An increasing number of patients with controlled diabetes, asthma and other diseases are getting the green light for an activity that was once off limits: scuba diving.
There is little evidence to suggest that having asthma or diabetes should preclude a patient from venturing underwater, according to researchers at the Dive Medicine Symposium at Rutgers University.
"There's not a lot of strong data to suggest that diabetics are at increased risk" of potentially serious adverse events, said Dr. Michael Madsen, a fellow in undersea and hyperbaric medicine at the University of Pennsylvania. Likewise for other depth-related illnesses such as arterial-gas embolism in the lungs or decompression sickness, also known as "the bends," he said.
The same thinking applies to most asthmatics, said Dr. David S. Lambert, who specializes in hyperbaric therapy at the Hospital of the University of Pennsylvania.
However, those with severe disease are often disqualified from diving after failing a required pulmonary test.
Earlier concerns about diving with diabetes led to bans in the United States, United Kingdom, and parts of Europe. The bans stayed in place until the mid-1990s -- and until 2004 for France.
Madsen said the major issue for diabetic divers is the potential for an underwater hypoglycemic episode that causes unconsciousness. These episodes are usually triggered by increased metabolic demands, since patients are "using more energy than usual when they're diving," he said.
They're particularly problematic for insulin-dependent diabetics, because their regular does of the hormone may be too high for someone undergoing increased activity.
There are also concerns about myocardial infarction (a heart attack) among diabetic divers from unrecognized vascular disease, Madsen said, although these threats are more frequently detected today and divers know about such risk in advance.
Even so, few studies have found evidence of an increased risk of adverse events among diabetic divers.
Data from research in 2005 performed by the British Sub Aqua Club, the diving regulatory agency in England, found only one instance of hypoglycemia among 447 diabetic divers who completed 14,000 registered dives.
And 2004 data from the Diver Alert Network (DAN), the diving regulatory agency in the U.S., found no symptomatic hypoglycemia cases among 80 divers on over 6,000 dives, although it did record some "fairly large glucose drops."
On the basis of that data and other studies, the American Diabetes Association guidelines recommend that divers remain physically fit and get regular exercise outside of diving.
They must also have no significant systemic disease, as well as excellent control of their diabetes, and their physicians "should have the final say in determining fitness to dive."
DAN guidelines recommend an annual physical that includes screening for heart disease if the diver is over age 40.
The agency also recommends that diabetic patients take blood glucose readings an hour, 30 minutes, and immediately prior to "splashing," or starting their dive.
Madsen said that blood glucose should be kept "a bit above normal" at 150 mg/dL since the diver will be using more energy than normal.
"When diving, we like to keep diabetics a little bit sweet," he said, adding that the dive should be cancelled if blood glucose tops 300 mg/dL.