Effects of propofol on brain activation in respond to mechanical stimuli.

Objective: To observe the effects of different concentrations of propofol on brain regions activated by mechanical stimuli, and then to investigate the analgesic effect of propofol.

Methods: Twenty healthy male volunteers were randomly divided into two groups: light anesthesia group (group L) (BIS 60-80) and deep anesthesia group (group D)(BIS 40-60). Propofol was administrated by target controlled infusion system in pilot study. The target effect site concentration (ESC) of propofol was defined as the average of the ESC from BIS 80 to 60 or BIS 60 to 40 in group L or group D respectively. Mechanical stimuli were applied using von Frey filaments at the center of the left foot, and the pain threshold and VAS scores were evaluated. fMRI examinations were taken 1 week after pilot study with the following sequences: structure imaging+ functional imaging: functional imaging=stimulus sequence+propofol sequence, in which the stimulus sequence was 6 × (20 s on + 20 s off). This sequence was repeated after propofol sequence.

Results: As shown by fMRI, in group L, active brain regions of (the second stimulation-the first stimulation, P2-P1) were seen in cingulate gyrus, thalamus, and cerebellum, while active brain regions of (P1-P2) were seen in temporal lobe, frontal gyrus, and occipital lobe. In group D, the active brain region of (P2-P1) was only seen in cerebellum, while active brain regions of (P1-P2) were seen in cingulate gyrus and thalamus. Active brain regions of (deep-low) with propofol infusion in response to vFFs stimulation were observed in cerebellum.

Conclusions: Propofol at different concentrations has different effect on the activation of brain regions. It may exert its analgesic effect via different mechanisms.