Chauvin Trial: Medical Expert Says George Floyd Died From A Lack Of Oxygen

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Dr. Martin Tobin, a pulmonary specialist who works in critical care, testified Thursday that George Floyd died from a lack of oxygen, bolstering the prosecution's argument that former Minneapolis police officer Derek Chauvin caused Floyd's death last May.

Tobin is appearing as an expert witness for the prosecution. He says the state asked him to review documents and videos depicting the circumstances of Floyd's death. Tobin watched some of those videos hundreds of times, he said.

"Have you formed an opinion to a reasonable degree of medical certainty on the cause of Mr. Floyds death?" prosecutor Jerry Blackwell asked.

"Yes, I have," the doctor replied. "Mr. Floyd died from a low level of oxygen, and this caused damage to his brain that we see. And it also caused a PEA [pulseless electrical activity] arrhythmia that caused his heart to stop."

Prosecutors say Chauvin killed Floyd by pressing his knee on his neck for about nine minutes. But Chauvin's defense attorney says that Floyd was experiencing a drug overdose and had an underlying heart condition.

Last year, the Hennepin County medical examiner's office ruled Floyd's death was a homicide, saying his heart and lungs stopped functioning "while being restrained" by police. But it also noted "other significant conditions," including fentanyl intoxication and recent methamphetamine use as well as heart disease.

Four factors led to Floyd's low oxygen level, Tobin says:

  • his prone position on the street;
  • the handcuffs that pulled his arms back;
  • a knee on his neck;
  • a knee on his back and down his side.

"All of these four forces are ultimately going to result in the low tidal volume, which gives you the shallow breaths" that can't effectively bring oxygen into the lungs, Tobin said.

Prosecutors say Chauvin and two other officers restrained Floyd for 9 minutes and 29 seconds, before he was moved onto an ambulance gurney. Chauvin kept his left knee in the area of Floyd's neck "for the vast majority of the time" as three officers held Floyd down on the asphalt, Tobin said.

His analysis was helped, he said, by an artist's computer rendering of the scene that was created by all the available video sources. Tobin said he focused on the first five minutes and three seconds of video, because "that is up to the time that we see evidence of brain injury."

Chauvin's right knee seems to have alternated between resting on Floyd's back and on his arm and "rammed into Mr. Floyd's left chest," Tobin said. He said that both placements would have an "extremely similar" effect on someone's ability to breathe in the position Floyd was in.

Tobin is a professor in the Division of Pulmonary and Critical Care Medicine at Loyola University Stritch School of Medicine, and affiliated with Edward Hines Jr. VA Hospital, both in the suburbs of Chicago. He has written a highly regarded textbook on respiration and is a researcher in clinical medicine who has published hundreds of papers.

All of his work, Tobin told the jury, is related to breathing, including apnea. As Blackwell noted the doctor's esteem in the medical community, Tobin said he has given lectures in more than 30 countries and most U.S. states.

Tobin testified as Chauvin's trial enters a new technical phase, with prosecutors expected to call a string of medical experts to testify about how Floyd died in police custody. The former police officer is facing murder and manslaughter charges.

Tobin told the court he isn't being paid to appear in the Minneapolis trial.

"When I was asked to do the case, I thought I might have some knowledge that would be helpful to explain how Mr. Floyd died," Tobin said, "and since I'd never done this type of work in this nature before, I decided I didn't wish to be paid for it."

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