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dhawkins71
08-30-1996, 07:39 AM
Hello all:
Given below is a summary of the responses I received from my request for
information regarding conditions which may lead to a person passing out or
going unconscious. The initial request is given first followed by a
summary of response.

Thanks to all who responded.


Initial Request:
I am looking for information on the conditions which may lead to a person
passing out or going unconscious. My particular interest relates to
athletes participating in contact sports such as football, rugby, the
martial arts, boxing, etc.. If any of you have experience in this area,
then I would appreciate receiving your comments. Are there any
experimental studies which have looked at this issue (maybe controlled
studies of primates)? Or any studies conducted after an incidence that
perhaps was captured on cine or video? What are the important variables,
head acceleration, displacement, linear vs angular movement? Can repeated
light impacts to the head have an accumulation effect that may lead to a
person passing out at a time when he is not being physically contacted?
What is the reaction of the rest of the body, for example, can the body
maintain some postural stability for a short period of time or does the
entire body necessarily relax immediately?

Summary of Responses:
1. One statement was given about long duration (greater than 15 seconds)
upper extremety isometric contractions which have led to blackouts. It was
suggested that the muscles in the neck were also contracted and cut the
flow of blood to the brain.

2. Look up the work of Tom Gennarelli and Larry Thibault on primates from
the early 80's. They have done a bunch of studies, and students (Dave
Meaney and particularly Susan MArgulies) of theirs did more modelling etc
of coma. Basically, it depends on the exact type of loading. They have
developed a relationship between angular velocity and angular acceleration
of the head for no injury-mild-moderate-severe for rotational injury, but
in contact sports it is more likely to be contusive injury, with a coup or
contre-coup type of injury. Jack (A.J) McLean for Adelaide Uni has been
doing things with sheep which might be interesting for you. There was some
stuff done on boxers a few years ago in France, but I think it was
published in an AGARD conference proceedings, which is hard to find. There
was a special ASTM publication on head injury in sports a couple of years
ago too. Do a literature search on biomechanics and head injury, in either
medline or the engineering index (Compendex).

3. Suggest that you contact Joe Notaro at NOTARO@nadc.navy.mil. Ask him
for phone numbers to researchers like Phil Whitley and Jim
Whinnery who do research on the Centrifuge. This isn't Joes area
but he can point you at some people who have worked the area.
Also look up GLOC (G-induced Loss of Consciousness) in Index Medicus
and PsycINFO.

4. Look for the work of Larry Thibault on Diffuse Axonal Injuries (DAI)
He publishes extensively in the Journal of Biomechanics and work
done at the University of Pennsylvania. I can't locate my cache of
references, but a quick search of J. of Biomechanics will get you there
fast. He has also done work related to sudden blacking out during
sports because of very light loads. I obtained his references by
looking at the scientific citations index.

5. This is not a scientific response to your questions posted on the
biomech listserv, but I can give you some anecdotal personal
information. I played rugby for 15 years and was knocked out a few
times in the course of those years. As far as what the body does
after being knocked out I can attest to at least two widely variant
responses. One time (at least this is what people tell me because I
do not remember) when I was hit in the back of the head (with a
casted arm) I was immediately and completely knocked out. Although my
body made contortions and writhing movements, I was, for all practical
purposes, completely unconscious. My teamates mentioned that I was
yelling some unkind things about my anatomy professor (I was in vet
school at the time), so there was some neural activity going on. I
"woke up' about 30 minutes later, but felt a little strange for about
2 days. Another memorable (or unmemorable) time near the beginning
of one game, I rammed heads while tackling someone bigger than myself.
He immediately left the game. Apparently I stayed in.
I remember nothing about the game except the last 2-3 minutes when my
teammates finally took me out. I played the whole game rather poorly, was
offsides a lot, passed the ball to the opposing team, etc. They all just
thought I was
playing badly. Finally, around the end of the game (we were losing
by some 20 points), I "came to" and starting rallying my teammates
telling them that we were only a couple of points behind (which we
were when I was first hit in the head). So my body was completely
functioning but my mind took a vacation. I know that this is
probably not what you were looking for but it has always intrigued me
somewhat.

6. There is an article by Reid et al in Surg Gynecol & Obstet 133(6), (1971)
that measured 230 g's when a football player was knocked unconscious.
Regarding the effect of multiple sub-concussive impacts resulting in
long-term brain injury, look at Ross et al JAMA 249(2) with regards to
boxing, and Tysvaer et al. AJSM 17(4) 1989 with regards to soccer. I
have recently completed a research project with the US Aerial ski
team measuring the head accelerations upon head impact. I recorded
measurements up to 92 g's without loss of consciousness.

David Hawkins, Ph.D.
Department of Exercise Science
University of California - Davis
Davis, CA 95616
dahawkins@ucdavis.edu