2000-11 Making Advances in Dive Medicine
In June of this year, scientists, physicians and other health care professionals interested in diving medicine attended the annual meeting of the Undersea and Hyperbaric Medical Society in Stockholm, Sweden. Each year, this meeting brings together researchers from around the world to present clinical and basic research on diving and hyperbaric medicine. Of particular interest this year were papers presented from the National Aeronautics and Space Administration (NASA) on decompression sickness risk during extravehicular activity (EVA) in space as the construction of the international space station begins.
The data from NASA is interesting because it is applicable to diving. Bubbles form when going to altitude in the same way that they form when ascending from depth. All of our tissues contain nitrogen that is equilibrated with the nitrogen in the air. Going to altitude has the same effect as ascending from depth.
For construction of the international space station, there will be many periods of work outside of the space shuttle, in a space suit. For flexibility, the space suit is pressurized to 4.3psi (about 0.3 atmospheres [ATA]). The suit becomes too rigid to use at higher pressures, and breathing oxygen at 0.3 ATA is adequate since we breathe oxygen on the ground at 0.21 ATA. Scientists at NASA conducted several studies of altitude exposure to examine bubble production during exposure at 4.3psi. They found that women below age 25 would be the least likely to develop decompression sickness (DCS), and men below age 25 would be the next safest group. Men and women over age 45 are higher risk. The scientists at NASA have developed a combination of oxygen breathing and exercise before the space walks to reduce the risk for DCS while working in the space suit. To date, these procedures have worked well and protected the astronauts from developing DCS while working in their space suits for long periods of time.
Other presentations included data collected by the Diver's Alert Network's (DAN) on diving fatalities. It provides insight into the problems that cause lethal accidents. DAN estimates that there are about 90 diving related deaths each year involving U.S. citizens. Considering that there are about 4 million sport divers, and more than 2 million dives performed each year, this is an extremely low risk. The most common cause of death was drowning (59 percent), second was a heart related problem (heart attack or arrhythmia) (10 percent), and third was air embolism (9 percent). Almost 40 percent of these cases involved separation from a buddy, and 23 percent were either untrained, students or recently certified divers. Men predominated over women by 4-to-1. Looking at these statistics, it is clear that most of these cases could have been avoided. Drowning while diving usually means running out of air or getting entangled or trapped underwater. Air embolism usually occurs during a rapid, uncontrolled ascent. Good dive training, planning and periodic medical evaluation for those over 40 years of age can lower fatalities.
The DAN group also examined diving reports where divers were paralyzed from severe decompression sickness. In those who had paralysis after diving, even when treated, 35 percent had significant residual handicaps that interfered with their normal life. Again, paralysis resulting from the extremes of diving can be avoided by good dive planning and training.
A group of investigators studied sport divers on multi-day repetitive diving profiles to determine whether bubbles would be present in the veins after sport diving. They used equipment that could detect bubbles in the artery to the lung from ultrasound signals beamed to the heart through the chest wall. When the device is placed over the chest, bubbles make a characteristic chirp in the acoustic signal that can be measured to determine the number of bubbles passing into the lung. When examining 67 divers, they found bubbles present in 91 percent. They found bubbles after 205 of 281 dives (73 percent). Severe bubbling was recorded in 102 (36 percent) of the dives. We usually associate increased risk for decompression sickness with more severe bubbling, but none of the divers had evidence of DCS. More men than women had bubbles, bubbles increased with age between 30 and 50 years old, and deeper dives produced more bubbles. However, the number of bubbles found after a dive went down throughout a week of diving.
In addition to the fascinating reports by DAN and NASA, a group from Houston reported on residual pain and numbness after treatment for DCS. They found a number of divers treated for DCS had other causes for their numbness or pain. Typical problems were carpal tunnel syndrome causing hand pain and numbness, and neck and shoulder pain and numbness not associated with DCS.
Fortunately, diving science is continuing to make our sport safer and more interesting. My hat is off to the clinical and basic scientists who bring us these advances each year.