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Inside Politics

Defense Questions Pathology Expert In Chauvin Trial. Aired 12:30-1p ET

Aired April 14, 2021 - 12:30   ET

THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.

[12:30:00]

LAURA COATES, CNN SENIOR LEGAL ANALYST: Question now being asked of now resigned Kim Potter against what happened to Daunte Wright.

JOHN KING, CNN HOST: Laura Coates, Cedric Alexander, appreciate the hustle on this breaking news story. And we're going to take you now right back into that trial. Again, this is Dr. David Fowler. He is a defense witness being -- he's in direct examination right now by Eric Nelson, the lead defense attorney.

DR. DAVID FOWLER, FORMER CHIEF MEDICAL EXAMINER, MD DEPT OF HEALTH: -- in your blood by looking at the color of your fingernail.

ERIC NELSON, DEFENSE ATTORNEY: How does carbon monoxide come into play in terms of pulse oximeter?

FOWLER: So the important thing is, it appears to be oxygen. It changes the blood to a color, which the pulse oximeter thinks is oxygen. So, if you take somebody who has 50 percent saturation with carbon monoxide, it will still read that the person is 95 percent oxygen. It doesn't tell you that this is 50 percent. So if a pulse oximeter was put on Mr. Floyd's finger in the vehicle, and again in the hospital, the pulse oximeter does not give us any information, allowing us to say he was or was not under the influence of some degree of carbon monoxide intoxication.

NELSON: How long does carbon monoxide typically stay in the bloodstream?

FOWLER: So it stays in the bloodstream, if you want to treat a person and put them on 100 percent oxygen, the half-life is about an hour and a half to two hours. If you're exposed to ambient air, it takes much longer to get rid of the carbon monoxide.

NELSON: And so I mean, essentially removing that carbon monoxide from the bloodstream is a reversible process?

FOWLER: It's not an irreversible blunt, it is reversible. So yes, it will, at some point slowly dissociate and be blown off. We do generate a small degree of carbon monoxide as part of our normal metabolism. It's a very low sub 1 percent. And it binds to the oxygen to the hemoglobin and eventually dissociates and is eliminated. So small amounts are not an issue and use it will dissociate and be blown off at some point as part of the normal metabolism.

NELSON: So how about how much carbon monoxide is needed to be absorbed into the bloodstream to diminish the oxygen supply?

FOWLER: Well, for a young healthy individual, you want to probably exceed the 60, 70, 80 percent range. That's what we typically see. However, in individuals who have risk factors that can be far, far less.

NELSON: How -- what type of risk factors would you look for?

FOWLER: So these are particularly -- the individuals that are particularly at risk of people with cardiovascular disease, as we saw in Mr. Floyd, and people with chronic obstructive lung disease would also be have a higher risk, and then other comorbidities, kidney disease, et cetera. But the real high risk one is going to be hard.

NELSON: And what percentage would you expect in when someone presents with those conditions?

FOWLER: Very difficult to predict in -- because everybody is different. There are studies out there where as little as 6 percent saturation of carbon monoxide in an individual who's exercising with heart disease will start causing arrhythmias. So it's a very low percentage. Now you have to have all of that, the heart disease and exercise. But at about 6 percent, there have been studies done in a controlled laboratory environment where people started showing EKG changes and premature ventricular contractions at about 6 percent. So it has potential to affect individuals at much lower levels than you would require for a young healthy individual.

NELSON: Now in terms of findings at autopsy, are there certain things at autopsy that can determine the -- what the presence of carbon monoxide or certain observations that physician -- the pathologists can make?

FOWLER: Yes. Typically carbon monoxide makes the blood appear. And in the terminology, it looks like it's cherry red in color. It's not the standard pink or slightly darker red color that we would see for deoxygenated blood. It's a fairly bright cheery red color. Hence the reason that pulse oximeters get somewhat confused as well.

Now when you get levels of 50, 60, 70 percent in the greater majority of the blood is carboxyhemoglobin, it stands out. But when you're looking at levels that are 10 percent, 20 percent, it doesn't and is not easy to see. A typical smoker, one pack a day will have and can have a carboxyhemoglobin of 6 percent. Two packs a day he can get up to 12 percent. We just don't see that as forensic pathologist because there is so much background color from the normal blood, that it's lost in that.

[12:35:15]

So I would expect a pathologist when there is substantial amount to spot it relatively easily. But I would not expect somebody to see the lower levels that can still be a factor. NELSON: And to do that you would need to test the blood?

FOWLER: That would be the gold standard, yes, test the blood and see how much carboxyhemoglobin is in the blood.

NELSON: So if, if you're not saying that carbon monoxide caused Mr. Floyd's death, can you likewise eliminate it as a contributing factor?

FOWLER: The only way to eliminate carbon monoxide as a contributing factor would be to ensure that there was none in his blood or a very, very low level in his blood. So in Mr. Floyd, it robs him of an additional percentage of oxygen carrying capacity. Whether that'd be 5 percent, 10 percent, 15 percent, it takes away from the important factor of getting blood to his heart muscle. So this is just another potential insult, another brick in the wall, unfortunately for circumstances, yes.

NELSON: Now, ultimately, the officers weren't affected by this?

FOWLER: No, they were not.

NELSON: And why would that -- why could that be?

FOWLER: Well, they're another two to three feet away. And potentially, hopefully, they're much younger, and hopefully don't have heart disease. So with every foot or more away, the amount of carbon monoxide in that particular bubble is going to decrease.

NELSON: OK. Now, so we've discussed the heart, we've discussed carbon monoxide, did you eliminate certain causes of death as well?

FOWLER: Yes.

NELSON: It's specifically referring to asphyxia.

FOWLER: Correct.

NELSON: How would you describe the investigation of custodial deaths compared to other types of deaths?

FOWLER: Very long, very complex, and something that needs to be done very, very carefully.

NELSON: Are there many variables to consider?

FOWLER: Absolutely, there are a huge number of variables, as we obviously can see in the case of Mr. Floyd as well.

NELSON: Now, in terms of this article here in your PowerPoint presentation, what's the significance of this?

FOWLER: So this is a -- an article that was put out in about 1992 by Dr. James Luke and Dr. Donald Reay. Dr. Donald Reay was one of the first pathologists to theorize that putting somebody in a facedown position was dangerous. And this was based on observations of cases where people were placed in a prone position, and they died. And so his conclusion was, that may well be effective, and needed to be considered.

But what Dr. Reay also does say, and later on he recanted that to a large extent. But what he does say is that these are very difficult, complex cases. Don't rush the judgment. Make sure you've considered all of the potential issues that are at play in these particular cases. And they even talk about a crystal ball in this particular case, and the risk of under estimating the importance of common sense, and the fact that there are no easy answers in such deaths.

NELSON: In your experiences as a forensic pathologist, if you had the opportunity to perform a death investigation and autopsies have in custody deaths?

FOWLER: Yes.

NELSON: So in this particular case, we've heard a lot about hypoxia, which organ is more sensitive to hypoxia?

FOWLER: The brain is the most sensitive or rapidly sensitive to hypoxia.

NELSON: In your review of the materials, did you have an opportunity to review some testimony of Dr. Baker in the prior proceedings?

FOWLER: Yes.

NELSON: Dr. Baker in his testimony referenced some studies in terms of the effects of positional asphyxia. Are you familiar with those studies?

FOWLER: Yes.

NELSON: Did you take those studies into consideration as far as your analysis of this case?

FOWLER: Yes. That is the current state of the science or the knowledge base with regard to this very difficult situation.

[12:40:00]

NELSON: All right. So let's talk to simply about the prone position. Do people sometimes sleep in the prone position?

FOWLER: Yes. Approximately 7 percent of the adult population sleep facedown.

NELSON: In terms of medical examinations, treatments are people kept in the prone position?

FOWLER: In certain situations, people are examined in the prone position. There are therapeutic maneuvers, where people are deliberately placed in the prone position. One of the best examples right now is COVID, where patients will be put in a prone position just facedown, and it improves their ability for oxygen exchange, not decreases it. So, you know, the proposition by itself does not have what needs, there is no evidence right now that that is a significant issue.

NELSON: In terms of this particular case, of course, the prone position is, you know, not in a hospital setting, right? It's on a street, agreed?

FOWLER: Correct.

NELSON: And just generally speaking, if I were, if a person were to lay down on the street in the prone position, with nothing on top of them is that in and of itself, inherently dangerous?

FOWLER: Now, the scientific studies basically have looked at the issue of the prone position with and without weight, and made a determination that there really is no significant impairment of individual's respiratory function. And those particular studies were very carefully crafted.

NELSON: Let me just interrupt you for a second, Doctor. Can you just -- what's the kind of the leading study on weights applied to someone in the prone position?

FOWLER: There are several but the one that I've recently read, well, not recently, but I know of is the one by Dr. Mark Kroll and a couple of other coauthors.

NELSON: And is that -- does that paper here?

FOWLER: Yes, I believe that is the one. Yes.

NELSON: Positional, Compression, and Restraint Asphyxia: A Brief Review?

FOWLER: Yes.

NELSON: Now, in terms of this study, can you just explain the study? Can you explain the setting of the study, et cetera?

FOWLER: So this is a review paper where he refers to various papers, including his own work, where no evidence of any kind of compressional asphyxia was found in individuals who were in the so called hogtie situation, which is prone, with their hands handcuffed behind their backs. Additional restraints glide around the ankles, and then the two tied together. That is the classical hogtie position.

And then, weights were applied to the individual up to 102 kilograms, which is 225 pounds, and found, again, no significant disturbance to their ability to exchange and breathe. And so the final conclusion was, and there are about 23 different studies out there. Dr. Baker referred to in his previous testimonies in that previous legal environment.

And in this paper, Dr. Kroll says positional asphyxia, as the term is used in court today is an interesting hypothesis, and then supported by any experimental data.

NELSON: So let me ask you, pursuant to the court's order, you were permitted to review the testimony or watch the testimony of other expert witnesses in this case, correct?

FOWLER: Yes.

NELSON: And did you do so?

FOWLER: Some of them, not all of them.

NELSON: OK. Did you hear criticism of this Kroll paper?

FOWLER: Yes, I did.

NELSON: And do you think that the study was flawed based on its methodology?

FOWLER: So, the study was asking one specific question, is the prone position dangerous? When you craft a experimental process to look at a particular process, in this particular case was the prone, you want to eliminate all other variables. You want to eliminate fear. You want to eliminate exertion. You want to eliminate environmental conditions other than and focus entirely on that one entity.

So agree that what is happening in this particular situation. They didn't use people who had heart disease. They used young healthy volunteers. The surface they were lying on was not asphalt. It was hard floor with a thin gym net on it. The individuals who are not in fear of their life, they knew that they could be pulled out of that at any time. And so there was no fear and hyper secretion of adrenaline and all of the other issues.

[12:45:17]

All they simply were doing is evaluating just the prone position and the weight on the back from the prone position, and found that it had no effect. So now you can go back and look at the other issues if you want to at some stage.

NELSON: OK. Now, in terms of this study, by putting weight on the back, how did that work?

FOWLER: So they were using bags of weight, sacks, and they continue to place them over the thorax, evenly distributed across the chest and upper abdominal area, the area which is where your lungs and the so called, pillows, and so it puts pressure on the diaphragm, if -- because of the abdominal weight and on the chest. And it looks to see whether or not individuals can still move in and then out. And they did not find any significant impact.

NELSON: Have you ever seen an image of like a team or baseball team winning the World Series?

FOWLER: Do you mean to a human pyramid?

NELSON: Right.

FOWLER: Yes.

NELSON: Is that -- is it kind of the analysis or analogy that they bring?

FOWLER: Yes.

NELSON: Kind of lots of people piled up on top, someone's got to be at the bottom, right?

FOWLER: Correct.

NELSON: Are there others, well, in terms of the Kroll studies, you talked about this particular study, are there or this particular paper that was a review of other studies, right?

FOWLER: His own and other work. Yes.

NELSON: And there were 23, I believe you said.

FOWLER: That was the testimony that Dr. Baker --

NELSON: OK, got you.

FOWLER: -- stated in my previous legal proceeding.

NELSON: So are these some of the other studies that they reviewed?

FOWLER: Yes. I mean, these are just a shortlist. It's not all of them. That's again, just illustrative of the developing information. And really, this has gathered a lot of steam over the last couple of years. So prior to many of these studies, the wisdom of the position is dangerous was still accepted. But you can see from 2007, 2012, 2013, 2014 people are really beginning to look at this with a critical eye. And really adding to the body of knowledge within the medical sciences and beginning to challenge some of these theories.

NELSON: Now, in terms of I mean, again, just the research, the criticism offered by previous experts, was that it wasn't real world. Were some of these studies looking at real world situations?

FOWLER: Correct.

NELSON: Which of those studies?

FOWLER: So the real world ones are the two papers by Dr. Hall, I think probably are the ones that stand out. The first paper where she took a city of 1.1 million, worth 1.1 million police restraints, it was a city of 1.1 million residents. And in that there were 1,296 cases where there was a forceful restraint. And the only death that they found in that particular case was a person who was not in the prone position.

And they evaluated prone versus non-prone, and statistically found no difference. That's it's a relatively small study. So they went under the biggest study, where they took four cities and looked at almost 5,000 consecutive force events and concluded and their valid conclusion was concluded that their data support the human laboratory data, which are these ones that are in the controlled environment, that the prone position has no clinically significant effects on subject physiology.

NELSON: Now, did Dr. Kroll also publish a paper relevant to the weight of a police officer?

FOWLER: Yes.

NELSON: And is that this study here?

FOWLER: Yes.

NELSON: And can you just describe for the jury, this study by Dr. Kroll and others and the impact of an officer's weight being a factor in the analysis of prone position and positional asphyxia?

FOWLER: So basically, his conclusion was it doesn't matter how much the officer weighs, you know, 140, 150, 200 pounds, it doesn't really make a huge difference to the outcome. What he did say is that with a double knee restraints, specifically, it's two knees on the person. It has a modest influence on the weight applied too. Now, these are not testing respiration. These were weight tests on dummies.

[12:50:26]

So what he's measuring here is, if a person weighs 140 pounds and they kneel on somebody, how much weight are they transferring? With a single knee, it didn't matter what weight the individual was, with a double knee, up to 23 percent of their body weight could be transferred to the dummy.

NELSON: Up to, I'm sorry, how much?

FOWLER: Twenty-three percent. So they were not looking, when you see it, it has a modest influence. It has a modest influence on the weight transferred, not respiratory activity.

NELSON: OK. Do you know, based on your review of the materials, were you able to ascertain Officer Chauvin's weight?

FOWLER: I was informed. Yes, I've seen that weight.

NELSON: And what is that?

FOWLER: One hundred and forty pounds is what I was told.

NELSON: Now you also, in reviewing the videos, you see that he has two feet on the ground with the exception of one small moment?

FOWLER: Yes, that was what I did actually see in the video.

NELSON: So what portion of Mr. Chauvin's weight was transferred on to Mr. Floyd's body?

FOWLER: He's using a single neat technique through the greater majority his other knee is either on the bicep area or on close to the left chest wall. So single knee tech, it's going to be less than 23 percent. But even if you'd applied both knees, which he would have transferred 23 percent of his body weight 440 pound person that would be between 30 and 35 pounds.

NELSON: Less than 225 pounds from the laboratory experiments?

FOWLER: Yes. Yes.

NELSON: So in terms of, you know, let me ask you this first. In terms of the placement of Officer Chauvin's, excuse me, knee to Mr. Floyd, is it your opinion that Mr. Chauvin's knee in any way impacted the structures of Mr. Floyd's neck?

FOWLER: No, it did not. None of the vital structures were in the area where the knee appeared to be from the videos.

NELSON: Now, again, in terms of your death investigations, you've reviewed photographs, you've reviewed the autopsy photographs, things of that nature, correct?

FOWLER: Yes.

NELSON: Were any signs of, well, generally speaking, do signs of injury play into your analysis as to the cause of death?

FOWLER: Yes,

NELSON: How so?

FOWLER: Well, you make an observation of, such as in this particular case, of a knee providing force to a particular part of the body. And then you go and you look at the same part of the body to see whether or not you can find corroborating evidence within the body itself, either an abrasion to the skin, subcutaneous hemorrhage, hemorrhage into the muscles, or other injuries that may be caused by the knee.

NELSON: And what injuries did you observe in the photographs of Mr. Floyd.

FOWLER: All of his injuries were in areas where the knee was not. In other words, they were on the front of his body, his face, his -- places where he was restrained. But there was absolutely no evidence of any injury on the skin, to the subcutaneous tissue, or the deep the structures of the back or the neck.

NELSON: Were there any broken bones, spinal injuries, anything of that nature?

FOWLER: There were no broken bones documented. I did not see a description of the spinal cord in the autopsy report. But given that there was really no external evidence of the area, the muscles around the spinal column. I would be very surprised if there was any spinal cord injury in this particular case.

NELSON: So you reference the back of Mr. Floyd, did you see any bruising to the skin?

FOWLER: I did not see bruising or abrasion to the skin.

[12:55:03]

NELSON: Did you see any bleeding into the subcutaneous tissues of the neck and back?

FOWLER: No, not on the autopsy photographs nor was it documented in the autopsy.

NELSON: How about to the muscles?

FOWLER: The same.

NELSON: And so in your opinion, the absence of such injury, how does that speak to the cause of death?

FOWLER: It speaks to the amount of force that was applied to Mr. Floyd was less than enough to bruise him.

NELSON: So in terms of the knee, can you, I'm looking at your PowerPoint here, can you help us understand how the knee relates to questions of injury and force?

FOWLER: Well, there are two structures that would be of concern in this particular case, one would be the actual knee itself and the other would be the tibia, which is the shin bone. This diagram shows the shin bone. And this is, this object right here. And if you remove that particular red circle that I've just put in, you can see that the tibia has a relatively defined front edge right over here. And you can feel it on yourself.

But there's a nice rich all the way down, which is actually quite prominent and hard and its right underneath the skin. And so that allows an unforgiving surface such as the shin bone to be placed on soft tissues which are more vulnerable and cause some degree of injury to that area. So that's the shinbone.

The knee isn't actually not that much different, the knee is somewhat spherical, you've got the patella, and you've got the ends of the femur, the thigh bone on either side, and you've got the ends of the tibia, just below, all of which are bony prominences. And again, right underneath the skin. And they can direct the amount of force. If you put a substantial, you know, 30, 40, 50 pounds worth of force focused with your knee onto somebody, in my opinion, the chances of a subcutaneous or intramuscular hemorrhage is very, very high.

NELSON: And you didn't see that in this autopsy.

FOWLER: It was not documented and it's not visible on the autopsy photographs.

NELSON: In your career as a forensic pathologist have you looked at other strangulation type cases?

FOWLER: I've, yes, strangulation and other restraint situations where knees have been used. Yes.

NELSON: Do you typically see marks in those cases? FOWLER: In the manual strangulation, often you will see hemorrhaging into the muscles of the neck. And in cases where the knee has been used on the back, we often see a bruise consistent. And with times, we have matched to video cam footage of where we see a knee pain placed. Yes.

NELSON: Including just fingerprint finger marks, I suppose.

FOWLER: Yes, so just the pressure from somebody's fingers is enough to cause muscle hemorrhage in a manual strangulation case. We're not talking about person putting weight on somebody. We're just talking about somebody squeezing your neck.

NELSON: When you look at this case, and you see the knee is involved, the shin bone is involved, would you expect to see a greater likelihood of bruising from just the fingers?

UNIDENTIFIED MALE: Objection Your Honor, off the speculation.

UNIDENTIFIED MALE: Overruled.

FOWLER: Sorry, can you repeat the question?

NELSON: Sure. In this particular case, where the knee is involved, there's allegations of it being used to force or subdue Mr. Floyd, would you expect the knee and shin bone to have a greater likelihood to produce bruising?

FOWLER: Than fingers? Yes.

NELSON: And is there any objective medical findings in the autopsy showing pressure placed to the back?

FOWLER: No.

NELSON: Now, again, we've talked about hypoxia and we can take this down now, Judge. We've talked about hypoxia. What are the effects of hypoxia that you would expect to see if that were present?

FOWLER: So there are some observable symptoms when a person becomes hypoxic, is that what you're asking, counsel (ph)?

NELSON: Yes.

FOWLER: Yes.

NELSON: What are those?

[13:00:00]

FOWLER: So people typically start to get a little confused, disoriented.