ASTHMA AND DIVING

by Samuel Shelanski, M.D.

In the past, a history of asthma has been considered by many doctors to be an absolute contraindication to diving. Even the individual who "grew out" of his asthma was precluded from diving "unless equipped to carry his own recompression chamber wherever he goes," the 1984 edition of The Physician's Guide to Diving Medicine firmly states. This has been the position of the Diver's Alert Network (DAN) because of the fear that asthmatics are more prone to air trapping and, thus, arterial gas embolism (AGE).

When it was suggested that the dive community reconsider its stance on asthma and diving at DAN's 26th diving accident and hyperbaric medicine course in May 1995, a hot debate ensued.

Asthma is a common condition, affecting approximately eight percent of children and five percent of adults in the United States. Asthma is characterized by hypersensitivity of the airway to a variety of stimulants including cold, exercise, psychological stress, and airborne irritants such as dust, pollen and animal dander. Stimulation of the airway leads to a constriction of the smooth muscle in the trachea and bronchioles, as well as increased secretions. This frequently leads to shortness of breath and hyperventilation. Many asthmatics are also found to have decreased elasticity of their lung tissue secondary to the chronic inflammatory component of the disease.

Conventional wisdom holds that there are several ways that asthmatics are at increased risk of injury if they have an attack while diving:

• A blockage caused by bronchoconstriction and increased secretions can lead to trapping of air in the lung tissue beyond the blockage. When the asthmatic diver ascends, this air expands according to Boyle's law. In this scenario, the expanding air does not equalize with the surrounding pressure quickly enough as a result of the blockage, and the lung tissue tears, resulting in AGE.
• The decreased elasticity of the lung tissue in asthmatics means that it tears under lower forces than normal lungs. This further increases the risk of arterial gas embolism.
• Shortness of breath and panic at depth may increase the risk of a diver ascending too rapidly.

These are, however, just theories. There is currently no data from the United States to support the claim that asthmatics comprise a disproportionate number of diving fatalities. This is not because asthmatics do not dive. Some do. In fact, there have been several attempts to determine what percentage of the diving population has asthma, but exact figures are impossible to obtain because many asthmatic divers are reluctant to admit their condition. The best estimates place the percentage of divers who have asthma at somewhere between 4 and 8 percent, about the same as in the general population. A study conducted by DAN in 1991 found that asthmatics appeared to have a 60 percent greater incidence of all types of decompression sickness (DCS), but the sample size was not large enough to be statistically significant. Efforts to determine the relative risk to divers with asthma continue, but increasingly, research shows that the risk is not as great as previously believed.

A certain population of asthmatics carry a risk of injury no greater than nonasthmatic divers, according to an article published in the Annals of Allergy in 1994. This group of low-risk asthmatics includes divers whose asthma is triggered by cold or exercise, previously considered an absolute prohibition, as long as their condition is completely controlled by medication. This view has continued to gather support, and there was a full-day symposium convened by Dr. David Elliot of England at the start of June 1995, the Undersea and Hyperbaric Medical Society meeting in Florida.

The purpose of this meeting was to refine the diving medicine community's official stance on asthma and diving. The results of this workshop were summed up in a correspondence from Dr. Richard Moon, medical director of DAN.

"It was recognized that the possible risks of pulmonary barotrauma, including arterial gas embolism, are not accurately quantified. However, it was also recognized that a large number of dives have been completed by known asthmatics, with low morbidity. ... If an asthmatic has normal [lung function], both before and after a provocative maneuver such as exercise, then the risks are low and probably tolerable. However, it was pointed out that individuals predisposed to asthma must be carefully instructed in the importance of slow ascent rate and of not diving if they have symptoms of asthma."

While DAN's official policy still has not been completely spelled out, Dr. Moon says it will be very similar to this.

What does all of this mean to asthmatics who dive, or want to start? Asthma is no longer an absolute contraindication to diving, but it is essential that asthmatics consult their doctors and obtain appropriate pulmonary function tests before diving. In the past, many asthmatic divers have concealed either their condition from their instructors, or their sport from their doctors, correctly believing that they would be denied the opportunity to dive. Hopefully, the changing perception of asthma and diving will encourage more asthmatics to seek appropriate medical clearance for diving from a doctor with experience in dive medicine. This should result in the screening out of those asthmatics who should not dive under any circumstances, while allowing proper instruction and education of the rest.