MINNEAPOLIS — The civil rights trial of three former Minneapolis police officers resumed Monday with a Harvard pulmonologist testifying that George Floyd died of asphyxia from pressure on his neck and restrictions to the movement of his midsection.
The pressure of Derek Chauvin's knee on Floyd's neck compressed Floyd's airway while being held in the prone position against the hard asphalt impeded his diaphragm's ability to expand and draw breath, Dr. David Systrom said.
Systrom, who is on staff at Brigham and Women's Hospital in Boston and has published extensively, went through a detailed explanation of heart-lung function through a series of demonstrative videos. He was the first witness after court was paused last Wednesday due to a positive COVID-19 test by a defendant.
Judge Paul Magnuson never said which defendant had the virus, but both Tou Thao and J. Alexander Kueng were in court Wednesday morning when the announcement was made. Thomas Lane was not there, but he was back in court Monday morning.
Systrom's testimony, for which he is paid $600 an hour, is critical to the prosecution's case, which seeks to show that Floyd died of asphyxia because of the actions of the former officers. The defense is working to cast doubt on that by claiming that Floyd suffered a cardiac arrest due to an enlarged heart, arterial disease and illegal drug use.
Systrom testified that he has worked as a pulmonologist and in critical care for the past three decades, studying how the heart and lungs work — or fail — in patients. He said he has published more than 120 peer reviewed articles.
Under questioning from assistant U.S. Attorney Amanda Sertich, he testified that he determined Floyd died of asphyxia caused by compression on his airway and being "hog-tied" on the ground.
Kueng's defense attorney Thomas Plunkett objected to the use of the word hog-tied, Magnuson upheld the objection. But Systrom restated that Floyd was being held in the prone position with his arm movement restricted.
He noted how the positioning was problematic for Floyd's breathing because the arms and shoulders work as "adjunct respiratory muscles" to help move and lift the torso.
Through detailed explanations and exhibits that showed blood flow and breathing mechanisms, Systrom testified that pressure on the abdomen impedes the abdomen's ability to descend and capture a full breath so less oxygen flows to the heart and brain.
Systrom said the "restrictive breathing" resulted in low lung volume and inability to draw in sufficient breath. He testified that typically a patient having trouble breathing would complain about "shortness of breath" followed by a loss of consciousness.
To support his assertion that Floyd died of asphyxia, not a heart attack, Systrom pointed to a medical measurement, end-tidal carbon dioxide level. The measurement reflects how well the body is processing carbon dioxide.
A normal level is 35 to 45 milliliters of mercury, Systrom said. Floyd's end-tidal carbon dioxide level was 73 milliliters of mercury, roughly twice normal level and "life threatening," Systrom said.
He said Floyd's level is often associated with acidemia, or an increase in the hydrogen ion concentration of the blood, and low oxygen.
"This tells me the primary process (of Floyd's death) was asphyxia." Systrom said.
Systrom said given that measurement, the chances Floyd died of a cardiac event would be "very low." In cardiac events, the measurement is as low as 10 milliliters of mercury.
The three officers are accused of violating Floyd's right by failing to render aid while detaining him. Thao and Kueng are also charged with failing to intervene in Chauvin's illegal restraint of Floyd.
Chauvin was convicted of Floyd's murder in state court last year and was sentenced to more than 22 years in prison. He also pleaded guilty in federal court to civil rights violations in December.
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