Whenever Naoshi Tamura is on a night shift at Ota Hospital in Tokyo, the surgeon works 36 consecutive hours with little sleep, seeing patients during the daytime and treating those transported to the emergency room at night.

"I work the night shift two to three times a month," said Tamura, 49, who also serves as the director of the 211-bed hospital. "It makes me exhausted physically and psychologically."

His current workload is extremely heavy. On weekdays, he works 12 hours a day, carrying out roughly 15 major and minor surgeries a month. On weekends, he attends business meetings or checks up on his patients who have just had operations. He can take only two days off work a month.