In a message of 09-28-1900, VERN FAULKNER wrote re: POTENTIAL
ACCIDENT
JT> There is no reliable and inexpensive protection availible to
JT> protect bicyclists against traumatic amputation.  There *IS*
JT> reliable and inexpensive protection for serious head injuries:
VF>  Incorrect. Most serious head injuries are either facial, or
VF> related to the neck. Helmets do not protect those areas, only
VF> those areas which are already quite protected with stuff called
VF> "bone." 
Beg to differ.  Non-neurological face and neck injuries are
seldom as serious as neurological ones.  The bone you claim will
protect you actually is a source of many of the post-traumatic
neurological problems we see, albeit in an indirect manner.  
When tissue is injured, one of the most common responses is edema
or swelling.  On the superficial areas of your body this is
unsightly and often uncomfortable, but seldom dangerous.  In the
enclosed area of your cranium, however, swelling is very
dangerous.  The tissue becomes edematous, but has little room to
expand. 
But expand it will, and as it does so, the ventricles of the
brain collapse, interfering with CSF fluid drainage and, with
nowhere to go, pressure begins to build up.  This effect may also
be augmented by sub-dural bleeding secondary to the trauma. There
is one significant opening in the cranium, however: the foramen
magnum, the site where the spinal cord exits the skull. 
As the pressure builds, brain tissue is forced through this
opening and blood circulation is cut off to the brain stem.  The
brain stem is what controls your basic life-support systems; ie,
temperature regulation, breathing, etc.  As ischemia increases in
the brain stem, respiration fails, blood pressure collapses and
death soon follows.  
A helmet helps prevent this from happening by absorbing some of
the energy of impact, lessening the trauma to the brain tissue
inside the cranium and reducing or eliminating the edema that
follows a "concussion."
* KWQ/2 1.2i * Internet: John.Thompson@ibm.net
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