Objective:The objective of this study is to detect the effects of normothermic

mild hypothermic

hypothermic cardiopulmonary bypass(CPB) on somatosensory

cortical evoked potential(SCEP) and super microstructure of cortex in rabbits. Methods:Thirty new zealand white rabbits

randomly allocated into three groups;group A:normothermia CPB(36℃～37℃); group B:mild hypothermia CPB (32℃～34℃);group C:hypothermia CPB (26℃～28℃);Made the open-heart CPB model

maintaining HCT 20%～25%

the duration of CPB is 2 hours;Stimulating from ischiadic nerve

recording SSEP by the time of the end of CPB

The animals were then killed and the cortex were removed for electro microscopic examination.Results:The latency of group C is longer than group B

the latency of group B is longer than the group A

compare between each group (P<0.01)

the diffreney is significant;The amplitude of group C is lowest

compare between each group(P<0.01)

the diffrency is significant

the super microstructure of neuron and fiber after CPB has no obvious difference among the three group:the nucleus and the cytoplast of the neuron in cortex is swollen

and the heterochromatin of chromatin in nucleus is agglomerated

the perinuclear space is enlarged slightly

the electron density of the nuclear matrix is degraded.Conclusions:the lower CPB temperature

the more inhibitions on the function of cortical neuron;the hypothermia CPB has no obvious protection on the super microstructure of cortex in rabbit.