52
|
SPRING 2014
RESEARCH, EDUCATION & MEDICINE
//
E X P E R T O P I N I O N S
well-controlled and
properly treated
asthmatics are at
increased risk for
AGE. The most
comprehensive
publication addressing
this issue, “Are
Ashtmatics Fit to
Dive?,” was from
a workshop held
by the Undersea
and Hyperbaric
Medical Society. The
conclusion of that workshop was that asthmatics who
had normal pulmonary function test results (whether
or not they were on medication) were candidates for
diving. Tobacco smoking incurs the theoretical risk that
damage to the airways (both reversible and irreversible
airway obstruction) could cause sufficient outflow
obstruction that air embolism might occur even on
a normal ascent. Currently there is no evidence that
smokers with normal airway function have an increased
risk of air embolism compared to nonsmokers.
Chronic marijuana smoking produces changes similar
to tobacco smoking and thus, at least theoretically,
chronic marijuana smokers would have the same risks as
tobacco smokers. However, in general, individuals who
use marijuana inhale far less smoke than tobacco users.
Clearly, however, this comment addresses only the
chronic effects of marijuana on the lungs. It would be as
foolhardy to dive while under the influence of marijuana
as it would be to dive while intoxicated with alcohol or,
for that matter, any drug.
Regarding the respiratory effects of asthma, tobacco
and marijuana, are there any differences in how
these conditions affect the respiratory system and
the potential diving hazards that may result?
Muth:
The key points were already mentioned in
the introduction to this article. In addition to the
inflammation smokers exhibit, the clearing mechanism
of the airways is impaired. The thick bronchial mucus
may create an air-trapping mechanism in the form
of a partial obstruction with a valvelike function that
allows air to get into the affected segment but not to
come out. As stated previously, the effects of marijuana
smoking on the respiratory system are very similar to
those of tobacco smoking. In asthmatics the problem is
more general: if the respiratory tract reacts to a certain
stimulus such as dry and cold air (which is common in
diving), air-trapping can occur all over the lung.
Neuman:
Asthma is most frequently characterized by
partial airway obstruction due to mechanical constriction
of the airways, increased mucus production and edema.
This is a process that generally is completely reversible
and preventable with appropriate treatment. On the other
hand, damage from the inhalation of marijuana and/
or tobacco smoke has both reversible and irreversible
components. Thus once structural damage to the airways
has occurred from the use of tobacco or marijuana,
the effects on the lung are frequently not completely
reversible, leaving the individual with an ongoing
obstructive defect which might result in an increased risk
of AGE. However, well-done studies that clearly indicate
this theoretical risk is real are still to be done.
Is diver preparticipation screening regarding
smoking status adequate, or does it need to be
changed or updated?
Muth:
Although there is strong evidence that smoking
has an impact, the number of diving injuries and even
fatalities is rather low and the number of divers that
smoke rather high. I think it is more useful to publish
articles like this one and to tell smokers that smoking and
diving is not good idea at all. Smokers who dive should
abstain from smoking immediately before and after the
dive. On the other hand, testing of lung function should
be part of every examination of fitness to dive; when
lung function is impaired, depending on the degree,
there should be advice against diving. There is more than
strong evidence that smoking will impair lung function
over time, and smokers may have to retire from diving at
a younger age than they would like to.
Neuman:
The question about appropriate preparticipa-
Acronyms
FVC —
Forced vital capacity: the volume of air that can be
exhaled from the lungs after maximal inhalation with maximal
expiratory effort.
FEV1 —
Forced expiratory volume in first second: the
volume of air exhaled from the full lungs in the first second of
expiration with maximal force.
FEV1/FVC —
The ratio of FEV1 to FVC; normally it’s greater
than 0.8.
FEF 25-75 —
Forced expiratory flow that occurs while the
volume of air in the lungs is between 25 and 75 percent of FVC.
STEPHEN FRINK
