HARRISBURG — John Fetterman, the Democratic nominee for Senate in Pennsylvania, released a doctor’s note Wednesday saying he is recovering well from a May stroke as he vies for an open seat in a bare-knuckle campaign against Republican rival Dr. Mehmet Oz, who has questioned Fetterman’s fitness to serve.

Five months after the medical emergency from which Fetterman said, “I almost died,” he is fighting some lingering effects of the stroke — “the elephant in the room,” he called it at a recent rally. He uses closed-captioning to quickly interpret and respond to questions, and sometimes stumbles over words.

In the one-page letter, Dr. Clifford Chen noted that Fetterman, the lieutenant governor, continues to endure effects of the stroke that involve speech and being able to respond quickly. But he said Fetterman exhibited no effects on his “cognitive ability” or his ability to think and reason after the stroke, which occurred just days before the primary election.

Fetterman, 53, “is recovering well from his stroke and his health has continued to improve,” Chen wrote after examining Fetterman on Friday.

Chen, a primary care physician in Duquesne affiliated with the University of Pittsburgh Medical Center, concluded that Fetterman “has no work restrictions and can work full duty in public office.”

With less than three weeks before the Nov. 8 election, Fetterman is trying to counter Oz’s relentless attacks on his health while also acknowledging, going into their Tuesday debate, that his recovery is not complete. The race to succeed retiring GOP Sen. Pat Toomey is one of the most closely watched and could determine party control of the Senate.

Fetterman has declined to release a fuller suite of his medical records or provide access by reporters to his doctors or specialists.

Still, some independent experts on strokes who were consulted by The Associated Press before Fetterman released Chen’s note said the candidate appears to be recovering remarkably well — and they are optimistic that he will continue to get even better.

“Someone who is speaking and moving and looking the way he does has a very good long-term prognosis,” said Dr. Alexandre Carter of Washington University in St. Louis, who specializes in neurologic rehabilitation.

Carter said it is hard to assess how rapidly Fetterman is recovering because certain basic details, including the stroke’s severity, what part of the brain was affected or how serious his earlier symptoms were, have not been made public.

Carter, who examined videos of Fetterman with voters and being interviewed, said campaigning was “a great stress test for his ability to do the job.”

Strokes often leave one side of the body weak or even partially paralyzed, but Carter saw no sign that Fetterman has trouble walking or favors one side, and he does not use a cane.

Despite Fetterman’s language-related difficulties, “he’s speaking quite well. His speech is fluent. He knows what he wants to say. Most of the time it comes out perfectly clear,” Carter added.

Fetterman had the stroke just days before winning the Democratic primary. It kept him from campaigning for much of the summer and, when he returned, the state of his recovery was on full display.

Oz, a heart surgeon-turned-TV celebrity who has treated stroke patients, has accused Fetterman of lying about his health and suggested that the stroke has left Fetterman unequipped to serve effectively in the Senate.

Fetterman’s critics seized on the candidate’s struggles to understand speech, also known as an auditory processing disorder, after his in-person interview with NBC News this month.

Fetterman had used closed-captioning in interviews going back to July. But for the first time, NBC News’ cameras showed Fetterman reading an interviewer’s questions off his computer monitor before he responded.

An auditory processing difficulty does not mean someone has trouble hearing — it’s about how quickly and accurately the brain’s language network turns sound into meaning, said Brooke Hatfield of the American Speech-Language-Hearing Association.

There are different types, but generally “the brain needs to kind of reroute itself” to decode speech signals after a stroke, said Hatfield, a speech pathologist who has worked extensively with stroke patients. Responding to speech “is asking the brain to work really fast. Somebody who’s recovering, their brain might need just a little more time to make those connections.”

Fetterman’s use of the closed-captioning system “implies to me that he’s got a very strong visual system — he can read information more easily than he can hear it and process it,” Hatfield said, adding that it is a tool much like wearing glasses.

About 20% of stroke survivors experience some type of auditory processing difficulty, said Dr. Babu Welch, a brain surgeon at UT Southwestern Medical Center. Improvement takes time, speech therapy and practice.

Chen said in his note that Fetterman has significantly improved after working with a speech therapist.

Welch said that he could not comment specifically on Fetterman’s progress but that someone who “appears to be doing pretty well in October from a May stroke, that’s pretty good. That usually suggests there’s going to be continued improvement.”

Problems with auditory processing do not mean someone also has cognitive problems, the experts agreed. The brain’s language network is different from regions involved in decision making and critical thinking.

“Just because you have a disability doesn’t mean that you’re cognitively impaired,” Carter said. He is baffled by controversy over Fetterman’s use of closed-captioning, saying, “People who have significant comprehension problems or cognitive problems, captioning’s not going to help them.” Fetterman will use closed-captioning in the debate.

Questions about Fetterman’s condition had swirled for weeks after the stroke, fueled at least in part by the campaign’s initial limited disclosures about the episode and later by Oz’s questions about Fetterman’s absence from campaigning for much of the summer and his refusal to engage in more than one debate.

Fetterman’s campaign first revealed the stroke on May 15, two days after he was hospitalized, and said it was caused by a condition called atrial fibrillation. Fetterman later acknowledged that his cardiologist said he could have avoided the stroke had he taken prescribed blood thinners. Fetterman said he thought — wrongly — that losing weight and exercising would be enough.

The campaign did not release key additional details for two more weeks.

Doctors implanted a pacemaker for the atrial fibrillation, along with a defibrillator that turned out to be a precaution for a different and more serious condition called cardiomyopathy. The defibrillator can deliver corrective shocks if it senses the weakened and enlarged heart muscle has fallen into a life-threatening irregular rhythm.

In a letter made public in June, Dr. Ramesh Chandra, Fetterman’s cardiologist, said the candidate would be fine and able to serve in the Senate if he ate healthy foods, stuck with his medication and exercised. Chen’s letter said Fetterman was doing that, noting that he can walk 4 miles to 5 miles without difficulty.