Day 9 of Chauvin trial: Expert witness says Chauvin's knee cut off Floyd's air

Testimony from pulmonologist Martin Tobin dominated the ninth day of former Minneapolis Police officer Derek Chauvin's trial, as the doctor provided jurors comment about George Floyd’s ability to breathe while under restraint.

During his time at the stand, Tobin refuted the impact fentanyl had on Floyd’s breathing just before he lost consciousness, and pushed back against claims that preexisting health conditions caused his death. 

The defense has contended throughout trial that both Floyd’s drug use and underlying health conditions played a role in his death, while prosecutors have alleged that Chauvin’s knee placement and applied use of force on his neck caused his death. 

Tobin testified that Floyd died from a low level of oxygen, which he said caused damage to his brain and led to a reaction that caused his heart to stop.

Chauvin’s knee placed on the man's neck was among a “series of forces” Tobin said contributed to Floyd’s death.

According to pool reports, jurors paid close attention to the doctor throughout the hours-long testimony and were seen taking notes and listening closely to the expert as he spoke.

The trial on Thursday also featured testimony from a forensic toxicologist who reviewed Floyd’s blood and urine, as well as an emergency medicine physician that specializes in forensic medicine.

The testimonies provided more insight into the amount of drugs found in Floyd’s system after his death and further opinion from experts on how Floyd died. 

Floyd's attempts at breathing before loss of consciousness

Tobin offered a detailed account of Floyd’s breathing during the arrest, noting body movements he made underneath Chauvin that the doctor said were an attempt to breathe. 

Tobin noted how a photo of the arrest showed Floyd appearing to push his knuckles and fingers against the ground and the tire of a nearby police vehicle as he was pinned to the street.

“To most people, this doesn't look terribly significant. But to a physiologist, this is extraordinarily significant,” Tobin said. 

“This tells you that he has used up his resources and he's now literally trying to breathe with his fingers and knuckles,” the doctor testified. “It's a very poor way of breathing. But it's what you have to do when everything else is failing,” he said.

Tobin also testified that in another photo captured from the arrest it appeared Chauvin had half of his body weight on Floyd's neck while restraining him. In the photo, the tip of Chauvin’s foot could also be seen slightly off the ground as he knelt on Floyd, who was still pinned to the street.

Tobin estimated the action put 91.5 pounds “down directly” on Floyd’s neck. “Everything is directed down on his knee,” he said.

While Tobin said during cross-examination that he did not personally weigh Chauvin or his equipment to arrive at the estimate, the doctor said he "took the measurements that are reported."

He also addressed the role that fentanyl had on Floyd’s breathing during the arrest. 

“If fentanyl is having an effect and is causing depression of the respiratory centers, the centers that control breathing, that's going to result in a decrease in the respiratory rate, and it's shown that with fentanyl you expect a 40 percent reduction in the respiratory rate,” Tobin said. 

“So, with fentanyl, his respiratory rate should be down at around 10, instead of that, it’s right in the middle of normal at 22,” Tobin said, adding that the evidence proves “there isn't fentanyl on board that is affecting his respiratory centers.”

The prosecution also sought to dispel claims that Floyd saying, “I can’t breathe,” during his arrest proved that he could still breathe because he could talk.

Tobin said such claims are “misleading” and offer an “enormous false sense of security.”

“Certainly, at the moment that you are speaking, you are breathing. But it doesn't tell you that you're going to be breathing five seconds later,” he said.

During cross examination later on Thursday, Chauvin defense attorney Eric Nelson raised into question Tobin's calculations from his testimony with prosecution.

"Now in terms of the calculations that you've made. You would agree that your calculations are generally theoretical, correct?" Nelson asked Tobin.

"No, they're not theoretical. I mean they're based on direct measurements. They're based on extensive research," Tobin said. 

Drug levels in Floyd’s body after death

Floyd’s drug use remained a focal point in the second witness's testimony Thursday, which came from Daniel Isenschmid, a forensic toxicologist who analyzed Floyd’s blood and urine. 

Isenschmid said in his testimony that fentanyl and methamphetamine were found in Floyd’s blood, while morphine was detected in his urine. He also testified that suboxone, a prescription medicine that has been used to treat opioid addiction, was found in his blood.

Floyd’s former girlfriend, Courteney Ross, testified during the trial last week that she and Floyd both struggled with opioid abuse, and tried to help each other overcome the addiction.

The prosecution and defense questioned Isenschmid over the amounts of fentanyl and methamphetamine found in Floyd’s system on Thursday.

Isenschmid said Floyd’s body contained an amount of methamphetamine that was “consistent with [a] prescription dose.” 

“Would that be considered a low level of methamphetamine?” a prosecutor asked Isenschmid.

“Yes, very low,” he responded.

Isenschmid also provided further testimony about the fentanyl detected in Floyd’s blood while discussing the ratio of the drug to norfentanyl found in his system.

“So, when the body gradually eliminates fentanyl, it breaks it down from fentanyl to norfentanyl,” Isenschmid said. “That's a gradual process that occurs over time. And it's one of the ways the body eliminates fentanyl.” 

“And you indicated that the amount of norfentanyl found in the hospital blood in this case was 5.6 nanograms per milliliter … what is significant about that amount of norfentanyl?” a prosecutor asked.

Isenschmid said it shows “that some of the fentanyl was metabolized to norfentanyl.”

Isenschmid said it's more often in cases of deaths involving fentanyl that “we frequently see fentanyl with no norfentanyl whatsoever, because after a very acute fentanyl intoxication, the body doesn't have time to break it down.”

The testimony could be helpful for prosecution as it works to dispel arguments by the defense that drug use played a role in Floyd’s death.   

Witnesses addressed Floyd's underlying health issues

At one point in his testimony, Tobin suggested that Floyd’s preexisting health conditions did not influence his death, adding that a “healthy person” would have died under similar conditions. 

When asked by prosecutor Jerry Blackwell if he was aware that Floyd had preexisting health conditions, Tobin answered “yes, I am.” He stated he read about them in records from Hennepin County and saw them mentioned in the autopsy report.

“Do you have an opinion to a reasonable degree of medical certainty as to whether a person who had none of those preexisting health conditions, a healthy person, would have died of the same circumstances as Mr. Floyd?” Blackwell asked.

“Yes, a healthy person subjected to what Mr. Floyd was subjected to would have died as a result of what he was subjected to,” Tobin answered.

Blackwell revisited the topic later in the testimony, asking if “any of those conditions have anything to do with the cause of Mr. Floyd’s death in your professional opinion, whatsoever?”

“None, whatsoever,” Tobin answered.

“And again, what was the cause, such that those conditions don't matter?” Blackwell asked.

“The cause of death is a low level of oxygen that caused the brain damage and caused the heart to stop,” Tobin responded.

During cross-examination of Tobin, Nelson suggested that Floyd’s preexisting health conditions contributed to his death.

Nelson noted that Floyd had “some heart disease” and “between 75 and 90 percent occlusion of his ventricular arteries.”

“And that’s going to affect blood flow in a person, right? It’s going to make the body work a little harder to get the blood through the body,” Nelson asked Tobin.

“No, not really, it’s not going to do that,” Tobin responded.

When asked how it would affect a person’s respiratory system, Tobin laid out two scenarios, before concluding “we don’t see either.”

Experts testify Floyd died while Chauvin's knee was on his neck

At another point in his testimony, Tobin said that Chauvin’s knee was on Floyd’s neck the moment his body’s oxygen level reached zero, adding that the knee remained there for more than three minutes afterward.

Blackwell presented a graphic illustrating the moment Floyd’s oxygen level reached zero.

When asked to explain to the jury what the exhibit was illustrating, Tobin said “We're seeing that the level of oxygen has gone down to zero, that there is at that point, there's not an ounce of oxygen left in his body.”

Blackwell then asked how long Chauvin’s knee remained on Floyd’s neck after his oxygen was depleted. 

“The knee remained on the neck for another three minutes and two seconds after we reach the point where there is not one ounce of oxygen left in the body,” Tobin told Blackwell.

During his testimony, Tobin also walked the jury through slowed-down bystander footage taken at the scene of Floyd’s arrest, which he says captured “the moment the light goes out” of Floyd’s body. At that point in time, Chauvin’s knee remained on Floyd’s neck.

“At the beginning you can see he's conscious. You can see slight flickering. And then it disappears,” Tobin said. 

“So, one second he's alive and one second he's no longer. … You can see his eyes, he's conscious, and then you see that he isn't. That's the moment the life goes out of his body,” he said as footage showed Floyd’s face pressed to the ground.

Bill Smock, an emergency medicine physician who specializes in forensic medicine, also discussed Floyd’s cause of death during his testimony. When asked by Blackwell what he believed was Floyd’s cause of death, he said he died from “positional asphyxia.”

“Mr. Floyd died from positional asphyxia, which is a fancy way of saying he died because he had no oxygen left in his body,” Smock said.

“So what we've been referring to as low oxygen?” Blackwell asked.

“Low oxygen is one way, no oxygen. When the body is deprived of oxygen, in this case, from pressure on his chest and back, he gradually succumbed to lower and lower levels of oxygen until it was gone, and he died,” Smock added.

Later in the testimony, Blackwell asked if Floyd died from anything other than positional asphyxia, including a heart attack, blood clots in his arteries and an arrhythmia, which would cause a sudden death.

“There was absolutely no evidence at autopsy of anything that suggested that Mr. Floyd had a heart attack,” Smock said.

“There's no evidence of a blood clot in any of the arteries, there's no evidence of hemorrhage from a ruptured plaque, and there's no evidence that Mr. Floyd had a heart attack,” Smock said. 

Smock also ruled out excited delirium as a factor in Floyd's death. Smock described this condition as “a physical and psychiatric state where, because of an imbalance in the brain, a patient will exhibit multiple symptoms,” including increased heart rate and respiration, and a “superhuman strength.”

Smock said that Floyd did not exhibit the 10 signs of the condition.

According to a report released by the Brookings Institution last year, the controversial term has been disproportionately used in cases involving Black people and law enforcement encounters.

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