By Dr. Richard Moon, DAN Vice President & Medical Director
(First appeared January 2000 – DAN Divers Alert Journal)
The human body consists of several different body systems, and each serves a specific purpose. For example, the central nervous system carries all our neural messages, from balance to sight and hearing, touch, smell and taste. We could not navigate our environment without our nervous system.Thousands of diseases can affect the systems in our bodies, but remarkably, enough reserve seems to be built into our systems that we can easily survive many traumas. Even with the removal of part of a body system, like part of the intestines, a kidney or even a lung, we can live on.
Today, with modern medicine and science on our side, we change our participation in very few activities to accommodate disease. After disease, people can maintain active lifestyles.
With specific diseases, however, we need to be aware of the systems they affect. If we’re involved with scuba diving, for example, we should pay special attention to diseases of the lungs. Although some divers may continue diving actively with little or no limitations after disease or other trauma, scuba diving carries a special risk for those who have suffered some types of lung disorders.
When they’re engaged in diving, scuba divers can usually tolerate the small changes that occur in the lung air spaces. In certain lung diseases such as sarcoidosis*, however, lung tissue can stiffen, causing potential problems for scuba divers. For anyone who wants to take up diving or continue diving after illness, any condition that restricts or impedes the flow of air into and out of the lung can be problematic.
"Dr. Richard Moon, DAN’s Medical Director and Professor of Anesthesiology at Duke University Medical Center, has explained the basic physiology of the lung and associated diseases we must consider when we choose scuba diving as a recreational activity. Although incomplete, the list of lung diseases does refer to the most commonly asked questions that DAN receives about lung disease. Healthy lungs are essential for safe diving."
??? Joel Dovenbarger, Vice President, DAN Medical Services
The human body consumes oxygen to generate energy from foods such as glucose; it also produces carbon dioxide as a byproduct of this activity. The lungs, vital to this process, add oxygen to the blood and remove carbon dioxide.
To accomplish this, gas must move into and out of the lungs (i.e., breathing, or ventilation) at a rate governed by the level of exertion. At rest, in normal breathing, gas moves at a rate of around 5 liters per minute, but during heavy exercise, the body accommodates an increased requirement for oxygen and greater production of carbon dioxide. This may increase the ventilation rate to about 100 liters per minute. Since the muscles of respiration, such as the diaphragm, can move as much as 150 liters of gas into and out of the lungs per minute, a reserve usually exists.
Breathing Capacity and Limits
However, during diving, two factors can limit the breathing capacity. First, the density of the breathing gases increases. At 33 feet / 10 meters, the density is twice as high as at the surface; at 66 feet / 20 meters, it is three times as high, and so on. Higher gas density increases the breathing resistance, which in turn reduces the maximum ventilation. In a dry hyperbaric chamber, experiments have demonstrated that at 130 feet / 40 meters a person’s maximum ventilation is reduced by 40 percent.
Additionally, immersion in water can further reduce breathing capabilities. This effect, mostly due to movement of blood from the legs into the vessels of the lung, causes the lungs to become slightly more stiff, and thereby increases the mechanical load on the breathing muscles.
Also, the breathing resistance of the regulator can reduce a diver’s ventilation. At high levels of exertion under water, maximum sustainable ventilation can be reduced below the level required for adequate carbon dioxide exchange. When this happens, the diver may experience shortness of breath and subsequent panic. Carbon dioxide levels in the blood rise and can exacerbate nitrogen narcosis. During extreme exertion, high levels of carbon dioxide may even cause unconsciousness.
For healthy divers, this is likely to occur only during heavy exertion at depths below 100 feet / 30 meters. However, lung disease, which can reduce maximum breathing capabilities even at the surface, may limit ventilation even during moderate exertion at shallower depths. Lung diseases such as asthma, emphysema, sarcoidosis and other diseases that affect large proportions of the lung can reduce maximum ventilation. A physician can quantify breathing capacity using a pulmonary function test.
Diving and Asthma
A medical conference on diving and asthma in 1995 recommended that a prospective diver should have normal spirometry, or pulmonary function test, before and after a maneuver that typically exacerbates asthma, such as exercise (see Elliott, D.H., ed. "Are Asthmatics Fit to Dive?" Kensington, MD: Undersea and Hyperbaric Medical Society, 1996).
The consensus was that divers with chronic asthma should dive only if they meet these guidelines: 1) that they have no symptoms (e.g., wheezing, cough, shortness of breath); and 2) that they have normal breathing function (determined, for example, by using a personal instrument such as a peak-flow meter).
In the United States, every diver does not need a pulmonary function test, but it is recommended that prospective divers with any lung disease that may affect breathing capacity receive a formal assessment of pulmonary function by a physician.
Formerly, individuals who suffered asthma of any kind were advised not to dive. However, if symptoms are eliminated and breathing capacity is normal, the evidence suggests that the risk of diving is not excessive.
For more information on this topic, see "Asthma & Diving" by Guy de Lisle Dear, M.B., FRCA, DAN Assistant Medical Director, in the January/February 1997 issue.
Another issue is the ability of the lungs to exhale gas during ascent. In training, divers learn that breath-holding during ascent can cause the pressure in the lungs to increase, producing rupture of air sacs. This in turn causes lung collapse (pneumothorax), entry of air into the tissues surrounding the heart (pneumomediastinum) or the skin (subcutaneous emphysema or crackly skin). Air can also track into the tissues around the larynx (causing an abnormal voice) and the pulmonary blood vessels (arterial gas embolism).
These three situations are referred to as pulmonary barotrauma. Some lung diseases can lead to pulmonary barotrauma during ascent, even if the diver does not engage in breath-holding. Examples include lung conditions in which there are cysts, or balloon-like extensions of air sacs (known as blebs or bullae). Because these sacs are thin-walled, and tend to empty their air slowly, pressure can build up during ascent and they may rupture, causing lung collapse.
Other conditions that have an increased risk of pulmonary barotraumas include:
??? lung diseases that cause obstruction of air passages (such as asthma that is not optimally medicated);
??? certain diseases in which there is scarring or inflammation of the lung tissue (such as sarcoidosis, eosinophilic granuloma, interstitial fibrosis or scarring due to other causes); and
??? previous spontaneous pneumothorax ??? anyone who has previously experienced a spontaneous (i.e. without diving) pneumothorax or pneumomediastinum faces heightened risk of this injury.
For individuals with any lung condition that has an increased risk of pulmonary barotrauma, diving physicians recommend that they avoid scuba diving.
In addition, individuals who have experienced arterial gas embolism, pneumothorax, pneumomediastinum or subcutaneous emphysema should not dive until they have been evaluated by a physician. Sometimes a specialized scan of the lungs (computed tomography, CT or CAT scan) can be used to look for a small bleb that cannot be seen on a plain chest X-ray. However, whether some people can be predisposed to one of these problems and yet still have a normal CT scan is unknown.
Some lung infections such as tuberculosis can cause scarring of the lung and enlargement of lymph nodes in the chest. This condition in turn could compress airways and predispose an individual to pulmonary barotrauma. Individuals who have had successful treatment of tuberculosis should get a chest X-ray and consult a physician prior to being evaluated to scuba dive.
Some individuals who have experienced two or more episodes of spontaneous pneumothorax have had surgery to reduce the probability of a future occurrence. This surgery may entail either removal of visible blebs (and hence the inciting factor) or introducing an irritant material between the two layers of pleura (called pleurodesis), rendering complete lung collapse impossible.
Another type of operation aims to prevent pneumothorax by surgically removing or stapling visible blebs. However, two instances of serious arterial gas embolism in divers who have had surgery for recurrent pneumothorax have been reported to DAN. Thus, although pneumothorax may be prevented by such operations, it appears that gas embolism in divers can still occur.
Other Risk Factors:
Pneumothorax can also occur due to trauma, either penetrating (e.g. from a stab wound) or blunt trauma (e.g. a non-penetrating external blow to the chest). Lung surgery requires that the tissue enveloping the lung (the pleura) be cut. Neither of these situations is likely to increase the risk of pneumothorax (lung collapse), but some diving physicians believe that a surgical incision into the lung causes an increased risk of arterial gas embolism. With any of these conditions, consultation with a diving physician is recommended.
After lung surgery (for example, lobectomy or pneumonectomy, removal of a portion of the lung or the entire lung, respectively) there may be some reduction in maximum breathing capacity, which could impair a diver’s ability to tolerate exertion underwater.
Smoking can cause chronic bronchitis, emphysema and atherosclerosis. In addition, it exacerbates asthma. While smoking is not recommended, there is currently little evidence that smoking by itself predisposes anyone to diving-related illness, unless it has produced or exacerbated lung disease.
After a respiratory infection such as a cold, bronchitis or pneumonia, some people develop an increased tendency for the airways to constrict, as with asthma. This often lasts for a few weeks after resolution of the infection. It can manifest as a cough, shortness of breath or wheezing. During this time there may also be excessive mucus in the airways, which could cause gas-trapping during ascent. Because of this, diving physicians recommend that diving should be postponed after a respiratory infection until all symptoms, including cough, have completely resolved.
Scuba Diver’s Asthma Attack Linked to Pollen in Air Tank
A scuba diver’s life-threatening asthma attack some 27 meters (almost 90 feet) below the surface was apparently caused by exposure to pollen from the Mediterranean nettle Parietaria, Italian researchers believe.
Investigators warn divers who are allergic to pollen to use a filter to remove allergens from air used in air tanks.
Reporting in the September issue of the Journal of Allergy and Clinical Immunology, Dr. Gennaro D’Amato and colleagues, of Azienda Ospedaliera ad Alta Specialita A. Cardarelli, Naples, note that their patient had had "long experience of underwater diving, without untoward effects."
The diver, a 37-year-old man, also had bronchial asthma and had tested positive for allergy to the nettle, including "positive skin test responses and a high concentration of specific serum IgE to Parietaria pollen allergen, together with …. symptoms in the Parietaria pollen season."
Before the dive in question, the diver used a new supplier to recharge his air tanks. When investigators later inspected the premises of this supplier, they found that "the compressor was not fitted with an air filter and the area was rich in Parietaria plants," suggesting that air containing pollen from the plant was used to fill the tanks. In subsequent experiments using air from tanks and pollen traps, D’Amato’s team detected "damaged granules of Parietaria pollen" that could have released specific allergens responsible for the diver’s asthma.
The evidence that the asthma attack was pollen-related is "very persuasive," D’Amato and colleagues say. They advise divers at risk for pollen-induced breathing disorders "to check that air used to recharge their tanks is filtered to prevent the passage of respirable pollen grains."
??? Reuters Health News Service
SOURCE: Journal of Allergy and Clinical Immunology 1999:710