Pupil dilation response to noxious stimulation: effect of varying nitrous oxide concentration.
OBJECTIVE
This report examines the pain-related pupil dilation response (PDR), tracking it across mixture concentrations of nitrous oxide (N(2)O) in oxygen (O(2)) and relating its variation to change in long latency somatosensory evoked potentials (SEPs) and visual analogue scale (VAS) pain report.


METHODS
We varied mixture concentrations of N(2)O in O(2) (0%, 10%, 30%, and 50%), measuring PDR, SEP and VAS responses to painful electrical fingertip stimulation at high and low intensities in 15 volunteers.


RESULTS
Mixed effect model statistical analyses revealed that: (1) PDR increased significantly with stimulus intensity and constricted significantly with mixture concentration; (2) SEP and VAS decreased significantly with increasing mixture concentration; (3) PDR correlated with SEP amplitude and VAS across mixture concentrations; (4) subjects differed significantly in: (a) baseline PDR and SEP amplitudes, (b) rate of change of these measures across mixture concentrations; and (5) VAS increased significantly with stimulus intensity and decreased significantly with mixture concentration without significant individual differences.


CONCLUSIONS
The findings support the hypothesis that the pain-related PDR is a complex brain-mediated response rather than a simple sympathetic reflex.


CONCLUSIONS
PDR may provide a useful indicator for studying the central processing of noxious stimuli and the effects of analgesic interventions.
Oka
Shunichi
S
Department of Dental Anesthesiology, Nihon University School of Dentistry, 1-8-13, Kanda Surugadai Tokyo 101-8310, Japan. oka@dent.nihon-u.ac.jp
Chapman
C Richard
CR
Kim
Barkhwa
B
Nakajima
Ichiro
I
Shimizu
Osamu
O
Oi
Yoshiyuki
Y
D000328:Adult; D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects; D005260:Female; D005385:Fingers; D006801:Humans; D009609:Nitrous Oxide / Q000008:administration & dosage / Q000494:pharmacology; D010100:Oxygen / Q000008:administration & dosage / Q000494:pharmacology; D010146:Pain / Q000209:etiology / Q000503:physiopathology*; D010147:Pain Measurement / Q000187:drug effects; D011930:Reaction Time; D012025:Reflex, Pupillary / Q000187:drug effects
D018712:Analgesics, Non-Narcotic; D004338:Drug Combinations; D009609:Nitrous Oxide; D010100:Oxygen