Good news?

As my mom always said, “You make your bed, you gotta sleep in it”. So even though I was sure I’d written my last post having anything to do directly with the Michael Schumacher tragedy, I just want to answer the hundreds of questions I’ve already gotten as to the import of todays statement.

1) It is obviously good news that Michael has left the hospital. Because of the length of time since Michael’s injury, and of the specific role of an Intensive Care Unit (ICU) in supporting and monitoring the function of the body’s major systems, it’s almost certain that Michael has not simply been discharged from the ICU to a rehab, without having “transitioned” by a stay on the regular wards. I have never seen a head injury patient with a 5 month ICU admission be transferred directly to a rehab facility . . . but anything’s possible. 

Remember that there are lots of rehab facilities that can handle ventilated patients, so this transfer also says nothing about whether or not Michael is breathing spontaneously.

2) The moment Sabine announced that Michael had moments of eye opening, we knew he was no longer in a coma. BY DEFINITION. Coma = no consciousness, no eye opening. Open your eyes but unconscious, it’s a vegetative state. Add fluctuating signs of interaction with the environment, it’s a minimally conscious state.

So what does that mean? Sabine is a professional. At the beginning of April, she told us Michael had moments of awakening AND of consciousness. Once again, by saying this, she told us in almost clinically perfect language that Michael was no longer in a coma. She used two terms that only specialists actually distinguish; for laymen being awake and being conscious are the same thing. This language, then, clearly was used based on discussions with Michael’s care team, and reflected a highly accurate description of his minimally conscious state.

Now, we’re told, with what appears to be a bit of a triumphal air, that Michael is no longer in a coma. As stated above, THIS IS NOT NEWS. I cannot help but think that this is a highly cynical use of language, using the truth to convey an impression that is almost certainly false. I cannot but think that if Michael had emerged AT ALL from the minimally conscious state that Sabine so accurately described in April, we’d be told that Michael is leaving for rehab, that he is having problems expressing himself and will work hard to get better. Or that he’s having to learn to walk,read, write, etc all over again. But no, we’re told what we already know, and pretty much told to not ever expect further updates. Kinda like what I was thinking.

This all leaves a very bad taste in my mouth. And a huge space of sadness for Michael’s family, and for you, his fans.

A brief announcement

I’ve decided that I’m going to stop writing about Michael Schumacher, about his accident, and about what his situation may or may not be.

There’s not much more really to say. It leaves me with a leaden feeling in my gut that Michael is in his sickbed, and that more words aren’t going to help anybody with anything. And in terms of my blog, I think I’ve pretty much covered it all.

I’ll read all your comments as I’ve always done. Forgive the odd deletion – the criteria are fluid, and are highly dependent on whether they’re the first comments I read upon awakening, or rather in the near-euphoria of returning home after a long day at the hospital! Bear with me about that, and if a given deletion SEEMS illogical, trust me, it is. I in no way intend disrespect for your thoughts and for the fact that you actually WRITE stuff here. It still blows me away. But I’ll try to maintain a bit of decorum (totally arbitrary I know) in the comments, and will rely mostly on YOU to keep things civil. Or at least make the incivility so good that we all are dying to use it somewhere else. THAT would be worth it. And no, I’m not going to have an incivility contest. Hmm…

My interest in head injury, and in concussion in particular, remains, and will be a source of posts. The POTUS just had people to the White House to discuss this issue – there is a HUGE, almost evidence-based cultural tsunami going on, and its ramifications are enormous.

Anyway, see all of you soon.

Michael – five months on

First of all, I want to thank you all for your comments and questions since last week. We’ve got lots to talk about – today it’ll be a bit about Michael Schumacher’s situation, but I’m also going to be writing about the fascinating duel between Lewis and Nico . . . AND continue the series about trackside medical intervention.

I’m also looking at starting a video blog, as a way to better interact with you all. This will probably be through a YouTube channel; one of the things I want to do there is answer your questions in a more comfortable format. (If you’ve got questions you want answered, send them here to comments, and I’ll get to them once the v-log is up and running.

Tons of you have asked about Michael’s current status. Obviously I have no direct information. And I’m STILL considering that if there were good news to be had, we’d have been told. I can conceive of no possible reason that Michael’s entourage, understandably extremely protective of his (and their) privacy, would NOT tell his fans if significantly good things have happened. So as always, I’m speaking based essentially on the published and consensus epidemiology concerning outcome in severe head injury. And of course, as always, a reminder. Every caregiver working with a significant number of head injured patients has seen surprising and unexpected emergences. But these are rare, achingly rare.

Let’s take a look at what’s called a “survival curve” for patients in a persistent vegetative state (PVS) after trauma:

Image

On the graph, we’ve got time (in months) along the bottom, and percent of patients along the y-axis. At time 0 (the day of injury), we’ve got 100% of the study population of patients in PVS. Just as a reminder, PVS means apparent wakefulness (eye opening, something resembling a sleep-wake cycle, etc) without signs of consciousness (awareness of self and/or the environment).

As we move left to right, we see three sub-populations opening up – from top to bottom, there are those who regain consciousness, those who die, and those who remain in a vegetative state. Michael is now 5 months post-injury, but for the sake of simplicity, let’s look at the 6 month mark. Look at the line indicated by the arrows. Notice how at 6 months, this line becomes very nearly horizontal.

This horizontal line says, in the most eloquent and desperately sad way, that after 6 months only a tiny tiny fraction of patients in PVS regain consciousness. In essence, persistence of the vegetative state or death are the primary outcomes remaining. The slope of the line separating “dead” from “persistent vegetative state” shows the approximate death rate of these patients – roughly 25-30% per year. And just to repeat what I’d said in an earlier post, essentially no one in a persistent vegetative state at ONE YEAR will ever regain consciousness.

If Michael is in a minimally conscious state (MCS, defined as the presence of objective, but fluctuating and inconsistently reproducible signs of either self-awareness or interaction with the environment), the outcomes are slightly better. There would then be a low, but real, possibility of improvement in the quality of consciousness over the next several months to years. That said, agonisingly few patients in an MCS at six months ever wind up speaking, walking, dressing themselves, etc.

As to the rumours of Michael being at home, they could easily be true, but I have no way of knowing. This would be the kind of information I’d assume would be EXTREMELY closely held, for obvious reasons.

There is no reason why this shouldn’t be possible. If Michael is still ventilator-dependent, taking Michael home would require a certain amount of equipment and the round-the-clock presence of a significant level of care, but thousands of ventilator-dependent patients are cared for at home. If Michael is breathing on his own, home care becomes even more feasible. As you can imagine, patients with prolonged severe disorders of consciousness require a high level of care, but this would be something that Michael’s family could organise with no major problems.

I’m quite afraid (and virtually certain) we will never have any good news about Michael. At this point, I rather dread seeing that the family has put out a press release. . .

Some important science on disorders of consciousness – part 2

Image

An MRI scanner

Imagine this: You’ve volunteered for a brain imaging experiment to help study consciousness. You come to the MRI suite, and lie down. The researchers put an IV drip in place, and then infuse a form of glucose that “lights up” the brain areas that are activated at any given moment. So far so good.

You’re told to close your eyes and imagine hitting a tennis ball back and forth with a partner. Sure enough, this consistently activates an area related to preparing the brain for motor activity (called the Supplementary Motor Area, SMA, in yellow below). Then you’re asked to imagine walking around your house, and to visualise all the things you’d see as you navigated like this. And once again, the corresponding area, called the Parahippocampal Gyrus, (PG, in green below) lights up. Here’s roughly what the images look like:

Image

Nothing unusual or unexpected here. But now let’s go a bit further with the technique.

Let’s now take a series of patients (54 to be exact) who have been diagnosed with either vegetative state (remember – that’s eye opening without any signs of conscious interaction with the environment) or a minimally conscious state (awake, but with fluctuating but consistent signs of consciousness), and let’s try the same experiment.

Incredibly, FIVE of these patients  (10%!) could manipulate brain activity in response to the researchers’ requests. These people were, in fact, obeying commands (“think about tennis”, “think about navigating”), but their response wasn’t behavioural, it was . . . metabolic; what’s crucial is that they clearly showed signs of consciousness.

This was an amazing finding, but the investigators took the work further still, and, using a very ingenious trick, what they revealed shocked the world of medicine.

Let’s quickly put you back into the fMRI machine. This time, here’s what I’m going to do. I’m going to ask you a simple, unambiguous question (like, do you have a brother?). I’m going to tell you to think “tennis” for YES, think “navigation” for NO. (Rather like using fMRI activation as a “blink once for yes, twice for no” kind of communication tool.) Turns out this works fine, with 100% accuracy with normal subjects.

I guess you see where I’m going with this. Let’s take one of the patients diagnosed as vegetative but who has shown the ability to “light up” his or her supplemental motor area or parahippocampal gyrus on demand. Let’s do the same thing with him. Let’s ask him or her questions – tennis if yes, navigation if no. What happens? Let me quote the researchers: “. . . for those five questions, the pattern (of activation) produced ALWAYS matched the factually correct answer.” 

I’ll let that soak in for a moment.

These scientists just took a patient who’d been diagnosed as vegetative (and again, I’ll insist that this means NO CONSCIOUSNESS) and not only TALKED TO HIM, but actually got answers!

What are the implications? First of all, this study shows how hard it actually is to make a proper diagnosis of the vegetative state. Until now, this diagnosis relied on confidently stating that there is evidence of absence of consciousness, based on detailed and lengthy observation of the patient’s behavioural responses. But remember, these patients have severely damaged brains; the behavioural repertory of responses that they can show may often be so limited that none will be found. But this study emphasises that absence of (behavioural) evidence is NOT necessarily evidence of absence (of consciousness). The infinitely more sensitive “behavioural” response of metabolic brain activation could allow, in the future, clinicians to make this diagnosis with much more confidence. This obviously has enormous implications in terms of medical and ethical decision-making as concerns any given patient.

More importantly for us, this tool would appear to open up the possibility of actually communicating with some of these patients (a small minority at best, but still . . .). The current procedure is much too cumbersome, difficult, and expensive to use routinely, but it’s not too much of a stretch to imagine a future where helmet-sized mini-MRI machines are placed on the heads of patients with prolonged disorders of consciousness to allow their care team and loved ones to communicate with them.

There is a huge amount of fascinating and useful research being done on consciousness – both normal and disordered. Functional imaging is one of the most powerful tools in this quest for knowledge. As they say, watch this space.

Here’s a link to the original NY Times article about this research. The second contains a video by Liege’s own Steve Laureys (the lead researcher), explaining the technique. And the third is to a pdf of the original article, published in the New England Journal of Medicine.

http://www.nytimes.com/2010/02/04/health/04brain.html

http://thelede.blogs.nytimes.com/2010/02/04/doctor-demonstrates-method-of-speaking-with-vegetative-patients/?_php=true&_type=blogs&action=click&module=Search&region=searchResults&mabReward=csesort%3As&url=http%3A%2F%2Fquery.nytimes.com%2Fsearch%2Fsitesearch%2F%3Faction%3Dclick%26region%3DMasthead%26pgtype%3DHomepage%26module%3DSearchSubmit%26contentCollection%3DHomepage%26t%3Dqry575%23%2Flaureys&_r=0

http://www.nejm.org/doi/pdf/10.1056/NEJMoa0905370

Odds and ends

Well it’s been a long time, hasn’t it? As always, I follow your comments closely, both here and on Twitter, and I think it’s time to address some of the points that have been raised recently, and perhaps clarify a few definitions (nothing new here, pretty sure this stuff was covered in earlier posts) – simply because I’ve got a feeling that we’ll be hearing some of them at some point in the not-distant future. More on this later.

WEIGHT LOSS

I’ve been asked about the report that Michael has lost 25% of his pre-accident weight.

This is entirely possible, and in fact, probable. A few factors explain this. First, the initial injury, operations, and those few harrowing weeks when Michael’s life itself hung in the balance, minute-to-minute. This kind of situation subjects the body to a tremendous level of stress. Not psychological stress, mind you, but physical stress, accompanied by liberation of massive quantities of stress hormones. These hormones evolved for the “fight or flight” response, and were designed by evolution to promptly mobilise fuel for action. They do this by causing (among other things) breakdown of muscle to form amino acids, which the body can use as fuel. The problem is that when these stress hormones remain present for too long, it becomes very difficult if not impossible to replace the lost muscle mass, at least in the short term.

So Michael’s muscle mass was already fairly significantly depleted by the time sedation was stopped. At this point, what is usually called disuse atrophy starts eating away at the muscles. Since a patient in coma has very little, if any, movement, the muscles lose the mechanical stimulus that is a major factor in maintaining them during normal day-to-day activity. And although coma patients get intensive physical therapy, this is aimed at preventing the joints from stiffening, not at maintaining (or building) muscle mass.

There may well be a more subtle contributing factor as well. You see, the normal brain kicks out growth hormone at night, during our sleep. This hormone helps the body to build and maintain itself, notably by helping the muscles take up protein. It is entirely possible, even probable, that this pulsed pattern of secretion is lost (any neurosurgeons reading this, or neurologists, anyone in the know, just jump in!) in patients who no longer have sleep-wake cycles. It’s even possible that secretion of the hormone falls to very low levels chronically. This would also have the effect of taking away an important “trophic” stimulus.

Happily, the consequences are not particularly dramatic, at least immediately. To be blunt, a patient in coma doesn’t really NEED his or her muscles . . . with the exception of the diaphragm. The diaphragm, which like the heart is pretty much always active, resists atrophy rather better than other muscles, but it does atrophy. And having a machine doing the breathing for you is one of the best ways to see how disuse atrophy affects the diaphragm too. Unfortunately, and assuming (as I have until now) that Michael is being ventilated by a respirator, there is probably some degree of diaphragmatic atrophy at this point.

Now remember where Michael is coming from – one of the fittest, toned, and conditioned 45 year-old men on the planet. This means that if and when he can be weaned from mechanical ventilation, re-training his diaphragm shouldn’t be problematic. As for the rest of his muscle mass, should he awaken, the same ferocious appetite for pushing himself will no doubt lead him back to most of his former superb condition.

TRANSFER

I’ve also been asked why Michael hasn’t been transferred to a unit closer to his home.

Obviously I have no idea of the answer to this question, but several factors need to be considered.

First, from a medical point of view, once we’re out of the phase with dramatic and life-threatening elevated intracranial pressure, and barring other significant problems causing physiologic instability, the patient can be transferred arbitrarily far. The transfer needs to be prepared carefully, of course, but even hours-long flights are possible with intubated, ventilated patients such as Michael. So why is he still in Grenoble? I’m basing myself on the notion that Michael is still in the Intensive Care Unit, and is still being ventilated.

First of all, it clearly shows that his entourage is totally confident with the quality of care Michael is receiving.

It’s important to remember that Intensive Care Unit (ICU) beds are a very limited resource. Every day intensivists are asked to admit critically ill patients to units whose beds are all filled. This requires TRIAGE – deciding who has the best chance of being improved by being admitted to the unit. The “chronically critically ill”, patients like Michael who depend on technology (a ventilator) to stay alive, are a tremendous conundrum for ICU personnel. As time goes on (more detail below), it becomes less and less likely that Michael will emerge to any significant extent. Therefore, I think it is inevitable that should the status quo continue, the ICU staff may well, at some point in the not-distant future, decide that the patient they’ve just been asked to admit has a higher need for that bed than Michael, given his clinical situation and prognosis. This then could be a reason to organise a transfer – to a private clinic, or to an ICU-like environment that his entourage could build at his home.

Lastly, as I’ve mentioned furtively here and there, I think that serious lapses in judgement were evident during Michael’s initial management (I have this from usually impeccable sources who have access to this information). Because these lapses could (and almost certainly did) worsen the outcome in Michael’s case, it is possible that the staff at Grenoble feel duty-bound to NOT place any pressure on the family to transfer out, despite the terribly dismal prognosis . . . because of the clear (but unquantifiable) contribution of medical misjudgement to that prognosis.

(RE) DEFINITIONS

I think it’s useful to look at a few definitions again, briefly, for when this all starts to get talked about in the press, as I’m sure it will be fairly soon.

Brain Death: A brain-dead patient is dead. There is objective, demonstrable, and irreversible cessation of ALL brain function. When you use arteriography (special x-rays that show the arteries and the flow in them) to look at the blood flow to the brain, you see that there is NO BLOOD FLOW AT ALL inside the cranial vault. There is no reaction to any stimuli except for simple reflexes (which originate at the spinal level), and the patient will not breathe spontaneously, even when carbon dioxide levels are elevated. There are no living brain cells in the skull. None. At all. Families do not have to approve disconnecting these patients, as they actually are no longer patients, they are . . . dead. These are the patients who become, under certain well-defined circumstances, organ donors. Because the brain, all of it, is needed for the body to survive satisfactorily, the hearts of brain dead patients will not continue to beat more than a few days or weeks (a few cases of longer circulatory persistence have been described but this is vanishingly rare), despite the most aggressive treatment possible.

Coma: coma is defined as a state where the patient shows neither wakefulness nor awareness. So the patient in a coma has closed eyes, shows no evidence of a “sleep/wake” cycle, and shows absolutely no sign of any awareness of (or interaction with) either the environment or him/herself. Even painful stimuli fail to cause meaningful interaction. Depending on the areas that are damaged, these patients may or may not breathe on their own. That said, they will essentially always be intubated, and then tracheotomised, to prevent episodes of airway obstruction caused by the brain being unable to coordinate the muscles of the tongue, pharynx and voice box. They are initially fed by a tube passed through the nose to the stomach, and later (as is no doubt the case with Michael) by a tube placed directly into the stomach or small intestine through the abdominal wall. Usually a coma is defined as persistent when it has lasted more than two months after the precipitating event. For info, I assume this is Michael’s current status.

Whereas brain death is inevitably followed by circulatory death within days to weeks, patients in a persistent coma have somewhat brain function, especially in areas associated with maintenance of physiological stability (body temperature, blood pressure, water volume, etc). This means that the life expectancy for a comatose patient who does not improve neurologically is measured in months to a relatively few years. Once again, the brain is necessary to integrate those of the body’s activities which contribute to a normal lifespan.

Persistent vegetative state: here we must distinguish two things that almost always go together: wakefulness and awareness. Patients in a persistent vegetative state show signs of “wakefulness”, in that they have periods of spontaneous eye opening, and can even show cycles that resemble sleep-wake cycles. They are, however, unaware. There is a total, rigorous lack of any sign of self awareness (including pain, other than reflex responses, thirst, etc) or of the environment. These patients often breathe for themselves.

A vegetative state is defined as persistent when it lasts two months after the precipitating event. As we’ve mentioned previously, the longer one remains in a vegetative state, the less the likelihood of emerging, and the higher the chances of severe sequelae if the patient does in fact emerge. Most definitions consider the vegetative state to be permanent one year after the injury.

Patients who are in a persistent/permanent vegetative state have lifespans that are measured in months to a few years. This depends on baseline function (extraordinary in the case of Michael, of course), the quality of nursing care, and other imponderables. They usually die of respiratory or urinary infections. Longer survivals have been described, but are exceptional.

Minimally conscious state: here, as with the vegetative state, there is wakefulness. But here, there are signs, inconsistent, variable, but clear, objective, and reproducible signs of awareness: interaction with the environment and/or of self. Like what? Eye tracking, motor responses, smiling, turning the head consistently to voices, etc. Or appropriate reactions to stimuli. This state can also be persistent; it is significant because it represents the first stage out of the vegetative state on the continuum towards normal consciousness . . . and the first interactions the entourage sees from their loved one.

Minimally conscious patients also have a severely shortened life expectancy, but not quite as dismal as for “deeper” levels of disordered consciousness.

PERSONAL NOTE

I always knew Michael was adored. I spent years at circuits drenched in red by the ferrari caps, flags, and shirts, and all of that for Michael. I’m still staggered by the depth and persistence of his fans’ love for him. And whereas I worried more than a bit about what was going to happen when and if really bad news got announced, I’ve realised that perhaps the lack of status updates has given us all a chance to move on a bit, to process what’s happening, and to start to . . . detach. And I think this is probably one of the unexpected “benefits” to the media strategy chosen by Michael’s family. Somehow, I get the feeling that people are going to be ok, no matter what happens, because they’ve now had the time to process this all. I just regret that to get here, you’ve all had to work through feeling abandoned. That will go away too. I hope.

Only a miracle

So now the Telegraph is reporting that the doctors caring for Michael have told his family that “only a miracle can save him”.

1) doctors, no matter their spiritual bent, do NOT talk to patient’s families about miracles saving anyone. Ever. From a practical viewpoint, this gives a patient’s family absolutely NO useful information on which to act. It provides hope, yes, but not for anything with any medical reality. And this hope will then cloud all subsequent decision-making.

A statement like this is more than ambiguous – it lets each recipient interpret it in his or her own context, the opposite of clear precise information. What would the care team mean with a statement like this? Are they saying “let’s wait a bit more for the miracle”? Or are they saying “miracles don’t happen in reality so we’re pretty much out of hope”?

I can only guess that what this report means by “save” is “recover sufficiently to have meaningful interactions with his loved ones”. So you see why this is kinda a dumb thing to say. And why it is impossible for me to imagine doctors EVER communicating like this with a grievously injured patient’s family.

If something like this WAS said, I can only try to “reverse engineer” it, and from there consider what they were saying and how it’d be said.

1) If there is now clinical, radiologic, physiologic and other data that leads to the conclusion that a resumption of any meaningful consciousness at all is impossible (see? no mention of miracles), they would be VERY unambiguous with this. In a situation like this, there must be no guesswork – NONE on the part of the medical team, who need to put the data together and reach an unquestioned and unquestionable conclusion. In this situation, ANY ambiguity in communication with the family is disastrous. They will often cling to any hope left, and this conversation is going to be, tragically, THE conversation that finally (and gently and compassionately) needs to remove all hope. This is crucial. If the message is misunderstood, it will almost inevitably lead to major problems, conflicts and tension subsequently.

Let me just say here that medical ethics allow, and virtually require, doctors to refuse to provide treatments they reasonably consider to be futile. My neighbour cannot show up at the hospital and demand that a surgeon remove her appendix. And in the above situation, where there is incontrovertible evidence of damage so severe as to make resumption of consciousness impossible,  doctors can certainly undertake the process of “therapeutic de-escalation”. Even if the patient’s family insists that “everything be done”, if there is NOTHING left to be done, there is no requirement to do anything more. At that point the patient’s family can make other care arrangements. It’s obviously critical to avoid this kind of situation, so once again you see the need for perfectly clear, concise information, with no ambiguity. Families need time to accept this, whether it’s in intensive care, or oncology, or genetic anomalies, and so on. But with open honest and clear communication, this will happen.

Please note that this is NOT the situation for a patient in a persistent vegetative state, at least not necessarily. This is the situation for a patient whose condition is even WORSE. The essential point is that the impossibility of recovery has to be as certain as current medical science can be AND that this certainty be transmitted to the family.

2) if the clinical situation is desperate, but not without all hope, the family would be told this, with as close to numerical precision as possible. In a situation where there is hope, it mustn’t EVER be taken away. On the other hand, families need to know, at the most basic level, that most patients like this get better, or that a few get better, or that really VERY few do. That 60%, or 20%, or 1% get better. No talk of miracles.

As I mentioned a few posts ago, if this conversation has happened, if Michael’s family has been told that it is extremely unlikely that he recover “satisfactorily”, then it is quite possible that the “several steps of separation effect” between hospital personnel and the press could have led to this kind of language appearing in these articles.

And again, despite a day during which we’ve been told Michael is breathing on his own AND that it would take a miracle to save him, we know nothing more than we knew yesterday or the day before.

This helmet cam stuff

Those of you who follow me on Twitter might have seen, in between the (well-deserved) rants about Putin, a long series of tweets about helmet issues. These were in answer to @jameyprice, who I’d like to thank for “inspiring” this. It’s something I meant to get to anyway, and I think the time is right.

But before we get to that (oh I should be in advertising) I also wanted to say that I read every comment any of you post. In detail. There are tons that I’d love to answer, and that deserve an answer for any of a number of reasons. I just don’t have the time! I’ll probably make notes and then blog answers in one fell swoop.

Don’t even think about asking about fell swoops. I have no idea what they are.

So. The question is whether having a helmet cam made the impact more severe.

I believe it was concluded that the camera had no influence on the severity of the injury. I will admit to not having read the report. But I’ll tell you what I know about this aspect of helmets. It also helps to understand a bit more about the mechanisms of head injury.

If we confine our analysis to linear forces, I think it’s reasonable to conclude (if the attachment was via suction cups, double-stick tape, etc i.e. a NON-invasive attachment) that the camera probably didn’t significantly weaken the helmet. The camera no doubt broke away on initial impact.

That said, I think it’s important to understand some of the more subtle problems with helmet appendages . . . of any kind.

Almost any interaction with its environment will make a helmet, and the head it contains, turn. Now this may only be a very few degrees, but the point is that the turning movement is an acceleration. Imagine an open wheel car having an angled frontal impact. The driver’s head pitches forward and to the side. As it contacts the cockpit side rest, an ANGULAR ACCELERATION , measured in (I think) radians per second per second, is produced. Since the head turns in a very short timespan, it all means very high acceleration. It’s intuitively obvious that any part of a helmet which increases interaction with the environment also increases angular acceleration (frictionally as in the example above, mechanically as with a helmet cam hitting a rock, or aerodynamically with the various aero appendages on modern racing headgear).

Why is this important?

Let’s take two nested tupperware bowls, put some foam between them. Oh yeah – the inside bowl contains jello, covered with some cling film. Let’s turn them over, and jam it all onto a piece of broomstick. Outer bowl =  helmet, inner bowl = skull. Jello = brain, and, yep, the broomstick is the brainstem.

Now we’ll grab the outer bowl, and twist it about 10° REALLY fast.

The “helmet’s” motion is coupled to the “skull”. The coupling is neither instantaneous nor perfect. The weight of the helmet’s contents cause some delays, as would any degree of slippage of the helmet. No matter.

Once the skull bowl has begun turning, the jello does too, but with another lag, And then, the jello brain transmits rotational energy to the broomstick brainstem. And again, there’s a lag. If you imagine some orange slices INSIDE the jello (thanks mom!) you can even imagine this kind of differential rotation occurring within the brain itself.

Each time contiguous structures are rotating at different speeds a SHEAR force is created. Shear forces are exactly what they sound like – forces acting parallel to each other but in opposite directions.

What’s shear doing at the skull-brain interface? Well among other things, it causes hematomas by tearing delicate veins running right there between the skull and the brain. That’s bad of course, for all the reasons we’ve spoken about in previous posts. Unfortunately, this can also happen WITHIN the brain itself, at areas of differing structural properties. And again, tearing of nerve tracts and blood vessels can occur in these areas. Damage and intracerebral hematomas result.

Worse still is what happens at the interface of the brain with the brainstem. Remember that the brainstem, in addition to maintaining and regulating the vital functions (breathing, blood pressure, etc), also sets up awakening and arousal of the brain. When rotational acceleration causes damage here, it is often devastating. Basically, these patients don’t wake up.

Because of how dramatically they contribute to the severity of head injury, helmet interactions with the environment, and the rotational acceleration they induce, need to be considered when designing a helmet for a specific purpose.

I cannot possibly know to what extent any of this contributed to Michael’s injuries. I, like most of you, am very preoccupied by the silence from Grenoble.