oxygen | John Clarke Online

Happy Hypoxia – A 2018 Warning

“Happy hypoxia,” or more properly, silent hypoxia, has been one of the most puzzling signs and symptoms of patients presenting to Emergency Rooms with COVID-19. The patient’s arterial oxygen saturation can be in the fifties instead of the normal values in the upper 90s, and yet the patient can be cheerful, fully coherent, and even chatty. Normally, with that low an oxygen concentration in the blood stream, a patient would be in severe respiratory distress.

I experienced silent hypoxia after a visit to Thailand in July of 2018, which makes me wonder: was there a coronavirus lurking in Southeast Asia in 2018 that later mutated to become the killer SARS CoV-2? Did I have SARS CoV-1.5?

Summertime was everything you would expect in Thailand. It was warm and humid, but not uncomfortably so. I had twelve hours ahead of me in the Bangkok Airport waiting for my return flight to Taiwan, then the long leg across the Pacific to Los Angeles. Eventually, I would make my way back to my home in Panama City, Florida, which would also be hot and muggy. No surprises there.

What was a surprise, was that a young lady wandering the airport asked if she could interview me for the Thai Ministry of Tourism. She had official looking IDs, and a load of interview questions. I wasn’t interested, and I was busy, I offered, already tired before the twelve hours of dead time even began.

In truth, I wasn’t that busy, but felt it best not to mingle. I seemed to be the only person not speaking Thai, except for that young lady. Surprisingly, she had no detectable accent and could pass for a Southern California blond.

After a couple of hours, she returned when I could no longer claim to be busy. She had a simple, youthful attractiveness and an unassuming manner. So, tiring of the boredom of waiting, I allowed her to sit beside me while she started running down her list of tourism related questions.

She wanted to know why I came to Thailand. It was to give a talk at a medical and scientific conference on sports medicine. My subject was “Oxygen,” a fact that would soon become ironic. I discovered later that my travel, ostensibly paid for by the Thai Sports Authority, was bankrolled by Beijing. But I didn’t know that at the time.

For 45 minutes the questions continued. They were business-like, the type of questions I would expect from a Tourist Bureau. But one thing caused me concern, her occasional hacky cough. She insisted it was nothing, and I was not alarmed. I thought no more about it as I finally boarded the plane for the first leg of my long journey home.

Eight hours after my arrival in Panama City, I felt ill as I lay in bed, trying to sleep after being exactly twelve hours time-shifted. I felt sicker by the minute. Jet lag doesn’t do that.

By morning, I had suffered chills and sweats, and my physician son insisted I be taken to the closest Emergency Room. As we neared the ER I felt I was going to vomit, and I leaned into a trash can that my wife brought for that purpose.

The next thing I heard was her screaming at me.

I yelled back, completely confused and annoyed. “Why are you yelling at me?”

“I thought you’d died,” she said. “You sighed, threw your back into the seat, and your arms were stiff and shaking.”

Apparently I had passed out from a drop in blood pressure. (I had not yet thought about hypoxemia.)

As I was being monitored in the ER, I felt OK. I conversed with my wife, and was half-joking and half-irritated at my unexpected welcome home event.

After awhile, I began to pay attention to the finger tip pulse-oximeter that was monitoring my arterial oxygen saturation. The reading was slipping lower than I had ever seen before, but neither the nursing staff nor the attending physician seemed the least bit concerned. My wife and I continued to chat. I was not in any discomfort, and ignored the monitors until I caught sight of the updated pulse-ox reading. It had plummeted down to a horrifically low 55%.

I told my wife to alert the nurse. They finally started me on a nasal cannula with oxygen. (For those who know, that was an incredibly delayed reaction.) I also knew enough to realize I should be almost stuporous, yet I wasn’t. I was content, except for my circumstances.

Within a few minutes, an ambulance transported me to a real hospital. Being aware of my overseas travel, they assumed I had a pulmonary embolism, which if detected, would have required immediate surgery. But after a perfusion scan, nothing abnormal was revealed.

After settling into a room, I had zero desire for any of the food they brought me. It was all tasteless, and remained that way for two days.

Initially they kept me on 3 liters of oxygen per minute by nasal cannula, which still wasn’t bringing my oxygen saturation above 84 percent. That was a problem.

At the urging of the CDC, the nursing staff came to my room fully gowned and face-shielded, and stuck that infamously long sampling swab up my nose. They tested me for the most recent viral illness in Southeast Asia at the time, the H7N9 Bird Flu virus of 2017. The results were negative.

In spite of my growing displeasure with being in the hospital, and not tolerating the taste, or lack thereof, of their food, I was happy and chatty with the nursing staff. But neither I, a respiratory physiologist, nor the medical staff could figure out what was wrong. My X-rays showed some consolidation in my lingula, a small lobe in the middle of my lungs, but that was not enough to cause hypoxia of the level I was experiencing.

After a while, I began to get a few signs of pneumonia in my lower lung lobes, but not enough to cause any discomfort, or difficulty breathing. While physicians clobbered the growing infection with antibiotics and steroids, I remained happily hypoxic.

After five days in the hospital, and slowly watching my oxygen saturation rise, a respiratory therapist snuck behind me and turned off the oxygen. My saturation remained low, at 88%, but it didn’t drop further.

That meant, I would remain on air until discharge. That encouraged me enough to call for a walking test, walking down the hospital corridor breathing nothing but air. Unfortunately, I failed that test, and was sent back to bed.

About that time, a pulmonologist came by and told me I had a good bit of atelectasis (collapsed alveoli or lung sacs) in my lower lobes. Finally, something I could fix. I knew what to do.

I wore out my incentive spirometer over the next couple of hours, and then called for another walking test. The Respiratory Therapist chided me…I would just fail again, she said. But I do love a challenge. With her by my side, I moved slowly down the hall, refusing to talk, and that time my oxygen saturation did not drop.

Due to that walking test, I was discharged from the hospital with an oxygen saturation of 92% and returned home to fully recover. (That is in itself an interesting story which I’ll write about next.)

However, the point of this post is that as I read about COVID-19, I’m finding that physicians are puzzled about some of the same bizarre symptoms I experienced in 2018, notably a silent hypoxia. I was never “short of breath” as would be expected with an arterial saturation in the fifties.

From my studies of respiratory physiology, I knew that what had happened to me in 2018 should not have happened, according to the text books. I did not have the SARS virus identified in 2017. But viruses mutate constantly. Could my symptoms have been the signs of a predecessor or cousin to COVID-19? Could it have been an unrecognized COVID-18?

When lungs are not filled with fluid from rampant pneumonia, the most likely way to become hypoxic breathing air is through something called ventilation-perfusion (V-Q) mismatch. A pulmonary embolus can cause massive V-Q mismatch, and can quickly kill if untreated.

However, a recent Science article suggested that COVID-19 might cause microemboli resulting in silent hypoxia. It seems reasonable that enough microemboli, if that’s what it was, could have caused my symptoms in the summer of 2018 without being detected on a pulmonary perfusion scan.

And that worries me for the current pandemic. Summer heat and humidity might not kill this virus. It certainly didn’t kill the virus that I presumably caught from a pretty young girl with a “nothing” of a cough in late July of 2018. It may have been nothing for her, but it was sure something for me.

None of my friends at the medical conference got sick upon returning home. I was the only one spending 45 minutes less than a foot away from that coughing girl. I feel pretty confident where I got it. My only question is, did I pick up a version of coronavirus that was beginning to mutate towards the destructive potential of SARS CoV-2 which erupted just over a year later?

As for the statue at the beginning of this blog post? It is the Yaksha Guardian Giant at the Bangkok Suvarnabhumi airport. If you ask me, he failed completely at protecting me from a tiny little virus. The guardian was awfully big, but sometimes size does not matter.

The Siren’s Call of Rebreather Oxygen Sensors

In Greek mythology irresistibly seductive female creatures were believed to use enchanted singing to beckon sailors to a watery grave.

Why this myth endured through the centuries is difficult to say. However, my theory is that it helped explain to grieving widows and mothers why ships sometimes inexplicably disappeared, taking their crew with them, never to be seen again. By the reasoning of the time, there must have been some sort of feminine magic involved.

The oxygen sensors in closed-circuit, electronically or computer-controlled rebreathers are a magic device of sorts. They enable a diver to stay underwater for hours, consuming the bare minimum of oxygen required. The only thing better than a rebreather using oxygen sensors would be gills. And in case you wondered, gills for humans are quite impractical, at least for the foreseeable future.

I have written, or helped write three diving accident reports where the final causal event in a rebreather accident chain proved to be faulty oxygen sensors. So for me, the Siren call of this almost magical sensor can, and has, lured divers to their seemingly blissful and quite unexpected death.

Those who use oxygen sensors know that if the sensor fails leading to a hypoxic (low oxygen) state, loss of consciousness comes without warning. If sensor failure results in a hyperoxic state (too high oxygen), seizures can occur, again leading to loss of consciousness, usually without warning. Unless a diver is using a full facemask, loss of consciousness for either reason quickly leads to drowning.

EX19 — EX 19 rebreather (U.S. Navy photo)

Due to the life-critical nature of oxygen control with sensors, three sensors are typically used, and various “voting” algorithms are used to determine if all the sensors are reliable, or not. Unfortunately, this voting approach is not fail-proof, and the presence of three sensors does not guarantee “triple” redundancy.

In one rebreather accident occurring during the dawn of computer-controlled rebreathers, a Navy developed rebreather cut off the oxygen supply to a diver at the Navy Experimental Diving Unit, and all rebreather alarms failed. The diver went into full cardiopulmonary arrest caused by hypoxia. Fortunately, the NEDU medical staff saved the diver’s life, aided in part by the fact that he was in only 15 feet of water, in a pool.

In two more recent accidents the rebreathers kept feeding oxygen to the diver without his knowledge. One case was fatal, and the other should have been but was not. Why it did not prove fatal can only be explained by the Grace of God.

The two cases were quite different. In one the diver broke a number of safety rules and began a dive with known defective equipment. He chose to assume that his oxygen sensors were in better shape than the rest of his rebreather. If he had been honest with himself, he would have realized they weren’t. If he had been honest with himself, he would still be alive.

The other dive was being run by an organization with a reputation for being extremely safety conscious. Nevertheless, errors of omission were made regarding oxygen sensors which almost cost the experienced diver his life.

In the well-documented Navy case, water from condensation formed over the oxygen sensors, causing them to malfunction. The water barrier shielded the sensors from oxygen in the breathing loop, and as the trapped oxygen on the sensor face was consumed electrochemically the sensor would indicate a declining oxygen level in the rig, regardless of what was actually happening. Depending on how the sensor voting logic operated, and the number of sensors failing, various bad things could happen.

During its accident investigation, when NEDU used a computer simulation to analyze the alarm and sensor logic, it found that if two of the three sensors were to be blocked (locked) by condensed water, the rig could lose oxygen control in either a hypoxic or hyperoxic condition. Based on a random (Monte Carlo) sensor failure simulation, low diver work loads were more often associated with hypoxia than higher work rates, even with one sensor working normally.

We deduce from this result that “triple redundancy” really isn’t.

The white circles at the top left of this scrubber canister housing are the three oxygen sensors used in an experimental U.S. Navy rebreather.

When the accident rig was tested in the prone (swimming) position at shallow depth, after 2 to 3 hours sensors started locking out, and the rig began adding oxygen continuously. The computer simulation showed that the odds of an alarm being signaled to the diver was only 50%. The diver therefore could not count on being alerted to a sensor problem.

Unfortunately in this near fatal case the rig stopped adding oxygen, the diver became hypoxic and the diver received no alarms at all.

After NEDU’s investigation, the alarm logic was rewritten with a vast improvement in reliability. The orientation of the sensors was also changed to minimize problems with condensation.

Today what is being seen are divers who extend the use of their sensors beyond the recommended replacement date. Like batteries, oxygen sensors have a shelf-life, but they also have a life dependent on use. Heavily used sensors may well be expended long before their shelf-life has expired.

the-siren — The Siren, by John Williams Waterhouse.

Presumably, the birthing pains of the relatively new underwater technology based on oxygen sensors have now passed. Nevertheless, those who use rebreathers should be intimately familiar with the many ways sensors, and their electronic circuitry, can lead divers ever so gently to their grave.

Like sailors of old, there are ways for divers to resist being lulled to their death by oxygen sensors. First among them is suspicion. When you expect to have a great day of diving, you should be suspicious that your rebreather may have different plans for you. Your responsibility to yourself, your dive buddies and your family is to make sure that the rebreather, like a Siren, does not succeed in ruining your day.

The best way to ward off sensor trouble is through education. To that end, Internet sites like the following are useful. Check with your rebreather manufacturer or instructor for additional reading material.

http://rebreathers.es/celulas%20o2/celulas%20o2.htm

http://www.rf30.org/

http://www.deeplife.co.uk/or_files/DV_O2_cell_study_E4_160415.pdf

What I Would Miss on Mars

When I first saw images from NASA’s various Mars rovers, I was almost crawling out of my skin with excitement. As I spoke at a NASA sponsored conference where scientists and engineers were discussing plans for a Mars mission and colonization, I was enthralled with the thought that humans are actually planning for mankind to leave our planet for a foreign world.

Lately, I’ve been thinking about what I would miss if I were a colonist on Mars. I’ve decided, what I would miss the most is something we take for granted in most places of the world; water.

Of course, Martian pioneers would have to have abundant stockpiles of drinking water. But I sure would miss Earth’s oceans; their awe inspiring breadth and depth, their multitudes of sea life, and the gentle shades of blue-green in clear water along sandy coasts.

I would miss the sound of the surf, the laughter of children chasing and being chased by harmless but persistent waves.

I would miss the sound of clicking shrimp, and the clicking of dolphins corralling schools of fish.

I would miss being able to open the windows on a perfect day. I would miss feeling a breeze on my bare face.

I would miss never having to wonder if I had enough oxygen to breathe. I’d miss not worrying that toxic carbon dioxide would seep into my tiny house and suffocate me and my family in our sleep, or that my home’s pressure barrier would fail and our blood would essentially boil, releasing a flood of deadly bubbles stopping our hearts.

I am concerned that those attempting to colonize Mars woud sink into a chronic melancholy simply because the water that pleases and sustains so many of us is absent on Mars. Could these homesick astronauts survive, and even thrive?

If the first wave of colonizers did survive, procreate, and nurture the next generation, the first generation of true Martians, then I suspect that generation would fare much better psychologically than the first. After all, they would never have known the verdant forests and splendorous seas of Earth.

As I pondered what it would be like to be a third and fourth generation colonist on Mars, growing up knowing nothing else, I realized that rather than space exploration being a guaranteed and common place activity at that time in the not too distant future, a bleaker possibility exists.

It is entirely possible that war, disease, asteroid and comet collisions, or even the failure of mismanaged banking systems could so impoverish the Earth that space travel to the Martian colony might not remain economically sustainable. Eventually, to the stranded Martians our Earth could be little more than a distant memory, perhaps even a legend. Martian children might grow up on the red planet hearing tales of Sky People who came to Mars from a far away place, a world of indescribable beauty, with colors of blue and green that are not even imaginable on Mars.

Some native Americans have in the past recounted tales of Sky People coming to Earth. Wouldn’t it be ironic if the next generation of Earthlings becomes the fabled Sky People that populate the planet Mars?

If offered the chance to be one of those Sky People on a one-way trip to Mars, would I sign up for the mission? Frankly I don’t think I could leave the most beautiful planet in the solar system, perhaps in the galaxy, even for something as exotic as a trip to Mars.