Dr. Martin Tobin simulates how George Floyd couldn't breathe

Tobin is a medical expert who testified at the Derek Chauvin murder trial.
13:29 | 04/08/21

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Transcript for Dr. Martin Tobin simulates how George Floyd couldn't breathe
Let us walk through exhibit 949. Where you can prevent. And I can tell us what we're seeing OK you. No you can see the car is being rotated curious to see. Officer show them here at C officer king and then officers laying down at his feet. You see underneath mr. Floyd's another cards being rotated the car has been removed. And so Erie it is to see how their positions at different points. In terms went off associating him with his left knee on the day. He's right neon. Mr. Floyd's arm and chest and then you can see here officer main holding his legs and then. You can see officers he would he's needs. On his torso. So this represents a snapshot in time as you told us. Did the officers positions. Change over time as they were there on the ground. He has stated that the officers positions changed over time and also the position of mr. Floyd himself. Changed over time and these become relevant. In how we evaluate everything. And it wasn't something you factored into your analysis yes. Did you consider where is to show ends left knee was during the encounter. Yes. Four. Officers show opens and that left knee is virtually on the neck forgotten that the vast majority of the time. And and when you say vast majority are you able to. What is more than 90% of the time in my calculations are certain times where it becomes difficult. Because you don't get a good view. Where two so for example I know. That an office who sharpens right he is on he's back 57%. Of the time. The reason I'm not able to save for the foreign PT percent is that I don't get a good view how can other times. Don't have a good view of exactly where it is. So did you focus on the first five minutes and few seconds yes focused on the phone first five minutes three seconds because that is. To the time that that we see evidence of brain injury. So it gives this is his children his right knee was on his back from time to time. At other times it was place where Europe's or and he didn't it was placed. On his arm or and then rammed in to mr. Floyd's left chest so really you. Where they are making a distinction of Clinton than the is. On the chest per say or whether it's on the left arm and rammed in against the left chest. From the point of view breathing. The effects are extremely similar. So let's let's turn to. Be their number one and only the four years either of them of that game. Someone would do to turn back to the notes that the number one here that written down for the reasons you told those four employees low oxygen tube for oxygen. Handcuffs and the street. To talk about the first U. Could you first our doctor Tobin tell us. How these various mechanisms before that you discuss handcuffs industries and the other man prone position. He on the neck back. Knee on the back arm inside how those mechanisms fall into your work either respiratory physiology. Or clinical medicine. They don't have an awful lot to do we can include medicine that they are directly related to my work in physiology. So in understanding the forces. That the body has to cope with these become fees are crucial into terms as the various forces that are involved in physiology. So then turning to leave the first one in handcuffs. And the street the very first one. What is the effect of the handcuffs in the context of what happened to mr. Floyd. He handcuffs are extremely important in mr. Claus. But the handcuffs on their role and just had cost per say are not that important it must be handcuffs combined with the street. And it's because. Positioning of the hang coax it back. Then how he's manipulated. With the handcuffs. By both officers shop and I'm by officers came how they manipulate the handcuffs and their Cushing the handcuffs. Into his back. And pushing them high. Dan on the other side you have the street so this three she's playing a crucial part. Because he's against the hard asphalt street so the way they're pushing down on his handcuffs combined with the street. He's the left side and its critique unity the left side we see that it's like the left side is in a fights. It's totally being. Pushkin squeezed in from each side from the street. At the bottom and then from the pad to waive it and handcuffs or manipulated it's not just handcuffs. It's how to hang Coetzer beat hello how they're being pushed queer that are being pushed. That. Totally interfere. With essential. Features of how we believe. So. Missed the point is is pancake between the pavement underneath them and enforced on top of presides. Now could you help us to explain how this mechanism. Leaving handcuffs and history. How does that explain the shallow breathing that you described. So this gets back to how we agreed. And this is fairly simple. So the way we breeze we have to be muscles that how this would greet the we have to die different. And we at the really cage muscles. To die from com does 72%. While we need for breathing and about Turkey percent to becomes from the UK each. And there's plan to die from contracts. Are to relocate its contract. They expand the chest and when you expand in the chest. Then here flows in from outside and is coming in and that's all that happened Sonny inspiration. But to expand their chest there's two crucial. Actions that have to happen and we prefers to do these but. The terms pumped hands and the patent. So is thought that Handel is simple and so if you have to have regular pocket that you carry walk through it. And you lift up the hands of the bulk of the hands of guns up like it's. And so when you contract your diaphragm. You are performing a bucket hand to movement. Here on the rib cage so you contracts or die from like that in each time. As you inspire you can see yourself as you inspire each of you there in the jewelry gates firing his seat that you read pages going out which like that that's the pocket hand movement. The second movement that you have is called to pump handle. And this reflects to an old water pump it could be in the are paid for that. It's pumping out water and so you have to hand the top of the pulp. He ended. The pulp each time and the water comes out just at the bottom so you're feeling up. Get your container of water so we better action your fifteen appeared this refers. To differ on to back movement of the chips fall so women that are pump hadn't. Your chest goes out with each breath. And so that you can do dangers has he taken deep rich you can feel that front to back here expanding your chest. The front to back expansion of your chest. Is what you're compact. This the same time you're doing both of them at the same time at the same time you're doing that. Your big chase is expanding from side to side and vastly richer. Though it took so both of these are occurring. And these are fights without peace she can't breathe. If you don't have the bucket hand to work and in the compound to work and there's nothing that now there's nowhere going to get in there. Doctor in this case were you able to observe. Whether this is for his breathing was impacted about a handcuffs and the placement on the street. Yes I want. What did you observe October. While what I observed is particularly. Is in terms are. The hands of the police and the handcuffs. Particularly on the left side so that they were. Forcing his left wrist on into his chest forcing it in tight against his chest forcing it high off. And you have to keep in mind that the opposite side of this is the street. So he was being squashed between the two sides and so this meant that he couldn't. Exert his home Patton book does that mean this three totally blocked his compound and there was no way he could do any. Front to back movement and again the way they were pressing in on the back there was absolutely no way that he could do any front to back movement. Dan in addition because of the me that was ram -- and against. The left side to his chest sometimes and he was found. On the arm arm pinned against the chest. So these would have the same effect so basically. On the left side of his long. It was almost like this search for the human and commitment was almost hit the effect as soon as surgeon had come in and removed along not quite but this along those lines so there was virtually. Fairy leaked to the opportunity for him. To be ms. guess and he shares moving into the left side these checks. Hell he was going to be totally dependent on what he he has to do with the right side. Have you selected any footage from the body worn cameras that you feel depicts mr. Ford struggles to read yes. I'm gonna show you what's been marked as State's exhibit and I'm 44. First would you describe what it is but what you're seeing here. He is. Unbeaten doctor told jurors aren't seeing emphasis describes our record doesn't. They will not see this I'm describing what crime scene for now yes yes OK that's an. Look what I'm seeing is that. He is left hand he's being grabbed him by the police officers. So that's how I'm cost left hand. And it's being pushed into his chest so he's just not able to expand that. In addition news what I'm seeing. Homes. Oh and I want to just yes I didn't solar cells alone fairly and they aren't. I'm misunderstanding Yahoo! offer states to deny 44 ended. Record he's. Are now doctor told the jurors can see who can select giant colleges. Memos. Quite all right would you tell us what's the significance of the. Let me now you're able to see here with the arrow -- curious to see. The officer is holding mr. Floyd's left hand. He's holding it very firmly there's a very firm grasp on it. And then mr. Floyd's left hand is being pushed in against his chest. Also we're it was to see just on the side. That officer shot guns hand need is coming in and that's compressing him against his side as well. So the ability to expand his lead shot. Left side here is enormously impaired. And also you're seeing that these signs that the chain between the two. The right side in the left side is very short. So he he's hole left arm is also being combed over. And so it's preventing him also from expanding the right side I've been focusing. Under rocket had food and de Palma had to on the left but you can also see here. That these are impaired his ability. To stand his chest. And of course the key factor you must keep that isn't kind of innocence seen here in one sense he's the street. Deceased his clutch his having a huge effect because he's jammed down against the street and so this three his trading the major role. Day in preventing him from expanding his chest.

This transcript has been automatically generated and may not be 100% accurate.

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