One of the many benefits of our recent relocation to the Durham NC area is I now live with in minutes of Duke University and the headquarters of Divers Alert Network, which are the heart of Dive Medicine Research and studies related to Decompression Sickness. This provides me with access to a wide range of seminars on related topics but also provides me with the chance to be directly involved in the related studies.
Most divers have a general understanding that flying after diving increases your risk of decompression sickness and accept the industry standard of 18 – 24 hours of surface interval before getting on a commercial airline but few divers actually understand what is behind these guidelines guidelines. The fact of the matter is the studies to determine the effects of flying after diving and its relation to decompression sickness are still ongoing.
Since 1993 Duke University in conjunction with Divers Alert Network and the US Navy have been doing research to study the effects of flight after diving and slowly the suggested surface intervals before a commercial flight continue to drop. The majority of these studies are conducted at Duke University.
For those who have never been to the hyperbaric center at Duke University, its very top of the line. Feature not one but multiple full size chambers. Additionally number of courses are offered here through Duke and DAN focused around Hyperbaric Medicine that are open to the public, including but not limited to the Dive Medical Technician course.
Today I participated in a test dive and flight for establishing guidelines for flying after diving. I completed a test dive to 60fsw, followed by a five hour surface interval and then boarded a simulated commercial air flight for four hours. Now this isn’t exactly something out of the ordinary for me, I have been ignoring the 18 hour flight guidelines for sometime now with out any adverse effects. Often reducing this time to less then 12 hours, due to the need to get to another destination. What most people don’t understand is the 18 hour restriction only actually applies to pressurized commercial airlines, so island hopping via airplane in the islands is often not an issue due the low elevations that turbo prop planes fly at.
Based on FAA guidelines the max cabin pressure of a commercial airline in 8,000′ so this study actually not only applies to flying but any situation involving increasing your elevation by 8,000′ after diving. Such as climbing a Volcano in Hawaii or other tropical locations.
One of the cool parts of the study is I got the chance to learn more about PFO’s (Patent Foramen Ovale) and how they relate to Decompression Sickness. For those who are not familiar with PFO’s, its a condition that is present in about 25% of the people on the planet. A PFO is a condition that is present in the heart where a hole that is present when we are being developed as a fetus, never fully heals. This hole is located between the right and left atrium. On a person who does not have a PFO, bubbles will form in the blood in right atrium and then travel to the lungs were it is filtered out before moving to the other parts of the body. When a PFO is present the micro bubbles are able to travel directly into the left atrium were they can then travel through out the body with out ever being filtered out by the lungs.
Before getting into the outcome of my tests, I will take a few paragraphs to walk you through the process of what being a test subject is like. Yesterday I visited Duke for a general physical and review of what would be occurring today. As a side note this is a great way to get a diving physical by someone who actually specializes in dive medicine. Following the physical the nurses take you aside to run some additional tests to establish baseline information for bubble formation. This is done using a Doppler Bubble Detector and a Trans-Thoracic Echo (TTE), which is similar to an ultrasound, and provides a view of the heart, allowing you to actually see the bubbles. After about two hours at the clinic I headed home for dinner and a good nights rest.
Today started extremely early, with a 5:00am wake up to head back to the hospital. At 6:30am a tender, two other test subjects and myself entered the chamber for our test dive. After a few quick safety checks we started our decent to 60′, unlike diving when you are in a chamber there is a massive change in temperature during the descent and ascent phases as a result of the change in pressure. Dropping at 30fsw we arrived at our target depth in two minutes. The temperature in the chamber quickly returned to normal when they cranked on the air conditioning on in the chamber. The next 55 minutes was extremely uneventful, unlike diving there was no pretty fish or cool wrecks to enjoy while sitting in the chamber. When the end of our “dive” arrived we ascended back to the surface at 30fsw, arriving back at surface pressure in two minutes. There was no “Safety Stop” performed on the way back to the surface.
With the dive portion behind use, we spent the next five hours in “restricted activity” mode, essentially don’t do anything except sit around. On the plus side it did give me the chance to get started on this post while everything was still fresh in my mind. For the first hour after the dive, the nurses would come in and visit us every 30 minutes to repeat the Doppler tests from the day before. The Doppler test allows the tester to listen for bubbles in your heart.
With out much to do the first couple hours passed slowly, but at ll:30am we headed out of the hospital and grabbed some lunch, because much like todays commercial airlines only light snacks would be served during our four hour simulated afternoon flight. After a quick lunch at Chipotle we headed back to the hospital to proceed with our afternoon flight. Feeding us mexican food seemed like a somewhat dangerous idea to mean, I mean lets think about this we are giving three guys beans and rice then locking them inside a sealed room for four hours.
The simulated flight actually reminded me of flying American Airlines, there was no seat assignments, I couldn’t bring a carry on and the use of electronic devices was not permitted. The big difference between the simulated flight and American Airlines is once every 30 minutes a cute nurse would come over, cover my chest with some cold ultrasound jelly and monitor my heart. Good luck getting an american airlines stewardess to come to your seat every 30 minutes and cover your chest with jelly, that only happened back in the days of PanAm.
The four hour flight was uneventful and if it wasn’t for constantly being woken up by my simulated stewardess I would have slept through the entire thing. Since we were not allowed to have any electronics onboard, it gave me a chance to catch up on some reading I have been meaning to do for quiet sometime but never managed to find the time. Sidemount Profiles and Cave Diving Articles & Opinions both by or edited Jill Heinerth helped me pass the time. Both books can also be purchased directly from Jill on her website but clicking here. No promises but by paying a little extra and ordering from Jill directly you may end up with autographed copies.
Although unexpected it turned out one of the books I had brought with me, Cave Diving Articles & Opinions has a wonderful article in it on the exact monitoring methods being used during the study on pages 173 through 180; for those looking for additional information.
So onward to the results of the test dive and test flight. Out of three test subjects myself included; one had heavy bubble formations, rated as class 3 bubbles on the spencer scale. Another subject had class 1 and 2 bubbles on the spencer scale. Last but not least I had no measurable bubble formation, so was in the class 0 bubbles ratings. It is worth noting that the only areas being tested during todays little experiment was the heart so it is possible that different results would have been present if other parts of the body had been tested. What this confirmed is my mind is something I already knew and is accepted as common knowledge in the dive industry that bubble formations greatly vary individual to individual and even day to day. Although bubble were present its important to note that the formation of bubbles is not an indication that DCS was present, in fact in most cases after the majority of dives bubbles are present. None of those involved showed any DCS symptoms at the conclusion of the day.
No part of this post is intended to imply that anyone should adjust the current recommended guidelines pertaining to the duration of a required surface interval before boarding a commercial aircraft.
With the test flight finished, we shifted into the monitoring phase of things day, which essentially means sitting around doing absolutely nothing. After about half an hour we headed out for a group dinner. For the next 48 hours I will call into the research center for a phone check in, but all and all it amounted for a pretty easy experience.
For me one of the coolest parts of being a part of the study was actually being able to see the bubble formations in a divers body following a dive. The below video is of a PFO test, so the bubbles are being injected but it will give you an idea of what it looks like on a subject with a PFO, sadly I couldn’t find any videos online of bubbles following a dive.
For those interested in getting additional information on the Flying After Diving project you can visit the DAN website by clicking here. Being part of this student is a great way for dives to see a operating chamber first hand, help the dive community and even get a little money in exchange for your time.