Having stepped out of his ride due to the discovery of blood clots – very unusual for an otherwise healthy 26-year old – Brian Vickers’ future in racing has been a big question mark.  Brian is one of the smartest (and kindest) drivers I’ve met.  He is one of the few drivers that could have his choice of a wide range of careers if racing were on the list of permanently prohibited activities.  Luckily, as we found out Saturday, it’s not.

The heart is a pump that circulates blood throughout the body.  The adult heart has four chambers:  two atria and two ventricles.   Ventricles send oxygenated blood through the arteries to muscles and organs.  The right ventricle discharges into the lungs, where the blood picks up oxygen molecules.  The left ventricle discharges its blood toward the rest of the body via the aorta.  Veins carry the de-oxygenated blood back to the atria (plural of atrium).  The picture is from wikipedia.

That’s the adult heart – you don’t start out with four chambers:  you start out with one ventricle and one atrium. The septum primum starts growing downward, which divides the single atrium into a left and right side, as I’ve tried to show schematically below .  (The word “septum” almost always denotes a flexible division, whether it is chambers of a heart or between a vial and air.  The cartilage that separates your nostrils is a nasal septum.)  The septum primum (literally “first septum”) that divides your atrium isn’t entirely continuous – there is a hole in this septum.

Somewhere around the third to fourth week of gestation, a second septum (the septum secundum) grows on the right side of the first septum.  This second septum, which is parallel to the first one, covers most of the original opening, but not all of it.  This opening, called the foramen ovale, is not a hole – a hole would allow blood to flow in either direction.  The foramen ovale is a one-way flap that allows blood to flow only from the right atrium to the left and not vice-versa.  In the womb, a baby gets oxygenated blood via the placenta through the umbilical cord.  Blood doesn’t need to make the trip to the lungs to gather up oxygen because the baby isn’t breathing air.  Bypassing the lungs isn’t a big deal for a baby in utero.

In 75% of the population, this one-way path closes within three months after birth.  The blood pressure in the left atrium becomes greater than that in the right, pressing the foramen ovale against the septum, which allows the tissue to grow together and seal the flap.  In about a quarter of people, the flap doesn’t seal over the hole completely, which is called a PFO – a patent foramen ovale.  The PFO is a shunt, which means a shortcut, in this case between the right and left atrium.  In most cases, the hole is a few millimeters in diameter – large enough to present a problem because it allows blood shortcut the circulatory system.

The symptoms of PFO are: well, none.  You’re unlikely to know if you have a PFO unless something dramatic happens, like extreme pain in your extremities, or (the worst case situation) a stroke.  The first medical report of undiagnosed PFO related to stroke was in 1877.  A young woman had an embolic stroke – blockage of an artery, usually by a blood clot, but blockages can also be caused by air bubbles, cancer cells, clumps of bacteria from an infection or even fat.  Brian noted that they found a blood clot in his left pinkie (I think it was his pinkie – I was driving and not taking notes.), which was an indication that there was someplace in his circulatory system that was allowing blood (and clots) to go where it shouldn’t.

As Brian mentioned during his press conference, diagnosing PFO (or any other kind of heart defect) requires invasive procedures, such as transesophageal echocardiography – an ultrasound device is threaded through the mouth, down the esophegous to allow better images of the heart that you could get from outside the body.  Other means of diagnosis include threading an ultrasound probe into the heart, or heart catheterization.  Although many people successfully undergo these diagnostic processes, there is an inherent risk anytime you start poking around the inside someone’s body.  Once a PFO is found in an otherwise healthy person, most doctors advise having the hole fixed.

It used to be that open-heart surgery was the only way to fix these types of heart problems – I think Brian telling us he was doing 30-60 miles of cycling in Denver within a month after the surgery is pretty strong evidence he didn’t go that way.  I have no inside knowledge as to the particular type of repair Brian had, but the most likely surgery would be catheter introduction of a device that seals the hole.

How do you fix a hole in the heart?  It’s actually a little like fixing a hole in drywall.  Most of the devices for fixing holes in adult hearts deploy through catheters (thin tubes that can be fished through your arteries and veins much like wire is fished through a wall when you’re wiring a stereo system).  Sorry for all the home repair analogies.  I spent a lot of time at Lowe’s this week.   The catheter is inserted into a vein in the groin and slowly threaded up to the heart.

Although there are a number of different types of devices, most work on the same principle – two discs designed to sit on either side of the hole.  The devices are usually made of Nitinol (an alloy of nickel and titanium) which forms a mesh frame onto which fabric is adhered.  Nitinol is popularly called ‘memory wire’.  You can form a material into a shape at high temperature, for example.  Let’s say we make a disk from a hot piece of nitinol.  Then we cool it down and deform it like an umbrella.  That allows us to stuff the device into the catheter (which is really just a tube).  (Here’s a YouTube video showing the effect with a spring shape.)

When the catheter reaches where it needs to be, it can be heated (by thermal conduction or current) and  recovers its original, disk-like shape.  An alternative method is simply to coil the device up inside the catheter and push it out once it reaches the target area.  One disk is inserted on either side of the hole and the two patches are pulled together.  The implant provides a scaffold for heart tissue to grow and cover the hole.  The tissue might not be able to span the hole by itself, but the implant gives it a path to do so.

Nitinol not only has a good memory, it is also biocompatible – the body doesn’t mind having it in there.  Some new eyeglass frames are made from nitinol – if you step on them (as long as you don’t actually break them) they can be heated and spring right back into shape.  We haven’t finished working on the self-healing materials problem.  Nitinol got its name from the elements from which it is made and the place it was discovered:   Nickel Titanium Naval Ordnance Laboratory.

A typical type of implant — and again, I do not know what Brian and his doctors chose -  is GORE HELEX – the nitinol is spiral shaped and uncoils when pushed from the tube, as shown in the picture at left.  The wispy white stuff is a polyer fabric.  The green tube in the picture is the catheter – you can see how small the device has to be to get in there and then how large it can expand.  There is a tether between the two disks that can be tightened to place the device so that it is entirely covering the hole on either side, and then locked in place.  I don’t know whether the shape-memory properties of Nitinol are being used here, or whether the superelasticity properties are the important thing.  I’m thinking it is the latter.  The primary competition is the Amplatzer septal occluder.  These are relatively new devices, earning FDA approval in 2001 and 2006.  Both have outstanding success rates in fixing holes in the heart.

Such a device shouldn’t set off metal detectors in the airport and, yes, you can have MRIs done after having such a device implanted.  The danger of the MRI is that metal heats up in the radio-frequency field of the MRI.  Also, MRI magnet strength is increasing – higher fields means better resolution – and there is always some concern that very high magnetic fields might cause a device to migrate.  The device could also blur MRI images in the region.  When you have such a device implanted, they give you a card with all these notices on it that you need to have and present anytime you get tests done.

The other issue Brian was facing is May-Thurner syndrome, which is when the left common iliac vein (which runs from the left leg to the large vein in the abdomen that leads to the heart) is compressed by the right common iliac artery.  The right common iliac artery runs to the right leg and normally travels over the left common iliac vein.  May-Thurner syndrome significantly increases the risk of deep vein thrombosis, which is forming blood clots in veins deep inside the body as opposed to surface veins.

Three primary components contribute to blot clot formation, a triad that is called “Virchow’s triad” after the German physician Rudolf Virchow, even though Virchow did not propose these elements, nor was he the one to suggest that there were three primary components for blood clot formation.  Those three components (in medical-ese and regular English) are:

• Hypercoagulability (the blood likes to form clots more than it should);
• Hemodynamic changes (the motion of the blood changes:  it slows down, lingers too long in one area, or becomes more turbulent); and
• Endothelial injury/dysfunction (the blood vessels are damaged in some way)

The first factor is the reason why people with blood clots are put on Coumadin, Plavix or other blood thinners/anticoagulents.  These medications decrease the ability of the blot to clot.

The second and third factors are affected by May-Thurner syndrome affects:  If the blood slows down, or has to move around an obstruction, clots are more likely.  The iliac artery crosses over the iliac vein:  In May-Thurner syndrome, the artery actually presses the vein against the spine, squishing the vein and preventing blood flow, as shown in the picture.

Your arteries and veins normally are pretty strong; however, your blood pulses with your heart contractions, so if the artery is too close, it doesn’t just rest on the vein, it actually rubs against the vein and causes the vein to rub against the spine.  All this rubbing can damage the vein, leading to compression and blood pooling.  Symptoms can include swelling and pain in the left-side extremities.

The solution to this problem is the same one you would use if you had an artery or vein that had collapsed due to other types of injury: a  stent.  A stent is a hollow tube, also often made of nitinol mesh, that is collapsed to fit in a catheter, then inserted into an artery or vein to help keep it open and allow blood flow.  A balloon is usually inserted through the target site (again using a catheter) to ensure that the area is clear before the stent is inserted.  (They use a balloon to measure how large the hole in the heart is, too.)   Stents can be impregnated with drugs to aid in healing the artery or vein, or even to discourage clots.

The prognosis for both these conditions is excellent, although frequent checks with the doctors are necessary to make sure that nothing unexpected happens.  Both conditions really needed to be addressed to minimize the likelihood of something happening in the future.  Although these types of surgery are inherently risky, the probability of success in a healthy young person is very high.

The main reason keeping Brian out of the car for the remainder of this season is the need to be on blood thinners:  blood thinners decrease the ability of the blood to clot, so what would normally be a minor injury could be major due to loss of blood.  A six-month course of blood thinners is recommended – the surgery was July 12th, so that puts mid-January as a perfectly reasonable time to return.

Here’s looking forward to seeing Brian back in the 83 at Daytona next year.

UPDATE:  I talked to a number of people this week while trying to resolve this because it was really bugging me not having a consistent answer.  They have some pretty convincing evidence that the angle was indeed significantly shallower than 90 degrees; however, if you run the numbers, I can’t get anything consistent with 100 g and a contact time of 0.008 seconds.  Just goes to show you what a challenge it is to try to figure out what happened without the evidence.  So despite how much it looked like a straight-on hit, it wasn’t.  It’s amazing to me that the camera provides such a distorted picture of reality.  I may never look at a NASCAR race the same way again unless I’m actually there.  So I’m wrong about the angle, but I think (unless I get data otherwise), I’m probably right about the time.  This is exactly why scientists have peer review.

Here’s where I think I got confused:  The attitude of the car (which way it is pointed) can be very different than the motion of the center of mass, especially when a car is sliding instead of rolling.  So even though the car hits head on, the center of mass can be at a shallow angle.

ORIGINAL POST:

While there is a lot of negative press about NASCAR keeping things “secret”, there really are some good reasons for not releasing crash information: One is simply that the data are pregnant with the potential for misuse. As is the case with everything from baseball to K-12 education, people want a single number to measure things against each other, even when it is meaningless to do so.

Sadler’s Pocono crash was really scary.  Thank goodness for the HANS device, the Hendrick carbon-fiber composite seat, and the redesigned car.  The folks at the NASCAR R&D Center – Tom Gideon foremost among them – have all the data (and the car) and will be analyzing it to learn even more about how we keep drivers safe.  Tom was one of the primary voices arguing for safety well, well before four NASCAR deaths in 2000-2001 made the need for action impossible to ignore.  Tom worked for GM Racing when racing safety wasn’t even on most people’s radars.  NASCAR didn’t start requiring black boxes on cars until the early 2000′s, but Tom was very active in advocating for black boxes in race cars in NASCAR and other racing series throughout his entire career.  He and John Melvin (another motorsports safety pioneer) gave a paper on the history of black boxes in motorsports at the last SAE Motorsports Conference.  (Indy cars were recording data as early as 1933!)  Tom is one of the good people in the business.

The biggest concern in a crash is the maximum force felt by the driver.  That force is the product of the driver’s mass times his acceleration.  Acceleration is how fast you change your speed, so we can also write the force in terms of the rate of change of the speed, or in terms of the acceleration. In the equation at right, the triangle v means the change in speed and the triangle t means change in time.  This equation says that if your change in speed is large (Δv large), it hurts. If you stop very quickly (Δt small), it hurts.

People talk about crashes in terms of “gs”. A ‘g’ is the acceleration due to gravity and it has a value of 32.2 feet per second per second, which means that, each second, your speed changes by 32.2 feet per second.  Everyone on Earth is (give or take a little depending on altitude) experiencing 1g of acceleration.  The force the Earth exerts on you is equal to your weight times the number of gs.

Let’s temporarily transport ourselves to another planet, exactly like Earth, but twice as massive. The doubled mass makes gravity twice as strong, so the acceleration due to gravity on this planet would be 2g.  If you weighed 150 lbs on Earth, you’d weigh 2 x 150 lbs = 300 lbs on this new planet.  (Don’t get me into the difference between mass and weight in the English unit system.  This is so much easier in the metric system.)  The ‘g’ is a handy unit:  multiply the weight of the object in pounds times the number of g’s  (unitless) and the product is the force.

Here are a couple caveats about “g” numbers:

1.  The black box is usually placed on the drivers’ side of the car, but it is attached to the car, not to the driver.  The car is designed to absorb the energy of the crash so that it is not transmitted to the driver. The seat is designed to absorb energy from the crash so that it is not transmitted to the driver.  The number from the black box isn’t necessarily an accurate measure of the driver’s experience.  If two cars’ black boxes have the same readings, but the drivers are in different types of seats, or the angles or speeds of the crashes are different, the drivers could experience very different forces.  The number is, however, a number that can be compared to other crashes in which the instrumentation was installed similarly.   NASCAR has a database of every bit of information they can gather from race car crashes and everything they learn during the investigation will be added to what they already know.

2.  You can not assume a spherical NASCAR driver (Make your own jokes here), or a spherical car.  The distance from axle to axle is 110 inches, so different parts of the car could experience very different forces.  The driver’s torso and head move very differently than his arms, for example.  The FIA (Federation Internationale de l’Automobile) is developing accelerometers (meters that measure acceleration) that fit into the radio earpieces drivers already wear.  These incredibly small devices can be less than a few millimeters cubed in volume.  If I were a driver, I’d want access to that technology so that I’d have an actual, real measurement of what happened to me.  Forget the car.  That is much more important than the deceleration of the car.  Something else we’ve learned is that the motion of the internal organs inside the body relative to the body is really important.  The driver may be strapped in securely, but remember that your brain, heart, lungs, stomach, etc. are basically floating around inside your body.  They don’t stop at the same time as the outside of your body.

Jeff Thompson, who’s done some forensic engineering (working backward from the scene of an accident to figure out how the accident happened) did a crash analysis to better understand what exactly happened.  A couple people asked me what I thought about the accident, since their intuition didn’t jibe with Jeff’s results.  Our intuition about the physical world is often wrong, so when I got back into town on Wednesday, I started looking into the situation.  Incidentally, Jeff is part of a great outfit called ten80 education, which has developed a lot of really neat RC car activities for kids of all ages.  They are doing a really neat job using motorsports to get kids (and their parents) interested in racing.  Jeff is also one of the good people in the world in my opinion.

Let”s start by calibrating ourselves with something closer to our own experience.  If you slow from 60 mph to a stop in a tenth of a second, you experience an acceleration of 27.3 gs.  If you weigh 150 lbs, that’s 4,095 lbs.  If you can extend that time to two tenths of a second, you halve the acceleration to 13.6 gs and 2,047 lbs.  The figure of merit  most safety researchers use in a crash is delta v – the change in speed.  That’s proportional to the product of the acceleration times the time.  I’ve written the formula, so all you have to do is pull up Excel, plug in the time of the collision and the number of ‘gs’.  If you do that, you get the graph shown on the right. (If you click on the graph, you can get a larger version of it, which is a little easier to read.  This is true of most of the diagrams in my blogs.)

I’ve drawn three lines representing 80 g, 100 g, and 120 g.  The horizontal axis is the  collision time — the time during which the speed of the car is changing, which is usually the time during which there is contact between the car and the barrier.  If you use 100 gs and a collision time of about 30 milliseconds (three one-hundredths of a second), then the change in speed would only be about 66 mph.  This confused me a little because my perception from watching the video was that Elliott’s crash took place over a relatively long time (as crashes go).  That didn’t seem consistent with Elliott’s reaction, either.  The berm into which he crashed is an earthen mound surrounded by Armco barriers.  The mound is pretty wide, but if you look at the video, you can very clearly see dirt being ejected from the other side.  That’s good because that’s energy absorbed by the barriers.  (If this crash had been into a concrete wall, it would have been an entirely different story.)

Another reason I would argue that the crash was longer is that the car was severely smushed, which means the center of gravity traveled further than it would have if the car bounced right off the barrier.  One of the front wheels was pushed back at least a foot or a foot and a half.  The time it takes for the center of mass of the car to travel 2 feet at 180 mph is 0.016 seconds.  That doesn’t even begin account to account for the time it took to crush the front end of the car and how much that slowed the car down.

We can break the car’s speed into two parts: a part along the wall, and a part perpendicular to the wall, as Jeff did in his analysis.  I’ve shown the part parallel to the wall in blue and the part perpendicular to the wall in red.  The angle at which you hit is important because the change in speed — along and perpendicular to the wall — is proportional to the force felt.

I’ve shown two angles in my drawing. The one on the right is a relatively shallow angle. The blue arrow is large and the red arrow is small. This is good because the force you feel when you hit the wall is (more or less) proportional to the length of the arrow in that direction. You feel a small force when you skim the wall. When you hit it at an angle, the component perpendicular to the wall grows.
It gets slightly more complicated, as I’ve shown in the next figure. The directions change when the car bounces off the wall. If you just look at the part of the motion parallel to the wall, both arrows point in the same direction.  The component of the motion that is perpendicular to the wall changes direction. That means that you actually undergo a much larger change in speed. If you were going 60 mph to the right, and you bounced off a wall so that you were going 60 mph to the left, you’d have a perpendicular speed change of 120 mph.

In most crashes with a barrier, the car continues in the direction it was originally headed and the change in speed in that direction is usually pretty small compared to the perpendicular component.  It isn’t, however, necessarily negligible, especially if the car hits at an angle and the wall creates a torque that causes the car to spin.  The drawing at right doesn’t show much difference between the before and after longitudinal speeds ; however, if the car slowed down a lot during the collision, it is possible that the force parallel to the wall was not negligible.  The angle at which the car hit the wall is incredibly important:  A glancing blow vs. a head-on collision.

Jeff makes a very important point I wouldn’t have thought to consider:  He notes that we have to take into account the orientation of the camera with respect to the  collision.  Have you ever looked at something exactly head-on?  It’s impossible to tell how far away it is.  The lack of perspective, he argues, makes the angle look very different than it is.  I’ve reproduced his sketch from his blog at left  (How I wish I had one-tenth his drawing skill!) His analysis comes up with an impact angle of 18 degrees, a change in perpendicular speed of 56 mph and a collision time of 0.008 seconds.  Those numbers just didn’t “feel right” to me.

Knowing the impact angle precisely is critical.  Calculating the perpendicular speed depends on taking the sine of the impact angle. Sine is a very nonlinear function (well, duh…), so not having an impact angle introduces significant error in the numbers.  The table below shows how the perpendicular speed changes with angle.  A change in angle of three degrees changes the perpendicular speed pretty significantly.  A change of 10 mph in impact speed corresponds to 21g if you assume a collision time of 0.01 seconds, (or 7 g if you assume a collision time of 0.03 seconds).  The sine of 90 degrees is 1, so a head on collision would correspond to a 180-mph perpendicular impact.

The video sure looks like Elliott hit at a 90-degree angle, but Jeff made his argument well.  Still, the 18-degree number was really bothering me, so I spent some more time looking at the video of the race and perusing Google Earth to try to understand where exactly the accident happened.  The video revealed that Google Earth isn’t necessarily very recent: the picture of the track doesn’t exactly match what the television shows.  In particular,  there are two perpendicular pieces of wall that run from the barrier to the access road that are not shown on Google Earth.  (You can see one of them in the still below).  So the angle of the bend might be different from what I’ve calculated, which is about 167 degrees.

The angle of the barrier isn’t the critical thing: the angle of impact is.  Here, the video gives us some additional information.  First, when the car hit the barrier, it sent dirt flying (the dirt is mounded a little over the Armco.)  Conservation of momentum allows us to use the dirt to tell us something about which way the car hit the barrier

That, in combination with the skid marks coming in, shows that Elliott actually hit the barrier pretty much head on, as shown in the diagram below (pulled from the ESPN coverage during the red flag.)  I think this makes it pretty clear that Elliott’s car was forced into making a hard turn and he hit the barrier nearly perpendicularly. (Thanks to Dr. Bob for watching out of the corner of his eye during the race and insisting that there were clearer pictures of the skid marks.  I was in an airplane during the race.)

You’d really like to slow down the car prior to its hitting anything.   Most large tracks have removed most of their infield grass because the coefficient of friction (especially when the grass is wet) is much lower than it would be on asphalt (even wet asphalt).  A high coefficient of friction (often attained with gravel traps, which aren’t great for the car, but much better than hitting the wall) helps scrub off some of the speed so that you’re not going as fast when you hit.  The explanation I heard is that Pocono is a designated wildlife refuge and that makes it difficult for them to remove grass.

If you were wondering (as I was) how Pocono installs 25 acres of solar cells and can’t pave over infield grass because it’s an environmental refuge, the answer is that the solar forest was put on some existing parking lots.  Major kudos to Pocono for taking this expensive, but important step to green.  More on that in another blog!

Let’s revisit the graph that tells us how speed change and time are correlated.  Here’s an expanded version of my earlier graph.  Let’s assume the worst possible case:  180 mph in and 180 mph out at a 90-degree angle (that’s exaggerated because a lot of energy was transferred to the barrier, but for the sake of worst-case argument…), this would suggest that the time of impact would have been a tenth or two-tenths of a second.  Reviewing the video, that’s not unreasonable.

We can never make racing 100% safe.  Buddy Baker mentioned on his Sirius radio show that the hardest hit he experienced was due to a stuck throttle at Martinsville, a track where speeds are rarely high and the thought of putting SAFER barriers around the inside seems almost silly.  Virtually all types of motorsport have had a reactive attitude toward safety, making changes only after something serious happens.  The sign that this attitude is changing is that the seriousness of the incidents that spawn changes has decreased.  (See Las Vegas and Watkins Glen for example.)  Pocono announced they were going to make changes in the interior barriers after the last race, but there simply wasn’t time to do it before this race.

There is no reason why the highest-speed tracks shouldn’t be required to have SAFER barriers around the entire racing surface, inside and outside.  Yes, it’s very expensive.  In Pocono’s case, there aren’t even existing walls on which to build the barriers, and it is not a coincidence that the fastest tracks are frequently also the longest.  But perhaps NASCAR should set a goal that Elliott’s impact remains the hardest the sport ever sees.

It’s really easy to knock NASCAR.  It’s equally important to praise them when they get stuff right.  Kudos to NASCAR for all they’ve done – requiring the HANS, doing series research into safer seating, and designing the new car – that allowed Elliott to walk away from what could have been a disaster for the sport.  Here’s hoping they continue moving in a proactive manner when it comes to safety.

I was frantically trying to finish this video blog this morning and still make my plane to Florida, where I’m looking forward to covering the 12 hours of Sebring American Le Mans Series (presented by Patron Tequila) race. You’ll have to excuse the glitches in the video editing while I am figuring out this new mode of communicating!