Dr. Robert Kurrle, M.D., Senior AME
All scuba divers are aware of the risk of decompression sickness (DCS) when they are surfacing after a dive. And most realize the increased risk of DCS if flying is undertaken soon after diving. Let's review a few of the definitions and risks, and some guidelines on how long to wait between the last dive and starting up the airplane engine.
At sea level, the body is exposed to one atmosphere of pressure (760mm Hg). As the diver descends, each 33 feet of depth adds one additional atmosphere of pressure to the body. At 33 feet, there is a pressure of two atmospheres and at 99 feet there is a pressure of four atmospheres.
Nitrogen, which comprises 78% of the atmosphere and is biologically inert, is the gas that causes the pathology as it follows the gas laws in the vessels and organs of a scuba diver. As a diver breathing air from a tank descends, the increased pressure causes more nitrogen to dissolve in the blood and enter the tissues than was present on the surface. The deeper and longer a diver goes, the more nitrogen enters the tissues. If the diver returns to the surface too quickly or stays down too long, the excess nitrogen will not have a chance to be eliminated ("blown off") gradually through the lungs. The nitrogen will come out of solution and go into a gas phase forming bubbles in the blood and tissues of the body. These bubbles account for the clinical entity that is called decompression sickness (DCS). For repetitive dives, the diver must consider the nitrogen retained from previous dives. Symptoms usually appear 15 minutes to 12 hours after surfacing. Visualize the bubbling froth of CO-2 that rushes out of solution from the sudden decrease in pressure that occurs when you open a can of soda.
Called "bends" by early investigators, DCS is now divided into Type I, Type II, and Type III depending on the severity. Type I includes joint pain most commonly in the elbow, shoulder, hip and knee, as well as a mottled appearance to the skin. Type II is more serious and involves the brain, spinal cord, and cardiopulmonary system. Symptoms include sensory deficits, paraplegia, pulmonary gas emboli or myocardial infarction. Type III is a combination of Types I and II with arterial gas emboli (AGE) originating in the lungs and often results in unconsciousness within minutes of surfacing.
Adherence to appropriate decompression tables and dive computers reduces the risk of DCS. DCS is treated with recompression in a pressure chamber with hyperbaric oxygen to promote inert gas elimination and to help cause a decrease in bubble size.
When we fly after diving, we may have an increased risk because of the decreasing atmospheric pressure as we ascend. You might have only a few tiny bubbles, causing no problems at all, in your body when you reach the surface after a dive. If, however, you go flying, then the small bubbles will expand (due to the reduction in pressure with altitude) and could cause the onset of DCS symptoms. The symptoms can show up hours after landing.
How do we minimize the changes of DCS if we are going to fly after diving? The risk exists for both commercial planes (cabin pressurized to 8000 ft), as well as our personal airplanes. The first thing is to dive conservatively and according to the profiles of a well recognized, well tested set of dive tables. The tables will specify how long you can stay at a certain depth as well as if you will need to make decompression stops on the way back to the surface. There are also several published guidelines for how long to wait before flying after diving, depending on the depth and frequency of the dives. One guideline suggests if the diving exposure has been less than two hours with no decompression diving in the last 48 hours - wait 12 hours. If the diving has involved multi-day unlimited diving and no decompression wait 24 hours. If the diving has involved decompression stops – wait 24-48 hours. It is also considered safe to fly at or below 1000 ft msl if the diving exposure has been less than 2 hours with no decompression. Age, poor physical condition, and overweight may greatly increase the time for nitrogen to leave the tissues. The original decompression tables were developed using less than a dozen Navy divers all in their early twenties in top physical condition. Fortunately, the dive computers commonly in use today are far more conservative.
Flying and diving can and should go together. We are so fortunate to live in Florida and have the Bahamas and Caribbean a short plane ride away. Just remember, use good judgement, and you can enjoy both. Happy flying and diving!