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GENDER AND BUOYANCY.
A: Although some
divers ask if women's breasts affect their horizontal 'trim'
underwater, it is not the case. Scientific techniques that analyze
center of gravity and buoyancy reveal that men seem to have
a greater predisposition to streamline or 'trim' problems. Men
usually carry their fat on their upper bodies compared to women
with fat distributed on both
upper and lower body. Men's longer, leaner legs are more likely
to sink, causing increased drag in the water.An interesting
study by Pendergast on competition swimmers found male swimmers
to have a poorer comparative power output than female swimmers
due to their buoyancy distribution. Their typically less horizontal
position increased drag
VALSALVA (OR VALSALVA'S) MANEUVER.
A: You were probably
taught that the Valsalva maneuver is a technique to equalize,
or "pop" your ears. It is described as done by breathing
out against a closed mouth with nostrils pinched shut. That
forces air from your mouth up through your Eustachian tubes
to your middle ear, increasing air pressure on the inside of
the eardrum to match increasing water pressure on the outside.
But it is probably technically incorrect to call this a Valsalva
Valsalva maneuver is named for Antonio Maria Valsalva (1666-1723),
Italian anatomist. The technique originally described by Valsalva
was to forcibly exhale against a closed glottis, by closing
the vocal cord together, as in a cough. This technique would
not equalize the ears. Now, both techniques are commonly called
a Valsalva maneuver. Either technique may increase pressure
in the chest cavity, impeding venous return of blood to the
heart, and because of that, is often used to study cardiovascular
effects of decreased cardiac filling and output. It is possible
that English physician Joseph Toynbee (1815-1866) may have developed
the maneuver for exhaling against a closed nose and mouth. To
make things confusing, Toynbee
also developed a different, gentler equalization method that
we call the Toynbee, consisting of swallowing with the nose
and mouth shut.
How deep can humans dive?
Q: We probably don't know just
how deep humans can go. It depends on the breathing mix to a
great extent. The military regularly dive to 1000+feet (304
a web site that reports a dive on trimix to 1100 feet (330m).
Carbonated beverages and DCI?
Q: I hear a rumor that carbonated beverages
are a contributing factor (contraindication?) to DCI. In fact
I think that I confirmed this rumor in the PADI basic diving
manual. Is this true? If so, what would be the underlying mechanisms?
A: It is doubtful
that carbonated beverages would increase the gas load to a sufficient
level to increase the chance of gas bubble growth in a decompression
situation. The lungs would excrete whatever was to enter the
venous system. Carbon dioxide would dissolve into the the fluids
in the stomach, and could ultimately be absorbed into the bloodstream.
The chemistry would suggest that the CO2 would react with H2O
and would be carried into the bloodstream as a HCO3- bicarbonate
ion, but some would
remain as CO2. Most CO2 produced by metabolism is carried this
way to the lung. There, the equilibrium is upset as the CO2
dissolves across the cell membranes and into the lung airway.
This drives the reaction of HCO3- + H+ --> CO2 + H2O and
the CO2 continues to be eliminated.
Increased partial pressures of CO2 increase the risks for O2
toxicity, nitrogen narcosis and dilutional hypoxia (SWB), but
I cannot find a similar increase in risk for DCI.
Planning a Marathon dive?
have questioned risks of a 12 hour extended bottom time stay.
Glen Egstrom writes about concerns with divers who have extended
bottom times for whatever reason.
have been done infrequently over the years. Generally for much
longer times than 12 hours. Guinness records has a nearly 50
mile swim in 24 hours underwater in '85. Obviously the depth
and gas purity are no brainers but important. Hypothermia, pool
chemistry, and skin care (Acutis Ancerinas) can be problems
but again relatively easy to solve for such a short exposure.
Boredom bothers some folks, consider mental stimulation. Periodic
moderate exercise is a good thing. Fluid replacement discipline
to maintain high levels of total circulating blood volume needs
to take into consideration the inhaled dry gas and urine output.
Fluid loss during working dives can be on the order of a liter
an hour. Balanced electrolyte may also become important. Knowing
more about the gear that will be used could also raise/eliminate
A: When you get
in the water and feel the urge to 'go,' is that all 'in your
head'? Not at all. It occurs from several physiologic mechanisms,
and becomes stronger as the water gets colder. It is also not
true that if you put a sleeping person's hand in a glass of
water they wet themselves. (But it is always worth a try for
the sake of science.)
know it's all right to pee in your wetsuit, and I don't have
any problem with it. I also read about why I get the urge to
pee when diving. My problem is that I _cant't_ pee. I've tried
relaxing, hanging back a little, different postures. I can't
seem to do it and get very, very uncomfortable on dives. Why
might this be, and is there anything I can do about it? It's
hard to concentrate on diving when my bladder feels like it's
going to pop.
A: This problem
is shared by many! It's the same psychoneurological response
that men get when standing in crowded bathroom full of beer
at a ball game. Just cannot get the sphincter to relax.
with your doctor about taking some medication that will relax
the bladder neck (Ditropan or any alpha blocker).
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