As a scuba diver, you experience an increase in pressure on your body as you descend. While underwater, your ability to expel the nitrogen that makes up almost 80 percent of the air we breathe is reduced due to the pressure of the water. Nitrogen is not used by the body so it has to get out of your system. The deeper you go and the longer you stay means that nitrogen accumulates in the tissues of your body. Avoid staying too long and/or going too deep and ascend at an appropriately low rate, perhaps stopping for a time at various depths, and the accumulated gas in your tissues slowly comes out of solution and is expelled as you breathe. Break the rules and the nitrogen comes out of solution as bubbles. Think about what happens when you open a soda pop bottle. The bubbles sometimes appear in the joints and a case of the "bends". Pain ought to be the least of your worries at this point. Crippling paralysis and death are a very real possibility. The protocol is to get the afflicted individual on oxygen and hightail it to a hyperbaric chamber. In a chamber, the patient, often accompanied by health care professionals when the chamber is large enough, is subjected to increased pressure, usually while breathing pure oxygen through a mask.
The higher pressure in a hyperbaric chamber (sometimes called a decompression and occasionally a recompression chamber) makes any bubbles in the patient's tissues get smaller and prompts the gas to go back into solution so that it can be expelled through respiration. Then the pressure is slowly reduced after the gas has hopefully been expelled. Hyperbaric treatments have also been shown to be effective against carbon monoxide poisoning, smoke inhalation, gas gangrene caused by certain bacteria, radiation tissue damage, thermal burns, non-healing skin grafts, crush injuries, wounds that fail to heal through conventional treatment and serious blood loss.
Taking A Chamber Ride For Fun
I hope never to have to "take a chamber ride" as we divers call it but it doesn't hurt to learn about the process and to experience it. So, with all this in mind members of the H2Ogres dive club went to Advocate Lutheran General Hospital in Park Ridge, Illinois recently to see what hyperbaric medicine is all about and to actually take a ride in their chamber.
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| Dan Mazzolini, director of chamber operations, presented a 40 minute program describing the chamber |
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| H2Ogres head to the chamber |
After hearing a presentation about the chamber and the hospital's hyperbaric medicine program, we walked over to the chamber which is kept near the west side of the hospital but is outside the walls of the hospital since it is a large pressurized vessel. This is what is called a multi-place chamber with room for 12. There were 13 of us so we just squeezed a little closer together. The chamber is designed to be pressurized to a simulated depth of 160 feet but we were advised that most of the time the chamber is used it is pressurized to a depth of 66 feet which is equivalent to 3 atmospheres.
On land at sea level we experience a pressure of 14.7 pounds per square inch. That pressure doubles at approximately a depth of 33 feet of seawater since water is much denser than air. Take an open gallon jug held with the mouth of the jug pointed down to a depth of 33 feet and you will see the volume of air reduced by about half. Put the cap on the jug before you descend and you will see the jug crushed to about half its volume when you reach 33 feet. We were to be pressurized to a depth of 130 feet and were told that demonstration "dives" like these were the highest pressure to which they run the chamber. The conventional recreational depth limit for scuba divers breathing compressed air is 130 feet.
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| The chamber is about 6 feet wide and 22 feet long |
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| Chamber interior (photo by my brother Rob) |
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| Chamber control panel (photo by my brother Rob) |
Once we had taken off our shoes or put booties over our footwear, we were seated in the chamber. We were given a list of math problems and many of us had brought things like a beach ball, balloons, styrofoam and tennis balls to see how they might react to the pressure. The door was sealed and many of us took off outer layers of clothes. Even though the weather was cool outside, more than a few of us had worn shorts. Increasing pressure brings a couple of interesting changes in the chamber. As we descended the chamber technician called out our depth in ten foot increments. We "cleared" our ears frequently. This involved yawning or flexing our jaws to allow air to flow up the Eustachian tubes in the back of our mouths to behind our eardrums so that the pressure in the inner ear was equal to the increasing pressure outside our bodies. One member of our group had some trouble equalizing pressure so the technician paused our descent and actually brought us up a few feet. That resolved her problem and we were on our way back down. The temperature moved past 92 degrees in the temperature as we approached maximum depth.
I Get High With A Little Help From My Friends
Dalton's law of partial pressures tells us that the total pressure we are experiencing is the sum of the partial pressures of the various gasses that made up the air we were breathing. The higher pressure of nitrogen meant that more nitrogen was being dissolved in our blood and tissues. Nitrogen impairs the conduction of nerve impulses and mimics the effect of alcohol or narcotics. As we passed 100 feet of simulated depth, most of were feeling the effects of nitrogen narcosis and things got very silly very fast. The technician held us at 130 feet for 5 minutes or so and reported that things sounded awfully jolly in the chamber. The situation was magnified by the fact that the higher partial pressure of nitrogen caused our vocal cords to vibrate faster making us all sound like characters from Looney Tunes.
Playthings
The increased pressure deflated the beach ball substantially before we even reached 30 feet. Styrofoam cups shrank in size and acquired a wrinkly appearance. Tennis balls were dimpled at 40 feet or so. While we were at depth, a few balloons were inflated and as we ascended, they grew in size an popped. Those of us who tried to do the math problems at this depth also made many more mistakes that we might have under normal circumstances.
To The Surface
Finally, it was time to go up and the technician's voice over the intercom called out the depth as we ascended. The temperature dropped immediately and many of us had brought sweatshirts to put on. the affects of narcosis went away immediately as we ascended. The moisture that had accumulated in the heated air condensed and a light fog was visible as you looked down the length of the chamber. Since we did not spend enough time under higher pressures to put much nitrogen into our tissues, we did not have to do any "stops" along the way as we ascended.
Groups and individuals can book this hyperbaric chamber experience for themselves by calling the hospital. We paid $20 each for the experience and it was well worth it. Be advised that this is a popular experience and that many dive groups and others have made reservations so you will probably have to book a year in advance.
As a diver this experience certainly gave me a close look at the chamber and its operation. I'm glad we have one close by and glad that Divers Alert Network, the diver association to which I belong, supports these chambers and keeps track of them worldwide in support of the dive community. Finally, I have new respect for the danger posed by nitrogen narcosis for deep dives. I'll continue to go deep but will watch myself carefully.
Smart Divers Play It Safe
There are any number of steps a diver can take to eliminate or reduce the possibility of an injury:
- Reduce the chance of an injury to as close to zero as possible by staying well clear of the depth and time limits of scuba diving.
- Don't dive beyond your experience level or in conditions that might provide too many complicating factors like frigid water, currents or substantial exertion.
- On deep dives, do a "safety stop" by stopping your ascent for three to five minutes at a depth of between 20 and 15 feet to allow gas in your tissues to dissipate. The dive tables that specify maximum depth and times might not require a safety stop but it is good idea.
- Maintain physical fitness since research does show that obese individuals are at greater risk for decompression illness and that less fit individuals are at greater risk for decompression illness, have a decreased ability to rescue themselves or their dive buddy and are at an increased risk of panic in stressful situations.
- If you are on a scuba charter boat make sure they have an oxygen kit on board.
- If you are diving on your own, have an emergency plan in place by knowing how to summon help and where the nearest decompression chamber might be.
- Carry insurance against the high cost of treatment.
