Expert says Floyd died from ‘low level of oxygen’ after officer had knee on neck

Timothy Bella and Kim Bellware
·4 min read

Testimony in the trial of former Minneapolis police officer Derek Chauvin continued Thursday with a breathing expert saying that George Floyd died due to a “low level of oxygen” that caused brain damage, rebuking the defense’s argument that drugs contributed to Floyd’s death.

Martin Tobin, a pulmonologist and national breathing expert from Hines, Ill., offered testimony as an unpaid witness that Chauvin’s knee was on Floyd’s neck for the “vast majority of the time” and that the pain from the pressure applied by the officer to Floyd was comparable to that of a surgery to remove a lung.

His testimony came after a use-of-force expert said that Chauvin had one knee on George Floyd’s neck and was pressing down with most of his body weight – not moving for the nine minutes and 29 seconds the Black man was restrained and handcuffed on the ground.“

Tobin offered his opinion that Floyd’s shallow breathing led to arrhythmia, which caused his heart to stop.

”Mr. Floyd died from a low level of oxygen, and this caused damage to his brain that we see,“ Tobin testified to prosecutors.

Tobin, who clarified he is not a paid witness, said four forces caused the low level of oxygen: the handcuffs, Chauvin’s knee on Floyd’s neck, Floyd being in a prone position and Chauvin’s other knee on Floyd’s back arm.

Tobin said that the combination of how Chauvin and the officers used the handcuffs on Floyd and the position they had the 46-year-old on the pavement essentially put Floyd in a ”vise“ that affected his breathing.

”The way they’re pushing down on his handcuffs, combined with the street . . . we see that it’s like the left side is in a vise. It’s totally being pushed and squeezed in from each side,“ Tobin testified. ”It’s not just the handcuffs. It’s how the handcuffs are being held, how they’re being pushed, where they’re being pushed that totally interfere with central features of how we breathe.“

Tobin added that Floyd was being ”squashed“ between the handcuffs and the pavement.

”The way they were pressing in on the back, there was no way he could do any front-to-back movement,“ said the breathing expert.

When police officers pressed on the left side of Floyd’s body, the pain was not that much different from the pressure felt in removing a lung, a breathing expert testified.

Tobin said Floyd’s inability to have any front-to-back movement coupled with the pressure applied by Chauvin and other police officers caused pain that left his left lung useless.

”Because of the knee that was rammed in against the left side of his chest, sometimes the knee was down on the arm or in against the chest,“ said Tobin, a pulmonologist and unpaid witness. ”So basically on the left side of his lung, it was almost like a surgical pneumectomy to me. . . . So there was virtually very little opportunity for him to be able to get any air to move into the left side of his chest.“

After reviewing the footage and materials, Tobin concluded that Floyd had to try to breathe by using his fingers and knuckles ”to try and crank up the right side of his chest.“

Before the midmorning break Thursday, Tobin estimated that Chauvin placed 91.5 pounds, including at least half of his body weight, solely on Floyd’s neck when the officer’s feet were off the ground.

In a graphic presented to the court, Tobin explained that since Chauvin had his heels and toes off the ground, he was pressing down nearly 100 pounds of his weight directly on the neck.

”What we’re seeing is that half of his body weight, plus half his gear weight, is coming down. That’s 91.5 pounds . . . coming down directly on Mr. Floyd’s neck,“ Tobin said to prosecutors. ”Everything is directed down on his knee.“

Tobin added that even when Chauvin’s toes were touching the ground, the officer was still placing nearly 87 pounds on Floyd’s neck.

Tobin used several visual aids as he unpacked his opinion that Floyd died of a low level of oxygen, breaking down the mathematical formula behind the physics of breathing with a line graph.

Tobin explained how a 46-year-old man like Floyd can sustain about a 60% narrowing of their airways without dramatically increasing the effort required to draw a breath; he described 60% airway narrowing as more narrow than breathing through a straw.

The lines showing the effort it takes to breathe with no airway narrowing and 60% airway narrowing diverged only gradually over time. But with 85% of airway restriction – the degree to which he said Floyd was restricted when Chauvin’s knee was on his neck – the increase in breathing effort increases exponentially.

”If you get 85% narrowing, now you see that the effort to breathe increases seven and a half times compared with what it was with no narrowing,“ Tobin said.

”Based on the formula here, you can tell that as you are narrowing and narrowing, the effort to breathe is going to become extraordinarily high and at some stage unsustainable,“ Tobin said. ”You’re just not going to be able to do it.“