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In response to David's postng: > I am interested in two things. Citations of any scientific studies on > humans that have shown convulsions due to trivial PO2 exposures, and first > hand (or reliable second hand, let's protect the innocent) experience of > people on these lists. For the first hand accounts, for want of > consistency, perhaps we should use the classification of Butler and Thalmann > as I remember it (accurately or not): > 1. convulsions > 2. definate symptoms = nausea, dizziness, muscle twitching (indicate which) > 3. probably symptoms = anything else (indicate what symptoms) > also indicate the PO2 (depth and gas mixture), level of exertion, > possibility of CO2 buildup and anything else I have forgotten. You asked for it.... TO ANYONE WHO IS *NOT* INTERESTED IN MY EXPERIENCES WITH HIGH PO2 OXYGEN, PLEASE DELETE THIS MESSAGE BECAUSE I KNOW IT IS GOING TO BE A LONG ONE! (even tho' I haven't written it yet) THOSE FOR WHOM THE PRECEEDING APPLIES AND WHO ALSO HAVE TO PAY TO DOWNLOAD THIS MESSAGE, SEND ME A BILL IF YOU FEEL SO INCLINED. The very last paragraph recounts an incident that occurred yesterday, which might be of some interest to the "oxygen narcosis" camp. Having said that... In the interest of inching closer to an understanding of the ways in which high PO2 affects human bodies, I want to summarize my experiences with symptoms that appear to be associated with high PO2 in my own human body. Since David asked the question, and since he might serve as some sort of repository for this sort of anecdotal information (which when combined with other anecdotal information may reveal consistent patterns), I hope this information might be worth the bandwidth. Some of you have seen some of this before, but not all in one place. One more thing before I get started. Several people have pointed out to me that my references to my "bad old days" of deep air diving might be construed by less-educated, overly-enthusiastic individuals as some sort of endorsement of deep air diving. Therefore, I will henceforth include the following disclaimer on all my message that refer to that aspect of my diving history: ***************************************************************** THE FOLLOWING MESSAGE CONTAINS GRAPHIC DESCRIPTIONS OF EXTREMELY HAZARDOUS DIVING PRACTICES, INCLUDING DEEP DIVING WHILE BREATHING AIR. THESE DESCRIPTIONS ARE NOT IN ANY WAY INTENTED TO BE AN ENDORSEMENT OF THE EFFICACY OF SUCH PRACTICES; THEY ARE PROVIDED FOR EDUCATIONAL PURPOSES ONLY. THIS MESSAGE MAY NOT BE SUITABLE FOR LESS-MATURE AUDIENCES! ***************************************************************** Now, on with the show... I've always tried to pay attention to any unusual feelings or symptoms I've encountered while diving. It's not always easy to identify what factors on the dive were responsible for which symptoms; however, after many dives under many conditions, some patterns start to emerge. For one thing, I am becoming increasingly convinced that "oxygen narcosis" is real, and is probably not caused by the same biochemical/physiological mechanisms that cause oxygen toxicity. Furthermore, it seems that O2 narcosis does not depend on PO2 alone, but rather there is a synergistic relationship betweeen PO2 & PN2 in causing narcosis severity. I hope my reasons for believeing this become apparent in the following discussion. Some of the most severe symptoms I've ever experienced underwater were during our first deep-reef exploration efforts in the Cook Islands. Chip Boyle and I conducted a series of 14 dives each to depths of 330-360 feet (12-minute bottom-times) over a 10-day period. We breathed air during all stages of these dives except the 50-foot and shallower decompression stops, whereon we breathed pure oxygen. Total in-water times were usually about 90 minutes. Although we were collecting fish specimens during these dives, we kept exertion to an absolute minimum (comparable to hanging on a decompression line). The symptoms I experienced while breathing air at depths greater than 330 feet consistently included all of the following: - severe tunnel vision - hampered cognition (e.g., looking at a pressure gauge, seeing that it is "close" to 2000psi, but having difficulty determining if it is a little more than 2000psi, or a little less than 2000psi) - impaired short-term memory (looking at gauges and immediately forgetting what they said, forcing a second look). - loud ringing in ears - "Serial" thought processes (i.e., cannot perform multiple tasks simultaneously. On a couple of dives I could not even swim and breathe at the same time) - impaired motor function (reduced dexterity in the arms and hands) - severe pins and needles in extremeties (Chip did not experience this. This symptom is VERY consistent for me, and is the primary symptom of what I call "cold narcosis". I have not heard from anyone else who experiences this symptom). There were some other symptoms, but none of them consistent or severe. Notably, Chip and I did *NOT* experience any nausea, dizziness, or muscular twitching at any time during any dive (we were careful to watch for these, so it's not that we just didn't notice them). I'd also like to point out that the severity (intensity) of some of these symptoms (particularly the cognition, memory and serial-thinking symptoms) diminished substantially throughout the course of the 10-day period, however all symptoms were still present (albeit some to a lesser extreme) even at the end of the expedition. So, the question is, how much of these symtoms were caused by nitrogen, and how much by oxygen? The answer to this may be partially revealed by our experiences during decompression. First I should explain that most divers who have been to 200 feet or more on air (including me) report that narcosis symptoms do not just disappear immediately upon ascent. Slight residual symptoms linger for minutes to hours after the dive. On our deep air dives in the Cook Islands, these residual symptoms lasted days (subtle symptoms lasted for 3 months, in my case). Most of the symptoms taper off during decompression, however. As I mentioned, we breathed pure oxygen at our 50-foot and shallower decompression stops. The interesting thing is that Chip and I both noticed that the rate of residual symptom disappearance dramatically INCREASED once we started breathing oxygen at 50 feet. In other words, switching to oxygen had an effect of *REDUCING* the residual symptoms. The only new symptom that was evident to me (but I'm not sure about Chip) after the switch to oxygen was the strange feeling I recently described that I have been getting on high PO2 with the rebreather (more explanation later in this message). So let's look at the numbers. During the deep-air part of the dive, the total ambient pressure was 11-12ata, with an approximate inspired PO2 of 2.3-2.5atm, and inspired PN2 of 8.7-9.5atm. At 50 feet on pure O2, the inspired PO2 was 2.5atm and the PN2 was zero. Thus, at 50 feet, with the same PO2 as the deepest dive, the symptoms all WENT AWAY faster than they were going away during our deeper decompression stops on air where there was a lower PO2 and higher PN2. From this I conclude that the majority of the symptoms I experienced at depth on air were caused by N2 (or if partially by O2, then only in conjunction with N2), but NOT O2 alone. Add to this the fact that, during the deep portion of the dive, we had not already accumulated a large O2 dose, but by the time we were at out 50-foot decompression stop, we had a much larger total O2 dose. Based on my understanding of current perspectives on the biochemical root-causes of O2 toxicity, the toxicity should only be a function of PO2 (and perhaps PCO2), but should not really be influenced by PN2. (If anyone knows otherwise, please correct me...) Therefore, none of the symptoms on those dives appear to be indicative of O2 toxicity. The following year, Chip and I began experimenting with trimix. On our very first trimix dive (to 360 feet), Chip was more concerned about DCS, and I was more concerned about O2 toxicity, so on our first mixed-gas dive he had a bottom mix of 16% oxygen, 64% nitrogen, and 20% helium; and I had a bottom mix of 12% oxygen, 48% nitrogen, and 40% helium. Both of us had nitrox-35 for decompression from 130 to 30 feet, and pure oxygen at 30, 20 and 10-foot stops. During the ascent, Chip ran low on trimix so had to switch to nitrox at about 250 feet on the way up. Not long afterward (at about 120 feet), he began feeling nauseated. By the time we were at our 30-foot oxygen stop, he was vomiting about every 5 minutes or so. He finally started taking air-breaks, and the vomiting subsided (but the nausea remained). Upon surfacing, we were not sure if the nausea was due to O2 toxicity or DCS, so Chip started breathing O2 on the surface. The nausea quickly returned so we figured that it must be due to toxicity. He did not breathe any more oxygen, and never developed any symptoms of DCS. Since then, he has kept his PO2 at 1.6 or less and has not had any other similar problems after hundreds of trimix dives. The only time I have ever experienced symptoms that seem to be related to oxygen toxicity was in a recompression chamber. I underwent a series of more than 30 chamber treatments after a bad bends case when I was 19 years old. The majority of these treatments included four 20-minute periods on pure O2 at 60 feet (PO2=2.8atm) with 5-minute air breaks in-between. At no time during any of these treatments did I experience symptoms of muscular twitching or dizziness. However, about half-way through the series of treatments, I began experiencing nausea, numbness on my fingertips, and temproary hearing impairment during and immediately after the treatments. All of these were mild at first, but became progressively more severe with each subsequent chamber treatment. I am quite certain that all of these symptoms are related to chronic or "pulmonary" oxygen toxicity, as was supported by the interpretations of my doctors at the time. One other noteworthy event: On one of the treatemtns, I was accidently given 100% oxygen to breathe at a simulated 220 feet (PO2=7.7!!). I breathed it for about a minute before the error was noticed, and at no time during that minute did I experience any unusual symptoms of narcosis or toxicity (the narcosis was roughly equivalent to what I would experience breathing air at 220 feet in a chamber). On the other hand, I *have* experienced some symptoms that appear to be related to high PO2, but which I do not believe to be oxygen toxicity. I break these down into two catagories. The first is what I would call "oxygen narcosis", and the second is a strange (but subtle) feeling I get when I breathe a PO2 higher than about 1.8 or 1.9. First, the O2 narcosis: I've already described this in detail in several recent messages, so I'll only summarize briefly here. I feel two distinct kinds of narcosis, one I call "warm", and the other I call "cold". Symptoms of cold narcosis are the same as I described earlier for our deep Cook Islands air dives. Warm narcosis is more of a buzz, sort of euphoric, classical narcosis. On air, the depth at which I get warm narcosis varies a lot depending on conditions. Cold narcosis, however, consistently kicks in at about 250-270 feet (remember folks, this is "bad old days" diving; I don't do deep air anymore). As I've describved several times in the past, I once did two dives to the same ledge at 200-220 feet in identical conditions on consecutive days; the first on air, the second on nitrox-29. The air-dive was warm narcosis as usual, but on the nitrox-29 dive, I felt obvious cold narcosis at only 200 feet, despite the fact that I had NEVER experienced such symptoms shallower than 250 feet on air under any conditions. Thus, the cold narcosis seems to kick-in only when the PO2 exceeds about 1.8-2.0atm. However, as mentioned earlier, I've never experienced cold narcosis when in the presence of high PO2 and ABSENCE of high PN2. Thus, cold narcosis seems to require BOTH high PO2 AND high PN2. Also, warm narcosis is more strongly affected by Now, the subtle high PO2 symptoms...I'm still trying to figure this one out, but I'll tell you how I'm thinking at this time. As I mentioned in a recent message, I get a strange feeling when the PO2 exceeds about 1.9 or 2.0atm, regardless of depth (i.e., regardless of PN2). I've only noticed the pattern since I began diving with a rebreather, but the more I think back on my diving history, the more I realize I've felt it before on more than a few occassions (such as when breathing O2 at 50 feet in the Cook Islands). I'm sorry, but I can't really describe the symptoms very well, other than it is a general "sumthin' ain't right" sort of feeling. There is a feeling that somewhat resembles an urge to burp, and there may be a ghost-like trace of cold-narcosis type symptoms, but nothing specific. The symptoms are very subtle, and can be masked by things like narcosis and heavy task-loading. For a variety of reasons, which I won't go into now, I do not think these are directly O2 toxicity symptoms. Exactly what they are, I'm not sure. Chris Hellas posted a message describing similar symptoms, so I may not be the only one who feels them. Yesterday I did a dive to 175 feet with the rebreather, and experienced symptoms that may link the "weird" feeling with O2 narcosis (or may not...you be the judge). For a variety of reasons which I won't go into, I did this dive without helium (I almost always limit my EAD to 130 feet these days). When I arrived at the ledge, I started feeling that "sumthin' ain't right feeling" and checked my PO2. Sure enough, the PO2 was about 1.9atm (It was a fast descent, and I started with about nitrox-40 in the loop at the surface; even with adding air on descent, it all worked out so that the PO2 was 1.9 upon arriving at the bottom.) I was wearing a full face-mask so I wasn't terribly concerned; I just stopped my exertion, added a burst of air, and waited for the PO2 to drop to appropriate levels. Before I brought the PO2 down, however, I realized that I was starting to get some rather severe warm narcosis. I even felt a slight touch of cold narcosis symptoms. For a moment, I resorted to my habitual deep-air mental habits and got it in my head that I was about 220 feet deep, because that's exactly what it felt like. But then I realized I was only at 175 feet, so I started paying close attention to the narcosis symptoms, realizing that this was a golden opportunity to accumulate yet another anecdote about O2 narcosis. After I brought the PO2 to 1.4atm, the "weird" feeling went away, but the narcosis lingered for a while, and I still felt deeper than 175 feet (although the narcosis was by then considerably less severe). I let the PO2 come down further to 1.2atm, and the narcosis diminished even further, but by that time I had to return to the surface (my companion was diving on air and we shared the same drift line, so I had to go when he wanted to go). This is the first time I've ever experienced the "weird" feeling and the O2 narcosis feeling at the same time, and they seemed to vary independently. I know this doesn't all have to do with oxygen toxicity, but I wanted to lay it all out in as much detail as possible because I want people to realize there may be more symptomatic effects of high PO2 than just O2 toxicity. It's really difficult to experiment with these factors because to tweak the system you have to expose people to potentially dangerous gas concentrations. In other words, I doubt anyone will ever be able to do extensive controlled experiments. So if we want to learn something, we need to all carefully pay attention to what we feel on the rare occasions that we find ourselves exposed to these potentially dangerous gas concentrations. Maybe if we accumulate enough anecdotal stuff, patterns will emerge. Some people might think it's useless bantor to discuss this, because in theory we'll never allow ourselves to be exposed to these gas concentrations. However, I think it could be very useful stuff. For example, if this "weird" feeling of mine is consistent, and is experienced by others, then maybe we can nail-down some definable things to watch for. Perhaps it is something people could be trained to recognize, and thus such training could be included in all mixed-gas rebreather courses. Who knows.... That is all. Aloha, Rich Richard Pyle deepreef@bi*.bi*.ha*.or* ******************************************************************* "WHATEVER happens to you when you willingly go underwater is COMPLETELY and ENTIRELY your own responsibility! If you cannot accept this responsibility, stay out of the water!" *******************************************************************
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