The first time I dived on the German U-boat 352, I was doing my Advanced Open Water Training with my daughter Elena. My most distinct memory of that experience was that it was so small, and how could all 42 of the German sailors live and work in that little tube of a submarine.

At the end of last week, I participated in a DAN study at the Duke Center for Hyperbaric Medicine. The study is being conducted to establish hard scientific data on the effects of flying in airplanes after scuba diving at depth. As a subject, I took 2 rides in the Hyperbaric Chamber, one in a simulated dive to 60 feet for 57 minutes, and the other is a simulated flight to a pressurized cabin pressure of 8000’ of altitude. When I entered the chamber, I had the distinct feeling that I was in a submarine, and thought of my first dive on the U-352.

The entrance to the Center For Hyperbaric Medicine

This was the second time I have participated in this study; the first time was in the spring of 2008. Originally, the studies were conducted with subjects doing their chamber dives dry and resting. When I volunteered in 2008, a second series of tests were being done with the subjects exercising on a stationary bike during the chamber dive. One subject did the dive riding an underwater bike in a big tub breathing from a regulator. In 2008, I did the study dry, riding the bike in the chamber maintaining a 50 rpm cadence for 57 minutes at a simulated depth of 60’.  After an overnight surface interval of 9 hours, I returned to the chamber for a 4 hour simulated flight to 8000’. I remember thinking then, that this study is not going to work until somebody gets decompression illness.

My initial motivation for participation in the study was two-fold. I saw it as a vehicle for getting a better understanding of dive physiology and the physics of compression and decompression during and after a dive. Next, I saw an even greater opportunity to evaluate my own physical ability and health to conduct the types of dives I wanted to experience. What better place to have your dive health evaluated than at Duke, with Doctors whose specialty is hyperbaric medicine? Decompression theory is just that, theory, and every single person is going to respond differently to compression, tissue nitrogen loading and their ability to “off gas” nitrogen during decompression. It is all about the bubbles.

This time was no different, and the health issues were even more at the core of my motivation for returning for another ride in the chamber. This study called for a 5 hour surface interval. I had an issue after diving last summer that caused me to take a 6 week break from diving, have a complete neurological evaluation and do a complete cardiac work up. I was totally cleared on all counts and the incident remains unexplained. Although I have successfully completed over 30 dives since then, I felt like if I participated in this study, I could put all doubt to rest.

Thursday afternoon, I went in to the center to have my physical, and complete all of the paperwork. Much to my dismay my weight was 19 pounds more and my body fat increased 4% since 2008. I was told that I would be doing the “wet” part of the study. I needed to be back at the lab the next morning at 6am and be ready to dive at 6:30.

The hatch leading into the chamber

It took them a while to get the “bike” adjusted to fit my 6’8” frame, but afterwards I was able to easily fit in and operate the device. It reminded me of my cycling days when you are so low in the curled handle bars that you actually feel horizontal. I was basically lying in the tub, face down while I spun the cranks at the requested 50 rpms. There was an emergency medical technician standing beside me in the tub in case of any mishaps. It turns out that I had been paired with him as a dive buddy in an underwater scavenger hunt at a quarry during an NCDivers.com picnic in 2006. I left my fins and mask on a rock by the water and he recovered them and we met days later so he could return them. Now that is a small world!

At first I was a bit claustrophobic in the tub while riding the bike. Being so tall, there was only about 8” between my mask and the blue vinyl liner. After about 10 minutes, my heart rate was at 130 beats per minute and my breathing got a bit labored and it was uncomfortable. While diving I am constantly aware of my breathing rate, and hard breathing means my gas supply is diminishing quickly. Once I got past the reflex to not breathe hard, and got into a steady rhythm in line with light exercise, I had no issues. Boredom set in and I began to monitor my watch, trying to break the hour up into 15 minute segments. At ten minute intervals, the attendant would put a slate in front of me that had a scale from 1 to 20 and asked my exertion rate. I chose 12 each time, moderately difficult.

I finished my dive without issue and we began our ascent. I was instructed to stay underwater, which was fine with me because I missed the drop in temperature and severe chill created by the release of pressure in the hyperbaric chamber. By the time I popped up out of the tub, the chamber door was already open.

Luckily, the lab had a wireless internet connection and I was able to pass the time of my sequestered “surface interval” by working and reading. Another subject came in to do the dry part of the study, but he was only doing a one hour surface interval before the plane ride in the chamber. Ironically, it was someone who had been the subject that did the wet part of the study back in 2008 when I participated. Again, it is a small world. After he got out of his dive, we had pizza in the conference room together. Apparently, there was not going to be any in-flight snack service.

Back in the chamber for our flight, we moved to the back portion through a small hatch at the other end. The temperature in the chamber cooled as the pressure was decreased to simulate ascending to an altitude of 8000’.  I was able to finish a book I brought, reading in small segments between the Doppler readings that were taken from my heart every 30 minutes. I did not experience any signs of decompression sickness during the 4 hour flight, nor did the other subject who was only out of the chamber an hour between the dive and the flight. When the flight was over and I made my way out of the chamber, I was happy to gather my things, say goodbye to the staff and be on my way. It was a long day and I am glad I had the experience again.