With veteran Marxist leader Jyoti Basu, who was put on ventilator on Wednesday morning, still being in a critical condition, Left Front sources said Prime Minister Manmohan Singh would be visiting the ailing former chief minister on Thursday noon.
Doctors said they were continuously monitoring the former West Bengal chief minister's health condition, but said Basu had shown some "positive changes".
"Basu's condition deteriorated in the morning and he was put on ventilator. His condition is still critical but he has shown some positive changes since the last bulletin at 1130 hrs," a medical bulletin issued by the hospital at 6 pm said.
"His blood pressure has been controlled a bit and one urine output was OK," AMRI hospital executive director told mediapersons when asked about the positive changes.
Doctors of the medical board were constantly monitoring the condition of the 95-year-old former West Bengal chief minister and would review his condition on Thursday at 11am, he said.
Communist Party of India - Marxist General Secretary Prakash Karat and politburo member Sitaram Yechury will visit Basu on Thursday, said an associate of the veteran Marxist leader.
Earlier, Superintendent of AMRI hospital in Salt Lake Debashish Sharma, where Basu is admitted, told PTI, "He has been put on ventilatory support this morning and his condition has turned serious".
Ninety-six-year-old Basu, who was admitted to the hospital on Friday last following a 'moderately severe' pneumonic infection, is under special observation at the ICCU, Sharma said.
A special medical board has been constituted to review Basu's condition. Dr A K Maity, Basu's personal physician and also a member of the board, said his condition was 'unstable'.