Undersea Diving Found Safe For Older Divers

The scientists report in the February 2003 issue of the Journal of Applied Physiology that as long as older divers remain healthy, the gradual decline in pulmonary function that is a normal part of the aging process is not large enough to keep them out of the water.

Using Duke's research hyperbaric chambers, the researchers stimulated dives at a depth of 60 feet while taking complex measurements of the levels of gases in the bloodstream of both younger and older participants, at rest and during exertion. Specifically, the researchers sought to determine the effect of age on the body's ability to balance oxygen and carbon dioxide levels under the water pressures experienced during normal dives.

"One of the key questions was whether older divers retain carbon dioxide at high levels while diving," said lead author Heather Frederick, M.D., an anesthesiology resident at Duke. "We found that even at a depth of 60 feet with moderate exercise, healthy older people experience increased levels of retained carbon dioxide that was statistically significant from at the surface, but clinically insignificant compared to younger subjects.

"The bottom line is that healthy older divers should be able to continue diving safely," she said. "Because this is the largest such study of its kind, and the fact that with the hyperbaric chamber we were able to have rigorous control over multiple physiological variables, the results of this study should help older divers feel confident about diving."

The researchers point out that they were studying the effects of carbon dioxide retention in divers, and not the condition known as decompression sickness, or the "bends," which occurs when divers surface too quickly. As divers surface, the pressure of the water decreases, allowing the nitrogen in the breathing mix to leave the blood and tissues causing painful nitrogen bubbles.

Carbon dioxide retention is a major safety issue for divers, particularly during heavy exertion and with high breathing resistance either from the regulator or due to lung disease. Carbon dioxide retention can cause mental confusion, seizures and, in extreme instances, can lead to loss of consciousness while diving, the researchers said.

"The results of this study should provide reassurances that from the point of view of the lungs, diving is safe for older divers," said Richard Moon, M.D., senior member of the team and clinical director of the Duke Center for Hyperbaric Medicine and Environmental Physiology. "Even while exercising, the older group performed very similarly in all measures as the young people. It was a real shock to me that they did just as well as the younger participants."

In their study, the researchers recruited 20 volunteers, with 10 ranging in age from 19 to 39, and another 10 ranging in age from 58 to 74. All divers had healthy lungs and hearts.

They then measured what is known as physiological dead space of all participants at rest and at two levels of exercise on an ergometer at both normal pressure and a pressure seen during dives of 60 feet. Diving depths of 60 feet are quite common among recreational divers.

Dead space is that part of the air inhaled in each breath that does not result in the exchange of oxygen and carbon dioxide. Earlier studies at Duke have shown that increasing dead space contributes to high levels of hypercapnia, or increased carbon dioxide levels in the blood.

"We know that in general, the dead space increases with age, so the major question was whether or not diving at a depth of 60 feet would lead to increased carbon dioxide levels," Frederick explained.

"When compared to the young group, the older group did experience slightly higher dead space under all conditions, though this increase was not associated with an increase in arterial carbon dioxide," Frederick said. "The excellent performance of the older group on every other measure of lung function and exercise ability make it unlikely that older divers in good health would experience significantly greater increases in carbon dioxide at depths."

The research was supported by the Divers Alert Network, Durham, N.C.

Joining Frederick were Duke colleagues Bryant Stolp, M.D., Guy De L Dear, M.D., Owen Doar, Michael Natoli, Albert Boso, Jason Archibald, Gene Hobbs and Habib El-Moalem, Ph.D.