Original researchRelationship Between Resting Blood Pressure and Laboratory-Induced Pain Among Healthy Children
Introduction
The relationship between blood pressure (BP) and pain has attracted the increasing interest of pain researchers during the past 2 decades. It was proposed that increased resting BP levels would allow for a more rapid stimulation of baroreceptor pain inhibitory activity with sympathetic stimulation, thus leading to reduced pain.1 Studies among adults have shown that hypertension is associated with decreased experimental pain responsivity.2, 3, 4, 5, 6, 7 The adult offspring of hypertensives also showed decreased pain responses to a variety of experimental pain stimuli compared with individuals without a family history of hypertension.2, 8 Among healthy adults with BP in the normal range, there was also an inverse association between resting BP and pain responses, such that a higher resting BP was correlated with lower laboratory pain responsivity. This laboratory pain relationship has been demonstrated with both resting systolic BP (SBP)1, 2, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27 and resting diastolic BP (DBP).12, 16, 17 Although several experimental studies involving adults have found an inverse relationship between resting BP and pain responses in both men and women.15, 16, 20, 23, 26 others have demonstrated this relationship in men only11, 13, 14, 17, 22 and in women only,2, 9, 10, 12, 18, 21, 24 suggesting the necessity of examining gender differences in the BPāpain response.
Despite convincing evidence of the relationship between BP and acute experimental pain responses in adults, few studies have examined this relationship among children and adolescents. Ditto et al28 found that resting SBP was negatively correlated with finger pressure pain intensity ratings in boys. The same research group found resting SBP to be negatively correlated with finger pressure pain intensity and unpleasantness among male adolescents at a 5-year follow up.29 However, this longitudinal study only involved boys, and thus the BPāpain relationship among girls is unknown. There is also a dearth of information on how the BPāpain association may change as a function of development.
The first goal of this study was to examine the relationship between resting BP and laboratory-induced pain among children and adolescents, and to investigate how this association varied as a function of gender and age. We hypothesized that resting BP would be positively correlated with pain tolerance, and negatively correlated with pain unpleasantness and pain intensity in healthy children and adolescents. We explored whether these BPāpain relationships were age and gender dependent.
The second goal of this study was to examine gender differences in BP in children and adolescents and explore whether such differences in BP account for gender differences in pain. Among adults, gender differences have been noted in BP, with women displaying lower average resting SBP levels than do men.20, 30 Similarly, studies among children and adolescents indicate that girls have lower resting SBP levels than do boys.31, 32 Based on the previous studies, we hypothesized that healthy females would exhibit lower resting BP levels than males.
Meta-analysis and review articles have suggested that adult women have greater experimental pain responses33 and higher prevalence of clinical pain compared with men.34 Gender differences in experimental pain responses are also evident among adolescents for pressure and cold experimental pain stimuli, although it remains unclear what mediates these gender differences.35, 36, 37 As studies have shown that elevated resting BPs are generally higher in males than females, and also that higher BPs are associated with decreased pain measures, it seems that resting BP might be a potential mediator for gender differences in pain responsivity. A better understanding of the factors that mediate gender differences in pain sensitivity among children and adolescents can help to guide future clinical treatment of pain, and might help us to better understand pain regulation and signaling.
Section snippets
Participants
All recruitment and study procedures were approved by the University of California, Los Angeles, Institutional Review Board (IRB), as well as the IRBs of recruitment sites. Study participants were recruited from a major urban area through mass mailings, posted advertisements, and classroom presentations. Telephone interviews confirmed initial eligibility of 472 (96.5%) of the 489 individuals who were screened; 17 children (3.5% of those screened) were excluded due to use of medications or acute
Results
Table I shows descriptive statistics for BP and laboratory pain response for boys and girls. Independent t tests did not reveal gender differences in resting SBP or DBP. However, further examination showed adolescent boys (12ā18 years old) exhibited significantly higher resting SBP levels (mean [SD] 110 [12] mm Hg) than adolescent girls (mean 104 [0.5] mm Hg), with a mean difference of 6.1 (two-tailed P = 0.003); whereas there was no such gender difference in SBP among children (8ā11 years
Discussion
We hypothesized that resting BP would be positively correlated with pain tolerance, and negatively correlated with pain unpleasantness and pain intensity in healthy children and adolescents. The hypotheses were supported among female children for thermal intensity, cold intensity, and cold unpleasantness. More specifically, girls (8ā11 years) with low resting DBP levels displayed greater cold pain intensity, cold unpleasantness, and thermal intensity ratings than did those with high resting DBP
Conclusion
Female adolescents and adults report greater clinical pain and have greater experimental pain sensitivity than boys of similar age. Among adults, women generally have lower resting BP levels than do men of similar age and health status. These findings indicate that BP might be involved in gender differences in pain responsivity. Our study found that for boys, age, rather than resting BP, was associated with experimental pain sensitivity measures. For girls, however, the relationship between BP
Acknowledgments
Dr. Haas was the primary author of this article and performed the statistical analysis under the supervision and guidance of the Pediatric Pain Program team, including Drs. Zeltzer, Tsao, Evans, and Lu. The authors have indicated that they have no conflicts of interest regarding the content of this article.
This study was supported by R01DE012754, awarded by the National Institute of Dental and Craniofacial Research (PI: Dr. Zeltzer), by UCLA General Clinical Research Center Grant M01-RR-00865
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