Diving and smoking : a surprising conclusion !

By seriniti , on 29 March 2022 - 12 minutes to read
plongée et tabac : une surprenante conclusion

Preliminary remarks

This brief was written in 2006.
The aim of this study was to investigate, in an objective way, if there were more diving accidents in smokers than in non-smokers and, in particular, undeserved accidents. Then, if so, to judge the speed and quality of recovery in both cases.

In 2006, there were very few, if any, articles on this subject. The “certainties” about the harmful effect of smoking while diving were still the rule. The effect of carbon monoxide (CO) in the development of atheromatosis was known, as were its risk factors on the coronary arteries.

On the other hand, in the purely gaseous phase of cigarette smoke, the puff brings, in the air stream, 3 to 6% of carbon monoxide, which takes the place of oxygen on 2 to 15% of the hemoglobin of the red blood cells (carboxyhemoglobin) with, as an immediate consequence, a downstream tissue hypoxia and a less efficient ventilation, because the carboxyhemoglobin does not take part in the gas exchanges and is not detached from the hemoglobin until after several hours.

It was also known that a smoker, in 100% of cases over time, sees a part of his pulmonary alveoli transform into sacs, inefficient in ventilatory exchanges. These sacs create emphysema bubbles that can be extremely dangerous when diving if they rupture in the pleura.

For this study it was necessary to solicit the main hyperbaric diving centers in France and in the DOM-TOM, so that they include the item “smoking” in their initial questionnaire – which was rarely the case, the essential points to treat the diving accident victim in the best way being elsewhere and the interrogation, itself quite difficult, sometimes subject to caution, in a shocked, worried diver, sometimes minimizing his acts or hiding them. These centers had all spontaneously accepted this addition.



Cigarette smoke

Due to the combustion of tobacco and paper, cigarette smoke releases more than 4,000 different substances in the gaseous and particulate phase, some of which are carcinogenic.
Some of these substances are of primary interest to us :

  • Carbon monoxide, present for 3 to 6% in the gas phase of smoke ;
  • Tars: a general term that includes all the condensate of a smoked cigarette, minus the water and nicotine. Tars include irritants and carcinogens ;
  • Nicotine: the main alkaloid in tobacco, which is addictive.

Effects of cigarette smoke on the body

1. Acute effects

10 minutes after the first puff of cigarette, the inhaled nicotine causes :

• An increase in heart rate.
increase is not necessarily negative for the diver, because it allows a better elimination of nitrogen during the ascent. However, it leads to a faster fatigue.

• An increase in blood pressure.
Stimulation of
the sympathetic system on the heart.

• Vasospasm at the microcirculatory level.
vasospasm continues for up to 10 minutes after smoking cessation and is also related to the stimulation of the sympathetic system. This phenomenon, because of its brevity, probably has little impact on nitrogen elimination.

This is probably not the case for carboxyhemoglobin, which is only released from hemoglobin after several hours. The diver’s ventilation will therefore be less efficient, fatigue more rapid, and the elimination of nitrogen gas less rapid.

2. Chronic effects

Without going into details, let us specify that carboxyhemoglobin has an effect on LDL (Low Density Lipoproteins or “bad cholesterol”) and leads to :

• A reactionary polyglobulia (increase in red blood cells),
• A hyperplateletosis (increase in blood platelets),
• A hyperleukocytosis (increase in white blood cells).

The whole contributes to increase the blood viscosity influencing the thrombotic risk (risk of intravascular coagulation).

Moreover, the muscular wall of the media (vessel wall) is fond of LDL. By different mechanisms, the muscular layer of the vessels fibers, loses its contractility, becomes secretory, favoring atherosclerotic plaque. Tobacco remains the first cause of atheroma of the vascular walls, well before the various dysmetabolisms (high cholesterol, diabetes, etc.)

At the pulmonary level, the ciliated mucosa undergoes cellular metaplasia. The ciliated cells are transformed into mucus-secreting cells, covering the bronchi with a film of mucus :

  • Decreasing the quality of gas exchange,
  • Increasing the risk of cancer,
  • Decreasing the diameter of the bronchioles,
  • Transforming the pulmonary alveoli, place of ventilatory exchanges, into totally inert and ineffective bags in gas exchanges.

These bronchial lesions are caused by the tars released during the combustion of tobacco.

Conclusion on the effects of cigarette smoke on the body

• Nicotine is not very toxic, playing only a punctual role on the heart rate, blood pressure and a vasoconstrictor role on the distal arterioles of little consequence (short time).

• Carbon monoxide is doubly harmful because of its stable fixation on hemoglobin and because of the chronic lesions produced on the arterial walls, thus increasing tissue hypoxia.

• The particular case of nitric oxide. The vascular endothelium produces a number of messengers, some of which are vasodilators, others vasoconstrictors.

Among the vasodilator messengers, the best known is the Endothelium Derived Relaxing Factor (E.D.R.F), which is nitric oxide (NO). It is secreted by the vascular endothelium at each pressure surge on the vascular wall. Its life span is very short. It could be assumed that inhaled nicotine, by the change in blood pressure it induces, releases endogenous nitric oxide and thus has a protective action. But the destruction of epithelial cells (vascular endothelium) modifies the performance and the responses of the heart to pressure variations, by decreasing the secretion of this endogenous nitric oxide.

• Basic reminder of the behavior and fate of gases breathed during diving.
the composition of the mixture in the diver’s tank, the basic rule is not to exceed the limits set by the maximum partial pressure of oxygen, i.e. 1.6 bar. Thus, if we take a mixture made up of 40% oxygen, we will obtain this partial pressure of 1.6 bar at an absolute pressure of 1.6 / 0.4 = 4 bar, i.e. a depth of 30 meters.

You might think that the carbon monoxide (CO) inhaled by the smoker before the dive will be eliminated by this overoxygenated mixture. In fact this will not be the case. The absolute pressure to “unhook” the carbon monoxide from the hemoglobin is 2.5 to 3 bars. Therefore, no matter how much oxygen is added to the mixture, the carbon monoxide attached to the hemoglobin will remain there for the duration of the dive.


Diving accidents

The only diving accidents considered in this thesis were the decompression accidents (DCI) which, because of their potential gravity, are treated in hyperbaric chamber centers, which allows us to analyze the files. As a result, the results, from the outset, may have been partially biased because other diving accidents were not included: 

  • ENT (sinus and ears in particular),
  • Toxic (CO2 intoxication). This hypercapnia may be more frequent in smokers (shortness of breath).

Symptomatology of decompression sickness

In the vast majority of cases, the symptoms appear after the diver has returned to the boat or even later. In almost all cases, the symptoms occur within 3 hours after the dive. The delay is an important diagnostic element. As a rule, the sooner the symptoms appear, the more serious or even fatal the ADD is likely to be. DCI can be :

  • Mild incidents,
  • Accidents of moderate severity (osteo-arthro-muscular or “bends”),
  • Serious accidents, leaving heavy after-effects even after passing through hyperbaric centers,
  • Fatal accidents.

Percentage of divers who smoke

This percentage had been realized during a survey in a diving center of Ile de France and, at the same time, with patients seen for Certificates of Absence of Contraindication (CACI).
Out of 214 divers, 59 were smokers, i.e. a percentage of 28% of smokers more or less superimposed on the percentage of smokers in the diving club analyzed (questionnaire) and superimposed on the national average (30% during the study). There are therefore, a priori, no less smokers than at the national level, which was a first surprise.


6 hyperbaric centers were contacted and 94 ADD files were collected, of which 80 were retained.
Of the 14 excluded cases, we noted :

  • A 15-year-old diver (age retained of 16 years for the tobacco survey),
  • 4 pulmonary barotrauma,
  • 6 barotrauma of the ear,
  • 1 nitrogen narcosis,
  • 1 procedural error,
  • 1 freediver.

Out of the 80 divers retained :

  • 21 are smokers or 26%,
  • 15 (or 19%) are ex-smokers (weaning for more than a year),
  • 3 are ex-smokers since a few weeks,
  • 55% are considered as non-smoking divers.

1. Sequelae

13 divers out of 80 have more or less important after-effects of their decompression illness (16%). Average age all together : 51 years. Among them :

• 3 after-effects in smokers or former smokers (23%) without any smoking in the 2 hours preceding the dive.  Among these sequelae:

> An anteroseptal infarction in a 52 year old diver who had dived to 10 meters, smoked 5 cigarettes/day and was overweight as a risk factor ;

> A minor paraplegia sequela in a 45 year old diver who smoked 1 pack of cigarettes/day ;

> A vestibular deficit of the inner ear in a 57 year old diver who quit smoking in 1997 (previously smoking less than 10 cigarettes/day) and who had a minor chronic obstructive pulmonary disease (evolutionary sequelae of smoking).

10 sequelae in non-smoking divers (77%).
the most part, minimal, with the exception of a complete non-regressive paraplegia. Average age all together : 44 years.

2. Speed of recovery

In the files where this information was specified, the recovery was done in a maximum of one week. The number of exploitable files is very insufficient (one year collected however) but, in spite of everything, we are surprised to note that :

  • Most of the smokers or ex-smokers recover within 48 hours (58%),
  • 8% of these divers recover on the 7th day,
  • While for the non-smokers, half of them recover on the 7th day !

If we consider the speed of recovery according to age, we can see that for divers who recover within 48 hours, the average age is 43 years.
For divers who recover within a week without any sequelae, the average age is 47 years. The difference in recovery according to age is not surprising.
The younger the diver, the faster the recovery without sequelae seems to be, and the same is true for the recovery with sequelae; the older the diver, the more likely it is that he will suffer sequelae.

At no time does the smoking element intervene here as a pejorative factor.


3. Attempts at explanations

As we can see, there is no evidence to support the hypothesis that the occurrence of ADD is greater in smokers or ex-smokers and that recovery is less good or less rapid: it is even the opposite that appears in our study, with a significantly different percentage of ADD in these patients, a lower percentage of after-effects and a greater speed of recovery, when complete, in smokers and ex-smokers.

The first hypothesis to consider is the existence of bias :

  • A very likely insufficient number of cases, hence the importance of continuing this investigation ;
  • An unknown number of novice divers, regardless of whether they smoke or not ;
  • The depth was not indicated, although it is known that the depth increases the risks ;
  • The number of consecutive dives was not indicated.

In spite of these unknowns, it seems essential to evoke a protective role of tobacco in diving .Can this protective role be attributed to nitric oxide ?

A cigarette puff is composed of a gaseous phase and a particulate phase (fine droplets suspended in the gaseous phase, where particles with a diameter of less than one micron can penetrate the respiratory tree to the pulmonary alveoli).

The gas phase is composed of :

  • Nitrogen for 60% (mono and dioxides of nitrogen in particular). The smoker inhales between 34 and 855 microg per cigarette ;
  • Oxygen (O2) for 12 to 15% ;
  • Carbon dioxide (CO2) for 12 to 15% ;
  • Carbon monoxide (CO) for 3 to 6% ;
  • Volatile organic compounds (hydrocyanic acid, ketone, aldehydes, ammonia).

Nitric oxide, which we have mentioned, like O2,CO2 or CO (carbon monoxide), interacts with the organism and therefore does not comply with Henry’s law (they are not inert gases). These gases, interacting with the organism, are therefore likely to induce a major (or minor) effect in ADD during diving. This is probably the case for CO which traps a part of the hemoglobin worsening the quality of gas exchanges (majoring effect).

Nitric oxide, whether of endogenous or exogenous origin (tobacco), is found in gaseous form under normal temperature and pressure conditions. Its endogenous secretion decreases in case of modification of the vascular endothelium, but certainly not its total secretion in the smoker diver.

It will diffuse across membranes and enter cells adjacent to those releasing it, into smooth muscle fibers and increase glutamate release. Without going into detail, nitric oxide induces, by different mechanisms, a relaxation of smooth vascular fibers and thus a vasodilatation, a broncho dilatation, an inhibition of platelet aggregation . All these positive effects are possible during diving, allowing the elimination of nitrogen gas and acting favorably on the vessels by reducing platelet aggregation and adhesion.

In addition to this protective effect of nitric oxide, the effect of smoking on alertness and its anxiolytic effect are perhaps also favourable and protective factors.

Conclusion of the study

For us doctors, it remains certain that despite all the convictions we have about the harmfulness of tobacco in diving, we can in no way assert such a hypothesis if it has not been irrefutably demonstrated. And, contrary to all logic, nothing has been proven in this thesis, which makes the challenge exciting and encourages us to continue the study.

I would be delighted if, at the end of this teaching, you had been able to develop in yourself those qualities which are the unique source of all progress: the absence of prejudice; scientific doubt, the questioning of everything that is presented as dogma. The whole history of science is a long and laborious struggle against certainties and revealed truths.

Professor Molimard, responsible for teaching tobaccoology at the Faculty of Kremlin-Bicêtre for many years.


© Alfred Minnaar Photography for all the photos in this article.


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