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SCUBA DOCTOR ONLINE

- 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 maneuver.

The 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 meters).

A:  Here is 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?

Q: Fund-raisers 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.

A: "Marathons 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 concerns."

- THE "P PHENOMENON."

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.)

- Can't Pee?

Q: I 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.

Check with your doctor about taking some medication that will relax the bladder neck (Ditropan or any alpha blocker).