Medical expert says George Floyd died from ‘low level of oxygen’
‘Like a surgeon had gone in and removed a lung’: Expert explains how force used to pin George Floyd to ground made it ‘impossible for him to breath’ – and killed him
- Dr Martin Tobin was the first to testify for the prosecution on Thursday on what has become the most contested issue of Derek Chauvin’s trial so far: Floyd’s cause of death
- The expert witness, who has worked in critical care and pulmonology for more than 45 years, told jurors Floyd died from a ‘low level of oxygen’ after he was pinned to the ground
- Dr Tobin said there were four forces that caused this fatal shallow breathing: The fact that Floyd was turned prone on the street, had his hands cuffed behind his back and had a knee on his neck and on his back
- The court was shown a graphic – a ‘snapshot in time’ – depicting the officers’ positions on Floyd
- Using this graphic, Dr Tobin explained the impact the four forces would have had on Floyd’s death
- The defense has claimed from the start that Floyd’s death was due to the impact of drugs, stuffed into his mouth in the moments prior to his arrest on May 25, 2020
Dr Martin Tobin was the first to testify for the prosecution on Thursday on what has become the most contested issue of Chauvin’s trial so far: Floyd’s cause of death
A pulmonology medical expert has told jurors that Derek Chauvin kept his knee on George Floyd’s neck for three minutes after ‘every ounce of oxygen had left’ his body and says the force used to pin him to ground was ‘like a surgeon had gone in and removed a lung’.
Dr Martin Tobin, who has been a lung and critical care specialist for more than 45 years, testified on Thursday during Chauvin’s murder trial that he believed Floyd’s cause of death was due to a lack of oxygen that damaged his brain and caused his heart to stop when he was pinned to the street by Minneapolis police officers.
During his lengthy testimony, Dr Tobin analyzed the mechanics of how Floyd would have been unable to breathe, relied on graphics to show jurors how the level of force would have contributed and offered specific calculations of what his lung capacity would have been at various points before he lost consciousness.
He said he had calculated that Floyd’s lung capacity was reduced by 43 percent when Chauvin was pinning him down and that the officer kept his knee on Floyd’s neck for 3.02 minutes after Floyd had ‘reached the point where there was not one ounce of oxygen left in the body’.
Floyd’s cause of death has become the most contested issue of Chauvin’s trial so far with the defense claiming he died as a result of a drug overdose. Dr Tobin took the stand as part of an effort by prosecutors to establish that it was Chauvin’s actions that killed the 46-year-old black man last May.
Tobin took direct aim at the defense’s theory, declaring in his testimony: ‘A healthy person subjected to what Mr Floyd was subjected to would have died as a result.’
When asked if Dr Tobin, based on his medical expertise, had determined a cause of death for Floyd after viewing videos from the scene, he said: ‘Mr Floyd died from a low level of oxygen… The cause of low level of oxygen was shallow breathing. Small breaths that weren’t able to carry the air through his lungs.’
The prosecution witness said there were several factors that he said made it difficult for Floyd to breathe, beyond Chauvin’s knee on his neck: Officers lifting up on his handcuffs, the hard street, lying face down, his turned head and a knee on his back.
During his testimony, Dr Tobin relied on graphics and images that depicted the officers’ positions on Floyd to analyze the impact the forces had on his death
During his testimony, Dr Tobin analyzed the mechanics of how Floyd would have been unable to breathe due to the officers pinning him down and relied on graphics to show jurors how the level of force would have contributed. He said Chauvin was exerting 91.5lbs of pressure directly down on his neck
During his testimony, Dr Tobin relied on graphics and images that depicted the officers’ positions on Floyd to analyze the impact those forces had on his death. He noted he came to these conclusions after focusing on the first 5.03 minutes of footage because that was the point at which he said Floyd started to show signs of brain damage.
‘He was being squashed between the two sides,’ Dr Tobin said as he described the position Floyd was in lying face down on the ground with the officers pinning him down.
Dr Tobin told the court that the impact of the pressure of the officers and handcuffs rendered movement so impossible that Floyd’s left lung was greatly affected.
‘Basically on the left side of his lung, it was almost to the effect of if a surgeon had gone in and removed his lung,’ he said, adding that Floyd needed to be ‘totally dependent’ on his right side.
At one point, Dr Tobin noted that Floyd had rammed his face into the ground to ‘try to crank up his chest’ so he could breathe.
Chauvin, 45, is accused of killing Floyd by pinning his knee on the 46-year-old black man’s neck for 9 minutes, 29 seconds, as he lay face-down in handcuffs after being detained for using an alleged counterfeit $20 bill to buy cigarettes
‘He’s actually using his nose and chin and forehead as a way of trying to help him get air into the right side of his chest,’ he said.
He pointed to an image taken from a body cam video of Floyd pushing his knuckles against the tire of the police car next to him. Of that moment, Dr Tobin said Floyd was trying to use his hands to push his chest up to get air.
‘This tells you he’s used up his resources and he’s literally trying to breathe through his fingers and knuckles,’ Dr Tobin said.
‘When you breathe you use your diaphragm, next thing you recruit is the big muscles in the neck, when those are wasted up then you’re relying on these kinds of muscles to get air into the right side.’
Dr Tobin pointed to images showing Floyd’s right shoulder, prominent and strained, as evidence that he was also trying to recruit his shoulders to facilitate breathing as he was being crushed between the officers and the street.
These were the tell-tale sides of a person trying to breathe ‘in extremis,’ Dr Tobin said.
Dr Tobin explained the impact of Floyd being placed in the prone position stating that his lung volume would have diminished in size by 24 percent – even without any pressure having been applied.
With smaller lung volume, his oxygen reserves were drastically reduced, his hypopharynx was constricted and, with his lung and chest walls having stiffened, the effort to breathe would have increased, the witness said.
With Chauvin’s knee on his back the reduction of his lung volume jumped to 43 percent, his hypopharynx became more constricted and his breathing increasingly shallow.
‘With each breathe [Floyd] has to fight against the street, he has to fight against the small volume, he has to try to lift up the against the effect of the officer’s knee on his back and the other officer pumping his arm into his chest [with the handcuffs].’
By the time Floyd lost consciousness – a moment that Dr Tobin placed at 4.53 minutes in – his blood oxygen levels, Dr Tobin said with absolute certainty, would have dropped from a normal of 89mm Hg to 36mm Hg.
As a physician of more than three decades experience of working in critical care and Intensive Care Units Dr Tobin said he has monitored ‘millions’ of patients for signs of unconsciousness and does so by observing their facial muscles and flickers
‘It’s a very important sign to be able to monitor,’ he said when caring for patients.
Floyd stopped breathing, according to Dr Tobin, at 20.24.16seconds. From then it would take, he said, only 25 seconds for every ounce of oxygen to be gone from his body.
‘The knee remained on the neck for another three minutes two seconds after every ounce of oxygen had left the body,’ Dr Tobin said.
Dr Tobin pointed to an image taken from a body cam video of Floyd pushing his fingers against the street and knuckles against the tire of the police car next to him. Of that moment, Dr Tobin said Floyd was trying to use his hands to push his chest up to get air
This image that Dr Tobin referred to during his testimony shows the different ways Floyd’s neck – or hypopharynx – was restricted at various stages when he was being detained
By the time Floyd lost consciousness – a moment that Dr Tobin placed at 4.53 minutes in – his blood oxygen levels, Dr Tobin said with absolute certainty, would have dropped from a normal of 89mm Hg to 36mm Hg
Chauvin’s defense attorney Eric Nelson has previously made much of what he describes as ‘camera perspective bias’, using the notion to suggest that Chauvin’s knee was not on Floyd’s neck all, if any, of the time.
Dr Tobin, however, said that by his calculations Chauvin’s left knee was ‘virtually on his neck for the vast majority of the time.’
‘It’s more than 90 percent of the time,’ he said.
As for his right knee, Dr Tobin said that it was on Floyd’s back for 57 percent of the time – the time when he could get a clear view.
‘At other times it was placed on his arm and then rammed into Mr Floyd’s left chest so really if you’re making a distinction on whether his knee is on the chest per se or on the left arm and rammed into the chest, from the point of view of breathing the effects are very similar.’
At certain points as Floyd struggled to breathe Chauvin was exerting 91.5lbs of pressure directly down on his neck, Dr Tobin told the court.
He made that calculation based on it being half of Chauvin’s bodyweight and half of his gear weight and said that, at certain points, all of this was brought to bear on Floyd as the toes of his left foot were off the ground and therefore bearing no weight.
When Chauvin’s foot was on the ground he calculated the pressure as 86.9lbs as some of the shank weight was supported by the toes at that point.
Of the different pressures placed on Floyd’s neck, back and chest he said: ‘It’s complex but all coming to the same point.’
Chauvin, 45, is charged with murder and manslaughter after being accused of pinning his knee on Floyd’s neck for nine minutes and 29 seconds in May last year
Chauvin, 45, is charged with murder and manslaughter after being accused of pinning his knee on Floyd’s neck for nine minutes and 29 seconds in May last year.
He has pleaded not guilty, arguing that he did only what he was trained to do in his 19 years as an officer.
Chauvin was fired by the city’s police department the day after he was captured on video kneeling on a handcuffed Floyd’s neck after he was detained for using an alleged counterfeit $20 bill to buy cigarettes.
The trial so far has been filled with testimony from a number of Minneapolis police officers who rejected Chauvin’s actions in restraining Floyd.
A use-of-force instructor testified that officers were coached to ‘stay away from the neck when possible’ and other experienced officers, including the police chief, said Floyd should not have been kept pinned to the pavement for so long with his hands cuffed behind his back.
Other testimony so far during the trial has come from emotional witnesses, including Floyd’s girlfriend Courteney Ross and bystanders who saw everything unfold.
In addition to the testimony, the prosecution has also introduced multiple videos, including footage from Chauvin’s body camera, and images of EMTs trying to resuscitate Floyd in an ambulance.
