A breathing expert said that George Floyd died of low oxygen, struggling for air under an officer’s knee. A police surgeon emphatically discounted that Floyd suffered a heart attack or had “excited delirium,” and a forensic toxicologist said Floyd’s blood contained only a small amount of methamphetamine.

Thursday’s testimony in the murder trial of former Minneapolis police officer Derek Chauvin spoke to what could be the heart of the case, challenging the defense’s central argument that Floyd died of a combination of heart disease, drugs and high blood pressure. Chauvin’s attorney has suggested Floyd’s already-compromised heart grew overwhelmed by his struggle with Minneapolis police. Andrew Baker, the chief medical examiner in Minnesota’s Hennepin County, is expected to testify Friday.

Here’s what to know:
  • Asked when authorities should have performed CPR on Floyd, police surgeon Bill Smock responded: “Way before it was. As soon as Mr. Floyd is unconscious, he should have been rolled over.”
  • Martin Tobin, a pulmonologist and breathing expert, said a person in good health would have died as a result of the restraint administered by Chauvin. He estimated that Chauvin placed more than 91 pounds on Floyd’s neck.
  • Floyd’s airways were 85 percent restricted, Tobin said, thus making breathing “at some stage unsustainable.”
  • Chauvin attorney Eric J. Nelson again focused on the traces of fentanyl and methamphetamine that were found in Floyd’s body, in an effort to show they were a contributing factor to his restricted breathing.
10:36 p.m.
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Police surgeon emphatically discounts heart attack, ‘excited delirium’

Louisville Metro Police Department surgeon Bill Smock testified that George Floyd died of lack of oxygen that would not be caused by a fentanyl overdose. (The Washington Post)

A police surgeon said Thursday that Floyd died of a lack of oxygen, emphatically denying that there was evidence of a heart attack or a controversial condition called “excited delirium.”

“Mr. Floyd died from positional asphyxia, which is a fancy way of saying he died because he had no oxygen left in his body,” said Bill Smock, an emergency medicine physician and police surgeon for the Louisville Metro Police Department.

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

Chauvin’s defense attorney is trying to show that Floyd died of a combination of intoxication, heart disease and high blood pressure, as adrenaline from his struggle with police “acted to further compromise an already compromised heart.”

Smock, who was compensated for his testimony Thursday, said that Floyd showed clear “air hunger” that would not be caused by a fentanyl overdose. Someone suffering an overdose would not be “alert,” he said.

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,” Smock testified. “That is somebody begging to breathe.”

Smock said he is well acquainted with the signs of excited delirium, a “physical and psychiatric state” in which the patients show a high heart rate, seemingly “superhuman strength,” garbled speech and other symptoms. Floyd did not show those symptoms, he said.

Critics have questioned the use of excited delirium, calling it “pseudoscience” used to protect officers who use excessive force.

Holly Bailey contributed to this report.

10:11 p.m.
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Chauvin’s legal team argues ‘excited delirium’ contributed to his death. But it has no definition.

Chauvin’s defense has attributed Floyd’s death in part to “excited delirium.” But that term has no commonly accepted definition, and many doctors do not believe it’s a legitimate syndrome.

Testifying for the prosecution, Bill Smock, an emergency medicine physician and police surgeon for the Louisville Metro Police Department, acknowledged that although he recognizes it as a valid condition, not all doctors agree. For instance, the American Psychiatric Association and American Medical Association do not recognize it, he testified, because some experts say the term is overly broad and has been used to justify police brutality.

Smock said he didn’t believe Floyd died of excited delirium because he didn’t manifest what Smock identified as the symptoms of the syndrome.

The definition of the term varies widely, according to a 2018 systemic review, which found that among excited-delirium deaths, the victims were predominantly male, with being Black and overweight among other listed risk factors. A more comprehensive study in 2020 found that deaths attributed to excited delirium often involve some sort of restraint used before the death.

Those who doubt its existence cite the instances in which officials blamed excited delirium after police used force on Black men, including Daniel Prude, who died after police in Rochester, N.Y., put a hood over his head, and Elijah McClain, who was put in a stranglehold by officers in Aurora, Colo.

“It draws upon aspects of real medical conditions such as delirium, psychosis, drug intoxication, and sudden cardiac death, but manipulates them to form a broadly-applicable blanket diagnosis that serves the interests of law enforcement and absolves them of accountability,” doctors wrote in a Brookings Institution editorial.

10:02 p.m.
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Floyd should have gotten CPR ‘way before it was’ given, expert says

Bill Smock, an emergency medicine physician and police surgeon, testified that Floyd should have received CPR far sooner than he did.

Asked when CPR should have started, he responded: “Way before it was. As soon as Mr. Floyd is unconscious, he should have been rolled over.”

Analyzing video of Floyd pinned to the ground, Smock also pointed out signs that the man was struggling to get oxygen.

Floyd’s voice grew weaker over time, the witness said. He repeatedly pushed his elbow against the car while on the ground, which Smock called an attempt to lift himself up and create room to breathe.

Smock said one can hear handcuffs shake and also see Floyd’s legs shake while Floyd has an “anoxic seizure” stemming from lack of oxygen to the brain.

Smock also said Floyd’s face had “deep abrasions” from being pressed into the pavement.

9:07 p.m.
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Floyd’s blood had fraction of fentanyl typically found in intoxicated drivers who survived, expert says

Floyd’s blood had a fraction of the fentanyl and methamphetamine levels found on average in the blood of drivers under the influence who did not die, a forensic toxicologist testified Thursday, as the defense seeks to convince jurors that drugs contributed to Floyd’s death. Chauvin’s defense attorney emphasized the limits of that data.

“What we’re really doing is we’re trying to isolate and create some form of a comparison of Mr. Floyd’s fentanyl levels and his norfentayl levels and some sample of population,” said the defense lawyer, Nelson.

“One sample of population we know is alive, right, because they’re driving a car. And the other sample, we have no frame of reference. Did they die from fentanyl overdose or did they die from some other reason? We have no context.”

Daniel Isenschmid, who did lab work for Floyd’s case at the request of the Hennepin County medical examiner, said he tested hospital blood as well as urine. He works at NMS Labs in Pennsylvania.

In terms of the ratio, was Mr. Floyd’s ratio more similar to the driving population where people were alive or more similar to the postmortem population where people were dead?” a prosecutor asked Isenschmid.

”It was more similar to the DUI population," Isenschmid said.

As the body eliminates fentanyl, it breaks the drug down into a chemical compound called norfentanyl, Isenschmid said. Floyd’s blood sample showed that “some of the fentanyl was metabolized,” he said.

When we see very recent deaths with fentanyl, we frequently see fentanyl with no norfentanyl whatsoever,” he said.

Isenschmid said Floyd could have taken fentanyl earlier, allowing it time to break down, then taken the drug again closer to his death.

People can develop a tolerance to opioids, Isenschmid said, meaning it takes more of the drug to produce an effect. Floyd’s girlfriend testified earlier in the trial that they both struggled with opioid addiction.

Nelson pressed Isenschmid on that issue: “Regardless of whether you have a tolerance or a non-tolerance, any single incident could cause an adverse reaction,” he said.

“Well, sure, if you suddenly had a pill that was 10 times the amount of fentanyl than another one,” Isenschmid said.

The level of methamphetamine found in Floyd’s blood (19 nanograms per milliliter) was “low,” Isenschmid said, “approximately the amount that you find in the blood of somebody that was given a single dose of methamphetamine as a prescribed drug."

7:29 p.m.
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Pulmonologist says there was no depression in Floyd’s breathing from fentanyl: ‘Absolutely not’

Martin Tobin, a pulmonologist from Hines, Ill., said on April 8 that George Floyd died of lack of oxygen, which did not result from a fentanyl overdose. (The Washington Post)

Toward the end of his testimony Thursday, pulmonologist Martin Tobin said there were no fentanyl-related signs of depression in Floyd’s breathing that would have contributed to his low level of oxygen while he was restrained by Chauvin.

“Did you see any depression in Mr. Floyd’s ability to breathe whatsoever before he went unconscious?” prosecutors asked.

“Absolutely not,” the breathing expert replied.

In response to the defense arguing that the traces of fentanyl and methamphetamine found in Floyd’s system played a role in his limited breathing, the prosecution laid out that someone suffering from a fentanyl overdose would show a reduction in their ability to breathe.

Chauvin’s defense focused much of its cross-examination of Tobin on the substances.

7:14 p.m.
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Defense again focuses on the traces of fentanyl, methamphetamine in Floyd’s system

During cross-examination of Tobin on Thursday, Nelson returned the focus of the questioning to the traces of fentanyl and methamphetamine in Floyd’s system at the time of his death.

Chauvin’s defense this week has questioned witnesses on two white pills found in the console of Floyd’s car that laboratory testing later confirmed to be fentanyl and methamphetamine, and two packets of Suboxone, an opioid addiction medication.

The defense mentioned the words “fentanyl” and “methamphetamine” at least 20 times in a matter of minutes.

When asked whether the substances would affect a person’s respiratory center, Tobin said that was not the case.

“Fentanyl is not going to have an effect on respiration by some other mechanism,” the breathing expert responded.

At one point of cross-examination, Tobin did not understand what Nelson was trying to ask him.

“You’re trying to really confuse me, Mr. Nelson,” Tobin said with a smile.

In one of the lighter moments of the week, Nelson apologized, saying, “I think I can actually say it’s been a long week now.”

7:00 p.m.
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Tobin disagrees with Chauvin’s defense that he boiled down the case to ‘a nanosecond’

After the lunch break, Nelson began his cross-examination of Tobin by saying the breathing expert had summed up the restraint on Floyd in his report down to “a nanosecond.”

“You’ve taken this case, and you’ve literally boiled it down into a nanosecond,” Nelson said.

Tobin disagreed with Nelson, saying he spelled out the chronology in his report to prosecutors of the time when Chauvin had his knee on Floyd’s neck and the time that followed.

Tobin agreed with Nelson’s statement that no one was at the scene to measure the amount of force Chauvin had on Floyd’s neck and back, but said the data was “culpable” and calculable. Tobin rejected Nelson’s argument that assumptions went into the calculations of how much weight was on Floyd.

Earlier in the day, Tobin estimated Chauvin had more than 91 pounds just on Floyd’s neck.

5:50 p.m.
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Minneapolis braces for possible unrest after Chauvin verdict

MINNEAPOLIS — As Chauvin’s trial proceeds at a faster than expected rate, city officials are bracing for the possibility of unrest after the verdict.

At a Thursday news conference announcing a new plan for community patrols, Minneapolis Mayor Jacob Frey (D) said the city will partner with neighborhood organizations to conduct street patrols throughout the city starting next week.

“We know that tensions build, especially as we head into deliberations and the verdict,” Frey said. “There’s been an enormous amount of work that our communities across our city, across the region that have been working on together.”

During the unrest that followed Floyd’s death, neighborhood patrols, many of them armed, sprang up across Minneapolis, though their presence has since dwindled. The plan announced Thursday represents the first time the city has become directly involved in the effort.

Sasha Cotton, director of the city’s Office of Violence Prevention, listed seven organizations the city funded to conduct patrols, and explained that they will help with de-escalation, conflict resolution and community engagement. She added that the patrols were meant to complement, not replace, the work of the police department.

“We believe that these groups are going to be successful because they are anchored in community,” she said.

5:30 p.m.
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Tobin rebuts key defense argument that heart condition, not asphyxiation, contributed to Floyd’s death

In testimony that could prove difficult for the defense, Tobin undermined key arguments that defense lawyers are relying on to make their case: that Floyd died due to contributing factors such as the drug fentanyl or a heart condition and not asphyxiation from the pressure of Chauvin’s knee on his neck.

Tobin’s medical opinion Thursday was that Floyd had been breathing normally and that fentanyl was not a factor in slowing his breaths — a slowdown that did not begin until Floyd was forced to the ground and pressure applied to his back and neck, the breathing expert said.

The level of carbon dioxide in the blood, expressed in millimeters of mercury, is normally 35 to 45 mm for a person breathing normally, Tobin said. Floyd’s level was at 89 mm when he was taken to the emergency room. Calculations of Floyd’s carbon dioxide levels provide evidence that “fentanyl is not causing the depression of his respiration,” Tobin said.

“The increase in his carbon dioxide that is found in the emergency room is solely explained by what you expect to happen in somebody who doesn’t have any ventilation given to him for nine minutes and 50 seconds,” Tobin said.

Tobin further noted that if someone had underlying heart disease that caused shortness of breath or difficulty breathing, it would manifest as higher respiratory rates. Floyd’s, he testified, were normal.

5:14 p.m.
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Breathing expert reviews ‘the moment that life goes out’ of Floyd: ‘One second he’s alive, one second he’s no longer’

While re-watching the final moments of Floyd’s life, Tobin noted the moment when “life goes out of his body” due to the restraint from police.

“You can see he’s conscious, you can see slight flickering and then it disappears. One second he’s alive, one second he’s no longer,” Tobin testified. He added, “That’s the moment that life goes out of his body.”

As the body-camera footage replayed in the courtroom, Tobin pointed out how Floyd made “repeated struggling movements” in an attempt for more oxygen.

During his testimony, Tobin has emphasized that Chauvin’s restraint on his neck and back limited Floyd’s breathing to the point that Floyd died from “a low level of oxygen” caused by the pressure by police.

4:56 p.m.
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Tobin says a person in good health would have died from the restraint placed on Floyd

During his testimony Thursday, Tobin confirmed to prosecutors that a person of good health would have also died from the restraint that Chauvin placed on Floyd last May.

“A healthy person subjected to what Mr. Floyd was subjected to would have died as a result of what he was subjected,” said Tobin, an expert on breathing.

When asked by prosecutors about the saying floated by Chauvin’s defense — “If you can speak, you can breathe” — Tobin said the mantra gives “an enormous false sense of security.” He added that when Floyd said, “I can’t breathe,” even though it was clear that he still had oxygen in the brain at that moment, “it doesn’t tell you that you’re going to be breathing five seconds later.”

“Very shortly after that, we’re going to see that he has a major loss of oxygen in the way that he moves his leg,” Tobin said of the footage of Floyd being detained.

Tobin said the line “If you can speak, you can breathe” was a “very, very dangerous mantra.”

4:55 p.m.
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‘Not an ounce of oxygen left in his body’: Expert witness details the timeline of Floyd’s dwindling consciousness and air supply

After Chauvin pinned his knee to Floyd’s neck for more than six minutes, Floyd had no more oxygen in his body, Tobin testified.

We can tell it precisely in terms of where the absence of consciousness occurs,” he said Thursday.

Floyd’s oxygen levels hit zero at 20:25:41, Tobin said, citing the time stamp from the body-camera footage submitted into evidence.

“At that point, there’s not an ounce of oxygen left in his body,” Tobin said.

Chauvin placed his knee on Floyd’s neck at around 20:19:21, about 6 minutes 20 seconds before Floyd had no more air. Chauvin continued to hold his knee on Floyd’s neck for about three more minutes — longer than originally known.

Tobin said that as an ICU doctor, he is always looking at a patient’s facial features to tell how conscious they may be.

“We can tell by how you flick your eyes or how you move the muscles in your face and that you’ll be able to tell is the person conscious or unconscious,” Tobin said. “It’s a very important sign in patients as we’re taking care to be able to monitor that in the primary way we monitor it is by inspecting it.”

People lose consciousness when the level of oxygen in the blood is at 36 — a number Tobin said was “associated with very hard data.” A normal level of oxygen for a man Floyd’s age was 89.

4:36 p.m.
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Chauvin placing knee on Floyd’s back also ‘markedly impaired’ ability to move, Tobin says

When asked about how Chauvin’s placing of his knee on Floyd’s back might have affected him, Tobin said the move from the officer further impaired Floyd’s ability to breathe.

“Whether it’s on the back around in against the side and down on the arm, all of these are just going to markedly impair your ability to be able to move your chest,” he said. “You just can’t do it. It’s all rammed in.”

Tobin stressed that being pressed up against the pavement played a “huge” role in the restriction of Floyd’s oxygen levels.

The defense team has argued the officer had his knee on the shoulder and back of Floyd, not his neck. Tobin testified earlier that Floyd died from a “low level of oxygen” caused by Chauvin’s knee on his neck.

4:00 p.m.
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Floyd’s airways were 85 percent restricted, making breathing ‘at some stage unsustainable,’ expert says

Martin Tobin, a pulmonologist from Hines, Ill., said on April 8 that George Floyd died of lack of oxygen, which did not result from a fentanyl overdose. (The Washington Post)

Tobin used several visual aids Thursday 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 percent narrowing of their airways without dramatically increasing the effort required to draw a breath; he described 60 percent 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 percent airway narrowing diverged only gradually over time. But with 85 percent 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 percent 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.”