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Why 100 % O2 Is A Dive Site Necessity|
Date:06/15/03 By Larry "Harris" Taylor
Diving Myths and Realities
The ability of oxygen to relieve the symptoms of decompression illness (Caisson’s Disease) has been known since the mid 1800’s. Much of this early work is summarized in Paul Bert’s classic work, Barometric Pressure, written in 1877. The use of oxygen by recreational divers as a first-aid measure has been promoted for more than three decades. A training organization, DAN, was founded in the US with a primary goal of getting the message of on-site O2 delivery to the recreational community. Yet, despite all the effort of diving educators, there is still a major lack of understanding in recreational divers for the need to deliver the highest possible O2 concentration to the victim of a diving accident. Perhaps, this stems from an unfamiliarity of the reason behind the hyperbaric medical community’s recommendation that those suffering from a diving malady be treated with100% O2.
A decompression event can be envisioned primarily as a “bubble disorder.” A bubble of inert (not used in body metabolism, so it accumulates) gas has formed within the body. This bubble may impede nerve impulses, block circulation, or trigger a variety of cellular processes designed to cope with foreign-to-the-body molecular invaders. The symptoms seen in the victim will depend on how much gas has formed bubbles and where these bubbles are located. Our mission, at the first responder level, is to reduce, as much as possible, the magnitude of this “bubble trouble.” An understanding of simple gas dynamics gives us the rationale for the need to deliver 100% oxygen.
From a standpoint of “molecular psychology,” gas molecules tend to ignore the presence of other types of gas and focus only on their own kind. Each element or compound present in the gaseous state will act independently, as if they were alone. If a gas-permeable barrier (like a cell wall or the interface between a liquid and a gas) is introduced into the system, then each type of gas will independently try, in terms of “molecular sociology,” to acquire the same population of their type of molecule on both sides of this barrier. Gas molecules will freely move in both directions across the barrier, but the net movement into or out of the gas pocket will be directed towards making the concentration the same on the inside and outside of the bubble. The movement of each gas type will be primarily dictated by the DIFFERENCE in concentrations between inside and outside of the gas pocket for each type of gas present within the bubble.
So, let’s consider a nitrogen (or any inert gas in the breathing mix) bubble inside a diver. In decompression sickness, the gas will be nearly all inert gas derived from the breathing mix that has percolated out of tissues. In an air embolism, the bubble initially will be about 80% nitrogen, but since oxygen can be used in cellular processes, the oxygen diffuses away and is rapidly consumed by metabolic reactions. So, for sake of argument, all DCI events can be considered primarily an inert gas bubble trouble event.
Since the body’s chemical machinery cannot utilize the inert gas, it just accumulates and interferes. If we want to “denitrogenate” (get rid of the offending inert gas bubble) the body, we must introduce an environment that contains NO NITROGEN (or whatever gas was used as the inert gas in the breathing mix). We could use ANY gas that was NOT nitrogen. Anything! Carbon monoxide, hydrogen cyanide, argon, or methane would do the job of removing nitrogen from the bubble. Of course, the gasses just mentioned are toxic to life, and, if, unused by the body, would themselves, accumulate in the bubble. So, although they would “denitrogenate,” it is probably best, because of their toxicity, that we do not use them. Instead, consider oxygen.
If we could surround the offending nitrogen bubble with a ZERO nitrogen concentration atmosphere by introducing a 100% oxygen environment, we give rise to the scenario shown in figure 1. In terms of “molecular sociology:” when we surround the nitrogen bubble with 100 % O2
Why all the hype about 100%? Does it work?
Now, let’s embolize the cat brain with a bolus of air injected into the carotid artery. This is shown in figure 3. Notice the lack of red in the brain region. The blood vessels are blocked by air. There is a “vapor lock” in the brain’s circulation and cells not receiving nutrients are beginning to die from lack of necessary fuel and oxidizer while drowning in their own waste. Within minutes, neural tissue will start to die and once dead, most likely will never function again.
Now, let’s put the cat on 100 % O2. It is clear that O2 shrinks bubbles. This process has been described as miraculous!
Microscopic examination (see references, below) of “bent” animal tissue surrounded by a 100% O2 atmosphere has shown that the bubbles shrink and disappear from view in about 2 hours. This “denitrogenation” is something YOU CAN DO on the dive site and the reason why delivery of 100% O2 is so emphasized in diving first-aid management classes.
So, why all of the hype about demand valves?
Most oxygen delivery equipment is meant to deliver lower than 100% O2. This is because most O2 delivery equipment is DESIGNED to treat shock-associated hypoxia that occurs from trauma or disease. This is NOT the same as using O2 to “denitrogenate!”
In diving, since our mission is primarily to “denitrogenate,” our O2 delivery devices MUST address this need. That is why the demand inhalator (only device available that delivers 100% O2 to a breathing patient while meeting the patient’s full respiratory needs) is considered the “best” device for treating a decompression illness incident and should be the delivery device of choice in the on-site first responder management of a dive malady.
On the Site
References On Bubble Shrinkage
Hyldegarrd, O. Moller, M. & Madsen, J. Effect of He-O2, O2, and N20-O2 Breathing On Injected Bubbles In Spinal White Matter, Und. Biomed. Res. 18,(5-6), 1991, 361-371.
Hyldegarrd, O. Moller, M. & Madsen, J. Protective Effect Of Oxygen And Heliox Breathing During Development Of Spinal Decompression Sickness, Und. Biomed. Res. 21,(2), 1994, 115-128.
Hydlegarrd, O. & Madsen, J, Effect Of Air, Heliox, And Oxygen Breathing On Air Bubbles In Aqueous Tissues In The Rat, Und. Biomed. Res. 21(4), 1994, 423-424.
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