Thanks for that Steve; yes, I figured 60 to 0 over 1 second is about 3G. And on second thoughts a head-on crash probably only takes around 0.3 seconds, so maybe 9 to 10G is more like it!
I'm not sure if it is entirely "perfusional". After all, we know that patients remain alert during pretty long sinus pauses, or post-adenosine, although I suspect such patients may keep perfusing even during diastole (something to do with elastic recoil of the great vessels). So maybe there is an element of concussion, who knows? It's accepted that sustained high G situations will lead to failure of cerebral perfusion, resulting in blackout. A sharp increase in G however may well have a concussive effect. Very difficult to research on humans...
Adrian Fogarty
> <[log in to unmask]> writes
> > The g-forces must have been considerable, 60 to 0 in less
> >than a second. That's probably around 4 or 5G I think (any mathematicians out
> >there?). I've never been sure if such blackouts represent a pure neurological
> >phenomenon, i.e. concussion, or merely a cessation/redistribution of blood
> >supply, i.e. a type of cerebral "syncope". Anyway, I agree with Duncan; such
> >blackouts are pretty innocuous. I had no neurological symptoms or sequelae of
> >any kind.
> >
> 60 to 0 in less than a second is a lot more than 4 or 5G. My aircraft is
> stressed to 6/-3 and it is not as battered as your motor would have
> been, and I do like to fly the arse off it!
>
> 60 mph is a very credible survivable crash (and landing) speed in an
> aircraft if you slow it down enough (recommended technique). Data in the
> aviation medicine literature shows deceleration of 48G peak and 24 G
> mean over 0.054sec in a surviveable accident. Ouch!
>
> I went up and seriously mishandled a manoeuvre last weekend. I started
> to grey out. There is no question of me hitting my head. It was
> 'orrible.
>
> If a motorcyclist decelerates or accelerates abruptly, then I have no
> doubt that cerebral bloodflow is transiently interrupted. If the head is
> not struck, the insult is perfusional rather than traumatic. It is
> rapidly reversible. That is, I believe, what Duncan is pointing out and
> I must say that I agree with him.
> --
> Stephen Hughes SpR Aerobatics and Everything.
|