We investigated the pathophysiological and morphological responses of
anaesthetized rats to fluid percussion brain injury generated by an or
iginal midline fluid percussion injury device. Following different gra
des of trauma, 1CBF was measured continuously in the right parietal co
rtex through a burr hole using laser Doppler flowmeter, and physiologi
cal parameters were monitored. Pathological changes also were evaluate
d microscopically. During the first 2 hours following trauma, we found
four patterns of cerebral circulatory responses. Little measurable pa
thophysiological response occurred after percussion pulses of less tha
n 1.33 atmospheres (atm). In animals subjected to pulses of greater th
an 4.30 atm, 1CBF increased synchronously with blood pressure, and the
n both parameters decreased continuously until death. In animals subje
cted to pulses of 1.53 to 2.33 atm, trauma produced a transient increa
se in 1CBF with no synchronous rise in blood pressure. In animals subj
ected to pulses of 2.70 to 3.87 atm, 1CBF increased synchronously with
blood pressure immediately following the injury, but had decreased ma
rkedly by 60 seconds and remained below the pre-injury baseline. Blood
pressure recovered to baseline within 4 minutes of the injury. The tr
ansient increase in 1CBF occurred within 5 seconds following percussio
n pulses of greater than 1.53 atm and appeared to be independent of th
e rise in systemic blood pressure. Apnoea occurred in animals subjecte
d to pulses of greater than 1.53 atm, and the duration of apnoea and m
ortality rate correlated with the magnitude of the applied injury. A p
ower decrease in the electroencephalogram post-injury and a delay in i
ts recovery, both depended on the magnitude of the injury with few reg
ional differences in the beta-2 band power. The distribution and exten
t of blood-brain barrier disruption and small haemorrhages also correl
ated with the magnitude of the injury. The number of neurons decreased
significantly in both hippocampi by 2 weeks following moderate trauma
. The four patterns of 1CBF changes demonstrated in the present study,
as well as the other responses to injury, may be useful for studying
graded models of various diffuse brain injuries.