Herndon Presentation Script

Slide 1: Title Slide

Slide 2: Introduction to Impact Biomechanics. The first chart outlines the three-step procedure necessary for a biomechanical evaluation: Head Impact Analysis, Human Body Dynamics Analysis, and Brain Injury Tolerance Analysis.

In order to initiate the first step (Head Impact Analysis), numerous scientific investigations must be carried out - viewing the accident site, testing the different materials involved in the accident, etc.

Slide 3: Identical Impact Load refers to an identical impact of the same severity.

Slide 4: After taking all parameters listed in the previous slide under consideration, we look at the motion of the brain inside the skull.

Slides 5-12: Engineers define the severity of brain motion using six parameters: three of them are linear (straight line) motions (red arrows); three of them are rotational motions (yellow arrows).

Slides 13-20: On the days prior to July 3, 2000, the Flamingo Hilton decided to replace carpet in the casino area. Slot banks, chairs and all fixtures were removed from the area where the carpet was to be laid, and the casino area was properly closed. Unfortunately, after the carpet layers had gone home for the weekend, the casino chose to reopen the casino for the Fourth of July weekend, despite that the carpet installation was not complete. The slides you are now viewing depict the accident that was destined to occur. Throughout the casino, various duct plugs exist so as to enable the casino the flexibility to place their banks of slot machines in any configuration they desire. As the carpet layers removed carpet, they noticed that one of the duct plugs was missing its cap. Unfortunately, when the casino chose to reopen the casino area for the holiday weekend (leave no floor space without a slot machine), the plug was not replaced. The carpet was simply placed over the open duct. Tape was placed so as to "seam" the carpet where the old carpet met the new. As Mr. Herndon leaned forward on his stool, the right front stool leg fell through the carpet seam (covered by duct tape), into the open hole. Mr. Herndon was thrown forward and his head struck the table holding the slots.

Slide 21: An engineering investigation includes a variety of laboratory testing. In this case, two groups of testing, Force Deflection testing and Coefficient of Friction testing, were performed. The Force Deflection testing evaluated the stiffness of different surfaces while the Coefficient of Friction testing defined how slippery the surfaces were.

Slide 22: Force Deflection - Testing was conducted on a compression machine which assessed how much "give" a particular surface has when external forces press on it. We used the machine to test multiple materials. In the following slides we show examples of testing on two different surfaces: carpet and particleboard.

Slide 23: Testing on carpet - these results are shown in graph form. As you can see in the background, the plunger used for the compression testing matches the geometry of the human body (legs, arms, etc.).

Slide 24: Testing on particleboard - This testing was done with a different plunger that matches head contact with the surface of the table that was supporting the slot machine.

Slide 25: Coefficient of friction - the purpose of the testing was to gauge the slipperiness of different surfaces. We tested a variety of different materials; in the following slides, we give two examples.

Slide 26: The test is performed with a precise force gauge that measures the pull force of the test sled.

Slides 27-29: The Greek symbol "Nu" is the engineering symbol for the coefficient of friction.

Slide 30: The Analysis section is divided into two parts: analysis of security video footage and computer model analysis using ATB software.

Slide 31: Analysis of video footage - based on this analysis we were able to accurately determine precisely how Mr. Herndon struck his head.

In this particular frame, the angle of the upper torso, head, and neck were evaluated. Other body segments were analyzed with different frames from different cameras, as you can see from the subsequent slides (slides 32-35).

Slide 36-37: Head Kinematics - in the Head Kinematics section, you'll find two frames from an overhead security camera depicting Mr. Herndon just before the head strike. You can visualize Mr. Herndon's motion by toggling back and forth between the two frames - the first frame is just a few inches before the head strike, and the second frame is at the moment of the head strike.

Slide 38-39: Detailed measurements of distances and angles are superimposed on the video frame.

Slide 40: This photo shows external abrasions on Mr. Herndon's head that occurred as a result of the head strike.

Slide 41: Based on the inspection and measurement angles, a detailed analysis was performed to consider any possible variations of the head motion.

Slide 42: Comb artifact effect - This specific case was unique in that there was a wealth of information available due to the video surveillance footage. However, in order to take advantage of this information, a detailed understanding of video surveillance techniques must be gained.

Video from a security camera has a certain number of fields per second. Each field was taken at a different time. Anything that moves will appear in a different place in each field. However, each field doesn't contain all the scan lines of an image; instead, they contain only half of them - that is, every other scan line. So if one field contains lines 0, 2, 4, and 6, the next will contain 1, 3, 5, and 7. When a computer displays the image it combines two consecutive fields to make a complete image. As a result, there are comb-like artifacts whenever there is motion.

Slide 43: Based on this science of video preparation, we can conduct a time/velocity analysis (i.e., we can see how quickly Mr. Herndon's head moved and how far it moved).

Slide 44: The remaining portion of the analysis involves a detailed study of Mr. Herndon's whole body using 3-D software called Articulated Total Body, or ATB.

Slide 45-47: This software is used by the United States Air Force and the National Highway Traffic and Safety Association (NHTSA) as described in their respective official publications.

Slide 48: The results from the software provide a complete assessment of impact severity, including parameters such as Head Impact Criteria (HIC), Head Impact Power (HIP), Head Angular Acceleration (HAA), and others. All parameters are engineering concepts used to describe the severity of motion.

The meaning behind these parameters becomes clear if you compare them against human tolerances, or the ability of the human brain to withstand certain severity of motion. In this case, only the last parameter, Head Angular Acceleration, is greater than human tolerances. Keep in mind that the tolerances given in this comparison are tolerances for "serious" brain injury. In the science of trauma biomechanics, this level of injury is described as the Abbreviated Injury Scale, or AIS, level 3.

The comparison between computer-based calculations and video footage is proof that the mathematical formulas and calculations that describe Mr. Herndon's motion are in agreement with images captured by video - in other words, the mathematics match the reality.

Slide 49: Animation - Two animations were prepared. The first depicts the general manner in which Mr. Herndon fell down.

Slide 50: The second animation depicts the last phase of Mr. Herndon's motion (right before the head strike).

Slides 51-56: These slides depict various causes of brain injury using mechanical engineering terms and concepts.

Slide 51: Internal Impact of Brain (click on picture to view animation). During the impact, the brain resists movement due to inertia, leaving a space at the back of the skull. Once inertial force on the brain starts to be overcome, a centrifugal force lifts the brain, leaving spaces under it. Both the inertial and centrifugal forces cause the brain to impact against the skull. At some point, the brain stops and rebounds. The brain impacts on the skull with two motions, toward the back of the skull and toward the base of the skull. The brain motion toward the base of the skull occurs because stopping negates centrifugal force. (In addition to the magnitude of the impact force, one has to recognize the fact that only the front, top, and back of the skull are relatively smooth. The base of the skull contains a number of bony ridges that can contribute to brain injury.) Finally, the head bounces back to a position similar to the one held before the incident.

Slide 52 (click on picture to view animation): This slide depicts a gel-like material that closely represents the human brain response. In this laboratory experiment, we filled a model of a human skull with enough gel to approximate the amount of brain matter in the skull and imitated the motion of Mr. Herndon's head strike. Looking at the gel motion, you can appreciate to what extend Mr. Herndon's brain deformed.

Slide 53-54: Cavitation (click on picture to view animation). Cavitation is the formation and destruction of vapor-filled micro-bubbles in a liquid behind a rapidly moving mass. Cavitation is a phenomenon that has been thoroughly studied and is well understood in the mechanical engineering field.

As the mass rapidly moves, pressure in the front of it is high; behind the mass, pressure is low. In this low-pressure zone, vapor-filled bubbles are formed. When the mass moves in a backward motion, the pressures return to a normal level and the bubbles collapse.

Slide 55: Shear (click on picture to view animation). In engineering, shear is defined as the force resulting from the sliding of one layer with respect to another. In the human brain, the layers that slide with respect to each other are the layers of the brain. Shear occurs within the brain because of the rotational acceleration or deceleration of the head, the placement of brain layers at different distances from the point of head rotation, and the difference in density between layers. As a result, the outside layers shift faster and farther than the inside layers.

Slide 56: (click on picture to view animation): A magnified view of one brain cell, a neuron, shows what can happen when an axon of the neuron extends over different brain layers that move with respect to each other. The forces resulting form this kind of motion can result in damage to the axon and may cause a loss of function. This type of damage that is often found throughout the brain's tissues is called "diffuse axonial injury."