Newsgroup: it.hobby.scuba
Titolo: subacquea e gravidanza

tempo fa qualcuno chiedeva informazioni al riguardo.:
Article reprint: Spring 1994
"Pregnancy and Diving"
By Edward H. Lanphier, M.D., Senior Scientist, Emeritus
Dept of Preventive Medicine, University of Wisconsin, Madison
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Instead of presenting a lot of data, I want to tell you a story from the
real life of diving medicine and research.
Once upon a time, there weren't any female divers except in faraway places.
So pregnancy just wasn't on the list of diving medical problems. But
beginning around 1950, with the introduction of practical scuba equipment, a
few women began diving -- for recreation, for scientific work, and a few
even for commercial purposes.
Some of these women divers wondered about diving during pregnancy and asked
their doctors about it. None of the doctors really knew what to say, so the
most honest ones said "I don't know." Some who knew absolutely nothing about
diving said, "Why not?" and a few who knew something about diving medical
problems said, "A lot of things could happen. Why take a chance?"
Some early observations with pregnant animals indicated that there might be
no problem. But in 1978, a group at a Texas university got some pregnant
sheep which were close to term, put Doppler bubble-detection devices on the
umbilical vessels of the fetus, sewed things up, and put the mothers in the
chamber. They exposed different ones to different "dry dives" on the US Navy
no-stop limit curve: depths and dive-durations that do not normally require
decompression stops on ascent. At 100 ft./25 min., most of the fetuses
showed a lot of bubbles on decompression even though their mothers appeared
to be okay. The investigators felt sure that the lambs would have died
except for prompt recompression.
In animals exposed at 60 ft./60 min., everything seemed to be all right. On
the basis of this one small sheep study, these university people put out
press releases and a paper suggesting that it is all right for pregnant
women to dive so long as they don't go deeper than 60 feet.
Not long after that, I was invited to attend an Undersea Medical Society
workshop on pregnancy and diving. That was in late 1978. I was glad to be
present, but I had little experience with pregnancy in divers and few
opinions to offer. However, at the University of Wisconsin, we had one of
the real world-class authorities on the physiology of the fetus. That was
Dr. John H.G. Rankin, and Dr. Rankin was also interested in diving. So I got
an invitation to the workshop for him, and we both went.
It was clear that nobody present really knew much about the topic, but the
emphasis on the Texas sheep study and its publicity was especially offensive
to John Rankin and me. We decided that it was important to have a new look
at the question using somewhat different methods.
At Wisconsin, we had very recently acquired a fine high pressure research
chamber. Dr. Rankin's regular research program involved a lot of pregnant
sheep, and many of those were available for what we wanted to do. Dr. Rankin
had well-tested procedures for measuring blood pressure, blood flow, and
other variables in the mother, the placenta, and the fetus. We put on some
extra effort and had a project going early in 1979.
A close look at one of the sheep ready for a "dive" in the chamber showed a
batch of small tubes coming out through her side. These tubes had been
installed in blood vessels of the mother and fetus during surgery a week or
so before. Enough time had elapsed for recovery.
After all the preparations were completed, the chamber compartment was
"buttoned up" and then pressurized to one of the points on the no-stop
curve -- like 100 ft./25 min. Automatic chamber controls produced the dive
profiles that the study required.
As soon as a simulated dive was completed, with the mother sheep back at
normal "surface" pressure, the door was opened and various instruments were
hooked up to recorders. Typically, the fetus seemed to be just fine at
first. Then, within 15 minutes or so, the hearbeat began to be irregular,
and the blood pressure started to fall. In most instances, the fetus died a
few minutes later. Then the mother was anesthetized and the fetus was
quickly brought out by cesarean section.
When the dead fetus was examined we always found many bubbles in the blood
vessels, and the heart was always full of bloody froth. There were also many
bubbles in the blood vessels of the placenta.
At this point we were just confirming what the Texas investigators had found
ãexcept that our animals were in trouble even at 60 ft./60 min. Then an
interesting thing happened: We had scheduled "control dives" without any
instrumentation, but one of the sheep provided an even better test before we
had a chance to carry out the plan. One morning, we dived a pregnant ewe
carrying twins, and only one of the twins had been instrumented for the
study. That twin died on schedule, but the other one was alive when it was
delivered, and we found no bubbles when it was autopsied. This suggested
that the instrumentation, the very minor surgery on the fetus, or something
about the measuring procedure was responsible for the massive bubbling.
We studied more twin pairs, and we exposed mothers to pressure without any
instrumentation at all. Uninstrumented fetuses were always free of bubbles,
and those that were allowed to go to term were born normally without any
evident abnormalities.
One time, twin lambs were born normally after surgery but before the
scheduled dive. We clipped off the protruding tubes on the intubated lamb
and sent both lambs along in the chamber when another pregnant ewe was
dived. The untouched lamb had no problems, but the one with tubes still in
place had a severe case of bends. Our results were published in The Journal
of Applied Physiology in 1980.
There could be no doubt that the experimental procedure was somehow
responsible for the bubble problems that we saw. This provides a fine
example of the fact that scientific measurements can sometimes change the
thing they're trying to measure. We feel quite sure that this explained the
Texas results also, although that study included no "control dives" without
instrumentation. In any event, neither study showed that diving to any
specific depth is safe during pregnancy whether anyone meddles with the
fetus or not.
A very important reason for caution has to do with the arrangement of blood
circulation in the fetus. The big difference from the adult is that the
fetus does not yet use its lungs, so little blood goes to them. Uptake of
oxygen and removal of excess C02 takes place in the placenta instead of the
lungs.
In adult animals and humans, the lungs not only take care of gas exchange
with the environment but also serve as a "full-flow filter" for the blood,
removing bubbles and Ietting them disappear harmlessly. In the fetus, most
of the blood bypasses the lungs through the foramen ovale or the ductus
arteriosus, channels which normally close when the baby is born and the
lungs start functioning. In the fetus, without filtration in the lungs,
bubbles that form for any reason whatsoever can circulate freely and may
lodge in some vital organ such as the brain or heart muscle. In some adult
humans, the foramen or the ductus has failed to close normally; and these
individuals are at unusual risk much like thc fetus, from bubbles that form
following a dive.
We once thought that bubble formation isn't as likely to occur in the fetus
as in the mother -- so that the fetus might be all right even if the mother
developed decompression sickness. In a study that we conducted at Wisconsin
for another purpose, we made simulated dives repeatedly with a lot of sheep.
All of them had mild bends on at least two occasions. Some of the ewes
became pregnant during the study, and most of them delivered nice, normal
lambs. But the number of stillbirths was much higher than normal, and all of
these fetal deaths followed a "bends event" in the mother. No lambs were
born alive to mothers who had decompression sickness following the last dive
before delivery.
Going back to the Undersea Medical Society workshop in 1978, one of the most
constructive participants was a young nurse from Florida, Margie Bolton. She
was in the midst of conducting a questionnaire survey of women divers who
had been pregnant. When the results of her study came out in 1980, the most
alarming finding was that 5.5 percent of babies born to mothers who had
continued diving during pregnancy had birth defects against none in those
whose mothers had stopped diving.
Five percent is not far from the overall national average for birth defects
in general; and surveys like Margie's are open to a lot of questions.
Nevertheless, there is reason for a lot of concern about the possibility of
causing developmenal defects tha would arise very early --perhaps even
before a woman realized that she was pregnant. Margie Bolton came to the
University of Wisconsin to work on a Ph.D. in physiology under Dr. John
Rankin. Among other things, she conducted a study involving 40 pregnant
ewes, half of which made repeated dry dives during the crucial 12-40 day
period when most development of parts and organs takes place in the sheep
fetus. Margie found few birth defects, and there was no significant
difference between "dived" and "non-dived" animals in that respect.
While the report of her sheep study was still "in press" in a leading
obstetrical journal, Margie was hurt in an accident that involved severe
head injury. She has not been able to conduct any further research. A number
of additional studies have been conducted by others, but whatever anyone can
show in animals, it is not safe to apply the conclusions direcly to human
divers.
No one is likely to conduct the sort of study that might really answer the
question: to have two evenly-matched groups of female divers of
child-bearing age and to encourage one group to dive during pregnancy and to
ensure that the other group did not do so. From the ethical standpoint, such
a study would be indefensible no matter what it showed or how important it
seemed at the time.
Then what advice can we give to a diver who is or may be pregnant? All I can
say now in good conscience is to stop diving if you are or may be pregnant.
If you intend to become pregnant, please stop diving first. These are hard
words, and surely some depths and times and kinds of diving must be all
right. The problem is that no one can yet be sure what would be safe and
what wouldn't. (And of course, decompression isn't the only factor in diving
that might harm a fetus - or the mother.) The only thing I'm sure about now
is that - until a lot more experience accumulates and gets analyzed --
anybody who tells you that such-and-such limits are safe for pregnant divers
is guessing -- and may very well be guessing wrong.
(Editor's note: This article was input by OCR scanning. Please report any
typographical errors you may find to the publisher. Thank you.)

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