The last thing you probably want to read is another tirade on the dangers of drinking and smoking. Besides, what can I say that’s new? Although some recent evidence points to drinking alcohol in moderation as a health benefit, no one doubts the dire consequences of imbibing in excess. And no informed person on Earth doubts that smoking is merely a form of protracted suicide. But while we’ve known about these dangers for decades, many of us still drink — at least occasionally — and a quarter of us smoke.

Smoking and alcohol are so much a part of our society that we no longer even consider that both are essentially a form of self-prescribed drug administration. In fact, we describe drug use, smoking and alcohol as if they were distinct and unrelated activities. In reality, all that’s different is the substance in question, its effect and the form of administration. I won’t delude myself into believing that this article will make any significant dent in the statistics on alcohol or tobacco use. I believe that in a free society, people should be able to do what they wish, provided it doesn’t hurt anyone else. But there is one important proviso in the decision-making process that many ignore, and that is that the consequences of our choices can vary according to the circumstance in which we find ourselves. For example, it may be OK to drink, but not drink and drive. Diving is another case in point.

For us, the effects of alcohol and smoking go far beyond the normal concerns of heart attacks, or cancer. Those who venture underwater have additional concerns when our mental or physical capabilities are impaired. We also must consider factors that are irrelevant to nondivers such as heat loss and decompression. So, to make a responsible and informed decision about drinking and smoking, divers must first understand the unique effects that alcohol and nicotine present to us.

Staying Warm

Diving requires surviving in a medium where heat is pulled from our bodies 25 times faster than it is in air. So no matter what the temperature, heat loss is a concern. It’s just a matter of degree. And who hasn’t been told that a great way to fend off the cold is with a good stiff drink? After all, alcohol feels so warm going down that it certainly must rekindle the internal fire, and give us that essential extra burst of energy, right? While it may sound logical, it’s just not true. Pharmacologically, alcohol is a peripheral vasodilator, meaning that it causes blood vessels in the skin to open up more than normal. As blood flow increases to fill the expanding vessels, we experience that warm, flushed feeling. But this momentary sensation is misleading because it masks a more sinister effect.

The blood flow responsible for that “warm and fuzzy” feeling is diverted from the body core. This loss of blood saps heat from a more vital area of our body and makes us more — not less — prone to hypothermia. Moreover, alcohol depresses shivering, the major symptom warning us of the onset of significant heat loss. There’s also a possible double whammy because some recent studies out of Canada have shown that nitrogen narcosis also delays the body’s shiver response. So, a predive drink or two compounds the heat loss problem, and post-dive alcohol consumption can impede the rewarming process. How much sense does it make to spend hundreds of dollars for an exposure suit only to reduce its effect by taking “a couple ’a belts”?

Bad as it is, problems don’t end with increased peripheral blood flow. Ironically, the blood vessels supplying our muscles do not dilate but constrict. This causes an increase in blood pressure, and is one reason those with hypertension are advised not to drink excessively. As muscle accounts for the greatest tissue mass in our body, this elevated blood pressure can place significant stress on the heart. Some believe this stress could be a contributing factor in the increasing number of diving accidents involving those with underlying heart disease.

Alcohol may also play a role in accidents blamed on poor physical conditioning. How so? Think back to the last time you had a few drinks. You probably didn’t feel a lot like exercising. This is partly due to mental impairment, but there’s another more direct reason for the feeling of fatigue; alcohol actually drains energy. One of the body’s primary fuels is sugar in the form of glucose, a substance produced by the liver. Alcohol consumption impedes the production of glucose, thus reducing our exercise ability far below normal. So, regardless of how you feel, an imbibing diver may be incapable of making the extra effort required to keep an unexpected situation from turning into an emergency. Alcohol also increases the likelihood of vomiting which, especially when diving, can easily lead to asphyxiation. So, in both the case of aggravating an underlying heart condition, or sapping our energy when it’s most needed, alcohol might be the final straw that tips the balance against us.

A Toast to Decompression

No one has ever established a direct relationship between drinking and any increased risk of decompression sickness. But prudent judgment tells us that, at least theoretically, such a relationship might exist. Most researchers who study the subject think it might work like this: We already know that alcohol consumption increases peripheral circulation. If you drink before diving, the increased blood flow could cause greater nitrogen absorption than that predicted by your computer (or tables). Therefore, this might increase your susceptibility to decompression sickness even if you are within the no-decompression limits. Some also believe that drinking could promote DCS in other ways, and point to alcohol’s diuretic (makes you urinate) property. The loss of fluid through urination contributes to dehydration. The decreased fluid volume, in turn, makes the blood “thicker,” reducing its circulatory efficiency and further altering the absorption and elimination of nitrogen.

The dehydration issue might also put divers at risk of the most serious form of decompression sickness, that with neurological symptoms (what’s sometimes called “Type II” bends). This is because the brain is especially susceptible to dehydration from alcohol consumption, and explains why a headache is the most common symptom of a hangover. It’s also important to understand that the effect of dehydration lasts even longer than the headache. This is why it’s particularly vital that anyone drinking alcohol the night before, even if they feel well the next morning, drink plenty of water prior to diving. Some researchers even argue that changes in blood flow caused by drinking after a dive could accelerate the release of nitrogen and indirectly enhance bubble formation. So it may be wise to avoid excessive drinking après dive.

Other researchers have suggested alcohol might actually contribute directly to DCS bubble formation. This, they contend, is at least theoretically possible because of alcohol’s ability to reduce surface tension. Surface tension refers to the tendency for a substance, such as a bubble, to exhibit properties resembling those of a stretched elastic membrane. The phenomenon is what’s responsible for the “skin” that seemingly arises on the surface of a pond or swimming pool, allowing a bug to literally walk on water. But surface tension is also important to divers from a physiologic perspective. It helps resist bubble growth in decompression sickness. So, anything that reduces the surface tension of a bubble could encourage the growth of bubbles that might otherwise remain too small to cause symptoms.

Indeed, this is all theory, but it may have an important role nonetheless. For example, many studies have shown that silent or asymptomatic bubbles are a common occurrence in divers (many of whom are nowhere near the normal no-decompression limits). This is especially the case for those who engage in multiple, repetitive diving, like when on a diving holiday. Common sense tells us, then, that even the theoretical possibility that drinking might push these silent bubbles to symptomatic bubbles shouldn’t be ignored. While the whole issue of alcohol’s contribution to decompression sickness is speculative, it’s still based on sound physiologic principles.

I’ll Have Tee Martoonis, Please

A fact probably known only to scuba divers and anesthesiologists is that alcohol shares a property with the atmosphere’s most abundant gas, nitrogen. Both substances have the ability to sedate. In fact, the similarity between the symptoms of alcohol intoxication and nitrogen narcosis was, in the early days of diving instruction, the rationale for what was termed “Martini’s Law.” This “law” — actually a rough estimation, at best — stated that for every 50 feet a diver descends, his impairment from nitrogen is the same as drinking one martini at the surface. So, accordingly, a trip to 150 feet is equivalent to a three-martini lunch. Of course, if even a slight amount of real alcohol is added to the formula by predive drinking, the effect would be magnified (though by how much no one knows). Even diving accident reports appear to support the premise that alcohol and depth are an especially dangerous combination. Data from the Divers Alert Network (DAN) has long shown that 30 percent to 40 percent of injured divers admitted to consuming alcohol the night before, and 2 percent to 3 percent reported drinking just before diving or between dives.

The Nicotine Fit

There’s no need here to relate the dangers of smoking. Only historical tradition, and a strong lobby, would allow the legal sale of a product that killed one-third of the people who used it. Clearly, if its effects were immediate rather than long-term, the sale of tobacco would be as illegal as heroin, and tobacco executives would be the bunkmates of imprisoned cocaine dealers. But this discussion is about diving, so what additional risks face divers?

Some of the effects of smoking on divers are, like most other consequences, chronic — the result from long-term use. Various chemicals — primarily tar — from inhaled smoke cause chronic irritation of the bronchi, resulting in chronic bronchitis. The tar also destroys tiny hairlike structures called cilia that line much of the respiratory tract. Cilia are important because they conduct mucus from the lungs up and out of the airway. When they no longer function, the effect is retention of mucus and partial clogging of the airway, causing the classic symptom of “smoker’s cough.” But there’s a far greater effect on divers than an irritating cough.

Various poisons in the smoke also eventually destroy alveolar walls, which produces cavities in the lungs. The result of this process, excluding death, is a condition called emphysema. This form of emphysema, however, is unrelated to the disorder divers get from lung overexpansion injury. But noted diving medical authority Dr. Ernest Campbell said: “Obstruction in the terminal airways and the emphysema that’s caused can — and does — produce air-filled dilations that can markedly increase your chances of pulmonary barotrauma and arterial gas embolism.”

Perhaps the most significant effect of smoking occurs long before any sign of emphysema, and it involves the restriction of airflow in the lungs. Smoking causes mucus retention and reduced alveolar flexibility that can easily cause air trapping deep within the lungs. Or, as Campbell puts it, “Smoking also causes an increase in bronchial mucous production with a concomitant paralysis of the cilia. Mucous plugs then become dangerous to the diver, setting the stage for air-filled sacs that lead to rupture upon ascent.” The result could be and has been, pulmonary barotrauma in smoking divers who were breathing normally. So, assurance of safety from the first rule of scuba diving — always breathe normally — doesn’t necessarily apply to smokers.

Some of the chemicals in inhaled smoke do not remain in the lungs but pass into the bloodstream. Their effect is to cause spasm and otherwise damage the walls of blood vessels. Damage is noted particularly in vessels supplying the heart, and thus is one of the reasons smokers are so prone to heart attacks. Other effects include stroke and various forms of peripheral circulatory disorders.

Of course, all this happens to people regardless of whether they dive. But for divers, there’s still more to be concerned about. Smoking just before diving results in reduced tissue oxygenation because the carbon monoxide (CO) in the smoke binds with hemoglobin 220-290 times more readily than oxygen does. The result is that a diver must work harder simply to maintain a normal level of activity. In other words, when someone smokes, they intentionally reduce their body’s ability to process oxygen. And just before entering the water seems an odd time for a diver to willingly lessen his ability to function at a peak level.

Again, Campbell puts the issue into perspective. “The effects of partial pressure on CO concentration in inhaled cigarette smoke would be the same as if the CO had come from some other source, such as the atmosphere or from oil-lubricated compressors.” He also relates the details, which are pretty startling. Acceptable CO level for diving is 10 ppm (parts per million) by volume (0.001 percent). A mere 10 percent to 20 percent increase yields a mild frontal headache, and just a 20 percent to 30 percent increase gives a throbbing headache associated with nausea. This is not a condition conducive to diving. Coma, convulsions and even death can occur with a CO increase of 50 percent to 80 percent beyond the maximum.

Of course, one’s CO level varies with the number of cigarettes smoked, the length of time since the last cigarette, how the cigarette was smoked and even the level of activity on that day. In heavy smokers, up to 15 percent of their oxygen is being replaced by carbon monoxide.

In terms of how smoking affects decompression sickness, no one really knows for sure. But most DCS susceptibility factors do involve changes in circulatory dynamics, and smoking has a definite effect on circulation. So, a logical but unproved conclusion is that smoking might increase the risk of bends.

The failure of the US 18th Amendment proved how likely it is that we’ll ever put a stop to alcohol use. Smoking is perhaps an even greater challenge because its active agent — nicotine — is one of the most addictive substances ever discovered. Yet what sets us apart from other animals is our capacity to learn, and change our behavior when we know something could hurt us. Mixing diving with either alcohol or nicotine is a recipe for disaster, but if you still insist on rolling the dice, at least do so with your eyes fully open.