Smoking and Diving

By Dr. Sawatzky

Smokers die five to eight years younger than nonsmokers, have twice the risk of dying from heart disease, and have 10 times the risk of developing lung cancer. In addition, they have increased risk of cancers of the mouth, throat, esophagus, pancreas, kidney, bladder, and cervix. Smokers have three times the risk of stomach and duodenal ulcers (that heal poorly), and two to four times the risk of fractures of the hip, wrist, and vertebrae. Finally, children of parents who smoke are born smaller, have more respiratory infections, reduced lung function, and more ear infections. Smokers tell me that a cigarette is a quick and easy short term treatment for anxiety. Unfortunately, research has shown this to be an illusion. When a smoker has a cigarette, the physiological signs and symptoms of anxiety actually increase! There are probably two reasons smokers think they are less anxious. First, smoking reduces the amount of oxygen delivered to the brain and this relative hypoxia might cause the smoker to feel less anxious. Second, smoking is an addiction, just like alcohol and drugs. When smokers feel the need for a cigarette, they generate anxiety about denying themselves their addiction, and/or they become anxious because they might actually have to admit that they are an addict. Having a cigarette reduces this self-induced anxiety. There are no beneficial effects of smoking.

There are several negative effects of smoking that are of particular concern to divers. The smoke from cigarettes (pipes, cigars, etc.) contains significant amounts of carbon monoxide and carbon-dioxide. The maximum allowed carbon-monoxide concentration in breathing gas is 10 parts per million (ppm) or 0.001%. The reason the limit is so low is that carbon monoxide binds to hemoglobin 250 times tighter than oxygen. This prevents the hemoglobin from carrying oxygen from the lungs to the cells and carbon dioxide from the cells to the lungs. Hemoglobin that is bound to carbon monoxide (carboxyhemoglobin) might as well not exist as it is doing nothing.

We are all exposed to some carbon monoxide (car exhaust, etc.) and a nonsmoker can have carboxyhemoglobin (COHb) levels of up to 2%. A light smoker will have COHb levels of up to 5% and a heavy smoker, levels up to 15%! This level of COHb will have a significant effect on a person's ability to exercise or respond to an emergency. A recent study suggested that divers had more white spots or areas of damage on MRI scanning of the brain than non-divers. In the same study, divers who dived deeper, longer and less safely, actually had fewer white spots than divers who were more conservative! Therefore, it is unlikely that diving causes significant MRI detected white spots. A different study suggested that smokers had more white spots than nonsmokers. This might indicate that smoking causes subclinical brain damage.

Other studies have shown that divers have more high frequency hearing loss than non-divers and this hearing loss is correlated with the number of years the diver has been diving. Further investigation has proven that these divers suffer hearing loss, not because of diving, but because they have had more noise exposure than non-divers (compressors, boat engines, etc.).

Although we now know that divers do not suffer hearing loss from diving, it has been clearly documented that smokers suffer more high frequency hearing loss than nonsmokers.

Smoking has many complex effects on the lungs. It paralyzes the ciliary hair cells lining the large airways for approxi mately one hour after one cigarette. In chronic smokers, the ciliary cells are destroyed. The function of these cells is to remove the mucous (and the dust/dirt that has been trapped in it) from the lungs (it ends up in the back of your throat and you swallow it). Without these cells, the only way to get the mucous out of the lungs is to cough it out (smoker's cough). If that were not bad enough, smoking actually increases the amount of mucous produced! This increased production of mucous combined with reduced removal of the mucous increases the likelihood that a mucous plug will block or partially block a large airway, trapping the gas beyond the blockage. This trapped gas greatly increases the diver's risk of pulmonary baro trauma and arterial gas embolism (often fatal), even on a normal ascent. To add even further insult to injury, if a smoker stops smoking, the production of mucous actually increases for the first week. Therefore, smokers should not smoke for at least a week before every dive (if they can do that, why not stop smoking totally?).

Smoking increases the production of mucous in the nose and sinuses. It also causes problems with the drainage of mucous from these areas. Therefore, smoking increases the risk of ear (blocked eustachian tube) and sinus barotrauma.

A large number of research projects have tried to determine if diving has any short or long term effects on the lungs. It is beyond the scope of this column to examine the controversial and conflicting results but in general, it seems that diving might cause a mild reduction in maximum mid-expiratory flow rates (MMEF). This is a measurement of small airways function and seems to correlate with the risk of suffering pulmonary barotrauma and arterial gas embolism. Therefore, diving might damage small airways but smoking definitely damages small airway function.

Breathing resistance has been shown to increase more in smokers than in nonsmokers with increasing depth (gas density). Smoking has also been shown to cause the airways in the lungs to constrict, increasing breathing resistance threefold for up to 35 minutes after one cigarette. If a smoker stops smoking, performance is measurably increased even after as little as 24 hours of not smoking.

Chronic smoking also damages the lungs so that the surface area where gas exchange takes place is reduced. Unfortu nately, the average non-active person only uses 25% of their lungs and they can smoke until over 75% of their lungs are destroyed before they notice shortness of breath in their day to day activities. This damage is permanent, even if they stop smoking.

Of more immediate concern to smoking divers, this process breaks down the walls between the alveoli, resulting in the formation of air sacks or bulla.

These bulla (trapped gas) increase the smoker's risk of pulmonary barotrauma and arterial gas embolism. One fascinating study I found looked at divers who had experienced neurological signs and symptoms within five minutes of surfacing from a normal dive. Of particular relevance were the divers who suffered pulmonary barotrauma (PBT) and/or arterial gas embolism (AGE). Of those divers, 50% had abnormalities on pulmonary function testing and 55% smoked! Less than 55% of divers smoke and therefore, smokers were far more likely to suffer PFT and/or AGE than nonsmokers. Finally, proof that divers who smoke are at increased risk of PBT and AGE, even during normal dives!

Cigarette smoke contains hundreds of chemicals that are known to cause cancer. These chemicals build up in the body of a smoker and not surprisingly, smokers develop many more cancers than nonsmokers. Lung cancer is most common but smokers also have a much higher risk of other cancers. We also know that smokers have a much higher risk of heart attack and stroke than nonsmokers. The exact mechanism for this effect is not known but the association is inarguable. In addition, smoking interacts with the other risk factors for these medical problems to make them even more deadly!

In conclusion, smoking has hundreds of damaging and detrimental effects on the body. Of specific concern for divers, smoking increases the production of mucous in the nose and sinuses, increasing the risk of ear or sinus barotrauma. Smoking also increases the production and accumulation of mucous in the lungs, increasing the risk of trapped gas and PBT/AGE. Smoking causes the airways in the lungs to constrict and damages the lungs such that the risk of PBT/AGE is further in creased. This increased risk has been proven in retrospective studies of divers who suffered PBT/AGE after normal dives. Smoking increases the level of COHb in the body and reduces exercise tolerance.

The bottom line is that there are no beneficial effects of smoking. Even the imagined stress relief is based on the reality that smokers are addicts.

Smoking is a slow but guaranteed way to commit suicide in general and possibly, a rapid way to die diving. If you can not admit that you are addicted to smoking, you will not quit. There are many programs through local addiction centres that help addicts quit smoking. If you can't do it alone, get some help before it's too late. If you currently smoke, stop immediately! If you are not a smoker, don't start.