Heart rate mediation of sex differences in pain tolerance in children.

Despite evidence supporting the existence of important sex-related differences in pain, the mechanisms underpinning such differences are not well understood. The aim of this study is to examine the relationship between sex and pubertal differences in autonomic arousal and pain tolerance to laboratory pain stimuli in healthy children. We tested the following specific hypotheses: (1) females would have greater autonomic arousal and less pain tolerance than males, and (2) this sex difference in pain tolerance would be mediated by autonomic arousal. Participants were 244 healthy children (50.8% female, mean age 12.73+/-2.98 years, range 8-18 years). Separate 4-trial blocks of cutaneous pressure and thermal pain stimuli were presented in counterbalanced order. Heart rate (HR) was recorded during 2-3 min periods preceding each block and a 1-min period between trials. Results indicated lower tolerance in females for cutaneous pressure, but not thermal pain, compared to males. In addition, pre-trial HR was greater for females than males. Mediation analyses suggested that sex differences in pressure pain tolerance were accounted for by sex differences in pre-trial HR. There were also significant effects for puberty, but these did not vary by sex. Overall, early pubertal children had greater pre-trial HR and less pain tolerance than those in late puberty for both cutaneous pressure and thermal pain across sex. These results suggest that autonomic arousal may be a mediator of sex-related differences in pain responses in children.