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 (8–11 years) with low resting DBP levels displayed greater cold pain intensity, cold unpleasantness, and thermal intensity ratings than did those with high resting DBP levels (–). These relationships did not occur among female adolescents (age 12–18 years) or boys of any age. In addition, the inverse relationship between SBP and thermal intensity was more intense among adolescent girls than among younger girls ().
Our results are unique, as resting DBP rather than SBP was significantly related to cold pain response measures as well as thermal intensity ratings among young girls. However, among adolescent girls, SBP was found to be related to thermal intensity ratings, which mimics findings among adult studies. Previous studies among children found resting SBP and DBP to be correlated with pain response measures; however, these studies included only boys who were of similar age.29
The majority of adult studies have found correlations between resting SBP and experimental pain measures, but a limited number of studies have found that resting DBP might be related to pain sensitivity. Among adults, resting DBP has been negatively correlated with ischemic pain unpleasantness in both men and women.16
Other studies involving adults have found positive correlations between DBP and thermal tolerance in women only12
or men only.17
However, several other studies have found no correlation between DBP and pain response measures for a variety of experimental pain tasks among adults.14,20,22,23
Thus, research among adults regarding the relationship between DBP and pain response measures is inconclusive.
Current research regarding BP and pain sensitivity among children and adolescents is very limited. One longitudinal study found that resting DBP and SBP were positively correlated with pressure pain tolerance and negatively correlated with pressure pain intensity in a group of 19-year-old males after controlling for parental history of hypertension and body mass index (BMI).29
These earlier data contradict our results, which found that pressure tolerance, intensity, and unpleasantness were not significantly associated with resting BP measurements among males. This might be due to the age difference in study participants; the previous study included 119 males of similar age, whereas our study included 120 males ranging from 8 to 18 years.29
Our study indicates that age, not resting BP, is a significant predictor of tolerance for all 3 pain tasks, pressure and thermal intensity, and thermal unpleasantness among boys 8 to 18 years of age.
To our knowledge, there are no studies involving female children or adolescents examining the relationship between resting BP levels and experimental pain sensitivity. Thus, our results indicating that girls (8–11 years) with low resting DBP have greater cold intensity and unpleasantness ratings and thermal intensity ratings than girls with high resting DBP levels are unique. It is unclear what mechanism leads to this relationship among female children, but not among boys or female adolescents. Our results indicating that adolescent girls with elevated resting SBP had lower thermal intensity ratings is also unique. It is unclear why these relationships were found among girls but not boys.
Although age was associated with pressure and heat tolerance among females, resting DBP had a unique predictive value for self-reported variables such as cold unpleasantness and cold and thermal intensity among girls (8–11 years). It is unclear why this relationship among girls only occurred for self-reported variables involving the cold pressor and thermal experimental pain stimuli. Studies among adults have shown that women rely more on external cues rather than internal physiological state alone to determine their response to a stimulus.44
Self-reported variables require a participant to integrate their internal physiological response with external cues, such as visualization of the cold pressor water bath, color change of the hand in water, or redness of the skin with the thermal task. Perhaps the young girls in this study also relied on these external cues more than boys to determine their subjective rating of pain intensity or unpleasantness.
In accordance with existing studies regarding BP in children and adolescents,31,32
our hypothesis that females would exhibit lower resting BP levels than males was confirmed only among adolescents for SBP. Adolescent males had significantly higher resting SBP levels than adolescent females. There were no gender differences for SBP in younger children; DBP did not differ between boys and girls irrespective of age. This study indicates there are gender and gender by age BP/experimental pain relationships in children. However, further studies are indicated to determine if resting BP is a mediator of gender differences in experimental pain sensitivity among healthy children and adolescents. These studies could help to clarify potential gender differences in pain regulatory pathways, such as baroreceptor modulation or adrenergic systems, and guide future clinical practice in pain management.
Most theories regarding the relationship between resting BP levels and pain response measures have focused on SBP rather than DBP. SBP and DBP are regulated by several complex mechanisms, including sympathetic tone and the renin– angiotensin–aldosterone system. The relationship between resting BP levels and laboratory pain responsivity might be explained by an interaction between pain regulatory pathways and BP levels through sympathetic activation and modulation of descending pain pathways.1,13
Pain induces sympathetic arousal, which increases BP levels and stimulates baroreceptors. One function of the baroreceptors is to initiate a signaling cascade that causes pain inhibitory activity. One theory suggests that increased resting BP levels would allow for a more rapid stimulation of baroreceptor pain inhibitory activity with sympathetic stimulation.1
Another study indicated that it is the degree of phasic baroreceptor stimulation, and not the tonic level of stimulation, that is important, because participants reported less pain during systole than diastole.45
Our data does not directly support this theory, as female children with high DBP, not SBP, reported lower cold unpleasantness and intensity levels. It is possible that this pain inhibitory system is regulated somewhat differently among children and adolescents than in adults.
A number of limitations to the study are worth noting. Previous studies with adults have controlled for BMI during analysis, as this provides a measure of obesity and might impact resting BP levels. Initial correlation analysis indicated that BMI was significantly correlated with age and resting BP levels. Although we attempted to collect height and weight information, BMI data were available for only 184 of the 240 participants. However, additional analyses of these 184 participants (data not shown) indicated that inclusion of BMI in regression analysis did not alter the previously mentioned results that were obtained without the inclusion of BMI. Future research in this area needs to be more vigilant about collecting BMI data, perhaps by increasing a sense of privacy during weight measurement, as this may impact an adolescent's willingness to be weighed. Future studies might incorporate continuous BP monitoring throughout pain tasks to assess BP reactivity and its relationship to pain sensitivity among children. Another useful variable to evaluate in future studies would be a measure of anticipatory anxiety before pain tasks to assess the relationship between anxiety, resting BP levels, and laboratory pain sensitivity. Future studies might also address the role of sex steroid hormones and how the timing of menarche might affect the BP–pain relationship as suggested in adult studies.46
Lastly, this study was a cross-sectional study that determined the association between BP and pain responsivity, but no causation could be assessed. Longitudinal studies or experimental studies would help to clarify the temporal or causal relationship between BP and pain.