Medical Update From the UHMS
By Fred Bove, M.D., Ph.D.
Last June, the Undersea and Hyperbaric Medical Society held its annual meeting and new information about current research was presented. There was considerable interest in unexplained lung congestion (pulmonary edema) developed while diving. This is associated with severe shortness of breath, cough, frothy material coming from the lungs and abnormal findings on the chest x-ray. The illness resolves spontaneously after leaving the water, is not associated with heart disease and appears to be unrelated to the diving environment (temperature, stress, depth). Initial reports associated the illness with cold water but recent cases have been reported from warm water. The cause is still unknown but discussion is being held on how to evaluate victims and avoid the problem. It is rare but can be dangerous if not managed properly. At a dive site, breathing oxygen, removal from the water and rapid transportation to a hospital is the current advice.
A study from England questioned women divers about diving during their menstrual periods. Although no problems were reported and no specific measurements have been made to date, some women felt their menstrual cycle might be changed by diving, while others felt they might not dive as safely. This study is ongoing and further data will provide more information.
An important review of diving accident cases was undertaken by the U.S. Navy to determine factors in the dive profile that might influence the risk of decompression sickness (DCS). It was found that dives with rapid ascent rates and long bottom times were more likely to result in neurologic DCS. This information is particularly applicable to sport divers who have a high proportion of neurologic DCS among total DCS cases. All divers should avoid deep diving and keep their ascent rates to around 30 feet per minute to minimize DCS.
The navy medical officers who supported the diving operations for the salvage of TWA flight 800 reported on their experience with more than 4,000 dives to recover aircraft and passengers. Both surface supplied hardhat and scuba divers were used. Eighteen divers were treated for actual or suspected decompression sickness; one diver had a lung overpressure accident and arterial gas embolism. All but one of the divers recovered fully, with no residual symptoms. Some of the cases may not have been DCS but the usual approach is to assume it is present and provide treatment. Recompression is not always necessary but is the best means of caring for divers working on an operation of this magnitude.
The use of hot water suits during the salvage operation seemed to be associated with an increased incidence of DCS but many scuba dives to 120 feet for 15 minutes were done safely.
There was significant psychological stress for the divers who recovered the passengers but there were no residual problems.
Navy medical officers also reviewed the experience of navy divers from 1990 to 1995. The divers made more than 650,000 dives in that period. The peak year was 1992, when 124,972 dives were made. The fatality rate was 0.9/100,000; the incidence of type I DCS was 13/100,000; type II DCS and AGE were 13/100,000 each. This is a .013 percent incidence for each illness. A disproportionate number of the DCS cases were from research dives, known to be riskier. As in the TWA flight 800 dives, they found that some of the treated cases might not be DCS but the supervisor chose to treat the diver just in case.
The Divers Alert Network (DAN) reported its data on diving related deaths. Researchers found the second most common cause of death, while diving, in divers above age 35 was a heart disorder (the most common was drowning). In this group, heart related causes accounted for 26 percent of deaths while diving. This information indicates screening for heart disease should be done in divers over the age of 35. In male divers below the age of 40 and female divers below the age of 50 who have normal menstrual periods, normal blood pressure, do not smoke, have normal cholesterol, are not overweight and exercise, screening for heart disease can take the form of a physical exam and assessment of the risk factors noted above. For those with one or more risk factors or who exceed the ages noted above, heart disease screening should also include an exercise stress test. Partial blockage of the coronary arteries to the heart may not produce symptoms in sedentary individuals but the exercise associated with diving may be enough to provoke a heart attack or dangerous heart rhythm.
We are developing new tools to diagnose the presence of brain and spinal cord injury associated with decompression sickness and air embolism. Several papers reported on use of magnetic resonance imaging (MRI) to evaluate neurologic injury. One study found brain lesions in 75 percent of divers who had pulmonary barotrauma and arterial gas embolism, while 25 percent of divers with decompression sickness had brain lesions identified by MRI scanning. Previous studies of divers found that many individuals had lesions that showed up in an MRI scan. The data presented at this meeting did not include the incidence of lesions in the nondiver population. When nondivers are studied, it is apparent many other people have abnormal MRI scans not related to evidence of any illness.
The information presented at this meeting indicates that research on diving medicine, particularly applicable to the sport diving community, is continuing to provide new insights.
For people interested in a textbook on diving medicine, the most recent edition of Diving Medicine has just been published. You can find more details about the book and answers to frequently asked questions about diving medicine at our Web site: www.scubamed.com.
Beneath The Sea's 1998 North American Underwater Video and Photo Contest: The Cayman Aggressor III will host the winner of Beneath The Sea's Stan Waterman Award for Underwater Video Excellence for a full week of live-aboard diving. The Caribbean Explorer will host the winner of the David Doubilet Award for Excellence in Underwater Photography with a week of live-aboard diving in Saba. The contest will have several subject categories, with several levels of winners and numerous prizes awarded by major manufacturers and resorts. The contest is open to divers from the United States and Canada.
The deadline for entries is December 31, 1997; winners will be notified in February 1998. The grand prize and first prize winners will be presented at Beneath The Sea's Evening Underwater Film Festival, Saturday, March 21; a major event at the 22nd Annual Underwater Exposition that will take place at the Meadowlands Exposition Center, Secaucus, New Jersey, March 20, 21 and 22.
Contest rules are available by mail by sending a self-addressed, stamped #10 envelope to: BTS, 495 New Rochelle Road, #2A, Bronxville, NY 10708 or calling (718) 409-0240 (7:00 to 9:00 pm EST). Get full contest and show information at the BTS Web site http://www.cy berus.ca/~bts/.