, and his personal history of asthma.
• In general, asthma that is triggered by exercise, cold, or stress is an absolute contraindication to diving because each of this triggers may be encountered when diving.
• Asthma that is triggered by allergens (such as pollen or cat hair) is usually not a contraindication to diving, as it is unlikely that divers will encounter these allergens when diving.
• Divers taking medication to control their asthma are not necessarily prohibited from diving. The key is whether or not a person's asthma is under control. Some medications that control asthma are approved for diving. A diving doctor will consider the kind of medication and how effective it is in preventing asthma attacks before allowing a person to dive.
Why Are Physical Tests Important in Evaluating Fitness to Dive With Asthma?:
Physical tests are vital in determining the condition of an individual's lungs and therefore his fitness to dive. People who have had no or few recent asthma attacks may still be unfit to dive if their lungs are weak or in poor condition. Be wary of doctors who issue a blanket “no” or “yes” response without a physical evaluation.
What Physical Tests Do Doctors Use to Evaluate Fitness to Dive With Asthma?:
The tests used to evaluate the health of a diver's lungs are generally simple and non-invasive.
• Spirometry: A spirometry test requires a person to breathe into a machine, which uses information gleaned from the way a person breathes to evaluate his lung function. For example, a person may be asked to inhale completely and exhale as hard and as long as he can.
• Peak Flow Test: A peak flow test can be conducted using a sophisticated spirometer or a simple peak flow meter. Results gained from a simple peak flow meter may be less reliable than the battery of variables usually tested by with spirometer.
• Bronchial Agitation Test: There is some debate as to whether this test should be used to determine fitness to dive, as some doctors have claimed to obtain false positives from this test. In a bronchial agitation test, saline water is aspirated into the lungs and then variables are tested to see how the lungs react.
• Exercise Tests: Spirometry or Peak Flow Test may be used to evaluate a subject before and after exercise. This helps a doctor determine if the asthma is exercise-induced.
• Post Bronchial Dilator Tests : A person's lungs may be evaluated after the use of an asthma controlling medication to see if the medication is effective. Many asthma medications are approved for diving if they are seen to effectively control asthma in an individual.
So, Should You Dive With Asthma?:
Guy de Lisle Dear, M.B., FRCA, DAN Assistant Medical Director, "Asthma and Diving", Divers Alert Network, http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=22
London Diving Chamber Website http://www.londondivingchamber.co.uk/index.php?id=advice&page=6&cat=14&sub_cat=27
Neuman TS, Bove AA, O'Connor RD, Kelsen SG. "Asthma and Diving" Ann Allergy, 1994 Oct;73(4):344-50.
Kay, Edmond, MD. "Are asthmatics Fit to Dive?" 2000, http://faculty.washington.edu/ekay/asthma.html