engleski

DIVING - WHAT TO TELL THE PATIENTS WITH ASTHMA AND WHY?

INTRODUCTION Traditionally, asthma has been considered to be an absolute contraindication to dive. Breath-hold diving was the only means of performing underwater work until the 17th century when a primitive diving bell was used to salvage cannons from a sunken ship in the Stockholm Harbor (1).The era of modern diving was spawned by Emile Gagnon and Jacques Cousteau&#8217; s development of the self-contained underwater breathing apparatus (scuba) demand regulator (2).This regulator automatically delivers the diver&#8217; s required tidal volume at the ambient pressure to which the diver is exposed and allows exhalation into the water. Scuba revolutionized commercial and recreational diving ; presently, more than 5 million individuals participate in this activity in the United States alone (3, 4).As the scuba diving community expanded, the population of divers with a history of asthma increased. Surveys of the sport-diving community have indicated that 5 to 9% of respondents had a history of asthma (3). British clinicians noted that divers in the United Kingdom have admitted to diving within 2 hours of a wheezing episode, without any pneumothorax or gas embolism developing (5).These findings, along with the fact that there are a growing number of potential recreational divers who have a history of asthma, have renewed debate as to the safety of allowing people with asthma to scuba dive. PHYSIOLOGIC EFFECTS OF DIVING A more recent study that compared 28 Navy divers, 31 diving candidates, and 59 healthy male nondiving volunteers showed a significant increase in airway reactivity to histamine-bronchoprovocation challenge among divers ; the amount of increase appeared to correlate to the length of diving experience (7). Changes in flow rates and airway reactivity noted in long-term compressed air divers are similar to the changes that occur in the airways of patients with asthma. PATHOPHYSIOLOGY OF ASTHMA AND RELATIONSHIP TO DIVING Unfortunately, asthma is one of the most common chronic diseases worldwide and the prevalence is increasing, especially among children. 57 Fortunately, asthma can be treated and controlled so that almost all patients can prevent troublesome symptoms night and day, serious attacks, require little or no reliever medication, have productive, physically active lives and at the end have (near) normal lung function (8). Asthma causes recurring episodes of wheezing, breathlessness, chest tightness, and coughing particularly at night or in the early morning. Regarding the definition asthma is chronic inflammatory disorder of the airways. Chronically inflamed airways are hiperresponsive ; they become obstructed and airflow is limited (by bronchoconstriction, mucus plugs, and increased inflammation) when airways are exposed to various risk factors among others exercise. What we know about exercise-triggered asthma indicates that some sports are more or less likely to provoke asthma. Swimming, water polo, and diving seem to be the least asthmogenic, since the athletes breathe in warm, humid air while exercising (8). The small airways of the respiratory system (< 2-4 mm in diameter) have been termed the &#8220; silent zone&#8221; of the lungs. Only approximately 10% of airways resistance can be attributed to the small airways, and abnormalities in these airways are not detected by measuring FVC or FEV1 in humans (10). A recent symposium was dedicated to the role of small airways dysfunction in asthma (10). Evidence was reviewed that showed that small airways are inflamed in patients with asthma ; if unchecked, this inflammation may result in airway remodeling, which has the potential to develop into chronic airflow obstruction. Superficially, this is similar to the changes that occur in the maximal mid-expiratory flow rates of long-term scuba divers (8-10). REFERENCES 1. Kindwall EP.A short history of diving and diving medicine. In Diving Medicine, edn 2. Edited by Bove AA, Davis JC. Philadelphia:WB Saunders ; 1990:1-8. 2. De la Hoz RE, Krieger BP.Dysbarism. In Environmental and Occupational Medicine, edn 3. Edited by Rom WN. Philadelphia: Lippincott-Raven 1998:1359-75. 3. Neuman TS, Bove AA, O&#8217; Conner RD, et al. Asthma and diving. Ann Allergy 1994, 73: 344-50. 4. Melamed Y, Shupak A, Bitterman H. Medical problems associated with underwater diving. N Engl J Med 1992 ; 326:30-5. 5. Bove AA. Pulmonary barotrauma in divers: can prospective pulmonary function testing identify those at risk (editorial). Chest 1997 ; 112:576-8. 6. Farrell PJS, Glanville P. Diving practices of scuba divers with asthma. Brit Med J 1990 300:166 7. Davey IS, Cotes JE, Reed JW. Relationship of ventilatory capacity to hyperbaric

Asthma; fitness to dive; maritime medicine

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