(CNN) -- Comedian Joan Rivers died of "therapeutic complications" during a procedure to evaluate her "voice changes" and stomach reflux, the New York medical examiner said Thursday.
"The classification of a death as a therapeutic complication means that the death resulted from a predictable complication of medical therapy," the report said.
Rivers, 81, died September 4, a week after an appointment at Manhattan's Yorkville Endoscopy clinic.
The medical examiner's investigation ruled that the cause of death was "anoxic encephalopathy due to hypoxic arrest," a medical description of brain damage caused by a lack of oxygen.
The arrest happened "during laryngoscopy and upper gastrointestinal endoscopy with propofol sedation for evaluation of voice changes and gastroesophageal reflux disease," the medical examiner's officer said.
The complication in this case was laryngospasm -- a spasm of the vocal cords that makes it difficult to breathe, pathologist and surgeon Bill Lloyd told CNN. The situation was compounded when Rivers went into cardiac arrest.
"She stopped breathing and her heart went into arrhythmia because there wasn't sufficient oxygen to maintain the heart muscle," said Lloyd, who was not involved in Rivers' autopsy. "The pump, the heart itself, was unable to move fresh oxygenated blood upstream to the brain."
At first, Lloyd said, Rivers was unable to bring oxygen into her body due to the vocal cord spasm. After a couple of minutes, her heart started to beat irregularly or completely stopped. Finally, her heart stopped delivering fresh oxygenated blood to her brain, which shut down, according to Lloyd.
"The unanswered question is why they did not do a combat (tracheotomy)?" he asked. "You've seen in the James Bond movies. You take a ballpoint pen and puncture the thyroid cartilage and create an emergency airway for her. Of course, they would do it with sterile instruments. ... And, after minute two, did anybody say, We need to start doing some CPR for her?"
The initial report did not name the doctor or doctors who performed the procedures.
Melissa Rivers posted this on Twitter on Friday afternoon: "In response to NYC's Medical examiner's report, we continue to be saddened by our tragic loss. No further comment at this time."
Several clinic workers told investigators that the August 28 appointment began with Rivers' personal throat doctor, Dr. Gwen Korovin, performing a laryngoscopy, which involves using a device to view a patient's vocal folds, a source close to the investigation told CNN last month.
Gastroenterologist Dr. Lawrence Cohen, who was the medical director of the clinic until resigning after Rivers' death, then performed an endoscopy intended to diagnose why she was suffering a sore throat and hoarseness, the source said.
Cohen detected something of concern, the source said.
Korovin then began a second laryngoscopy to again view River's vocal cords, the source said. It was at that time that her vocal cords began to swell, leading to a cutoff of oxygen to her lungs and ultimately to cardiac arrest, according to the source.
Korovin was authorized only to observe Cohen, who performed the procedure, since she was not certified by Yorkville Endoscopy clinic, as required by New York health law, the source said.
Investigators have found no prior consent form signed by Rivers authorizing a procedure by Korovin, the source said. It was unclear if Rivers had given verbal consent to the biopsy before being sedated.
But Korovin denied "performing an unauthorized procedure" before the comedian suffered cardiac arrest, a source close to the doctor told CNN last month.
Paramedics rushed Rivers from the clinic to New York's Mount Sinai Hospital a mile away, where she was kept on life support until she died a week later.
Doctor to the stars
Korovin is well known for helping an impressive list of celebrities with voice trouble. The list of famous patients who have sung her praises include actors Hugh Jackman and Nathan Lane and singers Celine Dion, Lady Gaga and Ariana Grande.
The walls of Korovin's Manhattan medical office are covered with autographed photos, including from operatic tenor Luciano Pavarotti, Broadway star Barbara Cook and actress-singer Julie Andrews.
"I've always been fascinated by the human voice and music," Korovin, 55, is quoted telling the New York Daily News in a profile story last year.
Korovin's lawyer sent a statement to CNN last month in response to reports that questioned whether her actions played any role in Rivers' death.
"Gwen S. Korovin, M.D. is a highly experienced, board certified otolaryngologist. She maintains privileges at one of the city's most prestigious hospitals. She is respected and admired by her peers in the medical community and she is revered by her patients.
"As a matter of personal and professional policy, Dr. Korovin does not publicly discuss her patients or their care and treatment. Further, Dr. Korovin is prohibited by state and federal confidentiality laws from discussing her care and treatment of any particular patient."
CNN's Ray Sanchez, Brian Vitagliano and Susan Candiotti contributed to this report.