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ASTHMA AND SCUBA DIVING
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ASTHMA UPDATE
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ASTHMA AND SCUBA DIVING Karen B. Van Hoesen, MD, and Tom S. Neuman, MD, FACE', FACPM
Until recently, asthma or a past history of asthma has been considered an absolute contraindication for scuba diving. We know, however, that asthmatic patients are diving and that there are many asthmatic individuals who wish to learn how to scuba dive. Divers, diving organizations, and diving physicians have struggled with the issues of safety for the asthmatic patient who wants to dive. Of concern is the theoretical risk that an asthmatic diver may develop acute airway obstruction while diving due to the unique conditions associated with breathing compressed air. Airway obstruction underwater could predispose that individual to pulmonary barotrauma during ascent. In addition, bronchoconstriction and panic on the surface may increased the risk for drowning. Our perception of diving with asthma has changed during the last 10 years. Asthma is not a single disease but a spectrum of disease with a wide range of severity and frequency of symptoms. The factors that precipitate attacks vary tremendously. Although we know asthmatic patients are diving safely, there are few controlled data on which to base risk assessments for asthmatic individuals who dive. Asthma is no longer an absolute contraindication for diving. The question now becomes which group of asthmatic patients can be considered at low risk from diving, what are the potential risks of diving for the asthmatic candidate, and how can we screen those individuals in whom there may be a relatively low risk for diving while excluding those individuals in whom the risk of diving may be unacceptable.
From the UCSD School of Medicine, La Jolla; and the Department of Emergency Medicine, Diving Medicine Clinic (KBVH) and Hyperbaric Medicine Center (EN), UCSD Medical Center, San Diego, California
IMMUNOLOGY AND ALLERGY CLINICS OF NORTH AMERICA
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VOLUME 16 NUMBER 4 NOVEMBER 1996
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THE PHYSICS AND PHYSIOLOGY OF DIVING
When a scuba diver descends in the water, the ambient pressure increases because of the weight of the water. In accordance with Boyle's Law, pressure and volume are inversely related at a constant temperature. As the diver descends, the surrounding ambient pressure increases and volume decreases. A volume of gas at the surface (1 atmosphere absolute = 1 ATA) will be compressed to half of its volume at 10 m of sea water (2 ATA). On ascent, surrounding pressure decreases and volume increases. A doubling of volume occurs from 10 m to the surface. Air pressure within the middle ears, sinuses, lungs, and other gas-filled spaces of the body must be equalized with changes in ambient pressure; if these spaces cannot expand or contract to accommodate the pressurerelated change in gas volume, tissue injury or barotrauma will occur. During scuba diving, a diver breathes compressed air at the same pressure as the surrounding water, hence he or she is able to maintain normal lung volumes at depth. On ascent as long as the diver exhales normally, expanding gas usually is vented off easily. If the airways have become obstructed, however, the diver does not exhale normally (as in the case of breath-holding) or if the rate of ascent exceeds the rate at which the expanding volume of air can escape, there is resultant expansion of gas in the lungs, which leads to alveolar rupture and pulmonary barotrauma (PBT). It has been shown experimentally that transpulmonic pressures (intratracheal pressure minus intrapleural pressure) of 95 to 110 cm of H,O are sufficient to rupture alveoli, allowing gas to escape into the interstitial spaces.23,31 Manifestations of pulmonary barotrauma include pneumomediastinum, subcutaneous emphysema, pneumothorax, and systemic embolization of gas into ruptured pulmonary veins producing arterial gas emboli (AGE). The formation of AGE is one of the most serious injuries associated with diving and is a major cause of death and disability among sport The most common cause of pulmonary barotrauma and AGE is a rapid or panic ascent while breath-holding. It occurs more frequently in novice and inexperienced divers. There may be a history of running out of air or panic associated with a rapid, uncontrolled ascent or uncontrolled positive buoyancy from inadvertent inflation of the buoyancy compensator or loss of the weight Additional conditions associated with diving that may be relevant to an asthmatic diver include an increased work of breathing with increased gas density and the added resistance of breathing through a demand regulator. This causes a reduction in inspiratory and expiratory flow rates, which can reduce ventilation and limit exercise performance.2'j Diving often is undertaken in cold water, where the inspired gas has a lower humidity and lower temperature than at the surface. RISKS OF DIVING FOR THE ASTHMATIC PATIENT
Lung structure and function in asthma are reviewed elsewhere.29.39 One of the major concerns of asthmatic patients diving is the susceptibil-
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ity to pulmonary barotrauma and AGE, even during a normal ascent. The risks for asthmatic individuals include (1) airway obstruction and (2) reduced exercise capacity. As described previously, airway obstruction, airway closure, and gas trapping caused by asthma and other pulmonary diseases can precipitate pulmonary barotrauma during ascent. Liebow et alZ2showed that partial pulmonary obstruction in large airways can lead to AGE. Weiss and Van MeteF reported two cases of AGE occurring in asthmatic individuals scuba diving in a swimming pool. Wagner et a140 demonstrated that indirect evidence for air trapping exists in asthmatic individuals with minimal or no symptoms. They showed marked abnormalities in ventilation perfusion ratios in asymptomatic asthmatic patients; as many as half of the lung units were perfused by closed airways that were ventilated by collaterals. It is important to note, however, that many of these individuals had abnormal baseline pulmonary function tests despite being asymptomatic. Certain conditions associated with diving may lead to acute bronchoconstriction. Scuba divers breathe air with a lower relative humidity, higher density, and lower temperature than air at the surface, and often are faced with strenuous exercise and potential inhalation of nebulized sea water. All of these conditions along with emotional stress may lead to bronchial constriction.ll,38 Airway cooling increases airway resistance in asthmatic subjects." Inhalation of hypertonic saline can provoke an attack in individuals with asthma." 3537 Shortness of breath and panic at depth may increase risk of rapid, uncontrolled ascent. The other concern for asthmatic individuals diving is the possibility of impaired exercise capacity. During exercise, any obstruction of the airways increases airways resistance, which prolongs the expiratory phase and demands a greater expiratory effort, leading to a rise in intrathoracic pressure.21Respiratory bronchioles tend to collapse, causing a fall in mid-expiratory flow (MEF,). Hard swimming against a strong current may cause normal divers to approach their maximum voluntary ventilation, hence increased airways resistance in an asthmatic patient can significantly reduce exercise t0lerance.4~ Asthmatic individuals who dive while on medication may have additional risks. All p2agonists are pulmonary vasodilators. Dilation of the pulmonary vasculature may allow venous bubbles that would normally be filtered by the pulmonary vasculature to enter the arterial circulation as gas emboli. This arterialization of otherwise asymptomatic emboli might result in AGE or decompression sickness (DCS).5, Conversely, the asthmatic diver may be safer because of increased awareness and education. The majority of cases of AGE are due to errors in judgment and behavior rather than structural abnormalities in the lungs. Those asthmatic divers who have been well educated and who understand the pathophysiology of diving and pulmonary barotrauma may take more precautions to avoid a rapid ascent, thus reducing their risk for AGE.
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DIVING STATISTICS Prevalence of Asthmatic Individuals in the Diving Population
There are estimated to be between 2.5 and 3 million sport scuba divers in the United States.24In analyzing dive accident statistics, the diving community has been criticized because asthmatic individuals have not been ”allowed to dive.” Therefore, they are not represented in the accident data. We know, however, that asthmatic individuals are diving. Several studies have shown the general prevalence of asthmatic patients in the diving population is approximately 5% to 8%, which is similar to the 4% to 8% of the general population who has Neuman et alZ9asked 1745 newly certified divers via questionnaire if they had asthma. Thirty-three (8.1%) of 405 respondents had asthma, and 19 of those divers had made 100 dives without accident. In another survey of 1000 divers, 37 of 696 respondents had a history of asthma (5.3%), of which 13 were currently asthmatic, which was defined as having an attack within 1 year or using bronchodilators on a regular basisy In a much larger survey in 1992, 10,422 divers responded to a questionnaire in Skin Diver Mugazine; 870 (8.3%) answered yes to the question ”have you ever had asthma,” 343 (3.3%) said they currently have asthma, and 276 (2.6%)stated they dive with a ~ t h m aIn . ~the United Kingdom, 4% of the amateur diving population is a~thmatic.’~ Thus, it appears the prevalence of asthma in the diving population is similar to that in the general population at large. To characterize asthmatic individuals who scuba dive, Corson et allo placed a questionnaire in Alert Diver magazine. In that survey, 243 (88.7%)of 279 respondents reported taking some medication for asthma, and 55.8% took medication just before a dive. Of those who wheezed, 13.3% had symptoms daily and 17.3% had symptoms weekly. Seventythree (26.4%)respondents had been hospitalized for asthma. Dive Accidents
In Britain, the British Sub-Aqua Club (BSAC) has allowed individuals with asthma to dive for many years. Farrell and Glanvillla reported the results of a questionnaire placed in a British dive magazine; 104 positive respondents had a history of asthma and logged 12,864 dives safely without any instances of PBT. Eighty-nine of the 104 individuals had asthma since childhood, 70 wheezed less than 12 times per year, and 22 wheezed daily. Ninety-six divers used an inhaler just before diving and some were using steroids. Nine individuals wheezed daily, dove within 1 hour of wheezing, and logged more than 1241 dives without incidents. Although this was a self-selected group that responded, it still suggests that some asthmatic individuals are diving safely. As a follow-up study, FarrellI6surveyed all the hyperbaric cham-
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bers during 1991 to 1993 for cases of decompression illness (DCI), which combines DCS with AGE. He found 393 nonasthmatic individuals and 9 asthmatic individuals, indicating no statistical difference between the normal population and the asthmatic population.16 The Divers Alert Network (DAN) has records of all dive accident data submitted in the United States, Canada, and the Caribbean. Every year they publish the DAN Report on Diving Accidents and Fatalities. A retrospective review of the DAN data from 1987 to 1990 was conducted to assess risk of asthma for DCI? It was determined that 54 of 1213 divers with DCI had a history of asthma, of which 25 were currently asthmatic (suffering an attack within 1 year or using bronchodilators on a regular basis). Sixteen (8%) divers with AGE had a history of asthma, of which 7 (3.6%) were currently asthmatic. In the control population of 696 divers, 37 divers admitted a history of asthma (5.3%) and 13 (1.9%) were currently asthmatic. Although the data suggest there may be a 1.6fold increase in the risk for AGE in asthmatic divers, the data do not reach statistical significance (confidence interval 0.80-2.99). No information is given about asthma severity, pulmonary function testing, or the role asthma played in the accidents. A more recent update of the DAN data was presented at the Undersea and Hyperbaric Medical Society (UHMS) workshop entitled Are Asfhmatics Fit to Dive?,which included all cases collected from 1987 to 1994.25In 3359 cases of DCI, 6.65% of the AGE cases had asthma (compared with 5.32% of controls), giving an odds ratio of 1.25. In addition, 3.09% of AGE cases had current asthma, resulting in an odds ratio of 1.65. Although the probability of AGE may be 1.25 times higher for asthmatic patients and 1.65 times higher for current asthmatic patients, the estimate of the risk does not reach statistical significance, as the 95% confidence interval contains 1.0. Surveys and retrospective reviews may not account for those asthmatic individuals who have selected themselves out of diving or discontinued diving for asthma-related problems. Additionally, the discussed studies do not compare the level of severity of asthma in these divers. There are no records of predive medication, pulmonary function tests, or characteristics of the dive, such as a rapid or uncontrolled ascent. Based on the information given, there is no firm statistical evidence for an increased risk of DCI in asthmatic patients who scuba dive. At the current rate of diving accidents and accident data collection, however, it has been estimated that it will take another 25 years to statistically exclude asthma as a risk factor.= FarrelP currently is conducting a prospective study of more than 250 asthmatic divers who have completed more than 20,000 uneventful dives, including more than 20 emergency free ascents, without incidents.16 Deaths Associated with Diving and Asthma
Approximately 80 to 100 diving fatalities have been reported annually in the United States during the last 10 years.l*,24 At the University
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of Rhode Island’s National Underwater Accident Data Center, only 1 of 2132 deaths was in an individual with asthma; however, no information about the death is available, and the role of asthma is uncertain.” Of 18 consecutive scuba fatalities at the Los Angeles Coroner’s office between 1985 to 1990, none were linked to asthma.32 In Australia and New Zealand, asthma was found to be a contributing factor in 9% of diving deaths.I4An autopsy identified drowning as the cause of death in seven and pulmonary barotrauma in two of the victims. The role of asthma in these deaths was not ~1ear.l~ When Walker4I reviewed 201 Australian and 120 New Zealand scuba diving fatalities, he found only four cases in which asthma could have been a possible contributing factor; however, there were significant additional factors that could have caused the fatalities.4l In 1994, there were 97 deaths reported by DAN. In only one case was asthma mentioned as a possible contributing factor. The victim had a past history of asthma, and the cause of death was drowning.12 Diving is not absolutely safe and there are inherent risks. Incidents will continue to occur; however, asthmatic individuals appear not to be overrepresented in the accident statistics for DCI or diving fatalities. Data are needed from prospective comparisons of asthmatic and nonasthmatic divers with concomitant evaluation of pulmonary function testing, dive profiles, and the number of incidents in each group. INTERNATIONAL RECOMMENDATION FOR DIVING AND ASTHMA
As asthmatic individuals appear to be diving without an increase in accidents compared with nonasthmatic divers, the question now becomes which asthmatic patients can dive with a reasonable degree of safety? Three diving medical societies recently have published statements regarding asthmatic individuals and scuba diving. Recommendationsfrom Britain
The UK Sports Diving Medical Committee Asthma Standard16 stated: ”The theoretical risks should be fully explained to the asthmatic diver. There is little, if any, evidence that the moderate, controlled asthmatic who follows the guidelines below is more at risk than the normal population. Asthmatics may dive if they have allergic asthma, but not if they have cold-induced, exercise-induced or emotion-induced asthma. All asthmatics should be managed in accordance with the British Thoracic Society guideline. Only well-controlled asthmatics may dive. Asthmatics should not dive if they have needed a bronchodilator in the last 48 hours or have any other chest symptoms.”
The committee also advise the a
p2 agonist may be taken pre-diving as
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a preventive measure but not to relieve bronchial spasm at the time
of diving. Recommendations From South Pacific Underwater Medicine Society (SPUMSY
SPUMS Policy Statement on the Prevalence of Asthma in Australian Diving Candidateslyis as follows: 1. A history of asthma is common in diving candidates. 2. The assessment of risk for a diving candidate with a history of asthma should be conducted by a medical practitioner who has had training in diving medicine.
SPUMS Policy o n the Importance of Asthma in Diving19 is as follows: 1. Asthma is a potential cause of mortality and morbidity in divers. The leveI of risk in this context needs to be measured. 2. Diving may precipitate an asthma attack. 3. Asthmatics may have limited exercise capacity and are at risk of shortness of breath, panic and drowning on the water surface. 4. Asthmatics who dive may be a self-selected (i.e., survivor) population and hence their experience may not be representative of the risks of diving for the general asthmatic population. 5. Current information (from descriptive database) suggests that the relative risk for asthmatics who dive (compared with nonasthmatics) for a decompression illness is about two.
SPUMS Policy on the Assessment of Risk for a Diving Candidate with a History of AsthmaI9 is as follows: 1. The determination of risk for diving in someone with a history of asthma requires a gradation of the severity and currency of their asthma. 2. Risk stratification for someone with a history of asthma who wishes to dive will require a thorough history, examination and often lung function testing, which may include provocation testing (and especially with exercise and/or hypertonic saline). This may need to be repeated if the person elects to dive. 3. Provocation testing with exercise and/or hypertonic saline (rather than with histamine and methacholine) may be more specific for asthma that is of concern in diving. The significance of a positive result is more easily understood by the diver. 4. As the risk for diving in someone with a history of asthma is uncertain, permanent records should be retained as part of a SPUMS-sponsored study.
Undersea and Hyperbaric Medical Society (UHMS) Conclusions In June 1995, the UHMS held a symposium entitled Are Asthmatics Fit to Dive?,which was attended by asthma and diving medical experts *Recommendations provided in this section are from the following: Gorman D, Veal A: SPUMS policy on asthma and fitness for diving. South Pacific Underwater Medicine Society Journal 25213, 1995; with permission.
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from around the world. They critically reviewed the pathophysiology regarding an asthmatic individual participating in diving and generated the following conclusions.15* 1. The following may be problems for an "asthmatic" recreational diver: 1.1 Although still a theoretical risk with no hard evidence, it was agreed that there may be greater risk in asthmatics with normal pulmonary mechanics than in the general population of gas retention leading to the pathological conditions of pulmonary barotrauma or air embolism. If present, this risk is likely to be low relative to other causes of decompression sickness. 1.2 It is agreed that evidence that there may be a greater risk than in the normal diving population of dissolved gas decompression sickness needs to be reexamined critically. 1.3 Limited exercise capability underwater. 1.4 The drugs used for the treatment of asthma may reduce the effectiveness of the pulmonary bubble filter. 2. Current policies may seem to be effective at reducing apparent asthmarelated incidents but not only may they exclude unnecessarily many potentially safe divers, but also paradoxically, they may increase the hazard for those asthmatics who do dive because these policies discourage appropriate assessment for asthmatics who do dive. 3. Asthma is an absolute or relative contraindication according to many guidelines but determined individuals have evaded medical scrutiny and disqualification. 4. A history of childhood asthma alone is not significant if there has been none since. 5. Hyperreactivity can be stimulated best in an evaluation by sub-maximal exercise. If quantitative assessment is required, it may be triggered also by histamine or methacholine. 6. Ventilatory capacity is best assessed by exercise capacity. 7. The diving candidate who has some "asthmatic" history is best assessed by first demonstrating a normal pulmonary function at rest (FVC, midexpiratory flow, FEVI, FEFu75) and then again after exercise. 8. Safety is not significantly diminished for those established and previously healthy recreational and/or professional divers who acquire adult-onset asthma but who can still meet the requirement of having normal pulmonary mechanics before and after exercise. 9. Chronic asthma, when quiescent and with adequate lung function, is acceptable even if corticosteroids are required. 10. Acute asthma, as evidenced by cough, wheeze, dyspnea or impaired exercise capability, is an obvious immediate contraindication,but recreational diving can be resumed when pulmonary function (FVC, expiratory flow, FEV,, FEFZs75) has returned to baseline. 11. There are insufficient data to exclude a slightly increased risk for asthmatic individuals who wish to participate in recreational compressed air diving. The degree of risk is not disqualifying, however, providing manifestations are completely controlled and pulmonary function is normal. 12. It is concluded that the degree of competency in making a medical assessment of fitness to dive is enhanced if the examining doctor has relevant knowledge or experignce of the underwater environment and its associated hazards. These conclusions are from the following source: Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea and Hyperbaric Medical Society, 1996, p 81; with permission.
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EVALUATION OF THE ASTHMATIC PATIENT FOR DIVING
Asthma is a condition in which obstruction to the airways is variable. There is a large degree of heterogeneity among asthmatic patients, and the factors that precipitate attacks vary tremendously. Some asthmatic patients demonstrate normal pulmonary function tests (PFTs) between attacks whereas others show evidence of airway obstruction despite being asymptomatic. Currently, there are no data on the effects of diving on airway mechanics in asthmatic patients. Which test will best determine the risk of diving for an individual with asthma? There are no standard testing protocols for the potential asthmatic diver; however, most experts are recommending baseline PFTs and exercise testing.', zo, zy Histamine, methacholine, and hypertonic saline inhalation challenge tests have been used for measuring bronchial hyperresponsiveness and have been ~ell-described.'-~, 34-37 These tests, however, are documented to have a high false-positive rate.8,44 The use of pharmacologic agents has a low specificity to identify asthma and a lack of relevance to the stimuli associated with diving. Hypertonic saline challenge tests more closely represent a stimuli to which a diver may be exposed to underwater; however, the sensitivity to detect asthma with hypertonic saline in the general community has been reported at 50%.30 Simpson and Meehan33performed standard hypertonic saline provocation tests on 50 unselected experienced divers to look for bronchial hyperresponsi~eness.~~ Five of these individuals had asthma and 23 were smokers. Twenty-three (45%) of this group would have been prevented from diving using the current standards in Australia. Of note, three of the asthmatic divers on prophylactic medication had normal testing. Hence, pharmacologic and saline challenge testing does not confer any additional information, and there is little rationale for their use to determine whether an asthmatic individual can dive. Because asthma does not appear to predispose to PBT, the limiting factor for asthmatic patients is determined by an adequate ventilatory capacity underwater. The UK Sports Diving Medical Committee recommends an exercise test, such as the 18-in step test. A decrease in peak flow of 15% would indicate exercise-induced asthma (EIA) and disqualify an individual.16 Harriesz0recommends that running in the open air is a more potent stimulus to bronchial constriction than exercising on a treadmill or bicycle ergometer.20In whichever test is used, the exercise level should increase heart rate to 80% of maximum (estimated 220 age in years X 0.8) for a duration of 3 to 5 minutes. Pre- and postexercise PFTs can compare peak flow (PEF) or FEV1, and a fall in either value of 20% is diagnostic. A fall in MEF 50%, however, is more sensitive.2l Another protocol is an exercise level to raise ventilation rate to approximately 20 times FEV, (50-60% maximum voluntary ventilation) for 6 to 8 minutes.' In this situation, a reduction of 15% or more in FEV, is considered evidence for EIA. Whichever exercise test is used, the exercise level should be above
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that expected to be reached while diving. (We use running in the open air as a challenge test with pre- and postexercise PFTs.) Normal is defined as within 2 standard deviations of the mean. The lower limit of normal at the fifth percentile level for vital capacity is less than 75% of predicted, functional residual capacity (FRC) is less than 70% or above 130%, residual volume (RV) is less than 65% or above 1359'0, total lung capacity (TLC) is less than 80% or above 12070, FEV, is less than SO%, FEV,:FVC is less than 85%, and FEF,,_,, is less than 65%.' Testing may be performed on medication if the asthmatic individual is well-controlled on inhaled steroids. OUR RECOMMENDATIONS
We recommend the following: 1. Individuals with a past history of asthma but who are asymptomatic, on no medications, and who have normal PFTs (flow rates and static lung volumes) can be considered for diving. (Normal is defined as within 2 standard deviations of the mean.) 2. Individuals with current asthma who are well-controlled on medications (including inhaled steroids and p agonists), have welldefined triggers, and who have normal PFTs can be considered for diving. An appropriate exercise challenge test should show no evidence of airway reactivity. 3. Individuals with exercise-induced, cold-induced, and emotionalinduced asthma should not dive unless airway reactivity can be controlled. PFTs with appropriate challenge testing should be normal. 4. After an episode of asthma, an individual should not dive until PFTs show that airway function has returned to normal. This can be measured at home with a PEF device.
SUMMARY
Asthma is no longer an absolute contraindication to diving. Individuals with normal airway function appear to be at low risk for idiopathic PBT. Proper screening with pulmonary function and exercise testing appear to be able to screen out those asthmatic patients who should not dive while identifying those who can be considered for diving. It is hoped that this change in perception will encourage more asthmatic individuals to seek medical advice prior to diving rather than not admit they have asthma on their diving medical form. Diving physicians then can explain the pathophysiology of diving and PBT to the asthmatic diving candidate and give that individual objective measurements of pulmonary function so that asthmatic patients can make informed decisions about diving. With proper education, the asthmatic diver can
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understand the importance of the various risk factors that may be associated with diving accidents.
References 1. Anderson SD: Special problems: Exercise-induced asthma. In OByme PM, Thomson
NC (eds): Manual of Asthma Management. London, WB Saunders, 1995, pp 621-643 2. Anderson SD, Smith CM: Osmotic challenges in the assessment of bronchial hyperresponsiveness. Am Rev Respir Dis 142:S43-S46, 1991 3. Anderson SD, Brannan J, Trevillion L, et a 1 Lung function and bronchial provocation tests for intending divers with a history of asthma. South Pacific Underwater Medicine Society Journal 25233-248, 1995 4. Bove AA, Neuman T, Kelsen S, et al: Observation on asthma in the recreational diving population [abstract]. Undersea Biomedical Research 19(suppl):18, 1992 5. Butler BD, Hills BA The lung as a filter for microbubbles. J Appl Physiol 4F537-543, 1979 6 . Butler BD, Hills BA: Transpulmonary passage of venous air emboli. J Appl Physiol 59:543-547, 1985 7. Clausen J: Pulmonary function testing. In Bordow RA, Moser KM (eds): Manual of Clinical Problems in Pulmonary Medicine, ed 4. Boston, Little, Brown, 1996, pp 9-18 8. Cockcroft DW, Murdock KY, Berscheid BA, et al: Sensitivity and specificity of histamine PC,, determination in a random selection of young college students. J Allergy Clin Immunol89:23-30, 1992 9. Corson KS, Dovenbarger JA, Moon RE, et al: Risk assessment of asthma for decompression illness [abstract]. Undersea Biomedical Research 18(suppl):16-17, 1991 10. Corson KS, Moon RE, Nealen ML, et al: A survey of diving asthmatics [abstract]. Undersea Biomedical Research 19(suppl):18-19, 1992 11. Deal EC, Wasserman SI, Soter NA, et al: Evaluation of the role played by mediators of immediate hypersensitivity in exercise-induced asthma. J Clin Invest 65:659-665, 1980 12. Divers Alert Network 1996 Report on Diving Accidents & Fatalities. Durham, NC, Divers Alert Network, Duke University Medical Center, 1994 13. Edmonds C, Walker D Scuba diving fatalities in Australia and New Zealand 1 The human factor. South Pacific Underwater Medicine Society Journal 19394-104, 1989 14. Edmonds C, Lowry L, Pennefather J: Diving and Subaquatic Medicine. Oxford, Butterworth Heinemann, 1992 15. Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea & Hyperbaric Medical Society, 1996; p 81 16. Farrell P:Assessment of asthmatic divers in the UK. In Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea & Hyperbaric Medical Society, 1996 17. Farrell PJS: Asthmatic amateur divers in the UK. South Pacific Underwater Medicine Society Journal 2522, 1995 18. Farrell PJS, Glanvill P:Diving practices of scuba divers with asthma. BMJ 300166,1990 19. Gorntan D, Veal A. SPUMS policy on asthma and fitness for diving. South Pacific Underwater Medicine Society Journal 25213,1995 20. Harries M: Why asthmatics should be allowed to dive. In Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea & Hyperbaric Medical Society, 1996, pp 7-12 21. Harries MG: Pulmonary limitations to performance in sport. BMJ 309113-115,1994 22. Liebow AA, Stark JE, Vogel J, et al: Intrapulmonary air trapping in submarine escape training casualties. US Armed Forces Med J 10:265-289, 1959 23. Malhotra MC, Wright HC: The effect of raised intrapleural pressure on the lungs of fresh unchilled cadavers. J Pathol Bacteriol82198-202, 1961 24. McAniff JJ: United States Underwater Diving Fatality Statistics, 1989 Report No. URISSR-91-22. Kingston, RI, University of Rhode Island, National Underwater Accident Data Center, 1991
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25. Moon RE: The case that asthmatics should not dive. In Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea & Hyperbaric Medical Society, 1996, pp 45-50 26. Morrison SC, Myburgh LD, Fourie ATJ, et al: The flow-volume curve, maximum voluntary ventilation and exercise capacity in divers under hyperbaric conditions [abstract]. Thoracic Society of Australia and New Zealand. Aust N Z J Med 19634,1989 27. Neuman T: Why restrict people who want to dive? In Linaweaver PG, Vorosmarti J (eds): Fitness to Dive. Thirty-fourth Undersea and Hyperbaric Medical Society Workshop, May 1987. Kensington, MD, Undersea & Hyperbaric Medical Society, 1987, pp 14-20 28. Neuman TS, Powers AT, Osborne DE: The prevalence of asthma, diabetes and epilepsy in a population of divers. Undersea Biomedical Research 15(suppl):62-63, 1988 29. Neuman TS, Bove AA, OConnor RD, et al. Asthma and diving. Ann Allergy 73:344350, 1994 30. Riedler J, Reade T, Dalton M, et al: Hypertonic saline challenge in an epidemiological survey of asthma in children. Am J Respir Crit Care Med 1501632-1639, 1994 31. Schaeffer KE, Nutly WP, Carey C, et al: Mechanisms in development of interstitial emphysema and air embolism on decompression from depth. J Appl Physiol 13:1529, 1958 32. Schanker H, Spector S: Relationship between asthma and scuba diving mortality [abstract]. J Allerg Clin Immunol 81:313, 1991 33. Simpson G, Meehan C Prevalence of bronchial hyperresponsiveness in a group of experienced scuba divers. South Pacific Underwater Medicine Society Journal 25249253, 1994 34. Smith CM, Anderson S D Hyperosmolarity as the stimulus to asthma induced by hyperventilation? J Allergy Clin Immunol77729-736,1986 35. Smith CM, Anderson SD: Inhalation provocation tests using non-isotonic aerosols. J Allergy Clin Immunol 84:781-790, 1989 36. Smith CM, Anderson S D InhalaSonal challenge using hypertonic saline in asthmatic subjects: A comparison with responses to hyperpnea, methacholine and water. Eur Respir J 3:144-151, 1990 37. Sterk PJ, Fabbri LM, Quanjer PH, et a1 Airway responsiveness: Standardized challenge testing with pharmacological, physiological and sensitizing stimuli in man. Eur Respir J ~ ( S U P P16):53-83, ~ 1993 38. Strauss RH, McFadden ER, Ingram RH, et al: Enhancement of exercise-induced asthma by cold air. N Engl J Med 297743-746, 1977 39. US Department of Health and Human Services: Executive Summary: Guidelines for the Diagnosis and Management of Asthma. National Asthma Education Program, Publication No. 91-3042A. Washington, DC, 1991 40. Wagner PD, Dantzker DR, Iacovoni VE, et al: Ventilation-perfusion inequality in asymptomatic asthma. Am Rev Respir Dis 118:511-524, 1978 41. Walker D Asthma and diving. South Pacific Underwater Medicine Society Journal 2488-90, 1994 42. Weiss LD, Van Meter KW: Cerebral air embolism in asthmatic scuba divers in a swimming pool. Chest 1071653-1654, 1995 43. Wood LD, Bryan AC: Exercise ventilatory mechanics at increased ambient pressure. J Appl Physiol44.231-237, 1978 44. Woolcock AJ, Peat JK, Salome DM, et a1 Prevalence of bronchial hyperresponsiveness and asthma in a rural adult population. Thorax 42:361-368,1987 Address reprint requests to Karen 8. Van Hoesen, MD Department of Emergency Medicine UCSD Medical Center San Diego, CA 92103-8676
ASTHMA UPDATE
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ASTHMA AND SCUBA DIVING Karen B. Van Hoesen, MD, and Tom S. Neuman, MD, FACE', FACPM
Until recently, asthma or a past history of asthma has been considered an absolute contraindication for scuba diving. We know, however, that asthmatic patients are diving and that there are many asthmatic individuals who wish to learn how to scuba dive. Divers, diving organizations, and diving physicians have struggled with the issues of safety for the asthmatic patient who wants to dive. Of concern is the theoretical risk that an asthmatic diver may develop acute airway obstruction while diving due to the unique conditions associated with breathing compressed air. Airway obstruction underwater could predispose that individual to pulmonary barotrauma during ascent. In addition, bronchoconstriction and panic on the surface may increased the risk for drowning. Our perception of diving with asthma has changed during the last 10 years. Asthma is not a single disease but a spectrum of disease with a wide range of severity and frequency of symptoms. The factors that precipitate attacks vary tremendously. Although we know asthmatic patients are diving safely, there are few controlled data on which to base risk assessments for asthmatic individuals who dive. Asthma is no longer an absolute contraindication for diving. The question now becomes which group of asthmatic patients can be considered at low risk from diving, what are the potential risks of diving for the asthmatic candidate, and how can we screen those individuals in whom there may be a relatively low risk for diving while excluding those individuals in whom the risk of diving may be unacceptable.
From the UCSD School of Medicine, La Jolla; and the Department of Emergency Medicine, Diving Medicine Clinic (KBVH) and Hyperbaric Medicine Center (EN), UCSD Medical Center, San Diego, California
IMMUNOLOGY AND ALLERGY CLINICS OF NORTH AMERICA
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THE PHYSICS AND PHYSIOLOGY OF DIVING
When a scuba diver descends in the water, the ambient pressure increases because of the weight of the water. In accordance with Boyle's Law, pressure and volume are inversely related at a constant temperature. As the diver descends, the surrounding ambient pressure increases and volume decreases. A volume of gas at the surface (1 atmosphere absolute = 1 ATA) will be compressed to half of its volume at 10 m of sea water (2 ATA). On ascent, surrounding pressure decreases and volume increases. A doubling of volume occurs from 10 m to the surface. Air pressure within the middle ears, sinuses, lungs, and other gas-filled spaces of the body must be equalized with changes in ambient pressure; if these spaces cannot expand or contract to accommodate the pressurerelated change in gas volume, tissue injury or barotrauma will occur. During scuba diving, a diver breathes compressed air at the same pressure as the surrounding water, hence he or she is able to maintain normal lung volumes at depth. On ascent as long as the diver exhales normally, expanding gas usually is vented off easily. If the airways have become obstructed, however, the diver does not exhale normally (as in the case of breath-holding) or if the rate of ascent exceeds the rate at which the expanding volume of air can escape, there is resultant expansion of gas in the lungs, which leads to alveolar rupture and pulmonary barotrauma (PBT). It has been shown experimentally that transpulmonic pressures (intratracheal pressure minus intrapleural pressure) of 95 to 110 cm of H,O are sufficient to rupture alveoli, allowing gas to escape into the interstitial spaces.23,31 Manifestations of pulmonary barotrauma include pneumomediastinum, subcutaneous emphysema, pneumothorax, and systemic embolization of gas into ruptured pulmonary veins producing arterial gas emboli (AGE). The formation of AGE is one of the most serious injuries associated with diving and is a major cause of death and disability among sport The most common cause of pulmonary barotrauma and AGE is a rapid or panic ascent while breath-holding. It occurs more frequently in novice and inexperienced divers. There may be a history of running out of air or panic associated with a rapid, uncontrolled ascent or uncontrolled positive buoyancy from inadvertent inflation of the buoyancy compensator or loss of the weight Additional conditions associated with diving that may be relevant to an asthmatic diver include an increased work of breathing with increased gas density and the added resistance of breathing through a demand regulator. This causes a reduction in inspiratory and expiratory flow rates, which can reduce ventilation and limit exercise performance.2'j Diving often is undertaken in cold water, where the inspired gas has a lower humidity and lower temperature than at the surface. RISKS OF DIVING FOR THE ASTHMATIC PATIENT
Lung structure and function in asthma are reviewed elsewhere.29.39 One of the major concerns of asthmatic patients diving is the susceptibil-
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ity to pulmonary barotrauma and AGE, even during a normal ascent. The risks for asthmatic individuals include (1) airway obstruction and (2) reduced exercise capacity. As described previously, airway obstruction, airway closure, and gas trapping caused by asthma and other pulmonary diseases can precipitate pulmonary barotrauma during ascent. Liebow et alZ2showed that partial pulmonary obstruction in large airways can lead to AGE. Weiss and Van MeteF reported two cases of AGE occurring in asthmatic individuals scuba diving in a swimming pool. Wagner et a140 demonstrated that indirect evidence for air trapping exists in asthmatic individuals with minimal or no symptoms. They showed marked abnormalities in ventilation perfusion ratios in asymptomatic asthmatic patients; as many as half of the lung units were perfused by closed airways that were ventilated by collaterals. It is important to note, however, that many of these individuals had abnormal baseline pulmonary function tests despite being asymptomatic. Certain conditions associated with diving may lead to acute bronchoconstriction. Scuba divers breathe air with a lower relative humidity, higher density, and lower temperature than air at the surface, and often are faced with strenuous exercise and potential inhalation of nebulized sea water. All of these conditions along with emotional stress may lead to bronchial constriction.ll,38 Airway cooling increases airway resistance in asthmatic subjects." Inhalation of hypertonic saline can provoke an attack in individuals with asthma." 3537 Shortness of breath and panic at depth may increase risk of rapid, uncontrolled ascent. The other concern for asthmatic individuals diving is the possibility of impaired exercise capacity. During exercise, any obstruction of the airways increases airways resistance, which prolongs the expiratory phase and demands a greater expiratory effort, leading to a rise in intrathoracic pressure.21Respiratory bronchioles tend to collapse, causing a fall in mid-expiratory flow (MEF,). Hard swimming against a strong current may cause normal divers to approach their maximum voluntary ventilation, hence increased airways resistance in an asthmatic patient can significantly reduce exercise t0lerance.4~ Asthmatic individuals who dive while on medication may have additional risks. All p2agonists are pulmonary vasodilators. Dilation of the pulmonary vasculature may allow venous bubbles that would normally be filtered by the pulmonary vasculature to enter the arterial circulation as gas emboli. This arterialization of otherwise asymptomatic emboli might result in AGE or decompression sickness (DCS).5, Conversely, the asthmatic diver may be safer because of increased awareness and education. The majority of cases of AGE are due to errors in judgment and behavior rather than structural abnormalities in the lungs. Those asthmatic divers who have been well educated and who understand the pathophysiology of diving and pulmonary barotrauma may take more precautions to avoid a rapid ascent, thus reducing their risk for AGE.
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DIVING STATISTICS Prevalence of Asthmatic Individuals in the Diving Population
There are estimated to be between 2.5 and 3 million sport scuba divers in the United States.24In analyzing dive accident statistics, the diving community has been criticized because asthmatic individuals have not been ”allowed to dive.” Therefore, they are not represented in the accident data. We know, however, that asthmatic individuals are diving. Several studies have shown the general prevalence of asthmatic patients in the diving population is approximately 5% to 8%, which is similar to the 4% to 8% of the general population who has Neuman et alZ9asked 1745 newly certified divers via questionnaire if they had asthma. Thirty-three (8.1%) of 405 respondents had asthma, and 19 of those divers had made 100 dives without accident. In another survey of 1000 divers, 37 of 696 respondents had a history of asthma (5.3%), of which 13 were currently asthmatic, which was defined as having an attack within 1 year or using bronchodilators on a regular basisy In a much larger survey in 1992, 10,422 divers responded to a questionnaire in Skin Diver Mugazine; 870 (8.3%) answered yes to the question ”have you ever had asthma,” 343 (3.3%) said they currently have asthma, and 276 (2.6%)stated they dive with a ~ t h m aIn . ~the United Kingdom, 4% of the amateur diving population is a~thmatic.’~ Thus, it appears the prevalence of asthma in the diving population is similar to that in the general population at large. To characterize asthmatic individuals who scuba dive, Corson et allo placed a questionnaire in Alert Diver magazine. In that survey, 243 (88.7%)of 279 respondents reported taking some medication for asthma, and 55.8% took medication just before a dive. Of those who wheezed, 13.3% had symptoms daily and 17.3% had symptoms weekly. Seventythree (26.4%)respondents had been hospitalized for asthma. Dive Accidents
In Britain, the British Sub-Aqua Club (BSAC) has allowed individuals with asthma to dive for many years. Farrell and Glanvillla reported the results of a questionnaire placed in a British dive magazine; 104 positive respondents had a history of asthma and logged 12,864 dives safely without any instances of PBT. Eighty-nine of the 104 individuals had asthma since childhood, 70 wheezed less than 12 times per year, and 22 wheezed daily. Ninety-six divers used an inhaler just before diving and some were using steroids. Nine individuals wheezed daily, dove within 1 hour of wheezing, and logged more than 1241 dives without incidents. Although this was a self-selected group that responded, it still suggests that some asthmatic individuals are diving safely. As a follow-up study, FarrellI6surveyed all the hyperbaric cham-
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bers during 1991 to 1993 for cases of decompression illness (DCI), which combines DCS with AGE. He found 393 nonasthmatic individuals and 9 asthmatic individuals, indicating no statistical difference between the normal population and the asthmatic population.16 The Divers Alert Network (DAN) has records of all dive accident data submitted in the United States, Canada, and the Caribbean. Every year they publish the DAN Report on Diving Accidents and Fatalities. A retrospective review of the DAN data from 1987 to 1990 was conducted to assess risk of asthma for DCI? It was determined that 54 of 1213 divers with DCI had a history of asthma, of which 25 were currently asthmatic (suffering an attack within 1 year or using bronchodilators on a regular basis). Sixteen (8%) divers with AGE had a history of asthma, of which 7 (3.6%) were currently asthmatic. In the control population of 696 divers, 37 divers admitted a history of asthma (5.3%) and 13 (1.9%) were currently asthmatic. Although the data suggest there may be a 1.6fold increase in the risk for AGE in asthmatic divers, the data do not reach statistical significance (confidence interval 0.80-2.99). No information is given about asthma severity, pulmonary function testing, or the role asthma played in the accidents. A more recent update of the DAN data was presented at the Undersea and Hyperbaric Medical Society (UHMS) workshop entitled Are Asfhmatics Fit to Dive?,which included all cases collected from 1987 to 1994.25In 3359 cases of DCI, 6.65% of the AGE cases had asthma (compared with 5.32% of controls), giving an odds ratio of 1.25. In addition, 3.09% of AGE cases had current asthma, resulting in an odds ratio of 1.65. Although the probability of AGE may be 1.25 times higher for asthmatic patients and 1.65 times higher for current asthmatic patients, the estimate of the risk does not reach statistical significance, as the 95% confidence interval contains 1.0. Surveys and retrospective reviews may not account for those asthmatic individuals who have selected themselves out of diving or discontinued diving for asthma-related problems. Additionally, the discussed studies do not compare the level of severity of asthma in these divers. There are no records of predive medication, pulmonary function tests, or characteristics of the dive, such as a rapid or uncontrolled ascent. Based on the information given, there is no firm statistical evidence for an increased risk of DCI in asthmatic patients who scuba dive. At the current rate of diving accidents and accident data collection, however, it has been estimated that it will take another 25 years to statistically exclude asthma as a risk factor.= FarrelP currently is conducting a prospective study of more than 250 asthmatic divers who have completed more than 20,000 uneventful dives, including more than 20 emergency free ascents, without incidents.16 Deaths Associated with Diving and Asthma
Approximately 80 to 100 diving fatalities have been reported annually in the United States during the last 10 years.l*,24 At the University
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of Rhode Island’s National Underwater Accident Data Center, only 1 of 2132 deaths was in an individual with asthma; however, no information about the death is available, and the role of asthma is uncertain.” Of 18 consecutive scuba fatalities at the Los Angeles Coroner’s office between 1985 to 1990, none were linked to asthma.32 In Australia and New Zealand, asthma was found to be a contributing factor in 9% of diving deaths.I4An autopsy identified drowning as the cause of death in seven and pulmonary barotrauma in two of the victims. The role of asthma in these deaths was not ~1ear.l~ When Walker4I reviewed 201 Australian and 120 New Zealand scuba diving fatalities, he found only four cases in which asthma could have been a possible contributing factor; however, there were significant additional factors that could have caused the fatalities.4l In 1994, there were 97 deaths reported by DAN. In only one case was asthma mentioned as a possible contributing factor. The victim had a past history of asthma, and the cause of death was drowning.12 Diving is not absolutely safe and there are inherent risks. Incidents will continue to occur; however, asthmatic individuals appear not to be overrepresented in the accident statistics for DCI or diving fatalities. Data are needed from prospective comparisons of asthmatic and nonasthmatic divers with concomitant evaluation of pulmonary function testing, dive profiles, and the number of incidents in each group. INTERNATIONAL RECOMMENDATION FOR DIVING AND ASTHMA
As asthmatic individuals appear to be diving without an increase in accidents compared with nonasthmatic divers, the question now becomes which asthmatic patients can dive with a reasonable degree of safety? Three diving medical societies recently have published statements regarding asthmatic individuals and scuba diving. Recommendationsfrom Britain
The UK Sports Diving Medical Committee Asthma Standard16 stated: ”The theoretical risks should be fully explained to the asthmatic diver. There is little, if any, evidence that the moderate, controlled asthmatic who follows the guidelines below is more at risk than the normal population. Asthmatics may dive if they have allergic asthma, but not if they have cold-induced, exercise-induced or emotion-induced asthma. All asthmatics should be managed in accordance with the British Thoracic Society guideline. Only well-controlled asthmatics may dive. Asthmatics should not dive if they have needed a bronchodilator in the last 48 hours or have any other chest symptoms.”
The committee also advise the a
p2 agonist may be taken pre-diving as
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a preventive measure but not to relieve bronchial spasm at the time
of diving. Recommendations From South Pacific Underwater Medicine Society (SPUMSY
SPUMS Policy Statement on the Prevalence of Asthma in Australian Diving Candidateslyis as follows: 1. A history of asthma is common in diving candidates. 2. The assessment of risk for a diving candidate with a history of asthma should be conducted by a medical practitioner who has had training in diving medicine.
SPUMS Policy o n the Importance of Asthma in Diving19 is as follows: 1. Asthma is a potential cause of mortality and morbidity in divers. The leveI of risk in this context needs to be measured. 2. Diving may precipitate an asthma attack. 3. Asthmatics may have limited exercise capacity and are at risk of shortness of breath, panic and drowning on the water surface. 4. Asthmatics who dive may be a self-selected (i.e., survivor) population and hence their experience may not be representative of the risks of diving for the general asthmatic population. 5. Current information (from descriptive database) suggests that the relative risk for asthmatics who dive (compared with nonasthmatics) for a decompression illness is about two.
SPUMS Policy on the Assessment of Risk for a Diving Candidate with a History of AsthmaI9 is as follows: 1. The determination of risk for diving in someone with a history of asthma requires a gradation of the severity and currency of their asthma. 2. Risk stratification for someone with a history of asthma who wishes to dive will require a thorough history, examination and often lung function testing, which may include provocation testing (and especially with exercise and/or hypertonic saline). This may need to be repeated if the person elects to dive. 3. Provocation testing with exercise and/or hypertonic saline (rather than with histamine and methacholine) may be more specific for asthma that is of concern in diving. The significance of a positive result is more easily understood by the diver. 4. As the risk for diving in someone with a history of asthma is uncertain, permanent records should be retained as part of a SPUMS-sponsored study.
Undersea and Hyperbaric Medical Society (UHMS) Conclusions In June 1995, the UHMS held a symposium entitled Are Asthmatics Fit to Dive?,which was attended by asthma and diving medical experts *Recommendations provided in this section are from the following: Gorman D, Veal A: SPUMS policy on asthma and fitness for diving. South Pacific Underwater Medicine Society Journal 25213, 1995; with permission.
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from around the world. They critically reviewed the pathophysiology regarding an asthmatic individual participating in diving and generated the following conclusions.15* 1. The following may be problems for an "asthmatic" recreational diver: 1.1 Although still a theoretical risk with no hard evidence, it was agreed that there may be greater risk in asthmatics with normal pulmonary mechanics than in the general population of gas retention leading to the pathological conditions of pulmonary barotrauma or air embolism. If present, this risk is likely to be low relative to other causes of decompression sickness. 1.2 It is agreed that evidence that there may be a greater risk than in the normal diving population of dissolved gas decompression sickness needs to be reexamined critically. 1.3 Limited exercise capability underwater. 1.4 The drugs used for the treatment of asthma may reduce the effectiveness of the pulmonary bubble filter. 2. Current policies may seem to be effective at reducing apparent asthmarelated incidents but not only may they exclude unnecessarily many potentially safe divers, but also paradoxically, they may increase the hazard for those asthmatics who do dive because these policies discourage appropriate assessment for asthmatics who do dive. 3. Asthma is an absolute or relative contraindication according to many guidelines but determined individuals have evaded medical scrutiny and disqualification. 4. A history of childhood asthma alone is not significant if there has been none since. 5. Hyperreactivity can be stimulated best in an evaluation by sub-maximal exercise. If quantitative assessment is required, it may be triggered also by histamine or methacholine. 6. Ventilatory capacity is best assessed by exercise capacity. 7. The diving candidate who has some "asthmatic" history is best assessed by first demonstrating a normal pulmonary function at rest (FVC, midexpiratory flow, FEVI, FEFu75) and then again after exercise. 8. Safety is not significantly diminished for those established and previously healthy recreational and/or professional divers who acquire adult-onset asthma but who can still meet the requirement of having normal pulmonary mechanics before and after exercise. 9. Chronic asthma, when quiescent and with adequate lung function, is acceptable even if corticosteroids are required. 10. Acute asthma, as evidenced by cough, wheeze, dyspnea or impaired exercise capability, is an obvious immediate contraindication,but recreational diving can be resumed when pulmonary function (FVC, expiratory flow, FEV,, FEFZs75) has returned to baseline. 11. There are insufficient data to exclude a slightly increased risk for asthmatic individuals who wish to participate in recreational compressed air diving. The degree of risk is not disqualifying, however, providing manifestations are completely controlled and pulmonary function is normal. 12. It is concluded that the degree of competency in making a medical assessment of fitness to dive is enhanced if the examining doctor has relevant knowledge or experignce of the underwater environment and its associated hazards. These conclusions are from the following source: Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea and Hyperbaric Medical Society, 1996, p 81; with permission.
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EVALUATION OF THE ASTHMATIC PATIENT FOR DIVING
Asthma is a condition in which obstruction to the airways is variable. There is a large degree of heterogeneity among asthmatic patients, and the factors that precipitate attacks vary tremendously. Some asthmatic patients demonstrate normal pulmonary function tests (PFTs) between attacks whereas others show evidence of airway obstruction despite being asymptomatic. Currently, there are no data on the effects of diving on airway mechanics in asthmatic patients. Which test will best determine the risk of diving for an individual with asthma? There are no standard testing protocols for the potential asthmatic diver; however, most experts are recommending baseline PFTs and exercise testing.', zo, zy Histamine, methacholine, and hypertonic saline inhalation challenge tests have been used for measuring bronchial hyperresponsiveness and have been ~ell-described.'-~, 34-37 These tests, however, are documented to have a high false-positive rate.8,44 The use of pharmacologic agents has a low specificity to identify asthma and a lack of relevance to the stimuli associated with diving. Hypertonic saline challenge tests more closely represent a stimuli to which a diver may be exposed to underwater; however, the sensitivity to detect asthma with hypertonic saline in the general community has been reported at 50%.30 Simpson and Meehan33performed standard hypertonic saline provocation tests on 50 unselected experienced divers to look for bronchial hyperresponsi~eness.~~ Five of these individuals had asthma and 23 were smokers. Twenty-three (45%) of this group would have been prevented from diving using the current standards in Australia. Of note, three of the asthmatic divers on prophylactic medication had normal testing. Hence, pharmacologic and saline challenge testing does not confer any additional information, and there is little rationale for their use to determine whether an asthmatic individual can dive. Because asthma does not appear to predispose to PBT, the limiting factor for asthmatic patients is determined by an adequate ventilatory capacity underwater. The UK Sports Diving Medical Committee recommends an exercise test, such as the 18-in step test. A decrease in peak flow of 15% would indicate exercise-induced asthma (EIA) and disqualify an individual.16 Harriesz0recommends that running in the open air is a more potent stimulus to bronchial constriction than exercising on a treadmill or bicycle ergometer.20In whichever test is used, the exercise level should increase heart rate to 80% of maximum (estimated 220 age in years X 0.8) for a duration of 3 to 5 minutes. Pre- and postexercise PFTs can compare peak flow (PEF) or FEV1, and a fall in either value of 20% is diagnostic. A fall in MEF 50%, however, is more sensitive.2l Another protocol is an exercise level to raise ventilation rate to approximately 20 times FEV, (50-60% maximum voluntary ventilation) for 6 to 8 minutes.' In this situation, a reduction of 15% or more in FEV, is considered evidence for EIA. Whichever exercise test is used, the exercise level should be above
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that expected to be reached while diving. (We use running in the open air as a challenge test with pre- and postexercise PFTs.) Normal is defined as within 2 standard deviations of the mean. The lower limit of normal at the fifth percentile level for vital capacity is less than 75% of predicted, functional residual capacity (FRC) is less than 70% or above 130%, residual volume (RV) is less than 65% or above 1359'0, total lung capacity (TLC) is less than 80% or above 12070, FEV, is less than SO%, FEV,:FVC is less than 85%, and FEF,,_,, is less than 65%.' Testing may be performed on medication if the asthmatic individual is well-controlled on inhaled steroids. OUR RECOMMENDATIONS
We recommend the following: 1. Individuals with a past history of asthma but who are asymptomatic, on no medications, and who have normal PFTs (flow rates and static lung volumes) can be considered for diving. (Normal is defined as within 2 standard deviations of the mean.) 2. Individuals with current asthma who are well-controlled on medications (including inhaled steroids and p agonists), have welldefined triggers, and who have normal PFTs can be considered for diving. An appropriate exercise challenge test should show no evidence of airway reactivity. 3. Individuals with exercise-induced, cold-induced, and emotionalinduced asthma should not dive unless airway reactivity can be controlled. PFTs with appropriate challenge testing should be normal. 4. After an episode of asthma, an individual should not dive until PFTs show that airway function has returned to normal. This can be measured at home with a PEF device.
SUMMARY
Asthma is no longer an absolute contraindication to diving. Individuals with normal airway function appear to be at low risk for idiopathic PBT. Proper screening with pulmonary function and exercise testing appear to be able to screen out those asthmatic patients who should not dive while identifying those who can be considered for diving. It is hoped that this change in perception will encourage more asthmatic individuals to seek medical advice prior to diving rather than not admit they have asthma on their diving medical form. Diving physicians then can explain the pathophysiology of diving and PBT to the asthmatic diving candidate and give that individual objective measurements of pulmonary function so that asthmatic patients can make informed decisions about diving. With proper education, the asthmatic diver can
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understand the importance of the various risk factors that may be associated with diving accidents.
References 1. Anderson SD: Special problems: Exercise-induced asthma. In OByme PM, Thomson
NC (eds): Manual of Asthma Management. London, WB Saunders, 1995, pp 621-643 2. Anderson SD, Smith CM: Osmotic challenges in the assessment of bronchial hyperresponsiveness. Am Rev Respir Dis 142:S43-S46, 1991 3. Anderson SD, Brannan J, Trevillion L, et a 1 Lung function and bronchial provocation tests for intending divers with a history of asthma. South Pacific Underwater Medicine Society Journal 25233-248, 1995 4. Bove AA, Neuman T, Kelsen S, et al: Observation on asthma in the recreational diving population [abstract]. Undersea Biomedical Research 19(suppl):18, 1992 5. Butler BD, Hills BA The lung as a filter for microbubbles. J Appl Physiol 4F537-543, 1979 6 . Butler BD, Hills BA: Transpulmonary passage of venous air emboli. J Appl Physiol 59:543-547, 1985 7. Clausen J: Pulmonary function testing. In Bordow RA, Moser KM (eds): Manual of Clinical Problems in Pulmonary Medicine, ed 4. Boston, Little, Brown, 1996, pp 9-18 8. Cockcroft DW, Murdock KY, Berscheid BA, et al: Sensitivity and specificity of histamine PC,, determination in a random selection of young college students. J Allergy Clin Immunol89:23-30, 1992 9. Corson KS, Dovenbarger JA, Moon RE, et al: Risk assessment of asthma for decompression illness [abstract]. Undersea Biomedical Research 18(suppl):16-17, 1991 10. Corson KS, Moon RE, Nealen ML, et al: A survey of diving asthmatics [abstract]. Undersea Biomedical Research 19(suppl):18-19, 1992 11. Deal EC, Wasserman SI, Soter NA, et al: Evaluation of the role played by mediators of immediate hypersensitivity in exercise-induced asthma. J Clin Invest 65:659-665, 1980 12. Divers Alert Network 1996 Report on Diving Accidents & Fatalities. Durham, NC, Divers Alert Network, Duke University Medical Center, 1994 13. Edmonds C, Walker D Scuba diving fatalities in Australia and New Zealand 1 The human factor. South Pacific Underwater Medicine Society Journal 19394-104, 1989 14. Edmonds C, Lowry L, Pennefather J: Diving and Subaquatic Medicine. Oxford, Butterworth Heinemann, 1992 15. Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea & Hyperbaric Medical Society, 1996; p 81 16. Farrell P:Assessment of asthmatic divers in the UK. In Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea & Hyperbaric Medical Society, 1996 17. Farrell PJS: Asthmatic amateur divers in the UK. South Pacific Underwater Medicine Society Journal 2522, 1995 18. Farrell PJS, Glanvill P:Diving practices of scuba divers with asthma. BMJ 300166,1990 19. Gorntan D, Veal A. SPUMS policy on asthma and fitness for diving. South Pacific Underwater Medicine Society Journal 25213,1995 20. Harries M: Why asthmatics should be allowed to dive. In Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea & Hyperbaric Medical Society, 1996, pp 7-12 21. Harries MG: Pulmonary limitations to performance in sport. BMJ 309113-115,1994 22. Liebow AA, Stark JE, Vogel J, et al: Intrapulmonary air trapping in submarine escape training casualties. US Armed Forces Med J 10:265-289, 1959 23. Malhotra MC, Wright HC: The effect of raised intrapleural pressure on the lungs of fresh unchilled cadavers. J Pathol Bacteriol82198-202, 1961 24. McAniff JJ: United States Underwater Diving Fatality Statistics, 1989 Report No. URISSR-91-22. Kingston, RI, University of Rhode Island, National Underwater Accident Data Center, 1991
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25. Moon RE: The case that asthmatics should not dive. In Elliott DH (ed): Are Asthmatics Fit to Dive? Kensington, MD, Undersea & Hyperbaric Medical Society, 1996, pp 45-50 26. Morrison SC, Myburgh LD, Fourie ATJ, et al: The flow-volume curve, maximum voluntary ventilation and exercise capacity in divers under hyperbaric conditions [abstract]. Thoracic Society of Australia and New Zealand. Aust N Z J Med 19634,1989 27. Neuman T: Why restrict people who want to dive? In Linaweaver PG, Vorosmarti J (eds): Fitness to Dive. Thirty-fourth Undersea and Hyperbaric Medical Society Workshop, May 1987. Kensington, MD, Undersea & Hyperbaric Medical Society, 1987, pp 14-20 28. Neuman TS, Powers AT, Osborne DE: The prevalence of asthma, diabetes and epilepsy in a population of divers. Undersea Biomedical Research 15(suppl):62-63, 1988 29. Neuman TS, Bove AA, OConnor RD, et al. Asthma and diving. Ann Allergy 73:344350, 1994 30. Riedler J, Reade T, Dalton M, et al: Hypertonic saline challenge in an epidemiological survey of asthma in children. Am J Respir Crit Care Med 1501632-1639, 1994 31. Schaeffer KE, Nutly WP, Carey C, et al: Mechanisms in development of interstitial emphysema and air embolism on decompression from depth. J Appl Physiol 13:1529, 1958 32. Schanker H, Spector S: Relationship between asthma and scuba diving mortality [abstract]. J Allerg Clin Immunol 81:313, 1991 33. Simpson G, Meehan C Prevalence of bronchial hyperresponsiveness in a group of experienced scuba divers. South Pacific Underwater Medicine Society Journal 25249253, 1994 34. Smith CM, Anderson S D Hyperosmolarity as the stimulus to asthma induced by hyperventilation? J Allergy Clin Immunol77729-736,1986 35. Smith CM, Anderson SD: Inhalation provocation tests using non-isotonic aerosols. J Allergy Clin Immunol 84:781-790, 1989 36. Smith CM, Anderson S D InhalaSonal challenge using hypertonic saline in asthmatic subjects: A comparison with responses to hyperpnea, methacholine and water. Eur Respir J 3:144-151, 1990 37. Sterk PJ, Fabbri LM, Quanjer PH, et a1 Airway responsiveness: Standardized challenge testing with pharmacological, physiological and sensitizing stimuli in man. Eur Respir J ~ ( S U P P16):53-83, ~ 1993 38. Strauss RH, McFadden ER, Ingram RH, et al: Enhancement of exercise-induced asthma by cold air. N Engl J Med 297743-746, 1977 39. US Department of Health and Human Services: Executive Summary: Guidelines for the Diagnosis and Management of Asthma. National Asthma Education Program, Publication No. 91-3042A. Washington, DC, 1991 40. Wagner PD, Dantzker DR, Iacovoni VE, et al: Ventilation-perfusion inequality in asymptomatic asthma. Am Rev Respir Dis 118:511-524, 1978 41. Walker D Asthma and diving. South Pacific Underwater Medicine Society Journal 2488-90, 1994 42. Weiss LD, Van Meter KW: Cerebral air embolism in asthmatic scuba divers in a swimming pool. Chest 1071653-1654, 1995 43. Wood LD, Bryan AC: Exercise ventilatory mechanics at increased ambient pressure. J Appl Physiol44.231-237, 1978 44. Woolcock AJ, Peat JK, Salome DM, et a1 Prevalence of bronchial hyperresponsiveness and asthma in a rural adult population. Thorax 42:361-368,1987 Address reprint requests to Karen 8. Van Hoesen, MD Department of Emergency Medicine UCSD Medical Center San Diego, CA 92103-8676