Kolkata, Dec 10 (IANS): The health of veteran Communist Party of India-Marxist (CPI-M) leader and former West Bengal CM Buddhadeb Bhattacharya has improved slightly but remained critical on Thursday, hospital sources said. He is on ventilator support now.

"The oxygen saturation level is now around 90-95% and he has regained consciousness," the sources said.

A five-member team of doctors is currently monitoring the septuagenarian leader at a Kolkata hospital.

Bhattacharya had a steady PCO2 level at 42 mmHg this morning, which is normal for COPD patients.

The veteran politician developed difficulty in breathing and his breathing-related problems aggravated on Wednesday afternoon. He was suffering from Chronic Obstructive Pulmonary Disease (COPD) and other old age-related ailments for quite some time.

The sources said that the oxygen saturation level in his body was low when he was admitted and he was kept on mechanical ventilation at the hospital. The Left leader started responding to treatment marginally since Wednesday night. Necessary tests were also conducted on the veteran communist leader at the hospital's flu clinic.