Former West Bengal Chief Minister Buddhadeb Bhattacharya remained critical on Monday as he continued to be on mechanical ventilation, doctors treating him said. Bhattacharya, 79, underwent a CT scan of his thorax in the morning, they said. "Mr Bhattacharya's health condition is critical but stable. He is still on invasive ventilation. We have conducted a CT scan of his thorax this morning. He is responding to treatment," a senior doctor, who is a part of the multidisciplinary team that is treating him, said.