Diving: what to tell the patient with asthma and why?

Until a decade ago, divers with asthma were uniformly barred from diving with compressed air. This prohibition was based more on theoretical concerns for barotrauma than on actual data. Follow-up studies, although retrospective, do not support a ban on recreational or commercial diving for divers with stable asthma. These studies have noted that, despite the prohibition on diving, many divers with asthma have logged multiple dives without negative consequences. When those who have suffered diving-related barotrauma have undergone physiologic testing, measurements of small airways dysfunction (maximal mid-expiratory flow rates) have been lower than measurements for comparable divers who have never suffered diving accidents. Follow-up studies with long-term commercial divers have shown that a small percentage of individuals who have sufferred diving-related barotrauma also develop abnormal maximal mid-expiratory flow rates and even some airway hyperreactivity. These latter findings correlate with the changes that occur in chronic asthmatic patients, especially those who are not well treated. The decision as to whether an asthmatic patient should be allowed to dive rests on the individual's physiologic function, maturity, and insight into the consequences of poorly managed airway inflammation and bronchospasm.     

Recreational scuba diving, patent foramen ovale and their associated risks

Scuba diving has become a popular leisure time activity with distinct risks to health owing to its physical characteristics. Knowledge of the behaviour of any mixture of breathable gases under increased ambient pressure is crucial for safe diving and gives clues as to the pathophysiology of compression or decompression related disorders. Immersion in cold water augments cardiac pre- and afterload due to an increase of intrathoracic blood volume and peripheral vasoconstriction. In very rare cases, the vasoconstrictor response can lead to pulmonary oedema. Immersion of the face in cold water is associated with bradycardia mediated by increased vagal tone. In icy water, the bradycardia can be so pronounced, that syncope results. For recreational dives, compressed air (i.e., 4 parts nitrogen and 1 part oxygen) is the preferred breathing gas. Its use is limited for diving to 40 to 50 m, otherwise nitrogen narcosis ("rapture of the deep") reduces a diver's cognitive function and increases the risk of inadequate reactions. At depths of 60 to 70 m oxygen toxicity impairs respiration and at higher partial pressures also functioning of the central nervous system. The use of special nitrogen-oxygen mixtures ("nitrox", 60% nitrogen and 40% oxygen as the typical example) decreases the probability of nitrogen narcosis and probably bubble formation, at the cost of increased risk of oxygen toxicity. Most of the health hazards during dives are consequences of changes in gas volume and formation of gas bubbles due to reduction of ambient pressure during a diver's ascent. The term barotrauma encompasses disorders related to over expansion of gas filled body cavities (mainly the lung and the inner ear). Decompression sickness results from the growth of gas nuclei in predominantly fatty tissue. Arterial gas embolism describes the penetration of such gas bubbles into the systemic circulation, either due to pulmonary barotrauma, transpulmonary passage after massive bubble formation ("chokes") or cardiac shunting. In recreational divers, neurological decompression events comprise 80% of reported cases of major decompression problems, most of the time due to pathological effects of intravascular bubbles. In divers with a history of major neurological decompression symptoms without evident cause, transoesophageal echocardiography must be performed to exclude a patent foramen ovale. If a cardiac right-to-left shunt is present, we advise divers with a history of severe decompression illness to stop diving. If they refuse to do so, it is crucial that they change their diving habits, minimising the amount of nitrogen load on the tissue. There is ongoing debate about the long term risk of scuba diving. Neuro-imaging studies revealed an increased frequency of ischaemic brain lesions in divers, which do not correlate well with subtle functional neurological deficits in experienced divers. In the light of the high prevalence of venous gas bubbles even after dives in shallow water and the presence of a cardiac right-to-left shunt in a quarter of the population (i.e., patent foramen ovale), arterialisation of gas bubbles might be more frequent than usually presumed.     

Pseudoephedrine for the prevention of barotitis media: a controlled clinical trial in underwater divers.

STUDY OBJECTIVE: To determine the efficacy and safety of decongestant prophylaxis among first-time underwater divers in the prevention of barotitis media (middle ear squeeze). DESIGN: Randomized, double-blind, prospective clinical trial. SETTING: Recreational diving schools in Panama City, Florida. TYPE OF PARTICIPANTS: One hundred twenty volunteer scuba divers under the supervision of certified instructors. INTERVENTIONS: After randomization, each subject received a 60-mg tablet of pseudoephedrine or placebo 30 minutes before diving. Prospective data were collected, including subject demographics, signs and symptoms of middle ear squeeze during the dive, and possible drug side effects. The otoscopic appearance of the tympanic membrane was graded according to the amount of hemorrhage in the eardrum, with Teed scores ranging from 0 (normal) to 5 (gross hemorrhage and rupture). chi 2 and t-tests were applied with significance set at P less than .05). The Mantel-Haenszel test was used to test the null hypothesis that the mean Teed scores of the two treatment groups were equal. RESULTS: A total of 116 subjects met the inclusion criteria and completed the study; 60 received 60 mg pseudoephedrine, and 56 received placebo. The treatment groups were similar with regard to age, sex, medical history, and depth of the first dive (P greater than .5). Ear discomfort and blockage during the dive were present in 8% (five of 60) of those receiving pseudoephedrine versus 32% (18 of 56) of the control group (P = .001). Similarly, the pseudoephedrine group had smaller Teed scores after diving than did the control subjects (P = .003). Adverse effects were minimal; two patients experienced dizziness and nausea. CONCLUSION: These results suggest that the use of an oral decongestant before diving decreases the incidence and severity of middle ear squeeze in novice divers.     

A Review of Asthma and Scuba Diving

An increasing number of asthmatics participate in recreational scuba diving. This activity presents unique physical and physiological challenges to the respiratory system. This review addresses the susceptibility of divers with asthma to diving accidents, acute asthmatic attacks, and long-term exacerbation of their disease. Recommendations on fitness to dive with asthma and airway hyperresponsiveness are provided.     

Patent foramen ovale in scuba divers. A report of two cases and a brief review of the literature.

Scuba diving (diving with a self-contained underwater breathing apparatus) has become a popular sport. Decompression illness may be due to the formation of gas bubbles in various body tissues at an increased ambient pressure. The gas can pass from the systemic venous circulation into the arterial circulation as a result of either pulmonary barotrauma or intravascular shunting. Gas emboli may be the cause of an increased prevalence of brain lesions in sport divers. The management of scuba divers (professionals and amateurs) with a patent foramen ovale is not clear. We present the cases of 2 subjects with decompression illness and a patent foramen ovale and briefly review the literature on this combination.     

Scuba diving is possible and safe for patients with haemophilia

Summary. For a long time, physical activities have been contraindicated in haemophiliacs or were restricted to few activities. Sports are nowadays advocated for haemophiliacs. Although various lists of physical activities have been proposed, scuba diving is never mentioned. Thus, with a group of haemophilic volunteers, a study was launched on whether, with strict medical follow‐up, scuba diving could be allowed for patients with haemophilia. All the participants followed a training program including theory and assessment. In 6 years, a total of 517 dives were performed by 20 patients with congenital bleeding disorders. Nine were under prophylaxis for haemophilia, and nine received on‐demand treatment. Two patients had type I von Willebrand’s disease. Among the 20 patients, 12 made 12–153 dives, whereas six made eight dives each. No incident was noted during or after the dives. Thus, scuba diving can be authorized for PWH, if they have none of the specific medical contraindications for diving and if they have received medical training allowing them to manage their disease themselves.     

Pulmonary edema associated with scuba diving : case reports and review.

Acute pulmonary edema has been associated with cold-water immersion in swimmers and divers. We report on eight divers using a self-contained underwater breathing apparatus (scuba) who developed acute pulmonary edema manifested by dyspnea, hypoxemia, and characteristic chest radiographic findings. All cases occurred in cold water. All scuba divers were treated with complete resolution, and three have returned to diving without further episodes. Mechanisms that would contribute to a raised capillary transmural pressure or to a reduced blood-gas barrier function or integrity are discussed. Pulmonary edema in scuba divers is multifactorial, and constitutional factors may play a role. Physicians should be aware of this potential, likely underreported, problem in scuba divers.     

Are recreational SCUBA divers with asthma at increased risk?

Background and objective: Asthma has traditionally been regarded as a contraindication to self-contained underwater breathing apparatus (SCUBA) diving, although large numbers of patients with asthma dive. The aim of the review is to provide an update on current knowledge on potential disease-related hazards in SCUBA divers with asthma. Methods: Systematic literature review based on the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. Results: Seven studies met the criteria for inclusion in the review (comprising a total of 560 subjects). Five studies reported an increased risk for developing diving-related injuries in divers with asthma, based on case reports (n = 1), case history combined with objective assessment (n = 1), and dives and/or simulated dives (n = 3). The remaining studies (n = 2) were based on self-reported diving habits in divers suffering from asthma, obtained from anonymous questionnaires in diving magazines, reported no diving-related injuries among respondents. Conclusion: Due to limited evidence it is difficult to draw valid conclusions, but there are indications that recreational divers with asthma may be at increased risk for diving-related injuries compared to non-asthmatic divers. However, it is of at most importance to obtain further evidence from large-scale, well-designed studies.     

Risk of decompression illness among 230 divers in relation to the presence and size of patent foramen ovale.

BACKGROUND: The risk of developing decompression illness (DCI) in divers with a patent foramen ovale (PFO) has not been directly determined so far; neither has it been assessed in relation to the PFO's size. METHODS: In 230 scuba divers (age 39+/-8 years), contrast trans-oesophageal echocardiography (TEE) was performed for the detection and size grading (0-3) of PFO. Prior to TEE, the study individuals answered a detailed questionnaire about their health status and about their diving habits and accidents. For inclusion into the study, > or =200 dives and strict adherence to decompression tables were required. RESULTS: Sixty-three divers (27%) had a PFO. Overall, the absolute risk of suffering a DCI event was 2.5 per 10(4) dives. There were 18 divers (29%) with, and 10 divers (6%) without, PFO who had experienced > or =1 major DCI events P=0.016. In the group with PFO, the incidence per 10(4) dives of a major DCI, a DCI lasting longer than 24 h and of being treated in a decompression chamber amounted to 5.1 (median 0, interquartile range [IQR] 0-10.0), 1.9 (median 0, IQR 0-4.0) and 3.6 (median 0, IQR 0-9.8), respectively and was 4.8-12.9-fold higher than in the group without PFO (P<0.001). The risk of suffering a major DCI, of a DCI lasting longer than 24 h and of being treated by recompression increased with rising PFO size. CONCLUSION: The presence of a PFO is related to a low absolute risk of suffering five major DCI events per 10(4) dives, the odds of which is five times as high as in divers without PFO. The risk of suffering a major DCI parallels PFO size.     

Blood glucose changes and adjustments of diet and insulin doses in type 1 diabetic patients during scuba diving (for a change in French regulations)

OBJECTIVE: In France, diabetic subjects were not allowed to dive. The principal risk is hypoglycemia during immersion. However scuba diving is allowed in many countries. To follow blood glucose changes, food intake and insulin adjustments in type 1 diabetic patients when diving, and to propose specific guidelines for such patients willing to practice recreational scuba diving. METHODS: Fifteen well-controlled (mean HbA1c: 7.2%) type 1 diabetic patients without complications were volunteer to dive under strict medical monitoring. They dove 8 times in 4 days in autumn at a depth of 20 meters, in 12 degrees C to 16 degrees C water. A strict protocol based on blood glucose was implemented to prevent hypoglycaemia. RESULTS: No case of hypoglycemia was observed and no faintness was reported underwater. Mean blood glucose before diving was 200 mg/dl (11 mmol/l). There was a mean fall in blood glucose of 40 mg/dl (2.2 mmol/l) during dives, a mean decrease in daily insulin doses by 19.3% on the last day. Daily energy intake was 3,225 Kcal in average. A continuous glucose monitoring (CGMS) was performed in one patient and showed a rather stable glycemia during immersion but a decrease within the 8 hours after. CONCLUSION: When respecting a strict protocol to prevent hypoglycaemia, the risk of hypoglycaemia appears quite low. We recommend an ideal glycemic goal of 200-250 mg/dl (11-13.75 mmol/l) before immersion, a higher reduction of insulin doses (-30%) and taking carbohydrates on board in any case. The present data have recently led the French diving federation (FESSM) to allow type 1 diabetic patients to dive with some restrictive qualification requirements: dives within the "safety curve" (no decompression curve), in above 14 degrees C water, depth limited to the median space range (6 to 20 meters), plus mandatory guidance by a diving instructor.     

Decline of FEV1 in scuba divers

STUDY OBJECTIVES: Obstructive changes in lung function have been reported with cumulative scuba diving exposure. The aim of this study was to investigate the decline in FEV1 in scuba divers over time. DESIGN: Prospective controlled cohort study. SETTING: German Naval Medical Institute. PATIENTS: Four hundred sixty-eight healthy, male, military scuba divers and 122 submariners (control subjects) were entered. MEASUREMENTS AND RESULTS: Pulmonary function tests were performed in all subjects on at least three occasions with a minimum interval of 1 year between first and last measurement. The decline in FEV1 was investigated fitting a general linear model to FEV1 across time with a factorial main-effects model for slopes and intercepts with respect to the factors group, smoking status, and baseline FEV1. Mean baseline age of all subjects was 32 years (SD, 9.1), and mean body mass index was 24.7 kg/m2 (SD, 2.4). Subjects were followed up for 5 years (range, 1 to 9 years) on average. Baseline FEV1 exceeded the predicted values in both divers and nondiving control subjects. There was no significant difference in the decline of FEV1 between divers and control subjects. Over time, FEV1 declined more rapidly in smokers than in nonsmokers (p = 0.0064) and declined more rapidly also in subjects with a baseline FEV1 above average compared to subjects below average (p < 0.0001). The annual decline of FEV1 peaked in smoking divers who had a high FEV1 at baseline. CONCLUSIONS: The data indicate that scuba diving is not associated with an accelerated decline in FEV1. Combined exposure to diving and smoking contributes to the fall of FEV1; therefore, smoking cessation is advised for divers.     

Increased elastic recoil as a determinant of pulmonary barotrauma in divers.

The elastic and conductive behaviour of the lungs were studied in sixteen divers during an interrupted deflation from total lung capacity (TLC.) The results in six divers, who had suffered pulmonary barotrauma (PBT) during shallow water diving, were compared with the findings in a control group of divers. Conductive behaviour and mean lung volumes were similar in the two groups. Compared with the control group, the PBT group had higher maximum transpulmonary pressures and a lower static pulmonary compliance, and deflated their lungs earlier. In relatively stiff lungs, an even distribution of elastance may increase susceptibility to barotrauma, because the more compliant zones are subjected to a greater strain. Pulmonary barotrauma appears to select from the total population of healthy divers those with lungs of decreased distensibility.     

Tauchen und Herz

Diving with self-contained underwater breathing apparatus (scuba) has become a popular recreational sports activity throughout the world. A high prevalence of cardiovascular disorders among the population makes it therefore likely that subjects suffering from cardiovascular problems may want to start scuba diving. Although scuba diving is not a competitive sport requiring athletic health conditions, a certain medical fitness is recommended because of the physical peculiarities of the underwater environment. Immersion alone will increase cardiac preload by central blood pooling with a rise in both cardiac output and blood pressure, counteracted by increased diuresis. Exposure to cold and increased oxygen partial pressure during scuba diving will additionally increase afterload by vasoconstrictive effects and may exert bradyarryhthmias in combination with breath-holds. Volumes of gas-filled body cavities will be affected by changing pressure (Figure 1), and inert gas components of the breathing gas mixture such as nitrogen in case of air breathing will dissolve in body tissues and venous blood with increasing alveolar inert gas pressure. During decompression a free gas phase may form in supersaturated tissues, resulting in the generation of inert gas microbubbles that are eliminated by the venous return to the lungs under normal circumstances. Certain cardiovascular conditions may have an impact on these physiological changes and pose the subject at risk of suffering adverse events from scuba diving. Arterial hypertension may be aggravated by underwater exercise and immersion. Symptomatic coronary artery disease and symptomatic heart rhythm disorders preclude diving. The occurrence of ventricular extrasystoles according to Lown classes I and II, and the presence of atrial fibrillation are considered relative contraindications in the absence of an aggravation following exercise. Asymptomatic subjects with Wolff-Parkinson-White syndrome may be allowed to dive, but in case of paroxysmal supraventricular tachycardia they must refrain from diving. Pacemakers will fail with increasing pressure, but some manufacturers have proven their products safe for pressure equivalents of up to 30 m of seawater, so that patients may dive uneventfully when staying within the 0-20 m depth range. Significant aortic or mitral valve stenosis will preclude diving, whereas regurgitation only will not be a problem. Right-to-left shunts have increasingly gained attention in diving medicine, since they may allow venous gas microbubbles to spill over to the arterial side of the circulation enabling the possibility of arterial gas embolism. Significant shunts thus preclude diving. The highly prevalent patent foramen ovale is considered a relative contraindication only when following certain recommendations for safe diving (Table 2). Metabolic disorders are of concern, since adiposity is associated with both, higher bubble grades in Doppler ultrasound detection after scuba dives when compared to normal subjects, and an increased epidemiologic risk of suffering from decompression illness. In conclusion, cardiovascular aspects are important in the assessment of fitness to dive, and certain cardiovascular conditions preclude scuba diving. Any history of cardiac disease or abnormalities detected during the routine medical examination should prompt to further evaluation and specialist referral.     

Bleomycin and scuba diving: to dive or not to dive?

Bleomycin is to treat patients with testicular cancer and lymphoma. Bleomycin can bind to DNA and chelate iron. The resulting complex can form an intermediate capable of interacting with oxygen to produce reactive oxygen species, particularly superoxide. Administrating high-inspired oxygen concentrations (e.g. during anaesthesia or acute illness) has been reported to exacerbate pulmonary injury. The duration of risk after bleomycin chemotherapy is unknown. Here we discuss our advice to a young male patient, who was successfully treated with bleomycin for testicular cancer, concerning the safety to return to scuba diving. Since scuba divers are exposed to high partial oxygen pressures (depending on the depth of the dive) we discouraged this patient from resuming scuba diving.     

Value of Bronchial Challenge in Scuba Diving Candidates

Bronchial challenges were effected with carbachol in 76 subjects who were candidates for a scuba diving group. Bronchial reactivity was assessed through airway resistance and forced expiratory volume in 1 sec (FEV₁) measurements. Medical interrogation had revealed symptoms of recent (RA) or ancient (AA) asthma, or allergic rhinitis (AL). Nearly half of the subjects (47%) presented bronchial hyperresponsiveness (BHR), which was much more frequent in the RA group, but whose strength did not depend on clinical presentation. Prevalence of BHR was fairly high (36%) in the AL group. BHR constituted a contraindication to scuba diving because it may promote pulmonary barotrauma.     

Value of Bronchial Challenge in Scuba Diving Candidates

Bronchial challenges were effected with carbachol in 76 subjects who were candidates for a scuba diving group. Bronchial reactivity was assessed through airway resistance and forced expiratory volume in 1 sec (FEV₁) measurements. Medical interrogation had revealed symptoms of recent (RA) or ancient (AA) asthma, or allergic rhinitis (AL). Nearly half of the subjects (47%) presented bronchial hyperresponsiveness (BHR), which was much more frequent in the RA group, but whose strength did not depend on clinical presentation. Prevalence of BHR was fairly high (36%) in the AL group. BHR constituted a contraindication to scuba diving because it may promote pulmonary barotrauma.     

Prevention of hyperbaric-associated middle ear barotrauma

STUDY OBJECTIVE: To determine the efficacy of topical nasal decongestant in the prevention of middle ear barotrauma in patients undergoing hyperbaric oxygen therapy. DESIGN: Prospective, parallel, double-blind, randomized trial. SETTING: University-affiliated community hospital emergency department with hyperbaric oxygen facilities. PARTICIPANTS: Sixty patients undergoing hyperbaric oxygen therapy; 30 subjects in each treatment arm. INTERVENTIONS: After randomization, consenting patients were given two sprays of oxymetazoline hydrochloride or sterile water, 15 minutes before hyperbaric oxygen therapy. Collected data included patient demographics, ear examinations before and after hyperbaric oxygen treatment, and subjective ear complaints. The otoscopic appearance of the tympanic membrane was graded according to the amount of hemorrhage in the eardrum, with Teed scores ranging from 0 (symptoms only) to 5 (gross hemorrhage and rupture). RESULTS: The treatment groups were similar with regard to age, sex, and medical history. Ear discomfort during hyperbaric oxygen therapy was present in 63% (19 of 30) of those receiving oxymetazoline versus 67% (20 of 30) of the control group (P = .99). Likewise, both groups had similar Teed scores after hyperbaric oxygen therapy (P = .88). No adverse effects were noted. CONCLUSION: The results of this pilot study suggest that topical decongestants may not be effective in preventing middle ear barotrauma during hyperbaric oxygen therapy.     

High flight costs,but low dive costs,in auks support the biomechanical hypothesis for flightlessness in penguins

Flight is a key adaptive trait. Despite its advantages, flight has been lost in several groups of birds, notably among seabirds, where flightlessness has evolved independently in at least five lineages. One hypothesis for the loss of flight among seabirds is that animals moving between different media face tradeoffs between maximizing function in one medium relative to the other. In particular, biomechanical models of energy costs during flying and diving suggest that a wing designed for optimal diving performance should lead to enormous energy costs when flying in air. Costs of flying and diving have been measured in free-living animals that use their wings to fly or to propel their dives, but not both. Animals that both fly and dive might approach the functional boundary between flight and nonflight. We show that flight costs for thick-billed murres (Uria lomvia), which are wing-propelled divers, and pelagic cormorants (Phalacrocorax pelagicus) (foot-propelled divers), are the highest recorded for vertebrates. Dive costs are high for cormorants and low for murres, but the latter are still higher than for flightless wing-propelled diving birds (penguins). For murres, flight costs were higher than predicted from biomechanical modeling, and the oxygen consumption rate during dives decreased with depth at a faster rate than estimated biomechanical costs. These results strongly support the hypothesis that function constrains form in diving birds, and that optimizing wing shape and form for wing-propelled diving leads to such high flight costs that flying ceases to be an option in larger wing-propelled diving seabirds, including penguins.     

Low bone mineral density in professional scuba divers

Scuba diving is associated with a 90% reduction in effective weight and with the loss of a weight-bearing effect on joints. These conditions are very similar to the continuous weightlessness that occurs in spaceflight and bed-rest, which are clearly associated with significant bone mass loss. Here, we studied the bone mineral density (BMD) of 66 professional scuba divers using a dual-photon densitometer, and have depicted a reduction in the BMD in comparison to a matched control group of non-divers. Our results suggest that diving is also an activity where the unloading effect alters bone metabolism, leading to a reduction in BMD.Abbreviations BMD Bone mineral density     

Hemodynamic changes induced by recreational scuba diving

OBJECTIVE: Cardiac changes induced by scuba diving were investigated using Doppler echocardiography. MATERIAL AND METHODS: Ten healthy scuba divers dove to a mean depth of 34.3 +/- 2.7 m of sea water (113 +/- 9 feet) and a mean duration of 25.3 +/- 3.5 min. RESULTS: One hour after the dive, microbubbles could be detected in the right-heart chambers of all subjects. Left atrial and left ventricular (LV) diameters significantly decreased after the dive. Cardiac output, assessed by aortic blood flow, remained unchanged. Heart rate increased and stroke volume (SV) decreased after the dive. LV filling was assessed on transmitral profile. An increase of the contribution of the atrial contraction to LV filling was observed. Right cavity diameters were unchanged, but an increase of the right ventricular/right atrial gradient pressure was found. CONCLUSION: The diving profile studied promotes a rather important bubble grade in all volunteers. A significantly reduced cardiac diameters and SV was found by our hemodynamic study 1 h after diving. Two factors can explain these results: low volemia secondary to immersion, and venous gas embolism induced by nitrogen desaturation. Consequently, restoration of the water balance of the body should be considered in the recovery process after diving.