Brazil's imprisoned former president Jair Bolsonaro has undergone a medical ‍procedure to treat persistent hiccups for the second time in three days.

The doctors carried out ​a "phrenic nerve block procedure" on Bolsonaro to block his left phrenic nerve, following a ⁠surgery on Saturday to treat the right one.

In medical literature, the phrenic nerve is described as a vital nerve originating in the neck that controls the diaphragm, the primary muscle for breathing.

The surgery at the DF Star hospital in capital Brasilia lasted for about ‌an hour, according to information ‍provided by his wife, former First Lady Michelle Bolsonaro, on social media.

Doctor Claudio Birolini told journalists later that Bolsonaro is expected to leave the hospital on January 1, if his recovery is uneventful, while a second doctor said his health conditions will be closely watched ​in the next 48 hours.

"I don't ‌believe the hospitalisation will be prolonged much longer," Doctor Brasil Caiado, the third doctor at the press conference, said. "His ​condition is stable."

Bolsonaro, 70, had been hospitalised on Wednesday for hernia surgery on ‍Christmas Day. His doctors then decided to also carry out procedures to treat his hiccups during his hospital stay.

The ex-president has faced health problems ​since ​a stabbing he suffered in September ​2018, during a presidential campaign event in the ​town of Juiz de Fora, in Minas Gerais state.

Bolsonaro was convicted and sentenced to over 27 years in prison by Brazil's Supreme Court in September for plotting a coup to overturn his 2022 election loss. He started to serve his sentence last month.

He was authorised by Supreme Court Justice Alexandre de Moraes to leave prison for the hernia surgery.