Some government meetings require cell phones to be left outside the conference room. We are told it is for security reasons, but I’m convinced it is for our own safety. Smart phones are becoming too darned smart, and any machine that is smarter than its user is dangerous.
Case in point: I recently attended a serious presentation by military flag officers. The meeting wasn’t classified, but it was important. Of course, not wanting to be one of “those people” I had placed my new phone on “stun” – vibrate, before the meeting started. But I did not turn it off. Like most supposedly clever and important people at the meeting I intended to occasionally use the phone to access my email between briefings.
During one such lull between briefings, I noticed a Pandora splash screen briefly pop up; I must have inadvertently touched the on-screen icon with an errant finger. But I quickly shut the application down with the “Home” button. Or so I thought.
If you don’t know, Pandora.com is a site for Internet-accessible music. It’s a convenient way to keep yourself entertained when taking long walks. What I did not know at the time is that the Home button hides the application, but does not shut it down.
As the flag officer started his talk I could hear soft music – some Irish girl singing. Is that part of the talk, I wondered? Then I noticed those in the audience near me were now looking directly at me.
Oh my Gosh, it was coming from my pocket. PANDORA!
I jammed my hand into my pocket, hitting buttons wildly to shut the phone up, but no luck. She kept singing, softly at first but slightly louder with each passing second. Panicked, I left my seat clutching the phone against my body, trying to muffle the sound, and headed for the door, bumping knees and knocking papers off chairs, drawing even more attention.
I refused to look at the General trying to speak over the commotion — he used to like me.
"Strangle that guy!"
By now I’m imagining the other Flag Officers signaling for my elimination.
"Never mind, I'll just shoot him."
Safely outside of the room, it took me at least 3 more minutes before I figured out how to shut that Irish chick up.
Sure enough, at the next break I heard someone asking who that guy was with the phone, and of course I cringed when I heard my name mentioned. In spite of my best efforts, I had become “… that guy!”
It is not an overstatement to say that I now have a well-earned love-hate relationship with my smart phone.
OK, I admit that those file photos above are taken slightly out of context. However, that’s what I thought was going on behind my back. (Photo credits: joyfulpublicspeaking.blogspot.com; stripes.com)
A three-year old was tasked by her father to gather foodstuffs from the sea and bring them to the kitchen for cooking. She never left the house, but was expected to find items around the house representing sea food. And the cooking was to be “pretend” cooking.
Her first scavenged item was a plush toy crab. “Good choice,” her Father responded proudly. “That will definitely go into our cooking pot.”
And then the child disappeared for a long while. Her father assumed she was looking for clam shells scavenged from the beach.
But instead, she brought back a plushy toy mermaid.
He was horrified. “Oh no, we don’t eat mermaids!”
I’m somewhat relieved that if she ever encounters a real mermaid, she will have learned that the mermaid is at least part-human, and therefore not a food item. But oddly enough, the eating of mermaids has some storied precedence. The best example I’m aware of is the Ningyo, a Japanese variant of the mermaid mythology. The Ningyo is a human-faced fish that some describe as being tasty, and bringing good luck if eaten. Perhaps it was inspired by carp similar to that at the right, which with selective breeding has developed some surprisingly human-like facial characteristics.
As for where the good-luck notion came from, I have no idea, and the three-year old doesn’t know either.
Most adults do not consider a variation in appendages to signify a food item. That is, if a baby has 6 legs, as was recently reported, they are nevertheless human and not food. If they have no normal appendages at all, then they are still obviously very human. Even children with the rare Mermaid syndrome (sirenomelia), where two legs are fused together into a relatively useless Mermaid-like tail, would never be mistaken as anything but wonderfully human.
So I wondered what triggered the thought in a three-year old mind that a mermaid would be edible?
"A Mermaid", 1901, John William Waterhouse, from WikipediaImage credit: www.dec.ny.gov
Then I remembered that same three year old has caught little fish, and she remembers the fins and scales, and associated the fish catching with really tasty food. So like Pavlov’s dogs, half a fish might be enough to start the salivation response.
So sorry little mermaid, it doesn’t matter how girlish (or womanly) your top half might be, it’s your fishy half that’s gonna get fried, grilled or blackened if one kid has anything to do with it. My advice to you – stay away from preschoolers.
Contributed by Dragon Boy to http://the-dragon.info/
We have a new game at our house. It’s called, “See What Dragon Speaking Does with the Diction of a Four-Year-Old.”
It’s endlessly entertaining.
It’s my son’s doing, really. I was complaining about how unhealthy it was sitting at a keyboard for seemingly endless hours writing, rather than getting up and moving around. I was considering putting my computer on a treadmill and walking while writing. His response was clever; use dictation software while walking.
That was an idea well worth considering. Fortunately my phone allowed me to download a free copy of Dragon Speaking, and I started experimenting with it. It’s amazingly accurate, and inserts commas, quotation marks and other punctuation as requested by the speaker. It works well with my wife and I, but when our four-year-old granddaughter visited, I learned something about Dragon Speaking that I had not known. It’s not for children.
There is apparently something about pre-schooler speech that the software is not programmed to handle. For instance, “I want an Oreo” became “I want to pick her up”. “I want a doggy” was transcribed as “I can like key time.” “I speak English very good (sic)” became “I ain’t English family game.”
Really?
It seems that the four-year-old spoke better English than the dragon did.
It was pretty weird watching a smart phone write “ain’t” with the proper punctuation for a very improper word. But of course if I were writing a novel about real people, that word would undoubtedly come up quite often, sad to say.
Nevertheless, my initial surprise spurred me on to a semi-scientific study of the phenomenon. (Some might call it a pseudo-scientific study, but the word pseudo is a considerable slur for a scientist, so I ain’t using it.) My plan was to speak a sentence into the phone to confirm that Dragon Speaking would correctly interpret it, then my granddaughter would say the same thing. The results were hilarious.
Under the “Actual” column, below, are my words as translated into text on my phone. The only error, if you could called it that, is when I meant “Sidney” it spelled “Cydni” which is of course identical from a phonics perspective. Under the “Transcribed” column we have the software’s interpretation of the four-year-old’s speech.
ActualTranscribed
I love flowers. I laugh laugh.
I like Hello Kitty. I like Atlanta can’t.
Feed me cookies. Can’t are you.
Give me pancakes. Call me home.
I like Cydni (sic) the giraffe. Are you guys don’t.
I like school. or my school
You like the sky. You bye.
I like Octopus. or I can
And one of the most complete but inexplicable translations:
Daddy is here to pick me up. Are you feeling Okay?
A preschooler using an iPhone.
No sentences were included in this listing if we adults did not understand completely what the child was saying. Apparently our brains are much better at interpreting kid-speak than are Dragon brains.
In case you haven’t been around a four-year-old recently, this is what PBS Parents Child Development Tracker has to say about the speech of four-year-olds. “The language skills of four-year-olds expand rapidly. They begin communicating in complex and compound sentences, have very few pronunciation errors and expand their vocabularies daily.”
In other words, four-year-olds may speak with a child’s accent, if you will, but their speech is well-developed in both content and complexity.
Mind you, this posting is not intended in any way as a slight towards the producers of Dragon Naturally Speaking. I have, after all, the free iPhone version of the software. Perhaps if I weren’t too cheap to pay, I might discover that the full version of the software does a better job, and in my judgement even the free version is brilliant. Nor am I poking fun at the speech of children. What I am doing is pointing out a free way to keep your child or grandchild entertained. They seem to find it every bit as amusing as I do.
My granddaughter simply says, laughing, “Silly phone”.
Are you a child of Lake Wobegon, where according to Garrison Keillor “all the women are strong, all the men are good looking, and all of the children are above average?” If you are, you may be headed for trouble with your rebreather scrubber canister.
Or expressed another way, do you know how long your scrubber canister will last?
Believe me when I tell you, it depends.
Below I explain why the above answer is necessarily evasive, and why the true answer is frustratingly elusive. Canister duration depends on things with which you, as a rebreather diver, are all too aware, and things which you may not have thought about before; namely probability and statistics.
Figure 1. CO2 concentration in canister effluent vs. time. Click for a larger image.
All of what follows is based on canister duration data for a particular rebreather of U.S. Navy interest. Data from other rebreathers are similar qualitatively, but the actual numbers may vary.
In Figure 1, the concentration of CO2 leaving the CO2 absorbent bed within a scrubber canister is plotted as a function of time for five “canister runs” for the same model rebreather. A fresh canister should absorb all the CO2 a diver exhales, leaving CO2-free gas to be inhaled by the diver on the next breath. As the absorbent becomes depleted, the scrubbing process loses efficiency and CO2 begins bypassing the canister. The amount of CO2 being inhaled by the diver begins rising exponentially, as shown in Figure 1.
For this example, canister duration tests were conducted at 70° F, at a fixed depth, with Sofnolime 812™ as the chemical absorbent, and at both a fixed minute volume of gas (representing the simulated diver’s breathing rate) passing through the canister bed, and a fixed rate of CO2 injection representing a fixed work rate and oxygen consumption. Therefore, you would expect results to be very similar from run to run, but Figure 1 shows variation in the amount of CO2 leaving the canister with time.
Figure 2. Fit of the summary data of Figure 1 to a single exponential curve. Click for a larger image.
The average data for the canister curves fit a simple exponential equation fairly well (Figure 2). We were thus justified in using an exponential equation to explore how canister duration might vary from dive to dive. Basically, the equation considered how the amount of CO2 absorbent in the canister, and the rate of CO2 production by the diver, would work together to determine the canister duration, with all else being fixed. The amount of CO2 produced depended on the rate of oxygen consumption, and from the respiratory exchange ratio which determines how much CO2 is produced for a given amount of consumed oxygen.
Fortunately we have data for those variables, in some cases coming from divers using the same rebreather as shown in Figure 1. We have estimates of oxygen consumed during prolonged swims. Most importantly, we have measures of the variability associated with all that data. For instance, Figure 3 shows the bell shaped curve for oxygen consumption data measured by an NEDU researcher during distance swims by Navy divers. We deduced the curve for this exercise from the reported statistics (mean or average, and standard deviation). Similar curves were obtained for the other factors that influence canister duration, except for water temperature. That was assumed constant.
Figure 3. Oxygen consumption bell curve.
We then treated all the known factors and their known variability to a mathematical process called Propagation of Error (H.H. Ku, Notes on the Use of Propagation of Error Formulas, Journal of Res. of the Nat. Bur. Stds., 1966.)
The result was Figure 4 which requires careful study to appreciate what it’s telling us.
If everything about a diver and his diving equipment were “average” then their UBA canister might be expected to follow the white canister breakthrough curve on the far right, identified as P = 0.500. Since that curve represents an average, fifty percent of canisters would be expected to last longer than that curve (fall to the right of the curve) and fifty percent would be expected to fall to the left of it; i.e., to last the same or shorter amount of time. Approximately 16% of the canister breakthrough curves would be expected to fall to the left of the black line identified as P = 0.159, and 2.3% would fall on or to the left of the yellow line (P = 0.023).
Figure 4. Results from the application of propagation of error formulas.Click to enlarge.
Now comes food for thought. What if, as Garrison Keillor says, you’re a child from Lake Wobegon, and are above average in your oxygen consumption? If your dive lasted to the point where the average canister broke through at 0.5% CO2 (about 255 min, white curve intersection with the horizontal blue-green line), then you might be seeing a dangerously high inspired CO2 of 3-4% (vertical blue-green line), depending on how far from average you are.
If you chose to dive for the average time for a canister to reach 2% CO2 (magenta lines), then your actual inspired CO2 could be 7 to 12%, an extremely dangerous CO2 exposure as described in a preceding post.
Keep in mind that in this particular example water temperature was constant. If you dive in a variety of water temperatures your canister duration will vary even more. If your work rate changes widely over the course of a dive, then the canister duration will be essentially unpredictable.
So regarding how long your canister will last on any given dive: Are you feeling lucky?
This material was presented by JR Clarke and DE Warkander in a 2001 meeting of the Undersea and Hyperbaric Medical Society. Undersea and Hyperbaric Medicine, 28:81, suppl., 2001.
I had a dream a couple of weeks ago and awoke knowing I had seen something very disturbing, but couldn’t remember what it was. Then on February 21st I had a lucid dream where I realized that what I was seeing was what I’d seen the previous week. Then I understood why I was disturbed.
It was a scene from a vantage point in space. It was cinematic in quality, big screen, IMAX, at least. I was there.
The troubling part was observing a space vehicle moving up to the space station, then seeing the vehicle suddenly yaw its nose away from the station as if slammed by some powerful but invisible force, followed a split second later by the white paint on the space station charring before my eyes. Not all of it, just the part closest to an out of view source of blistering heat. The curved portion on top of the station was spared; from a thermal radiation standpoint it was very realistic.
Curiously, the station was not the ISS: it was much smaller but the markings on the white paint were clearly U.S.. I overhead two men talking on the coms, supposedly ground control, saying the heart rates of the station occupants soared.
It woke me, and I realized the entire dream sequence had lasted about five seconds, at most. It must have been the sauerkraut from the night before.
To quote, “Beijing is developing missiles, electronic jammers, and lasers for use against satellites…The Chinese, as well as the Russians, are also developing space capabilities that interfere with or disable U.S. space-based navigation, communications, and intelligence satellites.”
Suddenly, the thought of either space-based or ground-based attacks on manned vehicles or space stations becomes a frightening possibility.
Then tonight I read that a NASA notebook computer containing codes for controlling the Space Station was stolen.
“These incidents spanned a wide continuum from individuals testing their skill to break into NASA systems, to well-organized criminal enterprises hacking for profit, to intrusions that may have been sponsored by foreign intelligence services seeking to further their countries’ objectives,” Martin said. “Another attack involved Chinese-based IP addresses that gained full access to systems and sensitive user accounts at the Jet Propulsion Laboratory in Pasadena, Calif.”
We tend to think of space as a neutral environment where brave souls put their lives at risk to be part of man’s push away from our planet. It is an environment for scientific pursuit. Of course we have raised a generation or two on images of space battles where humans are fighting to preserve humanity. There is lots of death and destruction, but it is heroic in scope and detail. If death can be glorious, then dying to protect Mother Earth from Klingons is a glorious way to die.
But what I saw in those five seconds of searing imagery left me with a profound sadness. I had witnessed, so to speak, the end of our honeymoon in space. Man’s evil nature was reaching way beyond our stratosphere.
I put no stock in dreams, at least not my own. But that particular dream did serve to increase my awareness of the not-so-subtle signs that man is determined to extend his malevolent reach into what was once considered hallowed ground; the firmament, the very heavens we have for so long dreamed of reaching.
Affordable, high definition cameras are opening up a world of sporting video to those who can’t compete with the pros. For aviators, we get to share our passion, the beauty of flight!
I recently borrowed a GoPro camera and gave it a try. The flight in the Piper Arrow was short, 29 nm, from the new airport at Panama City (ECP) to DeFuniak Springs. The sky was spectacular and the air was fresh from the north but at a mercifully pleasant temperature for February (low seventies in °F). The air was a little turbulent below 2500 feet, explaining the slight bumpiness of the video at low altitude.
After takeoff, climbing to smooth air, I circled over the cypress and hardwood-lined Choctawhatchee river which heads south from southern Alabama to empty into the Choctawhatchee Bay near Destin and Ft. Walton in the Florida Panhandle. As shown below, that river drains some of the best scuba and cave-diving springs in Florida, including Morrison Spring, featured in the previous post.
Locally, there seems to be some nonchalance about the spelling of Defuniak, De Funiak or DeFuniak. The French care of course, but the locals don’t. Surprisingly, the town was not named after a French trader with the Choctaw Indians. DeFuniak Springs was named after Fred de Funiak, the first president of the Pensacola and Atlantic Railroad who envisioned DeFuniak Springs as a resort for northern visitors.
A pilot can appreciate that in the video the approach to landing in DeFuniak Springs was not as well aligned as it should have been. I had fallen victim to the visual illusion spoken of in the blog posting Killer Optical Illusions – Size Does Matter.
I usually fly into runways between 150 and 200-feet wide, including current or former military runways and the airport at Panama City. It had been a year since I’d flown into DeFuniak’s narrow 60-foot wide runway, and even though I circled the field twice I still found myself too close-in on downwind (flying parallel to the landing runway, in the opposite direction). That, plus a strong tailwind on base (perpendicular to the runway) put me past the point where I would normally line up for landing.
Over-correcting close to the ground can be fatal due to an event called the stall spin accident. It occurs when aircraft are flown incorrectly close to the ground during that potentially fateful turn to “final”, trying to line up with the runway. Being mindful of that I kept my speed up and corrected no more than necessary to find my way to the runway.
I didn’t realize it at the time, but my wife was parked opposite from my intended landing spot watching the approach. I’m glad that, all things considered, it turned out well. At least it drove home my previous point that “Size Matters”.
Technical details: This HD video was taken from the cockpit of a Piper Arrow. A GoPro camera filmed the action. Royalty-free music was generated automatically by Cyberlink PowerDirector 10 with SmartSound technology.
The exit to the Morrison Springs cave. (photo credit: ZoCrowes255)
The young man in a swimming suit was lying lifeless at the bottom of a fissure on the floor of Morrison Springs, a popular underwater cave in Walton County, Florida. If his eyes had been open, he would have been staring straight up at me. But mercifully, his eyes were shut, as in sleep.
My diving buddies from the Georgia Tech Aquajackets dive club and I were breathing air from scuba tanks at about 110 feet sea water. We were in a portion of the cave that received no indirect light from the cave opening. Without the cave lights in many of the diver’s hands there would have been total darkness.
Who knew that on my second so-called “open water” dive I would find myself deeper than 100 feet in a cave, using the dispersed light from my buddies’ dive lights to examine a very fresh looking corpse? He looked to be about our age, late teens, high school or college age. A rock outcropping hid his body from about mid-hip level down. But the top portion of a bathing suit, his lean stomach, chest, and boyish-looking face and head was plainly visible.
There must have been some current at the bottom of the crevice because his brown hair was waving gently, being the only sign of motion from the deathly pale white boy with closed eyes, waiting patiently to be recovered to the surface.
I and the other divers stretched our arms and shoulders as far into the crevice as we dared, reaching towards the young man, hoping we could grab onto some part of his body. But it was futile – he was at least a foot out of our reach. Finally, checking our dive watches, we saw it was time to swim toward the cave entrance and start our ascent.
Since there was no scuba gear on him he must have been a free-diver, a breath-hold diver who entered the cave then passed out and sank to the deepest, most inaccessible portion of the cave. As I and the other divers rose along the limestone borders of the cave I watched the darkness surround the young man’s cold body once again. I felt lonely, almost as if I could feel his spirit’s loneliness.
As I reached the surface I turned to the closest diver, removed my regulator from my mouth, and panted, “How are we going to recover that body?”
His response stunned me.
“What body? That was no body – that was a Navy 6-cell flashlight!
How could it be? I would have signed a sworn affidavit to the police describing everything I had seen, in detail, just as I’ve reported it to you many years later. The visual details, the textures, the emotions will not leave me.
But they were not real.
As for why that happened, the only thing I can assume is that for a nineteen-year old novice diver, descending in the dark to 110 feet, in a cave, might be just a bit more than the diver’s mind is prepared for. The nitrogen in air is narcotic if found in high enough concentration, so I was undoubtedly suffering from nitrogen narcosis. Plus, at the time the entrance to the Spring was macabre, with a large photo of a diver with his back filleted open by a boat propeller, and signs prominently displaying warnings of the large number of fatalities in the cave from poorly trained and equipped divers exceeding their limits.
My mind was prepared to witness tragedy, and the normally mild nitrogen narcosis of 110 feet may have been just the trigger needed for a vivid hallucination.
I have had no hallucinations since then, from diving or anything else, except for one medical procedure reported on in this blog. But what remains remarkable to me was my absolute conviction that what I had seen in that cave was real. Consequently, I now know very well that what people testify as being real, whether they are diving or not, may in fact be only imagined.
The amount of carbon dioxide (CO2) that can be safely inhaled by rebreather divers is a continuing point of conjecture, and vigorous argument. Unfortunately, the U.S. Navy Experimental Diving Unit has confused that issue, until recently.
A non-diver might wonder why a diver should inhale any CO2. After all, the air we breathe contains only a small fraction of CO2 (0.039%). A rebreather is best known for emitting no bubbles, or at most very few bubbles depending on the type of rebreather. It does that by recirculating the diver’s breath, adding oxygen to make up for oxygen consumed by the diver, and absorbing the carbon dioxide produced by the diver. The CO2 scrubber canister is vital to keeping the diver alive. As pointed out in the first post in this series, carbon dioxide is toxic; it can kill.
A CO2 scrubber keeps the recirculating CO2 levels low by chemically absorbing exhaled CO2. However, the scrubber has a finite lifetime – it can only absorb so much CO2. Once its capacity has been exceeded, CO2 passing through the canister accumulates exponentially as the diver continues to produce CO2 from his respiration.
The question rebreather divers want answered is, “How much of that bypassed CO2 can I tolerate?” As we’ve discussed in previous posts, 30% CO2 can incapacitate you within a few breaths. I can personally verify that if you’re exercising you may not notice the effect 7% CO2 has on you, until you try to do something requiring coordination. I’d equate it to the effect of drinking too many beers. There is little controversy about CO2 levels of 5-7% being bad for a diver.
For levels below 5-7% CO2, the U.S. Navy has not been real clear. For instance, 2% CO2 is the maximum CO2 allowed in diving helmets. If CO2 were to climb higher the diver would most likely feel a need to ventilate the helmet by briefly turning up the fresh gas supply to clear CO2.
Since at least 1981, NEDU has defined the scrubber canister breakthrough point in rebreathers as 0.5% CO2. That means that at some point, which varies with CO2 injection rate, ventilation rate, water temperature, and grain size of CO2 absorbent, CO2 begins leaking past the canister, not being fully absorbed during its passage through the canister. Once that leakage starts, the amount of CO2 entering the diver’s inspired breath rises at an ever increasing rate unless work rate or other variables change. By the time the CO2 leaving the canister has reached 0.5%, the canister has unequivocally “broken through”.
I pointed out in my last post that even 0% inspired CO2 may be too much for some divers when they are facing resistance to breathing. And all rebreathers are more difficult to breathe than other types of underwater breathing apparatus because the diver has to force his breath through the rig’s scrubber canister and associated hoses. The deeper the dive the denser the breathing gas and the worse breathing resistance becomes.
In free-flow diving helmets like the old MK 5, and the short-lived MK 12, the diver did not breathe through hoses and scrubber canisters. But those helmets had a high dead space and to keep helmet CO2 at tolerable levels a fresh gas flow of 6 actual cubic feet per minute (acfm; 170 liters per minute) was required. The U.S. Navy allowed up to 2% CO2 in the helmet because 1) the helmets did not have a high work of breathing and 2) due to simple physics the helmet CO2 couldn’t be kept very low.
For rebreathers, none of the above apply. A high breathing resistance is inevitable, at least compared to free-flow helmets, and once CO2 starts rising there is nothing you can do to decrease it again, short of stopping work.
In 2000, NEDU’s M. Knafelc published a literature review espousing that the same limit for inspired CO2 which applies in helmets could be used in rebreathers. Nevertheless, in 2010 NEDU’s D. Warkander and B. Shykoff clearly demonstrated that in the face of rising inspired CO2 concentrations work performance is reduced, and blood levels of CO2 rise, in some cases to dangerous levels. More recent work by the Warkander and Shykoff duo have extended those studies into submersion, however those reports are not yet publicly available.
As a result of both physiological theory and confirmatory data in young, physically-fit experimental divers, NEDU has not relaxed the existing definitions of scrubber canister breakthrough, 0.5% PCO2. Furthermore NEDU will adhere to the current practice of using statistical prediction methods to define published canister durations, methods which are designed to keep the odds of a diver’s rebreather canister “breaking through” to no more than 2.5%, comparable to the odds of decompression sickness following Navy multi-level dive tables. Details of this procedure will be explained in later postings.
Most rebreather divers start off their diving career with open-circuit diving; that is, with scuba. And some of them pick up bad habits. I happen to be one of those divers.
With scuba you start the dive with a very limited amount of air in your scuba bottle. New divers are typically anxious, breathe harder than they have to, and blow through their air supply fairly quickly. More experienced divers are relaxed and enjoy the dive without anxiety, and thus their air bottles last longer than they do with novice divers.
So early in a diver’s experience he comes to associate air conservation with a sign of diver experience and maturity. When you are relaxed and physically fit, and your swimming is efficient, your breathing may become extraordinarily slow. Some call it skip breathing — holding your breath between inhalations.
I was once swimming among the ruins of Herod’s Port in Caesarea, and my dive buddy was a Navy SEAL. I started the dive under-weighted, so I picked up a 2000 year old piece of rubble and carried it around with me as ballast. In spite of the very inefficient style of swimming which resulted, my air supply still lasted longer than that of my SEAL buddy.
At first I was annoyed that I had to end the dive prematurely, but then I began to feel somewhat smug. I had used less air than a frogman.
As a physiologist I knew that I may well have been unconsciously skip breathing, which would have raised my arterial carbon dioxide level, potentially to a dangerous level. But all ended well, and I could not help being glad that I was not the one to call the dive.
It is important for rebreather divers to understand that they don’t have to be breathing elevated levels of carbon dioxide to run into physiological problems with carbon dioxide. It’s the carbon dioxide in your arterial blood that matters. It can render you unconscious even when you’re breathing gas with no carbon dioxide at all.
MK 16 rebreather diver
Normally the body automatically ensures that as you work harder, and produce more carbon dioxide in your blood stream, that you breathe more, forcing that CO2 out of your blood, into the lungs, and out through your mouth. It works like an air conditioner thermostat; the hotter it gets in the house, the more heat is pumped outside. In other words, arterial and alveolar CO2 levels are controlled by automatic changes in ventilation (breathing.) In fact you can predict alveolar levels of CO2 by taking the rate at which CO2 is being produced by the body and dividing it by the ventilation rate. This relationship is called the Alveolar Ventilation Equation, or in clinical circles, the PCO2 Equation.
Normally, CO2 production and ventilation is tightly controlled so that normal alveolar and arterial CO2 is about 40 mmHg, mmHg being a unit of so-called partial pressure. 40 mmHg of arterial CO2 is safe. [One standard atmosphere of pressure is 760 mmHg, so ignoring the partial pressure of water vapor and other gases, a partial pressure of 40 mmHg of CO2 is equivalent to exhaling about 5% carbon dioxide.]
When a diver is working hard while breathing through a breathing resistance like a rebreather, as ventilation increases respiratory discomfort goes up as well. For most people, when the respiratory discomfort gets too high, they quit working and take a”breather”. But there are some divers who hate respiratory discomfort, and don’t mind high levels of arterial CO2. We call these people CO2 retainers.
Navy experimental deep sea divers; photo credit: Frank Stout
As an example, I once had as an experimental subject a physically fit Navy diver at the Naval Medical Research Institute during a study of respiratory loading. The test was conducted in a dry hyperbaric chamber under the same pressure as that at 300 feet of sea water. The experimental setup in the chamber looked somewhat like that in the figure to the right although the diver I’m talking about is not in this photo.
The diver was exercising on the bicycle ergometer while breathing through a controlled respiratory resistance at 300 feet in a helium atmosphere. The diver quickly learned that by double breathing, starting an inspiration, stopping it, then restarting, he could confuse the circuitry controlling the test equipment, thus eliminating the high respiratory loading.
As he played these breathing pattern games my technician was monitoring a mass spectrometer which was telling us how high his expired CO2 concentration was going. The exhaled CO2 started creeping up, and I warned him that he needed to cut out the tricky breathing or I’d have to abort the run.
The clever but manipulative diver would obey my command for a minute or so, and then go back to his erratic breathing. He joked about how he was tricking the experiment and how he felt fine in spite of the high CO2 readings.
That was a mistake.
When you’re talking, you’re not breathing. Since his breathing was already marginal, his end-tidal CO2, an estimate of alveolar CO2, shot up in a matter of seconds from 60 to 70 and then 90 mmHg, over twice what it should have been. When my technician told me the diver’s exhaled CO2 was at 90 mmHg, I yelled “Abort the run”. But the diver never heard that command. He was already unconscious and falling off the bike on his way to the hard metal decking inside the hyperbaric chamber.
The diver thought he was tricking the experiment, but in fact he was tricking himself. Although he felt comfortable skip breathing, he was rapidly pedaling towards a hard lesson in the toxicity of carbon dioxide.
Keep in mind, this diver was breathing virtually no carbon dioxide. His body was producing it because of his high work level, and he was simply not breathing enough to remove it from his body.
In upcoming posts we’ll look at what happens when inspired CO2 starts to rise, for instance due to the failure of a carbon dioxide scrubber canister in a rebreather. I already gave you one example in the CO2 rebreathing study of my first post in this series. There’s lots more to come.
Of all the gases humans excrete, the most bountiful, and arguably the most deadly, is exhaled carbon dioxide.
There is a forgotten bit of American medical history that reveals the bizarre features of the toxicity of carbon dioxide. In 1926, before the advent of modern psychiatric medications, some American psychiatrists began experimenting with the use of inhaled carbon dioxide for the treatment of schizophrenia and psychoses. At the time, there were no effective treatments other than electroshock.
Dr Ladislas J. Meduna
One of the most successful of these researchers was Dr Ladislas J. Meduna, a Professor of Psychiatry at the University of Illinois College of Medicine in Chicago.
High levels of carbon dioxide (CO2) did in fact have some success in treating schizophrenia, but it also produced Out of Body (OBE) and seemingly spiritual experiences. The following text is quoted from a book called Carbon Dioxide Therapy. A Neurophysiological Treatment of Nervous Disorders, published in 1950 and authored by Meduna.Meduna administered by mask between 20 and 30 breaths of a gas mixture of 30% CO2, 70% O2. From pg. 22 of his book we find,
“Any attempt to define the sensory phenomena during CO2 anesthesia, in terms of dream, hallucination, illusions, etc., would be futile. The actual material would support any hypothesis. Some of the sensory phenomena would direct us to define them as hallucinations. Some of these phenomena are felt by the patients as “real dreams”; others obviously are dreamy repetitions of real events in the past or of past dreams. I believe therefore that any classification of these phenomena in terms of dream or hallucination would be not only meaningless, but directly misleading; the patient is not “sleeping” in the physiological sense, nor is he in the state of consciousness which we usually assume to be present in true hypnagogic hallucinations.”
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“One subject, after 20 respirations of the gas, reported seeing a “bright light, like the sun.”
“It was a wonderful feeling. It was marvelous. I felt very light and didn’t know where I was. For a moment I thought: ‘Now isn’t that funny. I am right here and I don’t know whether I am dreaming or not.’ And then I thought that something was happening to me. This wasn’t at night. I was not dreaming. And then it felt as if there were a space of time when I knew something had happened to me and I wasn’t sure what it was. And then I felt a wonderful feeling as if I was out in space.”
“After the second breath” — reported a 29 year-old healthy female nurse who had taken a treatment – “came an onrush of color… then the colors left and I felt myself being separated; my soul drawing apart from the physical being, was drawn upward seemingly to leave the earth and to go upward where it reached a greater Spirit with Whom there was a communion, producing a remarkable, new relaxation and deep security. Through this communion I seemed to receive assurance that the petite problems or whatever was bothering the human being that was me huddled down on the earth, would work out all right and that I had no need to worry.”
“In this spirituelle I felt the Greater Spirit even smiling indulgently upon me in my vain little efforts to carry on by myself and I pressed close the warmth and tender strength and felt assurance of enough power to overcome whatever lay ahead for me as a human being.”
Meduna summarized that preceding case by stating, “In this beautiful experience we can discern almost all the constants of the CO2 experience: (1) color; (2) geometric patterns; (3) movement; (4) doubleness of personality; and (5) divination or feelings of esoteric importance.”
Meduna went on to admit that “Not all of the sensory phenomena experienced by the patients are of celestial beauty and serenity. Some of them are horrifying beyond description.”
In 1971, Chris Lambertsen, M.D., Ph.D., from the University of Pennsylvania School of Medicine, and considered to be the father of special warfare diving by Navy SEALS, published a careful examination of the physiological consequences of the Meduna mixture. He found that inhalation of 30% CO2 in oxygen would cause unconsciousness and convulsions within 1-3 min. The precipitating event for loss of consciousness seemed to be a catastrophic increase in the acidity of the blood due to the large amount of carbonic acid produced by the CO2 inhalation. This raises the possibility that the experiences noted by Meduna were caused by pre-convulsive events within the brain.
Since then the medical community has deemed carbon dioxide “treatments” as not only dangerous but ineffective compared to modern psychiatric medication. Meduna’s mixture is no longer used.
While at the Naval Medical Research Institute, I was my own research subject in a study of the effects of rebreathing CO2 concentrations up to 8%. That was a carbon dioxide concentration that some Navy SEALS had claimed could be tolerated without impairment.
The simplest scrubber canister in the simplest rebreather, Ocenco M20.2
I was not under water, but riding a stationary bicycle ergometer in the laboratory, simulating breathing on a closed-circuit underwater breathing apparatus (in diving vernacular, a rebreather.) Although oxygen was being added as I consumed it, there was no carbon dioxide scrubber (a container of carbon dioxide absorbing material), so the test was examining what happens when a scrubber canister is no longer functioning properly. At 7% inspired CO2 I stopped the exercise, feeling a little abnormal. However, I was surprised at how unimpaired I seemed to be; that was, until I attempted to dismount the ergometer. I almost fell and needed help removing myself from the bicycle to a chair.
The single-minded and simple-minded task of exercising had hidden a growing central nervous system impairment. Like someone intoxicated with alcohol, I could not judge my level of impairment until a task requiring some coordination was required.
So we see that high levels of carbon dioxide intoxication can lead to profound disturbances of the central nervous system. In upcoming posts we’ll see how elevated carbon dioxide levels and the control of respiratory ventilation can interact to put rebreather divers at risk.
Much of the above is from a nonfiction book project currently under review. The working title for the book is “Collected Tales of the Spiritual and Paranormal.”
Some government meetings require cell phones to be left outside the conference room. We are told it is for security reasons, but I’m convinced it is for our own safety. Smart phones are becoming too darned smart, and any machine that is smarter than its user is dangerous.
The meeting wasn’t classified, but it was important. Of course, not wanting to be one of “those people” I had placed my new phone on “stun” – vibrate, before the meeting started. But I did not turn it off. Like most supposedly clever and important people at the meeting I intended to occasionally use the phone to access my email between briefings.
