Zhang Shifen, 30, from Jiangyin, Jiangsu Province, came to the hospital just after the May holiday break. She was in a coma after being poisoned by hydrogen sulfide at work.

Cai Zhongliang, 35, from Jiading, on the outskirts of Shanghai, woke up at the end of last month after three months in coma caused by a traffic accident.

Both of them were treated with hyberbaric oxygen therapy.

"We feel overjoyed now because doctors at our local hospital said my daughter will never wake up," said Tang Rendi, Zhang's mother.

Liu Qingle, the center's director, understands the joy and excitement but considers the two just normal cases. "We help comatose patients regain consciousness just like other doctors treat diseases such as colds," said Liu.

The hospital's statistics show that an average one or two patients in a vegetative state have awakened every month since 2002, when the center's hyperbaric oxygen therapy treatment swung into full operation.

According to Liu, their wake-ups account for more than 50 percent of patients. "We can tell whether the patient can wake up in most cases based on our experiences," said Liu.

Liu explained that the therapy helps cause a saturation of oxygen in the plasma and tissue fluids so the body can function more effectively.

"Hyperbaric oxygen therapy is one of the most effective methods to wake up people in a vegetative state," said Wang Guisong, a respected neurosurgeon at Renji Hospital.