George Floyd died of a lack of oxygen from being pinned facedown on the pavement with his hands cuffed behind him, a medical expert said at former officer Derek Chauvin’s murder trial.
Mr Floyd’s breathing while he was being held down by Chauvin and other officers was too shallow to take in enough oxygen, which in turn damaged his brain and caused an abnormal heart rhythm that made his heart stop, said Dr Martin Tobin, a lung and critical care specialist at the Edward Hines, Jr VA Hospital and Loyola University’s medical school in Chicago.
He took the stand as part of an effort by prosecutors to establish that it was Chauvin’s actions, not Mr Floyd’s illegal drug use and underlying health conditions, as the defence contends, that killed the 46-year-old black man last May.
Mr Tobin, analysing a graphic presentation of the three officers pinning Mr Floyd for what prosecutors say was almost 9 1/2 minutes, said Chauvin’s knee was “virtually on the neck for the vast majority of time”.
He said it was “more than 90% of the time in my calculations”.
He said it appeared that Mr Floyd was getting enough oxygen for about the first five minutes to keep his brain alive because he was still speaking.
But Mr Tobin explained to jurors what happens as the space in the airway narrows, saying breathing then becomes “enormously more difficult”, adding that it would be worse than “breathing through a drinking straw”.
Mr Tobin gave evidence that if the hypopharynx, the bottom part of the throat, becomes totally obstructed, it takes just seconds to reduce the level of oxygen to where it would result “in either a seizure or a heart attack”.
Prosecutors showed images of Mr Floyd side by side, one with the front of his face smashed against the pavement and another with his head turned.
Mr Tobin said that when Mr Floyd’s head was face down, a ligament at the back of his neck would have protected his airway.
But with his head turned, Chauvin’s weight would have compressed the hypopharynx.
The expert calculated that at times when Chauvin was in a near-vertical position, with his toes off the ground, half of Chauvin’s body weight, 91.5lb, was directly on Mr Floyd’s neck.
Mr Tobin said other factors worsened the effect on Floyd: He pointed out that Officer J. Kueng held Mr Floyd’s left hand upward, and Chauvin’s right knee compressed Mr Floyd’s side, meaning “the ability to expand his left side is enormously impaired.”
The handcuffs and the hard surface also interfered with Mr Floyd’s ability to breathe, Mr Tobin said.
Mr Tobin used simple language, with terms like “pump handle” and “bucket handle” to describe the act of breathing for jurors.
At one point, he invited them to “examine your own necks, all of you in the jury right now” to better understand the effect of a knee on a person’s neck.
Most of the jurors felt their necks as Mr Tobin instructed, though the judge later told them they did not have to do so.
Chauvin, 45, is charged with murder and manslaughter in Mr Floyd’s death on May 25.
Mr Floyd was arrested outside a neighbourhood market after being accused of trying to pass a counterfeit 20 dollar bill.
A panicky-sounding Mr Floyd struggled and claimed to be claustrophobic as police tried to put him in a squad car, and they pinned him to the pavement.
Bystander video of Mr Floyd crying that he could not breathe as onlookers yelled at Chauvin to get off him sparked protests and scattered violence around the US.
Defence lawyer Eric Nelson has argued that the now-fired white officer “did exactly what he had been trained to do over his 19-year career”, and he has disputed that Chauvin’s actions were what killed Mr Floyd.
Fentanyl and methamphetamine were found in Mr Floyd’s system.