Witness in trial of former Minneapolis officer Derek Chauvin offers detailed medical explanation for Floyd’s death.

George Floyd died of a lack of oxygen from being pinned to the pavement with a knee on his neck, a medical expert testified at former Minneapolis Police Officer Derek Chauvins murder trial on Thursday, rejecting Chauvins defence theory that drug use and underlying health problems killed Floyd.
A healthy person subjected to what Mr Floyd was subjected to, would have died, said prosecution witness Dr Martin Tobin, a lung and critical care specialist at a veterans hospital and medical school in Chicago.
Using easy-to-understand language to explain medical concepts and loosening his necktie to make a point, Tobin told the jury that Floyds breathing was severely constricted while Chauvin and two other officers held the 46-year-old Black man down on his stomach last May with his hands cuffed behind him and his face jammed against the ground.
The lack of oxygen resulted in brain damage and caused his heart to stop, the witness said.
Tobin, analysing a graphic presentation of the three officers restraining Floyd for what prosecutors say was almost nine and a half minutes, testified that Chauvins knee was virtually on the neck for more than 90 percent of the time.
He cited several other factors that he said made it difficult for Floyd to breathe; officers lifting up on the suspects handcuffs, the hard surface of the street, his prone position, his turned head and a knee on his back.
Chauvin kept his knee on Floyds neck for three minutes, two seconds after Floyd had reached the point where there was not one ounce of oxygen left in the body, Tobin said.
As prosecutors repeatedly played a video clip of Floyd on the ground, Tobin pinpointed what he saw as a change in the mans face that told him Floyd was dead.
At the beginning, you can see hes conscious, you can see slight flickering, and then it disappears, the witness said. He explained, Thats the moment the life goes out of his body.
A protester holds a sign across the street from the Hennepin County Government Center where the trial of former Minneapolis police officer Derek Chauvin is in its second week [Jim Mone/AP Photo]
Chauvin, 45, is charged with murder and manslaughter in Floyds death on May 25, 2020. Floyd was arrested outside a neighbourhood market after being accused of trying to pass a counterfeit $20 bill.
Bystander video of 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 what he was trained to do and that Floyds death was caused by illegal drugs and underlying medical problems that included high blood pressure and heart disease. An autopsy found fentanyl and methamphetamine in Floyds body.
But Tobin said he analysed Floyds respiration as seen on body-camera video and explained that while fentanyl typically cuts the rate of respiration by 40 percent, Floyds breathing was right around normal just before he lost consciousness. Similarly, he said people with severe heart disease have very high respiratory rates.
Tobin also said the high blood level of carbon dioxide measured in the hospital emergency room can be explained by the fact that Floyd was not breathing for nearly 10 minutes before paramedics began artificial respiration, as opposed to his breathing being suppressed by fentanyl.
The doctor explained that just because Floyd was talking and shown moving on video, it did not mean he was breathing adequately. He said a person can continue to speak until the airway narrows to 15 percent, after which you are in deep trouble.
Officers can be heard on video telling Floyd that if he can talk, he can breathe.Tobin also reviewed video that showed Floyds leg moving upward at one point, and he explained that it was involuntary.
A courtroom sketch of video of George Floyds arrest by Officer Derek Chauvin played for jurors in the trial of former Minneapolis police officer Derek Chauvin for murder [Jane Rosenberg/Reuters]
The doctor used simple language, with terms like pump handle and bucket handle to describe the act of breathing for the jury. He explained that when the airway narrows, breathing becomes enormously more difficult like breathing through a drinking straw.
At one point, he loosened his tie and placed his hands on his own neck and the back of his head to demonstrate how the airway works, inviting the jurors to examine their own necks. Most of them did so, though the judge later told them they did not have to.
The expert calculated that at times when Chauvin was in a near-vertical position, with his toes off the ground, half of Chauvins body weight 41.5kg (91.5 pounds) was directly on Floyds neck.
He said it appeared that Floyd was getting enough oxygen to keep his brain alive for about the first five minutes because he was still speaking. Tobin said that where Chauvin had his knee after the five-minute mark was not that important, because at that point Floyd had already experienced brain damage.