empressdiver:
He surveyed the research up to that date and concluded that oxygen narcosis is of no significance to recreational divers. Another diver has just stated that the doctor has confirmed that his article is still current.
QUOTE]
First, I am not an expert. Second the doctor is cracked. Oxygen does have narcotic effect, it can also kill you. I guess that part was of no significance to rec divers either.
Our reader, Rockjock, states that he is not an expert. He then goes on to say that the doctor in the quote above is "cracked".
This is an interesting opinion from someone who, admittedly, is NOT an expert. The good doctor whom he refers to IS in fact, an EXPERT!
The man he refers to is Dr. David Sawatzky, a noted researcher in decompression and related subjects, who works for DCIEM (now DRDC) in Canada. When someone who has no standing or professional training in the field posits that a noted resercher in that field does not know what he is talking about, I would suggest that it is NOT the good doctor who is more than slightly cracked in the old toboggan!
To add to Dr. Sawatzky's comments, I will report the findings of Dr. David Teubner, who is both a Hyperbaric Medicine and Trauma physician, and who is a technical rebreather diver with far more hours underwater than our reader, Rockjock.
Re: O2 Narcosis - 28th November 2005, 17:33-by Dr. Dave Teubner
O2 does not contribute significantly to narcosis because the partial pressure of oxygen in the neurons doesn't get very high, because oxygen is used up.
Moderately complicated explanation follows.
Oxygen is carried in blood in 2 ways, bound to haemoglobin and dissolved in the blood. The haemoglobin in 100mls of normal blood carries about 20ml of oxygen and the dissolved component is 0.003ml per mmHg O2 per 100mls of blood.
You use the dissolved component first. Your brain uses about a quarter of the available oxygen breathing normobaric air, so you have about 15mls of oxygen per 100mls blood in the veins which equates to a partial pressure of oxygen of about 40mmHg. The venous and tissue partial pressures are roughly the same.
If you are diving at a setpoint of 1.4, each 100mls of your blood contains a bit more oxygen than usual (20mls bound to haemoglobin and about 3.2 mls dissolved). If you are using the same amount of oxygen then there will be about 18mls O2/100mls blood, which means the haemoglobin is about 90% saturated and the partial pressure of O2 is about 75mmHg.
Even if oxygen were as narcotic as nitrogen, then you can see why the contribution of oxygen to the narcosis is negligible, and why narcosis worsens as the PO2 falls.
Say you are at 40m with air dil and a setpoint of 1.4. The partial pressure of nitrogen in the brain is 3.6 ATA (or 2736mmHg) and the partial pressure of oxygen in the brain is about .1 ATA (75mmHg) so the total "narcotic load" is 3.7 ATA.
Now say your setpoint changes to 0.2 (for whatever reason) The partial pressure of nitrogen in the brain is now 4.8 ATA (or 3648mmHg) and the partial pressure of oxygen in the brain is about .05ATA (40mmHg) so the total "narcotic load" is 4.85 ATA - much worse.
Dave T
I think that explains the issue fairly well, but perhaps Rockjock feels that ALL of the experts are wrong, other than himself. Oh, sorry, he did say he wasn't one. :11: