Breathing expert testifies in Chauvin trial: ‘That’s the moment the life goes out of his body’




Dr. Martin Tobin, testifying in the murder trial of Derek Chauvin.

A diminutive Irish doctor captured the attention of the jury deciding Derek Chauvin’s fate, explaining in simple terms Thursday how he believes three Minneapolis police officers killed George Floyd when they handcuffed and put him face down on the street and restrained him for more than nine minutes. 

Dr. Martin Tobin, a pulmonary and critical care doctor from Illinois, has researched breathing since 1981 and written books on respiration, including what The Lancet medical journal calls “the Bible on mechanical ventilation.”

Despite an impressive resume, Tobin used simple language to convey his opinion to the jury, using words like squashed, cranked and rammed.

Although he has been an expert witness in malpractice cases, he’d never testified in a criminal case before. He agreed to testify in this case because he thought he might be able to explain how Floyd died, waiving his customary $500 hourly fee.

His conclusion? You can call it asphyxia or hypoxia, but “What we’re really talking about is a low level of oxygen,” he said as almost every juror took notes.

Tobin said several factors led to Floyd’s death: He was face down on the pavement, handcuffed and Chauvin’s left knee was putting pressure in the neck area. 

During the first five minutes Floyd was prone, Chauvin’s other knee was on Floyd’s arm and “rammed into” the side of Floyd’s left chest.” With the handcuffs behind his back, constricted by the street, “It’s like the left side is in a vice,” he said.

As he explained how people breathe — using the analogy of a bucket and pump handle — the jurors almost all watched him intently, not taking notes.

Chauvin’s fellow officers J. Alexander Kueng and Thomas Lane were not just holding his lower body down, they were forcing his left wrist up so Floyd was being “squashed” into the street, Tobin testified.

Combined with Chauvin pressing into his left side, “Basically on the left side of his lung, it was… almost to the effect as if a surgeon had gone in and removed the lung — not quite, but along those lines — 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,” Tobin said. “So he was going to be totally dependent on what he’d be able to do with the right side.”

But Floyd’s ability to expand his chest was also impaired on the right side, Tobin said.

“The street is what is having a huge effect because he’s jammed down against the street and so the street is playing a major role in preventing him from expanding his chest,” he said.

The prosecution showed a still image of Floyd’s handcuffed left hand being pushed into his back, and Floyd pushing his fingers against the street and right knuckles against the tire to try to crank up the right side of his chest to get air into his lung.

“He’s now literally trying to breathe with his fingers and knuckles,” Tobin said as about half the jurors took notes and the rest watched the doctor. “This is his only way to try and get air into the right lung.”

He noted the sculpting of Floyd’s shoulder muscles was prominent, because he said that’s one of the last muscles people will use to breathe — however ineffective.

While explaining the impact of Chauvin’s knee on Floyd’s neck, Tobin showed jurors how to find their hypopharynx — the bottom of the throat used for eating and breathing — by first finding your Adam’s apple, and the rings of cartilage in the area. Most of the jurors did as he said, reaching up and feeling around their necks, then taking notes afterward.

The hypopharynx was significantly compressed when Chauvin’s knee was on the side of Floyd’s neck, he said, and if Chauvin put his full weight on the neck, within seconds Floyd’s oxygen level would drop, possibly causing a seizure or heart attack.

As Tobin explained the effect of Floyd’s nose being face down, instructing jurors to feel the back of their neck where the skull ends, almost every juror did so, along with the prosecutor, prompting Chauvin’s attorney, Eric Nelson, to ask the judge to speak to the attorneys privately. 

Afterward, Judge Peter Cahill told the jurors they weren’t required to do anything Tobin instructed them, but most of them did so anyway when Tobin explained how to find a thick ligament.

He calculated the amount of force on Floyd’s hypopharynx based on Chauvin’s weight, plus his gear, and the narrowed breathing canal caused by Chauvin’s knee. He said it was much worse than breathing through a straw.

He noted that when the toe of Chauvin’s boot was no longer touching the ground, “This means that all of his body weight is being directed down at Mr. Floyd’s neck.” 

Tobin said Floyd’s oxygen levels during the first five minutes on the ground were enough to keep his brain alive — since he continued to speak — but Chauvin’s left knee was on Floyd’s neck virtually all the time, and his right knee was on Floyd’s back more than 57% of the time.

Even when Tobin explained somewhat complicated medical terms, the jurors seemed engaged, listening closely. Just putting Floyd face down reduced his lung volume 24%, Tobin said, which isn’t a problem for someone sleeping on their stomach, but for someone with a knee on their neck, hands cuffed behind their back and unable to move their left lung, “then it’s a whole different kettle of fish.”

Tobin said the locations of Chauvin’s knee — back, neck, arm or side — made no difference. All would impair Floyd’s ability to move his chest against the street. Chauvin’s attorney has repeatedly shown video that seems to show Chauvin’s knee wasn’t always on Floyd’s neck.

By Tobin’s calculation, the work of breathing increased more than 75% just from the effect of what was happening on Floyd’s chest, not counting the impact of a knee on his neck.

“The work that Mr. Floyd has to perform becomes huge because… with each breath, he has to try and fight against the street, he has to try and fight with the small volumes that he has and then he has to try and lift up the officer’s knee with each breath, and also remember he has to try and also lift up the effect of the other officer pumping in his arm… they’re pushing it in, into his chest.”

A female juror appeared to look directly at Chauvin during this testimony.

Tobin said Floyd did not appear to have enough oxygen to remain conscious just before 8:25 p.m. He stopped breathing at 8:25:16, Tobin said, and within 25 seconds his oxygen went to zero.

“At that point he wouldn’t have an ounce of oxygen left in his entire body,” Tobin said.

Chauvin’s knee remained on his neck for another three minutes, he said — prompting almost every juror to begin writing on their notepad.

And while the defense has contended Floyd died from ingesting a lethal dose of fentanyl and methamphetamine — on top of myriad health issues — Tobin said even a healthy person would’ve died.

While an officer on the scene suggested Floyd could breathe when he could speak, Tobin said that’s true, but it gives “an enormous false sense of security” because they may not be able to breathe five seconds later — prompting a female juror to nod her head in agreement.

Floyd spoke for 4:51 minutes after Chauvin put his knee on his neck.

Tobin explained that when Floyd’s leg jerks up backwards at one point in the video, that was an involuntary reaction caused by a fatally low level of oxygen going to the brain.

Tobin also showed jurors how to gauge Floyd’s respiration rate of 22 breaths per minute while watching a video of Floyd, which he said was “extremely significant” because if fentanyl caused his respiration to go down, you’d expect a bigger reduction in the rate, down to about 10 rather than a normal rate of 22.

“You can see when you counted yourself, basically there isn’t fentanyl on board that is affecting his respiratory centers,” Tobin said.

Based on his experience working in an ICU, where 40% of people die, Tobin said, you can best see the effect of low oxygen in a person’s face. At 8:20:53 p.m., Floyd’s eyes flicker, and then he’s gone.

“That’s the moment the life goes out of his body,” Tobin said, as most jurors began writing.

Chauvin kept his head down, looking at his own notepad.

Floyd took his last breath at 8:25:16 p.m., he said. He remained face down on the street another three minutes.

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