George Floyd Showed Signs of Brain Injury 4 Minutes Before Officer Relented, Expert Says

Thursday’s testimony included medical witnesses who helped underscore prosecution claims that Mr. Floyd died from being held down by Derek Chauvin.

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The Hennepin County Government Center, where Derek Chauvin is on trial.Credit...Aaron Nesheim for The New York Times

Follow our live updates the day after the Derek Chauvin guilty verdict.

Marie Fazio
April 12, 2021, 10:51 a.m. ET

Dr. Jonathan Rich, cardiologist, testifies for the state.

The state called Dr. Jonathan Rich, a cardiologist from Chicago, to take the stand on Friday. He was expected to speak about George Floyd’s heart condition, which the defense has argued was a contributing factor in his death.

Dr. Rich is an associate professor at Feinberg School of Medicine, Northwestern University’s medical school. He attended Albert Einstein College of Medicine in New York and completed fellowships in cardiology and advanced heart failure and transplant at the University of Chicago Hospital’s Pritzker School of Medicine.

Dr. Rich holds certifications in internal medicine, cardiovascular disease and advanced heart failure and transplant cardiology from the American Board of Internal Medicine.

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The New York Times
April 8, 2021, 7:00 p.m. ET

A look at the security surrounding the courthouse.

Security is tight around the Hennepin County Government Center, where the trial is taking place.

Will Wright
April 8, 2021, 6:34 p.m. ET

Takeaways from Day 9 of the Derek Chauvin trial.

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Pulmonologist Details How George Floyd Lost Consciousness During Arrest

A veteran pulmonologist Dr. Martin J. Tobin testified that George Floyd’s death was caused in part by Derek Chauvin’s knees pressing against his neck and back, making it impossible for him to breathe.

“The work that Mr. Floyd has to perform becomes huge because he has to, 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, with the handcuffed arm there, pushing it in, into his chest. So he has to make all these efforts to try and breathe against that. At the beginning, you can see he’s conscious. You can see slight flickering. And then, it disappears. So one second, he’s alive, and one second he’s no longer.” “Is that the flicking?” “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.”

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A veteran pulmonologist Dr. Martin J. Tobin testified that George Floyd’s death was caused in part by Derek Chauvin’s knees pressing against his neck and back, making it impossible for him to breathe.CreditCredit...Still image, via Court TV

The ninth day of the Derek Chauvin trial brought key medical witnesses to the stand, two of whom said that George Floyd died from a lack of oxygen and that drugs appeared to play no role in his death.

The defense for Mr. Chauvin, who is charged with murdering Mr. Floyd, has tried to tie Mr. Floyd’s death to the fentanyl and methamphetamine that were found in his system. But on Thursday, Dr. Martin J. Tobin, a pulmonologist and critical care physician from the Chicago area, said that any normal person could have died from being pinned under Mr. Chauvin’s knee for nine and a half minutes.

Dr. Tobin’s testimony gave a moment-by-moment breakdown of the arrest of Mr. Floyd, identifying what he believed to be “the moment the life goes out of his body.” Here are the highlights from Day 9 of the trial.

  • Dr. Tobin’s testimony was extremely detailed. He counted Mr. Floyd’s breaths and zoomed in on a still image of the arrest to pinpoint the moment that Mr. Chauvin’s boot left the ground, putting additional pressure on Mr. Floyd. He even identified the few seconds where Mr. Floyd slipped from consciousness. Despite its nuance, the overarching message was clear: That Mr. Floyd died from the pressure applied by Mr. Chauvin. He testified that Mr. Floyd would have had to fight for every breath, but that, ultimately, “A healthy person subjected to what Mr. Floyd was subjected to would have died.”

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Pulmonologist Testifies Fentanyl Did Not Impact George Floyd’s Breathing

Dr. Martin Tobin, an expert pulmonologist, said that George Floyd’s breathing rate in the moments before he died indicated that the fentanyl in his system was not having any effect on his breathing, despite the argument by Derek Chauvin’s legal team.

“One, two, three, four … … five, six, seven.” “So that was roughly a 17-second clip?” “Right.” “Is that number, the respiratory rate of 22, significant to this case?” “It’s extremely significant.” “Why is that?” “Because one of the things in this case is the question of fentanyl. And 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. So with fentanyl, his respiratory rate should be down at around 10. Instead of that, it’s right in the middle, at normal, at 22.”

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Dr. Martin Tobin, an expert pulmonologist, said that George Floyd’s breathing rate in the moments before he died indicated that the fentanyl in his system was not having any effect on his breathing, despite the argument by Derek Chauvin’s legal team.CreditCredit...Still image, via Court TV
  • In addition to supporting the primary claim of the prosecution — that Mr. Floyd died from Mr. Chauvin’s restraint — Dr. Tobin also pushed back on the arguments of Eric J. Nelson, the lawyer leading Mr. Chauvin’s defense. Though Mr. Nelson has suggested that drug use played a role in the death of Mr. Floyd, Dr. Tobin said he saw no evidence of an overdose from the footage of the arrest. Mr. Floyd appeared to be breathing at a normal rate before he became unconscious, Dr. Tobin said.

    Had he been overdosing on fentanyl, his rate of breathing would have slowed. In addition, Dr. Tobin pushed back on the idea that because Mr. Floyd was speaking, he must have been getting enough oxygen. During the arrest, a police officer told Mr. Floyd that he seemed to have enough oxygen because he was able to tell officers that he couldn’t breathe. Dr. Tobin said that a person might be taking in enough oxygen to speak, but not enough to survive. They can be alive and talking one moment, and dead just seconds later, he said.

  • Dr. Bill Smock, the surgeon for the Louisville Metropolitan Police Department, also testified, saying he saw no evidence of an overdose. “Mr. Floyd died from positional asphyxia, which is a fancy way of saying he died because he had no oxygen left in his body,” he said. Mr. Floyd was alert and had a keen sense of space, which both indicate that he was not overdosing, Dr. Smock said. In addition, Mr. Floyd was begging for air — Dr. Smock called it “air hunger” — and said a person overdosing on fentanyl would typically have the opposite response, more like someone who falls asleep or slips into a coma. Asked whether Mr. Floyd was suffering from a fentanyl overdose, Dr. Smock said, “That is not a fentanyl overdose. That is somebody begging to breathe.” He also criticized the officers for not beginning C.P.R. as soon as they failed to find a pulse.

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Toxicologist Challenges Claim of Floyd Overdose

Daniel Isenschmid, a forensic toxicologist, testified on Thursday at the trial of Derek Chauvin that the level of norfentanyl in George Floyd’s system was not consistent with a typical fentanyl overdose.

“Can fentanyl levels vary widely, depending on an individual?” “Yes, they can.” “And why would that be?” “Because of tolerance.” “And could you just explain how an individual’s drug tolerance might affect the impact a particular drug like an opioid or fentanyl might have on them?” “So, I mean, if a person becomes tolerant to a drug, you need to have more and more of the drug to get the desired effect. So with chronic use, to get the same feeling that you would at a given concentration of fentanyl, you need to take more to get that effect.” “And so if someone is regularly using opiates or opioids would that individual, then develop a tolerance to an opioid like fentanyl?” “Yes.” “And you indicated that the amount of norfentanyl found in this, the hospital blood in this case was 5.6 nanograms per milliliters. Is that right?” “Yes.” “And what is significant about that amount of norfentanyl?” “Well, it shows that some of the fentanyl was metabolized to norfentanyl. It also could mean there was pre-existing norfentanyl with additional fentanyl given on top of that. But basically shows that when we see, when we see very recent deaths with fentanyl, 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.” “And you describe when you see a fentanyl overdose, typically, you may not see any norfentanyl or low levels of norfentanyl.” “Correct.”

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Daniel Isenschmid, a forensic toxicologist, testified on Thursday at the trial of Derek Chauvin that the level of norfentanyl in George Floyd’s system was not consistent with a typical fentanyl overdose.CreditCredit...Still image, via Court TV
  • A forensic toxicologist who testified on the issue of drug use provided the jury with data about fentanyl and methamphetamine, the two substances found in Mr. Floyd’s system after his death. Daniel Isenschmid, who works at N.M.S. Labs in Pennsylvania, said that the drug profile found in Mr. Floyd’s system appeared to be more consistent with patients who were still alive, rather than those found in autopsies. The lab that created a toxicology report of Mr. Floyd found 11 nanograms per millileter of fentanyl and 19 nanograms per millileter of methamphetamine in the blood that was tested, he said.

  • Mr. Floyd’s condition in the moments before his arrest do not line up with the symptoms of “excited delirium,” a term used to describe someone who has become aggressive or distressed from a mental illness or drug use, Dr. Smock said. The term has been disproportionately applied to Black people and has been used by law enforcement to justify police brutality, according to a report by the Brookings Institution. During opening statements of the trial, Mr. Chauvin’s defense briefly mentioned excited delirium and said “the adrenaline flowing through his body” might have contributed to Mr. Floyd’s death.

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Timothy Arango
April 8, 2021, 6:18 p.m. ET

Reporting from Minneapolis

A long day of medical testimony just ended for the evening. Back tomorrow at 9:15 Central Time, with more medical experts called by the state. This will likely include the testimony of the Hennepin County medical examiner who performed the autopsy on George Floyd.

John Eligon
April 8, 2021, 6:07 p.m. ET

Reporting from Kansas City

Derek Chauvin’s lawyer asks Dr. Bill Smock if, when people stop taking drugs for some time, they lose their tolerance. Perhaps he’s trying to use the testimony of George Floyd’s girlfriend against him. She testified last week that Floyd had stopped using opioids at some point early last year but then she believed that he started using again.

The New York Times
April 8, 2021, 5:59 p.m. ET

In their own words: ‘That is not a fentanyl overdose. That is somebody begging to breathe.’

Dr. Bill Smock, an emergency medicine physician who trains police officers, testified Thursday afternoon and discredited several theories about George Floyd’s cause of death, including defense claims that Mr. Floyd overdosed on fentanyl:

I mean, when you watch those videos — and we go through them — what is his respiration? He’s breathing. 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. That is somebody begging to breathe.

Dr. Smock added that fentanyl overdose victims will often be sleepy and disoriented.

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Timothy Arango
April 8, 2021, 5:57 p.m. ET

Reporting from Minneapolis

The prosecution’s witnesses today made clear how much distance the state is trying to put between its case and the findings of Dr. Andrew Baker, the Hennepin County medical examiner who conducted the autopsy of George Floyd. Baker noted no bruising to suggest asphyxia – and experts today said it's common for people who die in that manner to show no signs of bruising. Baker said Floyd had an overdose-level amount of fentanyl in his system, and experts today refuted that. Will be interesting to see how the state handles Baker tomorrow.

Timothy Arango
April 8, 2021, 5:58 p.m. ET

Reporting from Minneapolis

Baker notably said he didn’t watch the video before he conducted his autopsy. Experts today said the video was key to making their determinations about cause of death.

John Eligon
April 8, 2021, 5:49 p.m. ET

Reporting from Kansas City

On cross-examination, Derek Chauvin’s defense lawyer is continuing to double down on his efforts to portray this case as more complicated than prosecutors are suggesting. He suggests that the effect of a combination of meth and fentanyl would be different from the effect of fentanyl alone.

John Eligon
April 8, 2021, 5:51 p.m. ET

Reporting from Kansas City

The lawyer also raises the point that George Floyd was saying he couldn’t breathe before the officers took him down, suggesting that there was something else at play -- perhaps drugs -- other than the actions of Chauvin and the other police officers.

John Eligon
April 8, 2021, 5:42 p.m. ET

Reporting from Kansas City

Dr. Bill Smock is reinforcing what the prosecution’s previous pulmonologist expert said: that George Floyd was trying to turn and fidget so he could try to release some pressure on him so he could take breaths. Seems like prosecutors are trying to reinforce the medical expert from earlier with a medical expert who specifically trains police officers.

John Eligon
April 8, 2021, 5:44 p.m. ET

Reporting from Kansas City

The prosecution’s theory of George Floyd’s death is becoming clearer. They seem to be saying that the footage of him fading in energy is because his air is being restricted because of Derek Chauvin’s actions. If it were a drug overdose, that fading would have started even before the officers took Floyd to the ground. Feels like every time the prosecution goes back to the video, the emotion of that plays in its favor.

Nicholas Bogel-BurroughsMarie Fazio
April 8, 2021, 5:37 p.m. ET

A toxicologist’s testimony challenged claims by Derek Chauvin’s lawyer that George Floyd overdosed on fentanyl.

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Toxicologist Challenges Claim of Floyd Overdose

Daniel Isenschmid, a forensic toxicologist, testified on Thursday at the trial of Derek Chauvin that the level of norfentanyl in George Floyd’s system was not consistent with a typical fentanyl overdose.

“Can fentanyl levels vary widely, depending on an individual?” “Yes, they can.” “And why would that be?” “Because of tolerance.” “And could you just explain how an individual’s drug tolerance might affect the impact a particular drug like an opioid or fentanyl might have on them?” “So, I mean, if a person becomes tolerant to a drug, you need to have more and more of the drug to get the desired effect. So with chronic use, to get the same feeling that you would at a given concentration of fentanyl, you need to take more to get that effect.” “And so if someone is regularly using opiates or opioids would that individual, then develop a tolerance to an opioid like fentanyl?” “Yes.” “And you indicated that the amount of norfentanyl found in this, the hospital blood in this case was 5.6 nanograms per milliliters. Is that right?” “Yes.” “And what is significant about that amount of norfentanyl?” “Well, it shows that some of the fentanyl was metabolized to norfentanyl. It also could mean there was pre-existing norfentanyl with additional fentanyl given on top of that. But basically shows that when we see, when we see very recent deaths with fentanyl, 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.” “And you describe when you see a fentanyl overdose, typically, you may not see any norfentanyl or low levels of norfentanyl.” “Correct.”

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Daniel Isenschmid, a forensic toxicologist, testified on Thursday at the trial of Derek Chauvin that the level of norfentanyl in George Floyd’s system was not consistent with a typical fentanyl overdose.CreditCredit...Still image, via Court TV

A forensic toxicologist at the laboratory that tested George Floyd’s blood said it was common for intoxicated driving suspects who used fentanyl to have higher levels of the drug in their systems than Mr. Floyd did when he died. Prosecutors hoped his testimony would strike a blow to the argument by Derek Chauvin’s lawyer that Mr. Floyd’s death may have been an overdose.

The toxicologist, Dr. Daniel Isenschmid, works at N.M.S. Labs in Pennsylvania and testified on the ninth day of the trial against Mr. Chauvin, who has been charged with murder in Mr. Floyd’s death. Of more than 2,300 blood samples from intoxicated drivers that N.M.S. Labs tested last year — all of which were in cases where the driver survived and tested positive for fentanyl — about a quarter of the people had fentanyl levels that were the same or higher than Mr. Floyd’s, Dr. Isenschmid said.

Prosecutors had called him to the stand to rebut the argument from Mr. Chauvin’s lawyer that fentanyl, a powerful opioid, had caused Mr. Floyd’s overdose. Prosecutors say Mr. Chauvin is responsible for Mr. Floyd’s death, and earlier on Thursday, a lung doctor testified that Mr. Chauvin’s knees on Mr. Floyd’s neck and back were significant factors in his death.

Dr. Isenschmid said that last year, in cases where N.M.S. Labs tested blood from a person who died and who had taken fentanyl, the average amount that scientists found was 16.8 nanograms per milliliter, about 50 percent higher than the amount found in Mr. Floyd’s blood. But Mr. Chauvin’s lawyer, Eric J. Nelson, noted that average was among people who died of any cause and had fentanyl in their system, not just overdoses. And, he pointed out, the median level of fentanyl among that group was slightly below Mr. Floyd’s.

The testimony from Dr. Isenschmid, who previously worked as the chief toxicologist at the Wayne County medical examiner’s office in Detroit, was some of the most technical yet, but jurors appeared attentive, according to a reporter in the courtroom.

He said that as a person’s body processes fentanyl, it is turned into norfentanyl, and that Mr. Floyd had a relatively high proportion of norfentanyl, indicating that his body had already processed a substantial portion of fentanyl. That bolstered prosecutors’ argument that Mr. Floyd had not overdosed; fentanyl overdoses often occur shortly after the drugs are taken, before a person’s body can break down much of the drug.

But Dr. Isenschmid conceded, in response to Mr. Nelson, that it was also possible that Mr. Floyd had taken and processed fentanyl earlier in the day and then taken more in the moments before or during the arrest. The toxicology results, Dr. Isenschmid said, do not indicate when a specific amount of fentanyl was taken.

Mr. Nelson has pointed out that pills that had Mr. Floyd’s D.N.A. on them and may have been partially ingested were found in the back of the police car in which Mr. Floyd was briefly placed.

Still, Dr. Isenschmid said the same amount of fentanyl can have very different effects in a new user as opposed to someone who is addicted to the drug. Mr. Floyd’s girlfriend has said she and Mr. Floyd both struggled to stop using opioids.

“If a person becomes tolerant to a drug, they require more and more to get the desired effect,” Dr. Isenschmid said.

Methamphetamine was also found in Mr. Floyd’s system, though Dr. Isenschmid said the levels were so low that it likely had no intoxicating effect.

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John Eligon
April 8, 2021, 5:28 p.m. ET

Reporting from Kansas City

Dr. Bill Smock is differentiating between fentanyl overdose and intoxication. He said an overdose makes you sleepy and slows your breathing, while intoxication makes you high. Smock is basically saying what prosecutors said in their openings, that George Floyd would have had a much more depressed disposition if he were dying of an overdose.

John Eligon
April 8, 2021, 5:29 p.m. ET

Reporting from Kansas City

Smock said: “He’s breathing. 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. That is somebody begging to breathe.”

Timothy Arango
April 8, 2021, 5:20 p.m. ET

Reporting from Minneapolis

Dr. Bill Smock is talking about “excited delirium,” a controversial medical concept defined as extreme agitation and super-human strength, often induced by drugs. It has been used in the past to absolve the police of blame when someone dies in their custody. In this case Smock is going through the symptoms of excited delirium and saying George Floyd did not exhibit them. Important to note that much of the medical establishment does not accept the concept of excited delirium.

Timothy Arango
April 8, 2021, 5:12 p.m. ET

Reporting from Minneapolis

The prosecution is taking Dr. Bill Smock deeper into the tolerance issue, clearly a matter the state wants the jury to keep close when they start deliberating. He uses a drinking analogy – saying a “naïve” drinker might feel buzzed off one beer, while an alcoholic would need many drinks to feel the effects.

John Eligon
April 8, 2021, 5:11 p.m. ET

Reporting from Kansas City

Dr. Bill Smock gives his opinion on the cause of George Floyd’s death: “Mr. Floyd died from positional asphyxia, which is a fancy way of saying he died because he had no oxygen left in his body.”

John Eligon
April 8, 2021, 5:15 p.m. ET

Reporting from Kansas City

He says that he believes “excited delirium” is real, but he does not think it played a role in George Floyd’s death. The defense has suggested excited delirium, which Dr. Smock acknowledged was a controversial diagnosis in which someone dies from a psychiatric and physical imbalance. He says Floyd did not have the symptoms of excited delirium.

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John Eligon
April 8, 2021, 5:07 p.m. ET

Reporting from Kansas City

Interestingly enough, Dr. Bill Smock is the surgeon for the Louisville Metropolitan Police Department. That’s the department that was under fire last year for the killing of Breonna Taylor during a raid.

John Eligon
April 8, 2021, 4:58 p.m. ET

Reporting from Kansas City

Up now is Dr. Bill Smock, an emergency medicine physician specializing in forensic medicine.

Andrés R. Martínez
April 8, 2021, 4:58 p.m. ET

Kentucky police surgeon to testify about how police are trained to use force.

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Police Surgeon Says George Floyd Died of Asphyxia

Dr. Bill Smock, a surgeon for the Louisville Metropolitan Police Department, testified on Thursday that he had found no evidence to support claims that George Floyd died of an overdose.

“Mr. Floyd died from positional asphyxia, which is a fancy way of saying he died because he had no oxygen left in his body. When the body is deprived of oxygen — and in this case, from his chest, pressure on his chest and back — he gradually succumbed to lower and lower levels of oxygen until it was gone. And he died.” “Have you ever encountered a situation of a fentanyl overdose where a person was in the overdose displaying air hunger and essentially crying out for their life or crying out in pain?” “No, sir.” “Based on your experience in training police officers and your experience accompanying police officers to various arrest locations, you have observed police officers use a prone handcuffing technique.” “Yes, I have, for short periods of time, sir.” “And you’ve observed them place their knee in the posterior of the base of the neck, right?” “Yes, again, for short periods of times.”

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Dr. Bill Smock, a surgeon for the Louisville Metropolitan Police Department, testified on Thursday that he had found no evidence to support claims that George Floyd died of an overdose.

The prosecution in Derek Chauvin’s trial on Thursday called Dr. William S. Smock, a Kentucky surgeon who trains officers about the dangers of using pressure on a suspect’s back and neck and how it can lead to death from asphyxia.

Dr. Smock is the police surgeon for the Louisville Metro Police Department and leads its Clinical Forensic Medicine Program. He’s often called to testify in cases in Kentucky regarding causes of death.

He obtained his medical degree from the University of Louisville School of Medicine in 1990 and was licensed as a doctor in 1991, according to the Kentucky Board of Medical Licensure.

Dr. Smock has particular expertise in the medical impact of strangulation. In response to the prosecution’s questions, he also described the symptoms of fentanyl overdoses and testified that, based on Mr. Floyd’s behavior and appearance in the videos of his arrest, he was not experiencing an overdose.

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John Eligon
April 8, 2021, 4:57 p.m. ET

Reporting from Kansas City

Dr. Daniel Isenschmid finishes his testimony with the defense arguing essentially that his data was not sufficient to conclude that the amount of drugs in George Floyd’s system was not significant.

John Eligon
April 8, 2021, 4:52 p.m. ET

Reporting from Kansas City

Derek Chauvin’s defense lawyer just finished up his cross-examination with questioning about various combinations of drugs.

John Eligon
April 8, 2021, 4:26 p.m. ET

Reporting from Kansas City

The court is taking its afternoon break, but Derek Chauvin’s lawyer has raised a concern that prosecutors gave him an updated version of documents that was not clear to him. The judge said he did not believe there was anything nefarious at play.

Timothy Arango
April 8, 2021, 4:09 p.m. ET

Reporting from Minneapolis

The upshot of the state’s examination of Dr. Daniel Isenschmid was to show that George Floyd’s levels of fentanyl and meth were much lower than many DUI cases he had worked on in which the suspect lived.

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Nicholas Bogel-Burroughs
April 8, 2021, 3:51 p.m. ET

Reporting from Minneapolis

In his cross-examination, Derek Chauvin’s lawyer contested a lung doctor’s testimony and focused on fentanyl.

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Eric J. Nelson, the lawyer for Derek Chauvin, argued on Thursday that George Floyd could have died from an overdose.Credit...Still image, via Court TV

Derek Chauvin’s lawyer pushed back against a lung doctor’s testimony on Thursday that Mr. Chauvin’s knee had been a cause of George Floyd’s death, suggesting during his cross-examination that Mr. Floyd’s death may have been an overdose.

The argument from Mr. Chauvin’s lawyer, Eric J. Nelson, came after more than two hours of testimony from Dr. Martin J. Tobin, a pulmonologist and critical care doctor, in which Dr. Tobin said Mr. Chauvin had been a significant cause in Mr. Floyd’s death. Dr. Tobin said that Mr. Floyd’s breathing rate, in the moments before he died, indicated that the fentanyl in his system was not having any effect on his breathing.

Fentanyl and methamphetamine were found in Mr. Floyd’s system, and the possibility that they caused his death is a crucial argument for Mr. Chauvin’s defense as the trial enters a phase in which medical testimony is front and center.

Mr. Nelson suggested on Thursday that Mr. Floyd could have died of a fentanyl overdose if he had taken the drug in the moments before police officers pushed him to the ground. Dr. Tobin said that, unlike someone who died of a fentanyl overdose, Mr. Floyd had never gone into a coma. Mr. Nelson also sought to portray the medical care that Mr. Floyd received from paramedics as lacking; it took them nine minutes to insert a tube down Mr. Floyd’s throat after they arrived on scene, he said, but the nearest hospital was a five-minute drive away.

Mr. Nelson also noted that even doctors sometimes have trouble understanding that a patient who can talk is having trouble breathing. Mr. Floyd told police officers that he could not breathe, and in response, one officer told him that it takes oxygen to talk, implying that he must be able to breathe, something medical experts have said is false or misleading.

Dr. Tobin, who works in Chicago at Edward Hines Jr. Veterans Affairs Hospital and at Loyola University’s medical school, was called as an expert by prosecutors. He had testified on Thursday morning that Mr. Floyd’s death was a result of a lack of oxygen and that Mr. Floyd had showed signs of a brain injury about four minutes before Mr. Chauvin lifted his knee from his neck. He said that in addition to the pressure from Mr. Chauvin’s knees, the oxygen depletion was also caused by Mr. Floyd’s hands being cuffed behind him and his body being prone against the pavement.

Mr. Nelson is expected to call his own medical experts later in the trial.

Timothy Arango
April 8, 2021, 3:42 p.m. ET

Reporting from Minneapolis

In an effort to bolster the testimony last week from George Floyd’s girlfriend that he had a high tolerance for fentanyl, the prosecution asks Dr. Daniel Isenschmid to describe how a high tolerance impacts the effects of the drug on someone. This is a continued attack on the defense’s drug overdose theory.

John Eligon
April 8, 2021, 3:41 p.m. ET

Reporting from Kansas City

The prosecution is continuing to attack the defense assertion that George Floyd died of a drug overdose. Dr. Daniel Isenschmid testified that the presence of a certain type of fentanyl that Floyd had in his system suggests that there was not an overdose because that type is not typically found in fatal overdose victims.

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John Eligon
April 8, 2021, 3:36 p.m. ET

Reporting from Kansas City

Dr. Daniel Isenschmid testified that the amount of methamphetamine found in George Floyd was consistent with a dose of prescription meth. He called it a low amount. The defense has argued that Floyd died in part of a drug overdose.

John Eligon
April 8, 2021, 3:30 p.m. ET

Reporting from Kansas City

Now testifying is Dr. Daniel Isenschmid, a forensic toxicologist. He is a former medical examiner, and we’ll likely hear more from him about the causes of George Floyd’s death.

Marie Fazio
April 8, 2021, 3:29 p.m. ET

Dr. Daniel Isenschmid, who performed the toxicology tests for an autopsy of George Floyd, takes the stand.

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Forensic toxicologist Daniel Isenschmid of NMS Labs in Pennsylvania testifying on Thursday.Credit...Still image, via Court TV

Daniel Isenschmid, the forensic toxicologist who performed the toxicology tests for the autopsy of George Floyd, was called to the stand on Thursday.

Dr. Isenschmid works as a forensic toxicologist at NMS Labs, a toxicology and forensic sciences laboratory that provides analysis services to law enforcement, medical examiners, coroners, doctors, lawyers and others.

He said he performs 7,000 to 8,000 case reviews at NMS Labs per year.

Dr. Isenschmid is also a fellow at the Center for Forensic Science Research and Education and previously worked with the Office of the Wayne County Medical Examiner in Detroit, according to a biography on the Center’s website. He is certified by the American Board of Forensic Toxicology.

The Hennepin County Medical Examiner sent NMS Labs samples from Mr. Floyd, including hospital blood and urine collected at autopsy, he said.

The lab found 11 nanograms per milliliter of fentanyl and 19 nanograms per milliliter of methamphetamine in the blood that was tested, Dr. Isenschmid said. He said that the level of methamphetamine found was low.

The report also found 86 nanograms per milliliter of morphine in the urine that was tested, but not the blood. This could indicate a prior use, as morphine can remain present in urine longer than in blood, he said.

The report also found caffeine and evidence of smoking and prior marijuana use.

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Shaila DewanSheri Fink
April 8, 2021, 3:21 p.m. ET

Does it matter whether Chauvin knelt on Floyd’s neck versus his shoulder?

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Footage of George Floyd’s arrest presented during the trial of the former Minneapolis police officer Derek Chauvin on April 1.Credit...Still image, via Court TV

In the widely viewed bystander video of George Floyd’s arrest, it seemed plain that Derek Chauvin had positioned his left knee on Mr. Floyd’s neck.

But Mr. Chauvin’s defense has repeatedly suggested, and tried to get witnesses to agree, that his knee was actually on Mr. Floyd’s shoulder.

The most obvious reason for this is that the medical examiner, Dr. Andrew Baker, attributed Mr. Floyd’s death in part to neck compression.

But several experts said it did not matter: The knee could be lethal in either position, neck or shoulder.

“In my opinion, does it make a difference?” asked Dr. Alon Steinberg, a cardiologist who has published a review of the scientific literature on prone restraint deaths. “No.”

Dr. Steinberg said that multiple factors, including the restriction of breathing and of blood flow, contributed to death during prone restraint.

Dr. Judy Melinek, a forensic pathologist who has written extensively about the case, said, “Even in the absence of pressing on the neck, you’re putting strain on the cardiovascular system, especially if somebody is fighting or struggling against the restraint.”

The prosecution on Thursday appeared to be pursuing a similar argument. The first witness was Dr. Martin Tobin, a pulmonologist who specializes in the mechanics and physics of breathing.

He said that Mr. Floyd had died from a “low level of oxygen” that led to brain damage and an arrhythmia that “caused his heart to stop.” Dr. Tobin said terms such as hypoxia or the prosecution’s preferred word, asphyxia, are “really other words for a phenomenon that is a low level of oxygen.”

Mr. Floyd’s breathing was restricted, Dr. Tobin explained, by the way the officers pushed in his cuffed hands, squeezing his rib cage against the hard pavement, and by Mr. Chauvin’s placement of his left knee on Mr. Floyd’s neck and right knee on his back.

Mr. Chauvin’s left knee was on Mr. Floyd’s neck “more than 90 percent of the time,” Dr. Tobin said, and his right knee was on Mr. Floyd’s back at least 57 percent of the time. Dr. Tobin said that for the rest of the time, the available video did not provide a good view of the location of Mr. Chauvin’s right knee.

John Eligon
April 8, 2021, 3:18 p.m. ET

Reporting from Kansas City

Dr. Martin J. Tobin ends his testimony with one last explanation of why he believes fentanyl was not responsible for George Floyd’s death. People who die of a fentanyl overdose go into a coma, he said, but Floyd never did.

John Eligon
April 8, 2021, 3:15 p.m. ET

Reporting from Kansas City

On re-direct of Dr. Martin J. Tobin, the prosecution is establishing that not everything can be seen in an autopsy. That’s a crucial foundation to lay because prosecutors are departing from the medical examiner’s autopsy results.

John Eligon
April 8, 2021, 3:16 p.m. ET

Reporting from Kansas City

Dr. Martin J. Tobin also addressed an issue that the defense has brought up — that George Floyd didn’t have bruising on his neck. That doesn’t mean anything, Dr. Tobin said. “Whenever I go to church I sit on a hard bench,” he said. “I don’t get bruising of my buttocks when I leave, so I wouldn’t expect anything in terms of that.”

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Timothy Arango
April 8, 2021, 3:03 p.m. ET

Reporting from Minneapolis

In the morning, Dr. Martin J. Tobin said fentanyl had no effect on George Floyd’s breathing. To try to challenge that assertion, Eric Nelson, Derek Chauvin's lawyer, is pointing out the difference in quality between pharmaceutical-grade fentanyl and fentanyl bought on the street, the type presumably Floyd ingested. Another small way Nelson is trying to raise reasonable doubt.

John Eligon
April 8, 2021, 3:04 p.m. ET

Reporting from Kansas City

This is the challenge for a lawyer trying to poke holes in the testimony of a renowned scientific expert: The expert knows more than the lawyer, so he’s able to swat away some of the lawyer’s suggestions because they’re not specific enough.

Timothy Arango
April 8, 2021, 2:55 p.m. ET

Reporting from Minneapolis

Dr. Martin J. Tobin has corrected Eric Nelson, the lawyer for Derek Chauvin, a number of times. One key issue the defense has put forward is that when George Floyd said he couldn’t breathe, the very fact he was speaking meant he could breathe. Tobin says that is irrelevant because a few seconds after someone says they can’t breathe, they can be dead.

Timothy Arango
April 8, 2021, 2:46 p.m. ET

Reporting from Minneapolis

The hope of Derek Chauvin's lawyer here is to do whatever he can to obfuscate Dr. Martin J. Tobin’s findings and in essence confuse the jury — make them think that what Dr. Tobin said in the morning with so much certitude might be more complicated. One line of attack: pointing to the autopsy’s findings that there was no bruising on George Floyd’s neck.

Timothy Arango
April 8, 2021, 2:36 p.m. ET

Reporting from Minneapolis

Eric Nelson, Derek Chauvin’s lawyer, starts by pointing out that Dr. Martin J. Tobin didn’t accept a fee to testify for the state. The lack of payment, experts say, can cut both ways. On one hand, not accepting payment can bolster the witness’ testimony because it shows he wasn’t paid for it. On the other hand, as Nelson hopes to imply, it could suggest the witness has such a strong opinion — and therefore bias — about the case that he is willing to do it for free.

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Timothy Arango
April 8, 2021, 2:33 p.m. ET

Reporting from Minneapolis

We are back after the lunch break, with Derek Chauvin’s lawyer set to cross-examine Dr. Martin J. Tobin.

Matt Furber
April 8, 2021, 2:04 p.m. ET

The deaths of Philando Castile and George Floyd have left deep wounds in the Twin Cities.

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Posters bearing the likenesses of Philando Castile and George Floyd at a rally in July.Credit...Stephen Maturen/Getty Images

In 2016, Greg Traylor was working as a janitor in the emergency department where Philando Castile was brought after being fatally shot by a police officer in a Minneapolis-St. Paul suburb. Now, as a security guard for Hennepin County libraries, Mr. Traylor regularly struggles with his and others’ emotions about last year’s police killing of George Floyd.

“George Floyd’s death hurt and angered me,” said Mr. Traylor, a 30-year-old Black man. “I thought, OK, I know how police try to get their officers off in these situations, but this time there should be no excuses.”

Mr. Traylor said he had moved to the Twin Cities in part because Chicago, his hometown, was too violent. The death of Mr. Castile, who was killed during a traffic stop, opened his eyes.

“Minnesota’s got a whole lot of good things going on, but no place is perfect,” he said. “I’m afraid cops and Blacks will always be in conflict in this country.”

While marching in protests after Mr. Floyd’s death, Mr. Traylor carried a sign that said, “Four Cops Arrested — I’ll Be Happy With Four Cops Convicted.” He was overwhelmed by the outpouring of support, including from many white people.

But although he sometimes discusses Derek Chauvin’s trial with colleagues, Mr. Traylor said he had to limit the time he spent watching the coverage. “I can’t go to work with that heaviness and pain on my mind,” he said.

For his security job, Mr. Traylor carries mace and a baton. He has been trained in the reasonable use of force, he said, and thought the evidence was overwhelming that Mr. Chauvin had committed a crime.

“We don’t need this 20-day trial; it’s on camera,” he said of Mr. Floyd’s death. “I think it’s going to work out in everybody’s favor.

“God forbid if it doesn’t. People are on edge.”

Nicholas Bogel-Burroughs
April 8, 2021, 1:13 p.m. ET

Reporting from Minneapolis

The court is taking a break for lunch until 1:30 Central time after more than two hours of testimony from a lung doctor. After the break, Derek Chauvin’s lawyer will have a chance to cross-examine the doctor.

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Nicholas Bogel-Burroughs
April 8, 2021, 1:03 p.m. ET

Reporting from Minneapolis

George Floyd showed signs of a brain injury 4 minutes before Derek Chauvin lifted his knee, a doctor testifies.

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An image that prosecutors showed to jurors in the Derek Chauvin trial on Thursday as a lung doctor testified about what caused George Floyd’s death.Credit...Still image, via Court TV

A veteran lung doctor testified on Thursday that George Floyd’s death was caused in part by Derek Chauvin’s knees pressing against his neck and back, making it impossible for him to breathe, and that Mr. Floyd showed signs of a brain injury about four minutes before Mr. Chauvin lifted his knee from his neck.

Dr. Martin J. Tobin, a pulmonologist and critical care doctor in Chicago, said in court that the combination of Mr. Chauvin’s pressure, the handcuffs pulling Mr. Floyd’s hands behind his back and Mr. Floyd’s body being pressed against the street had caused him to die “from a low level of oxygen.”

The testimony from Dr. Tobin on the ninth day of the trial of Mr. Chauvin, the former Minneapolis police officer who has been charged with murdering Mr. Floyd, signaled a shift into a new phase in which medical testimony will be crucial. Mr. Chauvin’s lawyer has suggested that Mr. Floyd died from the fentanyl and methamphetamine that were found in his system, but prosecutors argue that Mr. Chauvin had killed him by kneeling on him for more than nine minutes and cutting off his air supply.

Dr. Tobin was adamant that Mr. Chauvin’s actions had caused Mr. Floyd’s death on May 25. He pinpointed the exact moment, in the graphic bystander video of the arrest, in which he said Mr. Floyd had died, noting that his eyes had opened wide and then closed again. At that point, Mr. Chauvin’s knee remained on his neck.

“You can see his eyes — he’s conscious — and then you see that he isn’t,” Dr. Tobin said. “That’s the moment the life goes out of his body.”

The doctor also rejected the defense’s arguments about drugs, saying that videos show Mr. Floyd breathing at a normal rate before he went unconscious, meaning any fentanyl in his system was “not having an effect” on his breathing.

“A healthy person subjected to what Mr. Floyd was subjected to would have died,” Dr. Tobin said.

Eric J. Nelson, the lawyer for Mr. Chauvin, pushed back on Dr. Tobin’s testimony during his questioning and suggested that Mr. Floyd could have died of an overdose. Dr. Tobin agreed that fentanyl could have hindered Mr. Floyd’s breathing if he had taken the drug in the minutes before police officers pushed him to the ground, but the doctor said Mr. Floyd had never gone into a coma, something he said would happen before a person dies of a fentanyl overdose. Mr. Nelson also sought to portray the medical care that Mr. Floyd received from paramedics as lacking, saying they had not inserted a tube down Mr. Floyd’s throat until nine minutes after they arrived.

In his testimony, Dr. Tobin said he had determined that Mr. Chauvin had pressed his left knee on Mr. Floyd’s neck for more than 90 percent of the time that Mr. Floyd was on the ground, and that he had kept his right knee on Mr. Floyd’s back for the majority of the time as well. That pressure, combined with having his hands cuffed behind his back and pushed into the street facedown, had cut off oxygen and caused his heart to stop, Dr. Tobin said.

“He was being squashed between the two sides,” he said.

Mr. Floyd was so desperate for air at one point that he tried to lift himself off the ground by pushing his right knuckle against a police car’s tire, the doctor said.

Dr. Tobin, who works in pulmonology and critical care at Edward Hines Jr. Veterans Affairs Hospital and at Loyola University’s medical school, spoke for more than two hours to jurors. He said he had asked not to be paid when prosecutors asked if he would testify in the case. At several points, he encouraged jurors to feel parts of their own necks to demonstrate what he was saying; most of them followed along.

Dr. Tobin said the factors that cut off Mr. Floyd’s air supply had led to what could be called “asphyxia,” which he said was just another word for oxygen deprivation; a prosecutor told jurors when the trial began that Mr. Floyd had died of asphyxia.

At one point in a video of Mr. Floyd’s arrest, Dr. Tobin noted, Mr. Chauvin’s left foot appeared to rise off the ground, which the doctor said meant that half of Mr. Chauvin’s body weight was pressing on Mr. Floyd’s neck.

After about 4 minutes and 51 seconds, Dr. Tobin said, Mr. Floyd stopped speaking or groaning. After just over 5 minutes, Mr. Floyd appeared to straighten out his legs, which Dr. Tobin said was a signal that Mr. Floyd was having a type of seizure because he had suffered a brain injury from the oxygen deprivation. He said Mr. Chauvin’s knee had stayed on Mr. Floyd’s neck for 3 minutes and 27 seconds after he took his last breath.

The doctor said the handcuffs were also an “extremely important” factor in Mr. Floyd’s death because Mr. Chauvin and another officer had pushed his hands upward and against his back, pressing his chest against the hard street.

“When you’re turned prone and with the knee on the back, now the work that Mr. Floyd has to perform becomes huge,” Dr. Tobin said, adding: “He has to try to lift up the officer’s knee with each breath.”

Shaila Dewan
April 8, 2021, 1:00 p.m. ET

Reporting from Minneapolis

Dr. Martin J. Tobin is turning out to be kind of a star because he’s not just opining, he’s done calculations to support all his points — from air intake to actually counting George Floyd’s breaths.

Shaila Dewan
April 8, 2021, 1:03 p.m. ET

Reporting from Minneapolis

And he’s able to translate the medical jargon into English, more or less.

John Eligon
April 8, 2021, 12:56 p.m. ET

Reporting from Kansas City

A lot of big words here, but an important point by Dr. Martin J. Tobin about George Floyd’s breathing. He essentially said that Floyd’s breathing did not slow down enough to say that fentanyl was a factor in his not getting enough oxygen. In other words, he was breathing at a normal rate before he became unconscious. The defense has argued that fentanyl was a cause of Floyd's inability to breathe.

John Eligon
April 8, 2021, 1:01 p.m. ET

Reporting from Kansas City

Dr. Martin J. Tobin also says the increased level of carbon dioxide in George Floyd’s body was not because of fentanyl, but because he wasn’t given any ventilation for nearly 10 minutes.

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Shaila Dewan
April 8, 2021, 12:52 p.m. ET

Reporting from Minneapolis

One thing that Dr. Martin J. Tobin is doing quite effectively is clarifying that multiple terms — hypoxia, asphyxia, anoxia — all mean essentially the same thing. He’s saying the jury doesn’t need to worry about the medical terminology because the words all refer to a “drastically low level of oxygen.”

Shaila Dewan
April 8, 2021, 12:47 p.m. ET

Reporting from Minneapolis

We think of asphyxia as a total cutoff of oxygen, like with strangulation. The prosecution is trying to get the jury to understand that reduced oxygen flow can also be lethal.

Shaila Dewan
April 8, 2021, 12:49 p.m. ET

Reporting from Minneapolis

Tobin says that the fact that Floyd was speaking creates “a huge false sense of security,” that just because someone is speaking (expelling air) does not mean he is not about to die.

Shaila Dewan
April 8, 2021, 12:45 p.m. ET

Reporting from Minneapolis

Addressing the fact that George Floyd was found to have a type of tumor called a paraganglioma, Dr. Martin J. Tobin said he did not consider it relevant to Mr. Floyd’s death, adding that the medical literature cites only six “sudden deaths” caused by paraganglioma.

Shaila Dewan
April 8, 2021, 12:45 p.m. ET

Reporting from Minneapolis

Asked if Floyd died a sudden death, Tobin said no.

John Eligon
April 8, 2021, 12:36 p.m. ET

Reporting from Kansas City

The defense has argued that George Floyd died because of his poor health and because he had drugs in his system. Dr. Martin J. Tobin said even a healthy person would have died under similar circumstances. “A healthy person subjected to what Mr. Floyd was subjected to would have died as a result of what he was subjected to,” he said.

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John Eligon
April 8, 2021, 12:29 p.m. ET

Reporting from Kansas City

Dr. Martin J. Tobin said that by 8:25 p.m., George Floyd had no more oxygen in his body. Derek Chauvin’s knee remained on Floyd’s neck for another 3 minutes 2 seconds after that, he testified. That sounds pretty gruesome.

John Eligon
April 8, 2021, 12:24 p.m. ET

Reporting from Kansas City

One really effective thing that the prosecution is accomplishing with Dr. Martin J. Tobin: They’re making it irrelevant whether Derek Chauvin’s knee was actually on George Floyd’s neck versus his back or shoulders. It’s all bad for his breathing is the main takeaway. That might be a reason why prosecutors are going with asphyxia (oxygen deficiency) as the cause of death, rather than what the medical examiner determined, “cardiopulmonary arrest,” which means the heart stops.

John Eligon
April 8, 2021, 12:17 p.m. ET

Reporting from Kansas City

Dr. Martin J. Tobin is now getting into some complicated terminology about oxygen reserves, but it all points to a general theme: George Floyd being in a prone position, handcuffed with a knee in his neck, led to a reduction in his oxygen reserves.

John Eligon
April 8, 2021, 12:18 p.m. ET

Reporting from Kansas City

“There’s a huge increase in the work that Mr. Floyd is performing just to cope with what was happening below the neck,” Tobin said.

Timothy Arango
April 8, 2021, 11:47 a.m. ET

Reporting from Minneapolis

Notably, no talk yet of drugs during the state’s examination of Dr. Martin J. Tobin. I wonder if prosecutors will bring it up when testimony resumes, in an effort to get ahead of what is likely to be Derek Chauvin’s lawyer’s line of questioning when he cross-examines Tobin.

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Shaila Dewan
April 8, 2021, 11:43 a.m. ET

Reporting from Minneapolis

Dr. Martin J. Tobin has done a moment-by-moment analysis of the officers’ positions on George Floyd’s body. The doctor said he focused on the first five minutes and three seconds because that is the point when he saw evidence of brain injury. The officers held Floyd down for nine minutes, 29 seconds.

Marie Fazio
April 8, 2021, 11:26 a.m. ET

In their own words: Pulmonologist says George Floyd had to ‘breathe with his fingers and knuckles.’

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Dr. Martin J. Tobin, a witness for the prosecution, used this image of Mr. Floyd’s arrest to show that he was digging his fingers and knuckles into his surroundings to try to breathe. Credit...Still image, via Court TV

Dr. Martin J. Tobin, a renowned expert on breathing, was a key witness for the prosecution on Thursday, agreeing to testify without pay to offer his opinion on what caused George Floyd’s death:

Mr. Floyd died from a low level of oxygen and this caused damage to his brain that we see and it also caused a P.E.A. arrhythmia that caused his heart to stop.

The testimony was an attempt to discredit defense arguments that Mr. Floyd’s drug use contributed to his death. Using video from the arrest, Dr. Tobin described how Derek Chauvin’s knees on Mr. Floyd’s neck and side and his hold on Mr. Floyd’s arms prevented Mr. Floyd from being able to breathe.

He’s jammed down against the street, and so the street is playing a major role in preventing him from expanding his chest.

He also showed two photos of Mr. Floyd’s finger and knuckles digging into the street and the police car’s tire as the police held him down:

To most people this doesn’t look terribly significant. But to a physiologist this is extraordinarily significant because this tells you that he has used up his resources and he is now literally trying to breathe with his fingers and knuckles.

Dr. Tobin said people who can’t breathe normally will use other ways to try to bring more air into their body:

So he’s using his fingers and his knuckles against the street to try to crank up the right side of his chest. This is his only way to try to and get air into the right lung.

Sheri Fink
April 8, 2021, 10:57 a.m. ET

Experts break down the critical medical terminology surrounding George Floyd’s autopsies.

As the trial enters a phase where George Floyd’s cause of death will take center stage, we talked with several forensic pathologists uninvolved in the case to explain some of the terms used in the proceedings, how they determine the cause and manner of death, and how this relates to the case. Here is what we learned.

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Marie Fazio
April 8, 2021, 10:34 a.m. ET

Dr. Martin J. Tobin, a pulmonologist, says shallow breathing led to George Floyd’s death.

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Pulmonologist Says George Floyd Died From a ‘Low Level of Oxygen’

Dr. Martin J. Tobin, a world-renowned expert on breathing, testified on Thursday that George Floyd died from a “low level of oxygen.” His testimony also highlighted how force from Derek Chauvin’s knee and Mr. Floyd’s position on the concrete obstructed Mr. Floyd’s airways.

“So let’s talk about your opinions with respect to this case, have you formed an opinion to a reasonable degree of medical certainty on the cause of Mr. Floyd’s death?” “Yes, I have.” “Would you please tell the jury what that opinion, or opinions, are?” “Yes, Mr. Floyd died from a low level of oxygen, and this caused damage to his brain that we see. And it also caused a P.E.A. arrhythmia that caused his heart to stop. The cause of the low level of oxygen was shallow breathing, small breaths, small tidal volumes, shallow breaths that weren’t able to carry the air through his lungs, down to the essential areas of the lungs that get oxygen into the blood and get rid of the carbon dioxide — that’s the alveoli at the bottom of the lung. The main forces that are going to lead to the shallow breath are going to be that he’s turned prone on the street, that he has the handcuffs in place combined with the street, and then that he has a knee on his neck, and then that he has a knee on his back and on his side. All of these four forces are ultimately going to result in the low tidal volume, which gives you the shallow breaths that we saw here. And so the air will not be able to reach those air sacs — we just saw in the video where the oxygen is exchanged and the carbon dioxide is removed. What you’re seeing is the orientation of Officer Chauvin, his body build is quite erect here. But in particular, what you’re seeing is that the toe of his boot is no longer touching the ground. This means that all of his body weight is being directed down at Mr. Floyd’s neck.”

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Dr. Martin J. Tobin, a world-renowned expert on breathing, testified on Thursday that George Floyd died from a “low level of oxygen.” His testimony also highlighted how force from Derek Chauvin’s knee and Mr. Floyd’s position on the concrete obstructed Mr. Floyd’s airways.CreditCredit...Still image, via Court TV

Dr. Martin J. Tobin, a pulmonologist and critical care physician from the Chicago area, was the first witness prosecutors called to the stand in the Derek Chauvin trial on Thursday.

When prosecutors asked if he had formed a medical opinion on what had caused George Floyd’s death, Dr. Tobin said, “Mr. Floyd died from a low level of oxygen, and this caused damage to his brain that we see, and it also caused a P.E.A. arrhythmia because his heart stopped,” referring to pulseless electrical activity, or cardiac arrest.

The low level of oxygen was caused by “shallow breathing,” he said. Mr. Floyd’s prone position and his being handcuffed, and Mr. Chauvin’s knee on his neck and back, he said, contributed to the shallow breathing.

Dr. Tobin added that the position in which Mr. Floyd was handcuffed, with the force of the officers compounding with the asphalt street, ultimately prevented him from being able to breathe fully.

“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,” he said.

Mr. Chauvin’s knee placed on the left side of his chest would have limited the amount of air being able to enter the left lung, Dr. Tobin said, as if “a surgeon had gone in and removed the lung,” he said.

Dr. Tobin attended medical school at University College Dublin and is an expert in acute respiratory failure, mechanical ventilation and neuromuscular control of breathing.

He is certified by the American Board of Internal Medicine and the American Board of Internal Medicine Subspecialty Pulmonary Disease.

Dan Levin
April 8, 2021, 10:10 a.m. ET

The trial is a difficult learning opportunity for Minneapolis students.

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Kyree Wilson, 16, the student council vice president at North Community High School, said the witness accounts in the Derek Chauvin trial had been “kind of hard to sit through.”Credit...Joshua Rashaad McFadden for The New York Times

In Minneapolis, educators have grappled over the past few weeks with how to talk with their students about the trial of Derek Chauvin, the former Minneapolis police officer charged with murder in George Floyd’s death.

Some teachers have shown segments of the televised trial in class and used jury selection or witness testimony as an opportunity to explore the complex issues of race, policing and the criminal justice system. Others have cautiously given students the chance to ask questions and share their opinions. And school administrators and counselors have scheduled talking circles, where children can open up about how the trial has rekindled feelings of racial trauma and fears of potential unrest stirred by the sound of helicopters flying over the city.

But the adult nature of the televised murder trial, marked by graphic videos and emotional eyewitness accounts, poses a challenge for educators, even as they say the court proceedings are too important to ignore.

“We have to engage even if we’re uncomfortable and we don’t have the answers,” said Kristi Ward, the principal for third through eighth graders at Lake Nokomis Community School in south Minneapolis.

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