George Floyd died of oxygen loss, not pre-existing conditions or overdose, prosecution experts say

George Floyd's pre-existing medical conditions and drugs in his system had nothing to do with his death, two medical experts for the prosecution testified at Derek Chauvin's murder trial Thursday. Rather, a combination of actions during his arrest that deprived him of oxygen caused his death, they said.

"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," Martin Tobin, a lung and critical care specialist at the Edward Hines Jr. VA Hospital and Loyola University's medical school in Chicago, told Hennepin County District Court.

Tobin said handcuffing Floyd and pinning him face down to the pavement — along with the knees of Chauvin pressed into his neck and back, all combined to reduce his ability to breathe and, ultimately, killed him.

"A healthy person subjected to what Mr. Floyd was subjected to would have died as a result of what he was subjected to," Tobin said.

'Pressure on his chest and back'

Dr. Bill Smock, a Louisville, Ky., physician and expert on deaths from asphyxia, agreed that Floyd died "because he had no oxygen left in his body," as a result of "pressure on his chest and back."

Floyd, a 46-year-old Black man, died on May 25, 2020, after Chauvin, who is white, pressed a knee on the back of his neck and back for around nine minutes as two other officers held him down. Video of the arrest captured by a bystander prompted widespread outrage, setting off protests over race and police brutality across the U.S. and around the world.

Chauvin, 45, a former Minneapolis police officer, is facing trial on charges of second-degree unintentional murder; third-degree murder; and second-degree manslaughter. Thursday marked the ninth day of the trial.

The prosecution says Chauvin pressing his knee into Floyd's neck while detaining him on suspicion of using a counterfeit bill at a convenience store, caused his death. But the defence argues Chauvin did what his training taught him and that it was a combination of Floyd's underlying medical conditions, drug use and adrenaline flowing through his system that ultimately killed him.

Floyd suffered from heart disease and high blood pressure, while toxicology results revealed fentanyl and methamphetamine in his system.

WATCH | Expert explains why fentanyl overdose is unlikely to have caused Floyd's death:

Medical expert says no evidence Floyd overdosed on fentanyl

3 years ago

Duration 0:23

Featured VideoDr. Bill Smock, an expert on deaths from asphyxia, said that based on the actions of George Floyd, there was no evidence he overdosed on fentanyl.

However, Tobin dismissed any suggestion that fentanyl in Floyd's system led to his death, saying that based on his calculations, Floyd's respiratory rate before he lost consciousness would have been much lower if this was the case.

"Do any of those conditions have anything to do with the cause of Mr. Floyd's death, in your professional opinion, whatsoever," prosecutor Jerry Blackwell asked Tobin.

"None whatsoever," he replied.

Instead, Tobin went through a detailed examination of Floyd's death, based on medical records, videos and interviews. Tobin said four things contributed to Floyd's lack of oxygen: That he was handcuffed; put in the prone position face down on the ground; that Chauvin's knees were pressed into Floyd's neck and back; and that his chest was pinned against the pavement, unable to fully expand.

"All of these four forces are ultimately going to result in the low tidal volume, which gives you the shallow breaths," he said. 

Tobin said the way the police were pushing down on Floyd's handcuffs, combined with Floyd being pressed against the hard pavement, had the effect of putting his left side in a vise "that totally interfere(s) with central features of how we breathe."

"There was virtually very little opportunity for him to be able to get any air to move into the left side of his chest," he said.

"He's jammed down against the street. And so the street is playing a major role in preventing him from expanding his chest."

Prevented from expanding chest

Based on videos of the arrest, Tobin said, he calculated that half of Chauvin's weight , 91.5 pounds, came down directly on Floyd's neck. 

Tobin explained to jurors what happens as the space in the airway narrows. Breathing then becomes "enormously more difficult," he said, comparing it to "breathing through a drinking straw," although he later clarified it would be much harder than that.

Tobin also explained that Chavin's knee on Floyd's neck "is extremely important because it's going to occlude (stop) the air getting in through the passageway."

"Officer Chauvin's left knee is virtually on the neck for the vast majority of the time," he said.

Under cross examination, Chauvin's lawyer, Eric Nelson, argued that Tobin was making certain assumptions when doing his calculations.

Tobin disagreed, saying he made "very few assumptions."

But Tobin agreed that, for example, he never actually weighed Chauvin on May 25, 2020, or weighed his equipment.

'That is not a fentanyl overdose'

Meanwhile, Smock, under questioning by Blackwell, stressed that in his opinion, Floyd wasn't exhibiting the signs of someone who had suffered a fentanyl overdose.

"When you watch those videos and we go through them, what is his respiration? He's breathing. He's talking, he's not snoring. He is saying, 'Please, please get off of me. I want to breathe. I can't breathe.' That is not a fentanyl overdose. That is somebody begging to breathe."

Smock also testified that the level of methamphetamine in Floyd's system was "really a nothing level."

Under cross-examination, Smock was asked whether a "methamphetamine and fentanyl" death is a much different type of a death than an exclusive fentanyl death.

"Depending upon the level, yes," he said.

Smock was also asked if he has experience with deaths in people who have ingested methamphetamine and fentanyl and also have cardiac disease.

"Not just necessarily from those, but maybe from something else," Smock said.

"But sometimes, it could just be from those," Nelson said.

"It would depend upon the case," Smock sad.

Smock was also asked if one of the side effects of prescribed amphetamine is a sudden heart arrhythmia. 

"Depending upon the level, it's a rare side effect, but it's certainly possible," Smock said.

And Smock agreed that people have suffered cardiac arrhythmias during struggles with police before.

But under redirect from Blackwell, Smock agreed there was no evidence that Floyd had a heart attack or a "sudden death that looked like an arrhythmia."

"Did you see any evidence that he died of an overdose?" Blackwell asked.

"No, sir, he did not," Smock said.