Observed outside the ambiance of a medical facility, the hyperbaric chamber at Phelps Memorial Hospital Center in Sleepy Hollow might be mistaken for an underwater vehicle or a large bronze space capsule. The 28-foot long, nine-foot diameter configuration makes it the largest such chamber in the northeastern part of the United States. The unit weighs 50,000 pounds and the door alone tips the scale at 5,000 pounds.

An increasing list of ailments are being treated within the chamber, according to Dr. Owen J. O’Neill, medical director of the Hyperbaric Medicine at Phelps.

“There are about 16 acceptable diagnoses for hyperbaric patients,” Dr. O’Neill said. “When I say ‘acceptable,’ that translates into what therapy Medicare and outside insurance companies will pay for.”

“Probably about 50% of what we do here is related to patients who have had radiation therapy for various cancers and are suffering the consequences of soft tissue radiation injury,” Dr. O’Neill said.

Another 30% of the patients are suffering from skin wounds, or skin ulcers often caused by diabetes or vascular disease. Among the remaining afflictions treated, the doctor said, are bone infections, carbon monoxide or cyanide poisoning, sensorineural hearing loss, air embolisms and what many people associate with a hyperbaric chamber, “the bends,” otherwise known as decompression sickness.

Patients are referred to the Phelps facility from a wide area, upstate New York, New Jersey, Connecticut and Long Island, as well as more distant places. They must be evaluated to determine if hyperbaric treatment is appropriate for their illnesses before undergoing the therapy. Dr. O’Neill said his staff of doctors, nurses and technicians are the most experienced in hyperbaric therapy in New York State.

The chamber’s size allows as many as 12 patients to be treated simultaneously. The therapy generally consists of 20 to 30 daily treatments, five each week, until the therapy is completed. Patients sit in comfortable chairs and can watch individual TV sets.

The chamber’s dual airlocks allow doctors or nurses to enter the chamber while treatment is taking place. Patients are monitored both from within the chamber by nurses and from outside via television cameras and other instruments. Each treatment lasts 90 minutes, although patients remain in the chamber two hours, Dr. ONeill explained. It takes10 minutes to reach the required pressure and there are 10 minute “air breaks” between three 30-minute segments. During those segments, patients inhale pure oxygen and while the pressure in the chamber can be raised to as much as six times the normal atmosphere, during treatment it usually remains between two and three atmospheres. Each atmosphere is equivalent to the pressure a person would feel 33 feet underwater in the ocean.

The high air pressure and resulting super oxygenation combine to promote and speed up tissue healing as well as help white blood cells fight infection.. The effectiveness of certain antibiotics is also improved by the therapy and it stimulates new blood vessel growth.

“There is a lot of very good evidence the therapy decreases bleeding, decreases pain and the need for hospitalization for internal radiation injuries,” the doctor said.

Dr. O’Neill described research now being conducted that demonstrates that hyperbaric conditions increase the mobilization and production of stem cells, possibly opening the way for the faster use of those cells for a variety of purposes. Studies are also taking place to determine its anti-inflammatory effects as compared with drugs designed for that purpose.

The hyperbaric chamber was installed at Phelps in late 2006 and was operational by December of that year with Dr. O’Neill in charge. The doctor has been involved with hyperbaric therapy since 1993. His initial training was in general surgery, and a scholarship at Westchester Medical Center in 1985 allowed him also to study internal medicine, and that led to his training in hyperbaric therapy. He is board certified as a specialist in wound therapy, as well as hyperbaric therapy. He has an office in Sleepy Hollow, adjacent to the hospital.