A simulated swarm of millions of particles potentially laden with bacteria encircled several doctors around an operating room table, as the surgical team switched on a patient-warming system from 3M Co.

Each animated particle, displayed on courtroom screens this week, represented a skin flake 10 microns wide. Within 36 seconds, air turbulence deposited at least 60 of these flakes near a patient’s knee incision in the animated computer simulation.

The sophisticated computer-generated animations depict a key theory in thousands of surgical infection lawsuits that center on 3M’s Bair Hugger machine. It could be important evidence for jurors in litigation where microscopic particles are alleged to have been moved by invisible air currents into places in the body that skin normally would cover.

In a real surgery, 3M’s critics say, small numbers of such particles could be sufficient to trigger a serious deep-joint infection.

Maplewood-based 3M says the animations are misleading, if not wholly inaccurate. 3M stands behind the safety of the Bair Hugger forced-air warming system, which doctors use in tens of thousands of surgeries a year.

South Carolina’s Louis Gareis, 76, and his wife, Lillian, are the first Bair Hugger litigants to go on trial from thousands of similar cases. The trial began last week and is expected to run through next week. Gareis took the stand in court Tuesday.

He said a nasty deep-joint infection set in around his artificial hip shortly after it was implanted at a hospital in Columbia, S.C., in 2010, causing him to undergo another surgery to replace the infected joint. In both surgeries, he was swathed and warmed by a Bair Hugger device as a way to maintain his normal body temperature, a technique that is thought to prevent infections and speed up healing.

Gareis’ infection was caused by methicillin-susceptible Staphylococcus aureus bacteria, but his legal team has no direct evidence of a specific pathogen originating inside a Bair Hugger or being propelled by air turbulence created by the device. Rather, they presented a supercomputer simulation showing how it might have happened.

Following a preview during opening statements last week, several different versions of the simulation were shown to jurors in court on Monday.

Jurors also heard from California professor Said Elghobashi, the turbulence expert who led the team that created the operating-room simulation. Elghobashi was described to the jury as being well-respected in his industry, having done turbulence research for NASA among other past projects. In 2014, he was elected to the prestigious National Academy of Engineering for work including computer modeling of turbulent flows.

On the witness stand, Elghobashi said he has “99 percent” confidence in the results of the simulation.

His computational fluid dynamics (CFD) simulation shows how 3 million individual particles called “squames” should react to air turbulence created by the Bair Hugger’s system for warming air and moving it into inflatable blankets draped on patients. The CFD accounted for factors like the positions of clinicians in the operating room and the locations of inflow vents on the ceiling and air-return grilles near the floor.

In the simulation played for jurors, whorls of colored specs representing potential carriers of infection enveloped every participant in the operating room quickly after the device was turned on, as if the surgery were taking place in a dusty room where someone was using a leaf blower.

Elghobashi’s confidence on the stand was challenged under tough questioning from 3M attorney Jerry Blackwell of Blackwell Burke, who tried to show jurors that the simulations could be misleading, even if the supercomputer accurately applied the laws of physics to all 3 million particles in the CFD modeling.

For example, the simulation used a generic rectangular operating room, instead of the irregularly shaped Operating Room No. 4 at the Providence Health hospital in Columbia, S.C., where Gareis was treated. The CFD didn’t account for other heat-producing machines in Gareis’ operating room, nor the half dozen times that the room’s doors were opened during Gareis’ procedure.

And Blackwell got Elghobashi to admit that he didn’t know that the air-outflow vents in O.R. No. 4 contained fans that actively pulled air and particles out of the room:

“So when you created a CFD model that has 3 million squames all over the floor, billowing up like a cloud, you were assuming that there was not a powered air-return vent that was actively drawing air out of the room,” Blackwell said. “True?”

“True, but irrelevant,” Elghobashi replied.

“Of course. Thank you, doctor,” Blackwell said, smiling as he returned to the defense table.

The trial is expected to continue through next week.