by inflammation, hyperproduction of mucus and the
contraction of muscles around them. Respiratory flow
may be reduced by 10 to 20 percent in mild cases and
40 percent in severe cases. In some cases respiratory
function appears normal, but challenge tests cause
hyperresponsiveness and reduced expiratory air flow.
Narrowing of airways may be reversed by medications
such as anti-inflammatories and bronchodilators. Anti-
inflammatory medications such as inhaled steroids
reduce swelling and mucus production in the airways.
This relieves symptoms, improves airflow and makes
airways less sensitive to provocative factors (cold, dry air,
etc.). Asthma attacks may be stopped by bronchodilators
— short-acting beta-agonists that relax bronchial
muscles and open airways for easier air flow. Exercise-
induced asthma may be prevented by long-lasting beta-
agonists. People whose asthma is well controlled may
lead normal lives that include exercise; they are less likely
to experience an asthma attack while diving.
Tobacco smoking affects breathing both chronically
and acutely. Acute effects of smoking include increased
carbon monoxide and reduced oxygen levels in the blood
as well as paralysis of cilia in the airways, which impairs
removal of mucus. Mucus can block terminal airways and
cause overexpansion of alveoli during ascent from a dive,
which puts a diver at risk for arterial gas embolism (AGE).
In smokers as in asthmatics, airway hyperresponsiveness
(as detected by a metacholine test) may be present even at
a young age. In teenagers with a short history of smoking,
a dose–response relationship was found between smoking
and decreased respiratory flow measures (FEV1/FVC and
FEF 25-75). Boys that smoked 15 cigarettes or more per
day had an average reduction in respiratory flow with
a reduced volume of air in the lungs (FEF 25-75) of 4.0
percent and in some cases up to 7 percent. The effect
on lung function of smoking one pack of cigarettes per
day for a year (one pack-year) was a 0.36 percent annual
loss of FEV1 for men and a 0.29 percent annual loss for
women. In smokers as young as 30 to 40 years, clinical
and pathologic manifestations resembling early-stage
COPD may be present. However, only divers 45 and
older who smoked are prompted to undergo medical
evaluation by a physician if they acknowledge their habit
in the RSTC form.
Marijuana smoking exposes respiratory airways to a
smoke that contains more tar than tobacco smoke, and
smokers may retain it for a longer time in the lungs.
One marijuana cigarette is similar in dose of smoke
exposure to 2.5 tobacco cigarettes, but in general,
marijuana is smoked less frequently and for a shorter
period in life than tobacco. Acute effects seem to
relax airways. Effects of chronic marijuana smoking
on respiratory functions are controversial. However,
frequency of cough, phlegm production and wheezing
increases with chronic exposure, and diffusion capacity
of the respiratory membrane decreases, all of which is
suggestive of chronic obstructive disease.
When assessing fitness to dive one should keep
in mind that asthma is a condition that affected
subjects have to live with, and thus they should not be
unnecessarily excluded from scuba diving if they wish to
dive and the risks are reasonably low. On the other hand,
smoking tobacco or marijuana is a matter of choice;
divers are discouraged from it but some still do. How
risky is it, and what interventions, if any, are necessary?
Is there evidence that asthma, tobacco smoking or
marijuana smoking increases the injury rates (such
as barotrauma and AGE) in scuba diving?
Claus-Martin Muth
: Although it is reasonable
to consider that smoking increases the risk for
decompression-related injuries in diving, there is no
clear evidence. Researchers from Duke University
Medical Center could show that when decompression
injury occurs, smoking is a risk factor for increased
severity of symptoms.
In addition, we have to keep in mind the effects
of tobacco smoking on the cardiovascular system,
specifically vasoconstriction which decreases
cardiovascular tissue perfusion. There is scientific
evidence that this has an influence on the rate of
nitrogen elimination after the dive. Again, this
may increase the risk for a decompression injury.
Furthermore, chronic marijuana smoking produces
changes similar to tobacco smoking, and therefore
it is very likely that it would have the same risks as
tobacco smoking. Smoking marijuana immediately
prior to diving means diving intoxicated and therefore
represents a serious threat to diver safety. It is justified
to advise against smoking and diving.
With regard to asthma the answer is “it depends.”
Each asthma case is different, and evaluation of fitness
to dive in people with asthma requires a thorough
examination and must be evaluated on an individual
basis. Divers with asthma should be instructed on how
to behave and how to use a peak-flow meter for airway
testing before planned dives.
Tom Neuman:
Although it’s tempting to hypothesize
asthma would increase the risk of AGE in sport
scuba divers, there is really no reliable evidence that
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