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Apr. 8 highlights for the murder trial of Derek Chauvin Day 9

Highlights from Day 9 of the trial of Derek Chauvin. A pulmonologist and forensic toxicologist took the stand in the trial for the death of George Floyd.
Image: The trial of former police officer Derek Chauvin
Activist Stephen Parlato stands outside the Hennepin County Government Center during the trial of former police officer Derek Chauvin, in Minneapolis, Minn., on April 7, 2021.Nicholas Pfosi / Reuters

Live coverage on this blog has ended, please click here for the latest in Derek Chauvin's trial.

Two medical doctors and a forensic toxicologist testified on Thursday in Derek Chauvin's murder trial in the death of George Floyd. Both doctors testified that Floyd died of a lack of oxygen after he was pinned to the ground with his hands cuffed behind him and Chauvin's knee on his neck. The forensic toxicologist said that the fentanyl found in Floyd’s system was lower than levels found in 94% of DUI cases.

Hennepin County Medical Examiner, Dr. Andrew Baker, is expected to testify on Friday. The medical examiner said an autopsy listed Floyd's cause of death as a "cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression."

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Forensic toxicologist: Type of fentanyl in Floyd's body not typically found in fatal overdose victims

The state called a forensic toxicologist to the stand Thursday afternoon.

Dr. Daniel Isenschmid is a forensic pathologist for NMS Laboratory in Pennsylvania. The lab did testing of blood work in the case of George Floyd’s death.

An autopsy found fentanyl and methamphetamine in his system.

Isenschmid testified the type of fentanyl found in Floyd's system is not usually found in fatal overdose victims, suggesting that Floyd did not overdose. He said that the fentanyl found in Floyd’s system was lower than levels found in 94% of DUI cases.

The defense has claimed drug use, underlying health conditions and the adrenaline flowing through his body led to Floyd's death.

Pulmonologist reiterates that he does not believe fentanyl was responsible for George Floyd’s death

Near the end of Dr. Martin Tobin’s testimony, Derek Chauvin's attorney again attempted to link the fentanyl found in Floyd's system to this death, a central part of the defense's case. The renowned expert pulmonologist made clear he did not believe there was a connection.

“Generally speaking, fentanyl can also cause death as a result of low oxygen to the brain, right?” defense attorney Erik Nelson asked.

“But it would have to be through respiratory depression,” Tobin responded.

The defense repeated the question, looking for a yes or no response. Tobin would not concede that the science was that simple.

Prosecutor Jerry Blackwell followed up by asking Tobin if people go into a coma before they die if the cause of death is fentanyl. Tobin replied that they do.

“Was Mr. Floyd ever in a coma?” Blackwell then asked.

Tobin responded with a simple: “No.”

'You will never know as much as an expert as they do about their area of expertise'

Mary Moriarty, the former chief public defender of Hennepin County, where Derek Chauvin is being tried on charges of second- and third-degree murder and second-degree manslaughter, weighs in on how difficult it can be to cross examine an expert:

Chauvin's attorney, Eric Nelson, is cross-examining Dr. Martin Tobin, a lung and critical care specialist at the Edward Hines, Jr. VA Hospital and Loyola University’s medical school in Chicago.

Tobin, a pulmonologist and world renowned expert on breathing, has corrected Nelson a number of times. Nelson asked Tobin a series of open-ended questions, including what he believes caused George Floyd's death. Tobin testified earlier Thursday that Floyd died "from a low level of oxygen."

Pulmonologist casts doubt on role of fentanyl in Floyd's lack of oxygen

Dr. Martin Tobin, a renowned expert on breathing, testified Thursday that George Floyd’s respiratory rate was normal before he lost consciousness and fentanyl “was not having an effect” on his respiratory centers based on his rate of breathing.

Tobin said while Floyd was restrained on the ground he was still experiencing a normal respiratory rate of 22. He said if fentanyl were causing a depression of his respiratory centers, one would expect a 40 percent reduction in his respiratory rate.

He said if Floyd’s respiratory rate was 22, then one would expect a respiratory rate of 10 if fentanyl was having an effect.

Tobin agreed with prosecutor Jerry Blackwell that he did not see a depressed rate of breathing in Floyd and that his respiratory rate was normal just before he lost consciousness. 

The defense has argued that fentanyl, which was found in Floyd's system at the time of his death, and other drugs can lead to insufficient oxygen in the body as part of the defense argument that Chauvin was not the cause of Floyd's death.

Pulmonologist: 'Very dangerous' and 'misleading' to think 'if you can speak, you can breathe'

Dr. Martin Tobin, a renowned pulmonary expert, testified Thursday that the idea of “if you can speak, you can breathe” is both “very dangerous” and “highly misleading.”

Tobin said even though such a statement was technically true in the sense that when a person speaks, they are exhaling, it also gives “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.

Tobin added that at the time Floyd was restrained on the ground and telling officers he could not breathe he still had oxygen in his brain.

“And again, it's a perfect example of how it gives you a huge false sense of security because 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,” he added.

Tobin said this showed how dangerous the concept of “if you can speak, you can breathe,” actually was.

“Yes, that is true on the surface, but highly misleading. A very, very dangerous mantra to have out there,” he said.

Dr. Martin Tobin: 'A healthy person subjected to what Mr. Floyd was subjected to would have died.'

Dr. Martin Tobin testified that he was aware that George Floyd had pre-existing conditions as mentioned in his autopsy and medical records. 

"Do you have an opinion to a reasonable degree of medical certainty as to whether a person who had none of those pre-existing conditions, a healthy person, would have died under the same circumstances as Mr. Floyd?" prosecutor Jerry Blackwell asked him.

"Yes. A healthy person subjected to what Mr. Floyd was subjected to would have died," Tobin said. 

The prosecution has said Floyd died from Chauvin's kneeling on his neck. The Hennepin County Medical Examiner's Office classified Floyd's death as a homicide that occurred while he was being restrained by police.

Floyd's cause of death was listed as a "cardiopulmonary arrest complicating law enforcement subdual, restraint, and neck compression." Under "other significant conditions" it said Floyd suffered from hypertensive heart disease, and listed fentanyl intoxication and recent methamphetamine use. 

Pulmonary expert: Chauvin held knee on Floyd’s neck for 3 minutes after there was no oxygen left in his body

A renowned pulmonary expert testified that he calculated Derek Chauvin’s knee was on George Floyd’s neck for more than 3 minutes after “there was not an ounce of oxygen left” in his body.

Dr. Martin Tobin said at 8:25 p.m. on the day he died Floyd reached the point where he did not have “an ounce of oxygen left in his entire body” as Chauvin continued to have his knee pressed against his neck while he was handcuffed on the ground.

“The knee remained on the neck for another three minutes and two seconds after we reached the point where there was not one ounce of oxygen left in the body,” he added.

Dr. Martin Tobin, expert on breathing, testifies half of Derek Chauvin's body weight was on George Floyd's neck

Dr. Martin Tobin, a world-renowned expert on breathing, testified as jurors were shown a photo in which Derek Chauvin's toe is lifted slightly off the pavement as he kneels on George Floyd's neck.

Tobin says that by his calculation, at one point, 91.5 pounds — half of Chauvin's body weight and half the weight of his gear — was on Floyd's neck.

"This means that all of his body weight is being directed down at Mr. Floyd's neck," Tobin said.

Pulmonary expert says knee on Floyd's neck 'extremely important' when considering lack of oxygen

A pulmonary expert testified Thursday morning about why the knee on George Floyd’s neck and back was “extremely important” when considering what caused the lack of breathing that led to his death.

Dr. Martin Tobin loosened his tie, unbuttoned the top button on his shirt and instructed the jurors to feel their necks as he testified about why a knee on the neck was so important.

He said that a knee on Floyd’s neck was “extremely important because it's going to occlude the air getting in through the passageway.”

He walked the jurors through a demonstration of their own neck anatomy, pointing them to the  hypopharynx, which he called “vulnerable.”

“The hypopharynx is very important for understanding this case for a number of reasons. Because it's so vulnerable, because it has no cartilage around it, it's going to be an area that is compressed,” he said. “It's extremely small to breathe through and it becomes very important for being able to continue to breathe through."

Tobin added that Chauvin's knee was on that area of Floyd's neck at points, with enough pressure to cut off his breathing.

Pulmonologist: Derek Chauvin's knee among four forces that caused shallow breathing that led to George Floyd's death

Dr. Martin Tobin, a pulmonologist, testified Thursday that he believes there were four forces that caused George Floyd's shallow breathing and led to his death. 

"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," Hines said. "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." 

The prosecution has argued that George Floyd died from Derek Chauvin kneeling on his neck for more than 9 minutes.