Dr. P. J. Farrell
The theoretical reasons why asthmatics should not scuba dive are well known. In the U.K. the British Sub-Aqua Club (BSAC) has always allowed certain asthmatics to dive. The subjective opinion has been that we do not see asthmatics at the hyperbaric treatment centres in the U.K. and hence our practices work. In 1994 the reality of the situation was investigated. Are asthmatics over-represented in our accident statistics?
To determine the prevalence of asthmatics in the U.K. diving population, twenty five BSAC medical referees were randomly selected who determined the total number of divers in their diving clubs and the number of asthmatics. The data was pooled to provide the prevalence figures. Members of the British Hyperbaric Association and Royal Navy were asked to provide the number of cases of dysbaric illness (decompression illness and gas embolism) treated in the period 1989 to the end of 1993 and the number of asthmatics seen.
Out of twenty five BSAC medical referees questioned, nineteen replied. They recorded 813 active divers of which 31 were asthmatics giving a prevalence of 3.96%. The chambers reported 402 cases of treated dysbaric illness in the period 1989 to 1993 of which 9 were asthmatics. Statistically chi-squared with Yates correction was 3.607 (P > 0.5) i.e. asthmatics showed no increase in dysbaric illness over the general population.
The 4% prevalence of asthmatics in the U.K. scuba-diving population is interestingly similar to Bove et al.  where 2.6% of his sample dived despite being asthmatic, in a country where asthma is considered to be an absolute contra-indication to diving. I included all cases of decompression illness and air embolism as one illness as many people believe that they cannot be separated clinically in most cases. Only one of the chambers contacted failed to record if a patient was asthmatic and so their data are not included. However all the hospital case notes were reviewed and asthma was not mentioned in a single medical history.
In the U.K. the National Sport Diving Medical Committee (representing the BSAC, the Sub-Aqua Association and the Scottish Sub-Aqua Club) are happy with the existing guidelines in allowing carefully selected asthmatics to dive, as there is no evidence that asthmatics are more at risk of decompression illness than the rest of the U.K. diving population.
Interestingly, Corson et al.  in their survey from "Alert Diver" found 279 asthmatics of whom 26.4% had been hospitalized for asthma; of these 5.8% had been hospitalised 6 times or more and they had a highly significant increased risk of decompression illness.
The authors commented that the risk needs quantifying according to the severity of the asthma. It is suspected that in the U.K. many of the divers in this group would have been advised not to dive. The U.K. policy of enabling some asthmatics to dive has allowed the exclusion of the more severe cases of asthma. The asthmatics who are allowed to dive have been educated as to the safest way of diving.
Interestingly, a recent paper by Neuman et al.  has come to much the same conclusions concerning the fitness of asthmatics to dive. The medical ban on asthmatics diving has not prevented them diving in the rest of the world, where an unselected and uneducated group have been shown to be at increased risk of suffering from decompression illness.
The current U.K. National Sport Diving Medical Committee is currently reviewing the old BSAC asthma standard to bring it into line with the British Thoracic Society Guidelines for the treatment of asthma.