(CNN)Covid-19 shoved Jeff Sweat into a medical coma for three weeks last winter, face down on a ventilator, on death's trap door.
"I took care of him when he was literally near death," said Dr. Nida Qadir, a pulmonologist and co-director of the Intensive Care Unit at UCLA Medical Center. "He has no memory of meeting me."
But now the pair are well acquainted -- the lung specialist and the 49-year-old married father with three teenagers -- as he sings his way to recovery in a unique therapy program at UCLA.
Sweat and several other patients with serious medical complications caused by the virus attend weekly opera classes via video conference, conducted by members of the Los Angeles Opera and music educator Rondi Charleston.
"When you are intubated, you forget how to drink and breathe," Sweat said. "It was like breathing was a second language. Singing helps me connect. Breathing to a purpose. It gave me reason to learn how to breathe again."
During a recent opera therapy session, Sweat, a publicist, and fellow patients received instructions from LA Opera stars Nani Sinha and Michele Patzakis.
"See if your breath can go a little deeper here," Sinha told her students.
Sinha told CNN she knows intimately about healing and strengthening the heart and lungs. That's because she suffered a broken back during an emergency plane landing in 2007 and has debilitating asthma.
"I'm bringing something (opera training) that relaxes the limbic system, bringing breathing therapy and music," Sinha said, referring to the part of the brain involved in behavioral and emotional responses. "Bringing that to people who are suffering so badly -- it's just the greatest opportunity to be of service."
Singers use diaphragmatic breathing in training, which strengthens the principal muscle used to breathe, the diaphragm.
"In turn, it helps you take a deeper breath," Qadir said. "Singing also involves sustained, controlled exhalation. Similar to a modality we teach in pulmonary rehabilitation, called pursed lip breathing."
Qadir says that training leads to slowing down the breathing rate, giving patients more time to exhale, to get rid of carbon dioxide and take the next breath with greater ease.
She says opera singers' breathing exercises reach Olympic athlete level, so who better to train beginners.
Marcelo Olavarria, a barrel-chested 78-year-old, is still attached to an oxygen tank after his four-week hospitalization in January at UCLA Santa Monica Hospital.
He heard the ominous beeps of monitors in the ICU.
"It was very traumatic, all the tubes coming in and out of you," said the married retiree, originally from Chile.
Months later in recovery, Sinha, a mezzo-soprano, tried to help Olavarria rebuild his lung capacity through singing.
She recalled that in the first lesson, he could not do the breathing exercises.
"He was hunched over and he was coughing," the opera teacher said.
But Olavarria persisted after that low note.
"Now you listen to that robust voice, that tremendous instrument coming out of Zoom. It's incredible," Sinha said.
"It's wonderful, it's very soulful therapy," said Olavarria.
In the video lesson, Olavarria sang powerfully with his fellow Covid-19 survivors, urged on by their trio of instructors.
The amateurs continued pushing on "Amazing Grace."
"I once was lost, but now I'm found," came from the chorus of recovering Covid-19 patients,
As Sweat and his classmates sang those words, Qadir watched the video concert unseen.
"I had my camera off for a reason," she said. "I did get a little teary-eyed when I heard that."
Months after perilous weeks in intensive care, Sweat, Olavarria and classmates breathed new life into the classic lyric, "how sweet the sound."
CORRECTION: A previous version of this story incorrectly characterized Dr. Nida Qadir. She is a lung specialist.