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.