The Dry Bends

While divers understand that flying after diving may induce decompression sickness, it's a problem more complicated than waiting for a computer to say "OK to fly." In fact, cases of bends appear when flying several days after diving or, believe it or not, when riding an elevator.

Recent Australian research has uncovered important information for any traveling diver. The interesting results were initially published in the South Pacific Underwater Medical Society Journal in an article by Dr. Ian Millar. With reprint permission from SPUMS, we have taken the liberty to provide our revised version of Dr. Millar's article.

In the study of 401 cases of decompression illness treated, 44 had post-diving symptoms after reaching altitude by air, auto, or foot. In less than half the 44 cases, symptoms were prevalent before altitude exposure and, in most cases, were mild and unrecognized. After flying, however, symptoms increased even when divers waited several days to fly. In one case symptoms increased while flying 2 1/2 weeks after diving.

In more than half the cases, divers were without symptoms until they flew. Seven became symptomatic when flying 12-24 hours after multiday, repetitive, deep dives. One became symptomatic after waiting two days to fly after a single extreme dive.

While all trained divers have learned the risks of flying after diving, what we may not think about is there are other ways to gain height. Of the 44 cases studied, 12 divers developed initial symptoms while ascending on terra firma. These are some interesting elements of these 12:

Eight of these involved altitude ascent several hours after multiday repetitive diving.

Five involved post-dive exercise and alcohol as risk factors.

One diver became symptomatic after returning to home at 2,500 feet altitude after a routine entry-level training weekend.

The lowest altitudes associated with initial symptoms were 1,000 feet, although these cases involved other risk factors including alcohol, exercise, and prior multiday deep diving.

What's important to North American divers is that certain diving venues -- Saba, St. Kitts and Nevis, and Dominica in the Caribbean, and Maui and Kaui in Hawaii -- are great for divers who like to hike in the great outdoors. Furthermore, after diving, exercise produces a surge of bubbles from moving limbs. Maybe that explains why a reader wrote to us a year ago, wondering why his shoulder ached like hell when he climbed to the top of 3,000-foot Mt. Scenery after two dives on the Saba Pinnacles.

Even treated divers are at risk. In one case, symptoms were exacerbated with an altitude gain of less than 400 feet when the patient traveled between his home and the hospital. In another case, symptoms recurred when the patient took an elevator to the top of a 650-foot building.

Theoretical Considerations

Many flying-after-diving tables are based upon prediction of nitrogen washout using tissue half-time models; they do not consider the effect of bubbles that remain after diving.

DCS occurring after altitude exposure is likely to result from tissue bubbles that were present and from newly generated blood bubbles that arise from the supersaturation of nitrogen in "slow" tissues after extensive diving. The presence of "silent bubbles" may help explain the unpredictability and variable consequences of travel to altitude following diving.

When bubbles are present, they will expand about nine percent in diameter upon ascent and may remain enlarged after return to ground level. At lower altitudes -- say 1,000 ft -- the diameter increases a mere one percent. However, it's unlikely diameter is the critical determinant of DCS severity. Rather, trapped bubbles seem to trigger inflammation and swelling in adjacent tissues. Furthermore, decreased oxygen -- commercial aircraft may involve a decrease in oxygen partial pressure in the order of 30 percent -- may be critical for tissues that have marginal blood supply because of bubbles and inflammation. Persistent bubbles, tissue inflammation and sensitivity to reactivation of inflammation and edema may remain for days or weeks.

What this means to the traveling diver is that after treatment on foreign soil one is again at risk when flying home. Most Australian hyperbaric units use one month as the interval recommended before flying, with longer intervals appropriate for some patients. These "at risk" patients should experience altitude by diving or short haul domestic flight before embarking on an international flight.

Recommendations

Surely, there is need for guidelines to cover land travel after diving. In fact, one can apply the flight table to divers who, right after diving, decide to go hiking. Table Pioneer Dr. A. Buhlmann, seeing a need for guidelines for road travel in his home country of Switzerland, said that for dives involving less than 60 minutes in the previous 12 hours, a diver should wait 4 hours before traveling to altitudes up to [00,000] feet.

Divers with DCS prodromal symptoms -- lethargy, malaise, and transient "pins and needles" or "niggles" -- or who have exceeded dive limits or experienced undue exertion need to be extremely cautious about flying. If bent on a plane, the usual treatment of 100 percent oxygen will not be available -- only the low-concentration therapy oxygen. Therefore, multiday, deep repetitive dives should be followed by 36 hours or more before flying (two night's rest).

Furthermore, abnormal symptoms, injuries, or intercurrent illnesses following travel to hilly locations should be an indication to cancel or at least severely restrict remaining diving or delay flying.

DCS isn't fun. It can injure you and curtail your diving forever. Just because you keep your feet firmly planted on Mother Earth after a week of diving doesn't mean you can't become a victim.

In fact, one of our wise readers, Nancy Bitner of Orlando, Florida, knows that. She went diving on the Big Island of Hawaii last year and wrote,"Wish we had known to go to the active volcano before beginning our dives. The 7,000-foot altitude prevented us from going the last day."

Conservative diver? Yes. And one smart lady.

Ben Davison