Updated April 14, 2021 at 12:06 PM ET
Former Minneapolis police officer Derek Chauvin's defense attorney continued to present their case on Wednesday.
The defense's first witness for the day is Dr. David Fowler, a retired forensic pathologist who waschief medical examiner for the state of Maryland. Chauvin is charged with the murder of George Floyd, who died after Chauvin held his knee on Floyd's neck for nine minutes and 29 seconds on Memorial Day last year.
Medical experts called by the prosecution have stated that low oxygen levels, caused by the restraint, were the cause of Floyd's death. Chauvin's defense has suggested that Floyd's heart condition and drugs in his system were primary factors.
"In my opinion, Mr. Floyd had a sudden cardiac arrhythmia ... due to his atherosclerotic and hypertensive heart disease ... during his restraint and subdual by the police," Fowler said.
In Fowler's determination, "fentanyl and methamphetamine" contributed to Floyd's death. He also said that "there is exposure to vehicle exhaust, so potentially carbon monoxide poisoning or at least an effect from increased carbon monoxide in his blood stream, and paraganglioma norma, or the natural disease process that he has."
Under questioning from defense attorney Eric Nelson, Fowler discussed the guidelines for manner of death classification from the National Association of Medical Examiners, as well as the autopsy report prepared by Dr. Andrew Baker, the Hennepin County medical examiner, who testified earlier in the week.
Baker had concluded that Floyd's death was a homicide. "In my opinion, the law enforcement subdual, restraint and the neck compression was just more than Mr. Floyd could take, by virtue of those heart conditions," Baker told the court last week. He said he did not believe the drugs in his system were a direct cause of death.
Floyd's heart was enlarged, Fowler said, which can be associated with hypertension. He also testified that methamphetamine can be associated with narrowing of the arteries.
Fowler testified that Floyd had "significant narrowing of all of his coronary arteries close to their origin, which really is consistent with all of his heart unfortunately being subject to reduced supply [of blood]. Not just a portion of his heart, but the entire heart."
He said that 70-75% narrowing of coronary arteries can be a risk factor for sudden cardiac death. Nonetheless, Fowler said, a person can be walking around with 90% narrowing of the coronary arteries.
"We know Mr. Floyd had 90% narrowing ... and that was not affecting him, as part of his daily activities. So when he was at rest, walking around, doing his normal daily activities, I know of no information that he was symptomatic or having any problems," Fowler added.
Nelson also asked about Floyd's blood pressure, which was taken by paramedics following the 2019 traffic stop and discussed in court on Tuesday.
His blood pressure on that day was recorded at 216/160. A "markedly elevated" blood pressure like that "could be due to his hypertension being out of control," or it could be due to stress and adrenaline, Fowler said.
Fowler is one of several parties being sued by the family of Anton Black, a Black 19-year-old who died in police custody in 2018. The Maryland Medical Examiner's Office, which was then helmed by Fowler, ruled the death an accident and said there were no signs police did anything wrong, The Baltimore Sun reports.
No officers were charged over Black's death.
"Two years before George Floyd died after being restrained and pinned down by police, 19-year-old Anton Black ... was killed by three white law enforcement officials and a white civilian in a chillingly similar manner on Maryland's Eastern Shore," says the lawsuit filed by Black's family. "This lawsuit arises from the wrongful death of Anton Black at the hands of officers from three different police departments on September 15, 2018, and the ensuing efforts by public officials to protect the officers involved from the consequences of their excessive use of force against a Black teenager."
Chauvin's lawyer began laying out the defense's case on Tuesday, including showing police body camera footage of Floyd from a 2019 traffic stop. The jury also heard from witnesses including a woman who was seated in Floyd's car when he was approached by police last May.
A major component of the prosecution's case has been testimony from other officers and experts who have said that Chauvin's restraint of Floyd was not justified and ran counter to police training.
On Tuesday, Chauvin's lawyer called upon Barry Brodd, a former officer and use-of-force expert, who said Chauvin "was justified, was acting with objective reasonableness, following Minneapolis Police Department policy and current standards of law enforcement."
Judge Peter Cahill has said closing arguments in the case will likely begin on Monday.
NPR's Merrit Kennedy contributed to this report.
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