Pain sensation and nociceptive reflex excitability in surgical patients and human volunteers.

Pain threshold, nociceptive flexion reflex (NFR) threshold and responses to suprathreshold stimulation were investigated in 15 female patients (mean age 32 yr (range 22-48 yr)) before and 68 (range 48-96) h after gynaecological laparotomy. Control measurements were performed in 17 healthy human volunteers (five males, age 30 yr (range 24-41 yr)). In the surgical patients, pain threshold decreased and pain to suprathreshold stimulation increased significantly (P = 0.006 and P = 0.04, respectively) from before to after surgery. A corresponding trend was demonstrated in neurophysiological measurements, although the decrease in NFR threshold and increase in NFR amplitude to suprathreshold stimulation were not significant (P = 0.08 and P = 0.24, respectively). The correlations between the relative change in pain and reflex thresholds, and time from surgery, were statistically significant (pain threshold: rs = 0.53, P = 0.04; NFR thresholds: rs = 0.54, P = 0.04). In the healthy volunteers, no significant differences in thresholds and responses to suprathreshold stimulation were observed between two recordings with an interval of at least 48 h. The allodynia and hyperalgesia observed in postsurgical patients may be related to postoperative sensitization of central neurones.