The condition of former President K.R. Narayanan, who was admitted to the Army Research and Referral Hospital in Delhi last week, continues to be critical, according to hospital sources.‘‘There has been no improvement in Narayanan’s condition and he continues to be on ventilator,’’ said Brg Pradeep Bhargav, in charge of the hospital.Narayanan (85) was admitted in the hospital on October 29 with acute artery blockages and kidney failure. He slipped into coma.