Asthma and Diving

Asthma is a disease characterized by narrowing of the breathing tubes (bronchi) in response to a variety of stimuli. The response can be variable, and a person can have a sudden worsening in lung function called an “attack.” An asthma attack can be triggered by pollen and other so-called allergens, cold air, irritants in the atmosphere, a cold or the flu. The topic of asthma and diving has long been controversial in the recreational diving community. Historically, divers with asthma were excluded from diving.

Epidemiology

• 1 in 13 Americans have asthma.
• More than 25 million Americans have asthma, which translates to 7.7% of adults and 8.4% of children.
• Asthma is more common in adult women then adult men.
• 10 Americans die from asthma each day.

Sources: U.S. Centers for Disease Control and Prevention; and Asthma and Allergy Foundation of America

Symptoms

The bronchial narrowing that occurs with asthma has two effects. One is a decrease in the amount of air that can be moved in and out of the lungs. This can reduce exercise capacity — especially for a diver, who already has reduced breathing capacity due to the resistance of the breathing apparatus and increased internal resistance due to higher breathing gas density at depth. Secondly, narrowed airways could cause trapping of gas in the lungs during ascent. If trapped gas expands faster than it can be exhaled through the narrowed airways, lung rupture may result, potentially causing arterial gas embolism or pneumothorax (collapsed lung). People with asthma who dive are at risk not only from gas-trapping but also from reduced exercise capability. While it is often easy to stop, rest and catch one’s breath while exercising on land, this may not be possible underwater.

The South Pacific Underwater Medical Society (SPUMS) has stated that diving may precipitate an asthma attack. People with asthma are at risk of shortness of breath, panic and drowning during diving activities, including while on the surface.

Management

There are four kinds of asthma, and the treatment is based on the diagnosis.

• Mild Intermittent Asthma: Symptoms occur less than once a week and are associated with less than a 20 percent decrease in peak flow (the maximum rate of air flow during exhalation). This type of asthma involves brief increases in the severity of symptoms (called exacerbation) that last a few hours to a few days. Nocturnal symptoms occur less than twice per month, and between acute attacks the patient should be asymptomatic with normal lung function. Treatment includes the use of short-acting bronchodilators on an as-needed basis.
• Mild Persistent Asthma: Peak flow should be near normal (with less than 20 percent variation), but symptoms occur more than once weekly. Exacerbation affects sleep, with nighttime symptoms often appearing more than twice per month. Treatment involves use of short-acting bronchodilators during the day and long-acting bronchodilators at night.
• Moderate Persistent Asthma: Symptoms, which may include coughing, can occur daily and often interfere with activities or sleep. People with moderate persistent asthma may require a short-acting bronchodilator. Peak flow is generally between 60 and 80 percent of normal. Ironically, many patients with these symptoms do not believe they have asthma. Coughing with exercise or at night is a notable symptom and a likely indicator of this type of asthma. Daily medication, usually inhaled steroids, is required; short- acting bronchodilators may be needed for acute episodes.
• Severe Persistent Asthma: People with this type of asthma have continual symptoms and peak flows of 60 percent of normal or less. Increases in symptom severity occur frequently, limiting physical activity, and nocturnal symptoms occur frequently. Regular use of long-acting bronchodilators and oral steroids is required as is use of short-acting bronchodilators during acute episodes.

If the treatment regimen can return the pulmonary function test results to normal, especially following exercise, people with asthma may be able to safely dive (and perform the strenuous exercise that may be required during diving).

Complications

The treatment of asthma is relevant in determining its severity and the associated risk of diving. According to discussions among experts at the Undersea and Hyperbaric Medical Society (UHMS), divers who have mild intermittent asthma, mild persistent asthma or moderate persistent asthma, may be allowed to dive, provided their asthma is well controlled.

Implications in Diving