Saturday, March 3, 2018

Bend Me Shape Me

The one thing that affects all scuba divers, regardless of the water temperature, is pressure and the deeper they dive the greater is the surrounding pressure their body has to face.  At sea level the atmospheric pressure (ATM) is only 1 but every 10 metres or 33 feet deeper adds another ATM. The deeper you go the faster you consume your air supply because at 2 ATM you are inhaling twice the number of air molecules as you would at the surface and, at 4 ATM, or 30 metres deep, each breath is 4 times what you would at the surface. Understanding how the body reacts to all this pressure is the key to safe diving. 

Pressurized air in a scuba tank still contains the approximate 79% nitrogen and 21% oxygen we are accustomed to breathing on land. However, during a dive, the body tissues are absorbing nitrogen in proportion to the surrounding pressure, which is anywhere from 2 to 5 times more than normal depending on depth. As the diver ascends and the pressure decreases the excess nitrogen will slowly leave the body (off gassing) but if the pressure is reduced too quickly the nitrogen will form bubbles in the tissues and bloodstream causing decompression sickness or what is referred to as the "bends".

There are two types of decompression sickness (DCS) with Type 1 usually characterized by musculoskeletal pain in the joints and mild skin itching and rashes. Type 2 on the other hand is much more serious and life threatening as it can affect the lungs, spinal cord or brain and the symptoms include difficulty with bladder control, and numbness and paralysis in the legs. The only treatment for DCS 2 is hyperbaric oxygen therapy delivered in a recompression chamber. Getting the bends and having to go to the "Chamber" is every diver's worst nightmare.

The "Chamber" at VGH - photo by Junie Quiroga

Unfortunately for me I came down with DCS 2, following an otherwise very pleasant day of scuba diving in Howe Sound with my friends and the good folks at Sea Dragon Dive Charters this past weekend, and had to be taken by ambulance to the "Chamber" at Vancouver General Hospital. Luckily a hastily gathered team of 5 specialists were there to make me comfortable and put me through the standard regimen of being taken down to the pressure of 2.8 ATA, or 60 feet below sea level, and given pure oxygen to breathe for a session that lasted just over 7 hours. 

Nelson in the Chamber - photo by Junie Quiroga

As I sat in my chair watching movies I could feel the nitrogen slowly leaving my legs, and I happily began to regain all normal feeling, but I wasn't out of the woods yet. While I appear to have avoided serious permanent injury it will be 6 months before my recovery can be properly assessed and I may never be able to go scuba diving again. How and why the nitrogen built up to such an extent in my bloodstream is something I'm still examining from my dive profile, but there's no arguing with the physiology and the frightening power it had to bend and shape me.

No comments:

Post a Comment