Dr. Martin Tobin, a professor at Loyola University Medical Center near Chicago, a doctor at the Edward Hines Jr. Veterans Affairs Hospital and the author of what's considered the "bible" on ventilation, testified for several hours on Thursday about the factors that contributed to Floyd's death. He illustrated his points with diagrams and graphs, clips from officers' body-worn cameras and bystander videos, and occasionally by loosening his tie to point out the anatomy of the neck.
Tobin testified that Floyd's position in the street where he died — lying prone with pressure on his back and his neck —made it difficult for him to breathe. He calculated Floyd's lung capacity and oxygen level as the restraint wore on. He counted out Floyd's respiratory rate. And he pinpointed in the video clips when Floyd's brain oxygen level grew fatally low, noting a final spasm and a change in Floyd's facial expression, which Tobin called "the moment the life goes out of his body."
Tobin also rebutted one of Chauvin's key defenses: the possibility that Floyd died of underlying heart conditions and an overdose of fentanyl and methamphetamine, which a toxicology report found in his system, not asphyxiation.
"A healthy person subjected to what Mr. Floyd was subjected to also would have died as a result of what he was subjected to," Tobin told the jury in Hennepin County District Court in Minneapolis.
The murder charges against Chauvin became international news last spring, after millions of people viewed a bystander's video of Floyd's arrest. It showed Chauvin pinning Floyd's neck down for about nine minutes, as Floyd — who was suspected of using a counterfeit $20 bill — begged him to stop, said he couldn't breathe and eventually lost consciousness.
The image of a Black man gasping for breath under the knee of a white police officer rekindled a nationwide racial justice movement that continued through the summer. Floyd's cries of "I can't breathe" — which, by prosecutors' count, he said 27 times as he died — became a rallying call at protests.
On Thursday, it was also a medical diagnosis.
"Mr. Floyd died from a low level of oxygen. This caused damage to his brain," Tobin said. "It also caused a [pulseless electrical activity] arrhythmia that caused his heart to stop."
The doctor said it was the way in which Floyd was restrained that caused his "shallow breathing."
Chauvin and another Minneapolis police officer, J. Alexander Kueng, each had a knee on Floyd's back, and pressed his handcuffed wrist into his back, pushing his chest into the hard asphalt of the street, Tobin said. That put so much pressure on Floyd's left side, Tobin said, that it was as if Floyd's left lung had been surgically removed. He was relying entirely on his right side to breathe.
The doctor pointed to moments in the body-worn camera video when Floyd pushed his right hand into the ground and the tire of the nearby squad car, when he pressed his face into the street, and when he rolled his shoulder. During all of those moments, Tobin said, Floyd was attempting to make room for his chest to expand.
Chauvin's knee on Floyd's neck would have restricted his hypopharynx, Tobin said. Pointing to the spot on his own neck just above the Adam's apple, Tobin said the hypopharynx is extremely vulnerable, because it's not protected by cartilage, and is also a very small opening through which air travels to the lungs. Half of Chauvin's body weight was pressing into that spot whenever he lifted his toes from the ground, Tobin said. Videos from that day show that Chauvin's feet were at times hovering above the street, with all his weight on his knees.
Just lying in the prone position for several minutes would have reduced the oxygen stores in Floyd's body by 24%, the doctor testified. The knee in Floyd's neck would have reduced it by an additional 19%.
"The work Mr. Floyd has to perform becomes huge," Tobin said. "With each breath, he has to try and fight against the street, fight with the small [lung] volumes he has, and try to lift up the officer's knee."
Tobin also said officers' assertion as they held Floyd down that "if you can speak, you can breathe," while true, "gives an enormous false sense of security," because "it doesn't tell you you're going to be breathing five seconds later."
Jerry Blackwell, founding partner of the Minneapolis law firm Blackwell Burke, who is working pro bono for the prosecution, used Tobin's testimony to rebut Chauvin's defense claim that Floyd died of long-term heart disease and a drug overdose.
The doctor's testimony came a day after several investigators with the Minnesota Bureau of Criminal Apprehension testified that they'd found pills containing fentanyl and methamphetamine in Floyd's car, and partial tablets covered in Floyd's saliva in the back of the cruiser that officers had tried to shove him into.
On cross-examination, Chauvin's attorney, Eric Nelson of Halberg Criminal Defense, noted that Tobin was assuming that Floyd was a "healthy individual," when he had numerous health problems.
Floyd's autopsy showed that he had 70% to 90% occlusion in some parts of his coronary artery, Nelson said. He'd tested positive for COVID-19 a few months before his death. He was a smoker. He had a paraganglioma, a type of tumor that in 10% of cases can cause a surge of adrenaline. And he struggled with addiction.
Nelson asked Tobin if he'd heard of "wooden chest syndrome," a rigidity of the chest wall found in people who take fentanyl. Tobin conceded that the condition can "impede the ability of lungs to expand."
Nelson also noted that in his report, Tobin said he would expect the peak of respiratory suppression from fentanyl to come on fairly quickly — about five minutes after taking a pill.
Nelson used this to ask about the partial tablets with Floyd's saliva on them that were found in the back of the police cruiser. If, hypothetically, Floyd had those pills in his mouth as he struggled in the back of the squad car at 8:18 p.m., Nelson asked, would Tobin would expect the fentanyl Floyd ingested to affect his breathing five minutes later, when he was on the ground?
Tobin said yes, but that it would depend on "how much of it was ingested."
--Editing by Karin Roberts.
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