Hypoxia was in the news recently after a small aircraft went down near Jamaica. After initialing radioing for permission to descend from 25,000 to 20,000 feet due to an indication of an issue, all communication was lost. NORAD tweeted that two F-15s were scrambled to the location and that hypoxia was suspected. The military pilots reported the windows were fogged and the pilot was slumped in his seat, though breathing. The plane continued to fly on autopilot until it crashed north of Jamaica.
From time to time, we like to showcase the research of our customers. Our team is always interested in learning more about the huge variety of research projects and discoveries made in labs using Environics systems.
The Environics Reduced Oxygen Breathing device is used worldwide in the training of aviators and others who regularly are flying at altitude. Using the ROBD2, they learn what it feels like to be hypoxic. However, the system is not solely used for training. Several researchers have used the ROBD2 for hypoxia related projects. Today, we focus on the results of a recently published study by lead author, Leonard Temme (Vision Sciences Branch, Sensory Research Division, U.S. Army Aeromedical Research Laboratory at Fort Rucker, AL).
Mild traumatic brain injury (mTRI) is more commonly known as concussion. In general, it is suggested the recovery from this type of injury takes 7-10 days, although there is more and more research in terms of those who suffer mTRI repeatedly (such as football players). This recovery time is based on observations made in individuals under unstressed environmental conditions such as a doctor’s office or hospital. The authors wanted to examine how putting someone under stress would affect people who have a history of such a trauma. The question was would a person with a medical history of a concussion who seems recovered become symptomatic when exposed to a stress such as sleep deprivation, pharmaceuticals, extreme temperature, anxiety or hypoxia.
A chance observation made during a training study led the authors to this question. Pilots were exposed to a normobaric hypoxic condition that simulated conditions seen at 18,000 feet using an ROBD2. While “flying” under standard conditions, the pilots behaved comparably. However, when the pilots were breathing air with only ~10% oxygen, one pilot lost control of the aircraft without realizing it. Looking into this pilot’s medical history, the researchers found he had experienced a significant concussion ejecting from a high-performance aircraft. This chance observation led the authors to this question: Would a stressor, in this case hypoxia, help uncover a symptom that was unobservable under normal conditions?
To begin, two sets of 36 subjects between 18-50 were gathered from the community: one group with a history of mTBI and one without. The subjects were then matched “on the basis of age, gender, tobacco smoking consumption, weight, height, and body mass index” for comparison purposes. Utilizing eight tests from the BrainCheckers test battery, the subjects were examined under both standard conditions and three different reduced oxygen conditions.
While seven of the tests showed no significant difference between groups, the performance on the M2S test, which is a measure of short-term visual memory, did. Under reduced oxygen stress, those with a history of mTBI showed a significant impairment when compared with the control group.
The researchers’ findings open up potential avenues for using hypoxia to test brain stress following mTBI. The authors’ state, “Such a capability would be particularly important since mTBI, even when apparently completely recovered using conventional examination strategies, may include deficits observable only under stress.”
Having a way to clinically measure recovery from mTBI would be a great advantage. It will be interesting to follow these studies.
Last week, in the YouTube program "Scrubbing In" presented by Navy Medicine, focused on training Naval and Marines for the feeling of hypoxia. In this week's show, the hosts are at Navy Medicine Aviation Survival Training Center in Patuxent River, Md, and the training application of the Environics Reduced Oxygen Breathing Device (ROBD2) is featured.
LCDR Corey Littel, the Director of the Aviation Survival Training Center, discusses what hypoxia is and how the pilots are trained. The Leutenant Commander discusses the use of hypobaric chambers for hypoxia awarenewss training. He explains this method is "slightly outdated." We then are shown training lab containing a number of ROBD2 systems, as well as the use of the "much more modern means of delivering a mask on version" of hypoxia training.
A few weeks back, I shared some information on the flight restrictions enacted due to concerns of hypoxia and hypoxia symptoms in pilots of the F-22 Raptor. Yesterday, it was reported that a potential cause of has been identified.
The flight restrictions, which limit flights within 30 minutes of a landing field, are still in place. According to Col. Kevin Robbins, a commander of the First Fighter Wing at Langley Air Force Base, 11 incidents of hypoxia have been reported in the last 10 months.
There have been and still are many speculated reasons for the hypoxia (which we review here and here). The latest release suggests that it is not the aircraft itself, but a piece of equipment worn by the pilots, a vest, that is to blame.
Due to the 9Gs the F-22 pilots may endure, an inflatable vest is worn. The vest provides counter-pressure during rapid decompression. While protecting the lungs, it also has the effect of restricting breathing, potentially being a hazard in terms of hypoxia.
As a followup to my last post about the restrictions on F22 flights, Stars and Stripes published an interesting article which discusses some of the possible causes. One suggested cause is the oxygen system. The on-board oxygen generation system, or OBOGS, in the Raptors does not use liquid oxygen like the F16. Instead, air is drawn in through the engine and then filtered to increase the oxygen in the pilots' breathing air.
While the OBOGS is one possibility, Air Force investigators are considering other possiblilities, such as contimination as well. Several suggested contaminates are discussed, including the components that are used to create the F22 skin. The skin is created in a unique way to help the fighter evade radars.
For more details on this perspective, please click here. To learn more about the restrictions on the F22, check out our last post.
In the news recently, there have been a number of stories regarding the F-22 Raptor and the concerns of pilots and others regarding symptoms of hypoxia in flight. Yesterday, Defense Secretary Leon E. Panetta ordered the Air Force Tuesday to limit all F-22 flights to distances that would allow pilot to make an emergency landing at any given time. In addition, the time line for addition of backup oxygen to the aircraft has been moved up. The Secretary requested monthly updates on the efforts to local the root cause of the oxygen deficiency in the cockpit.
The symptoms of hypoxia vary between individuals. The initial symptoms can include a general dulling of the senses, clumsiness or drowsiness. Some compare the feeling to being slightly intoxicated.
Without suplemental oxygen or flying to lower altitudes, the symptoms then worsen. Pilots may suffer from any combination of the following symptoms:
tingling in the skin
changes in vision
bluish tint to the lips.
Due to the effect on the brain, however, the pilot may be completely unaware that they are having any problems. The Reduced Oxygen Breathing Device is used to train pilots on the early symptoms of hypoxia in a simulated environment so that they may take preventative actions prior to becoming incapacitated.
Over the past year, I have written several times about the effects of hypoxia, including a video, which showed not only how hypoxia may present itself, but how the hypoxic person may be oblivious to the effects. I also shared information regarding the use of the Reduced Oxygen Breathing Device (ROBD2), and how this system is used in military training to allow pilots to better prepare and understand the symptoms of hypoxia. You can read more here and here.
Today, I wanted to share an interesting study from the Department of Preventive Medicine and Biometrics, Uniformed Services University of the Health Sciences in Bethesda, Maryland, and the Aviation Survival Training Center, Naval Survival Training Institute, Naval Operational Medicine Institute in Washington. The researchers were attempting to determine how effectively the ROBD (the earlier version of the ROBD2) reflected the reported symptoms of hypoxia when compared to in-flight occurrences.
The researchers began by surveying 566 aviators with a 20 question, anonymous survey about their flight experiences with hypoxia PRIOR to ROBD training. The survey included basic demographic questions followed by questions regarding in-flight hypoxia symptoms they may have experienced. For those who responded that they had experienced hypoxic symptoms in flight, additional questions were asked regarding which symptoms they had experienced.
A second group of 156 pilots were surveyed, also anonymously, following ROBD training at a simulated altitude of 25,000 ft (following the Navy's standard training protocols). Again, the survey included demographic questions as well as questions regarding any symptoms of hypoxia they may have experienced during the training.
Once the data was collected, the results were analyzed using a variety of means (including Chi-square analysis (alpha=0.05), Fischer’s exact test (alpha=0.05), and incident risk ratios). I won't review all of the data and analysis, but some of the key findings are reviewed below.
For those surveyed regarding in-flight symptoms:
20% reported hypoxia symptoms at an average altitude of just over 25,000 ft
Of those who had experienced in-flight symptoms, over half (57%) were not wearing an oxygen mask when the symptoms started and only 21% reported the experience in naval aviation hazard reports (HAZREPs).
The most common symptoms reported were tingling, difficulty concentrating and dizziness.
When comparing the results of the two surveys, the researchers found:
5 of the 16 symptoms listed on the surveys had statistically significant differences in the reported levels (tingling, difficulty concentrating, air hunger, blurred vision, and lights dimming.
For the other 11 of the 16 symptoms, there was NO significant difference between the frequency reported during in-flight experiences and ROBD2 training experiences.
The authors conclude that some of the symptoms differences found may be minimized with some of the updates in the ROBD2, and that additional customization may reduce these still further. Regardless, they state, "Ultimately, the authors recommend the continued use of ROBD as an operationally focused and seemingly valid training tool," recommending it be used as part of a total program which includes instruction on both the similarities and potential differences between training symptoms and in-flight symptoms.
To read the full article, click here (there is a fee for download. AsMA members have free access).
This week, we are excited to meet with customers and friends, new and old, at the Aerospace Medical Assoc. Annual Meeting in Anchorage, Alaska. We'll be sharing some exciting technology that is in the pipeline and giving attendees a chance to interact with our ROBD2 (reduced oxygen breathing device) systems. Stop by Booth 307 to see for yourself!!