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Chronic Pain and Anxiety in Children:
Physiological and Emotional Factors in Stress Responses
Madeleine E. Jackson
Thesis completed in partial fulfillment
of the requirements of the
Honors Program in Psychological Sciences
Under the Direction of Professor Bruce E. Compas, Ph.D.
Vanderbilt University
April, 2007
Approved:
Date:
_________________________________________
________________________
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Acknowledgements
Many thanks to my research advisor, Dr. Bruce E. Compas, for his constant
encouragement and untiring attention and care to both this thesis and my learning
experience. I attribute to him my love of psychology and research.
Many thanks also to Lynette Dufton, M.S., the graduate supervisor of the project.
I thank her for her extensive role in teaching me about research methods and data
analysis, and for her generous nature as a consultant for so many questions.
I thank my fellow Honors Students in the Compas lab for their camaraderie over
the last two years.
I thank the rest of the Compas lab for their generosity in sharing the lab space at
the busiest of times.
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Abstract
The current study examined physiological and emotional factors in stress responses of 21
children with recurrent abdominal pain (RAP), 21 children with anxiety disorders, and 21
gender- and age-matched healthy controls. Children’s heart rates were monitored as they
performed two psychological stress tasks and one physical stress task. Pain intensity and
tolerance were measured during the cold pressor task. Parents and children completed
questionnaires to assess children’s psychological and somatic symptoms and responses to
social stress. Findings indicate that children with RAP and anxious children report
different levels of stress reactivity and provide different pain assessments of the cold
pressor task. Findings also demonstrate a positive association between physiological
stress reactivity and self-reported stress reactivity and psychological symptoms.
Psychological and somatic symptoms were incrementally accounted for by physiological
and self-reported stress reactivity.
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Introduction
The most common complaint of chronic or recurrent pain among children is
recurrent abdominal pain (RAP) (Colletti, 1998). RAP is defined as the occurrence of at
least three episodes of abdominal pain in a three month period severe enough to impair
functioning or interrupt activities (Apley, 1975). Prevalence data show that between 10
and 20% of children are affected by RAP in a manner serious enough to impair
functioning (Apley & Naish, 1958). Children with RAP frequently miss school, activities,
and social interactions with their peers, and many also change their eating patterns in
response to their pain.
RAP and Anxiety
Because there is no identifiable organic cause of RAP in the majority of cases,
theory postulates that RAP is related to a maladaptive pattern of psychological and
physiological stress reactivity, including symptoms of anxiety and anxiety disorders.
Research has demonstrated a high comorbidity between RAP and anxiety disorders
(Blanchard & Scharff, 2002) and other internalizing symptoms of psychopathology (Dorn
et al., 2003). For example, Dorn et al. (2003) found that somatic symptoms reflective of
RAP were positively correlated with symptoms of anxiety and depression. On a
somatization index, children with RAP did not differ from anxious children, but both
differed from healthy controls, and parents of children with RAP reported that their
children experienced more somatic symptoms than parents of anxious children or healthy
controls (Dorn et al., 2003).
The findings of previous studies suggest that differences between children with
RAP and children with anxiety disorders may be less pronounced than initially assumed.
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RAP and anxiety may be similar not only in the manifestation of symptoms, but also in
many of the underlying correlates or causes of these conditions. The current study used
an experimental task involving the presentation of psychological and physical stressors to
children with RAP and to a comparison group of children with DSM-IV anxiety
diagnoses in order to compare their psychological and physical responses to stress.
The Role of Stress
One of the main factors associated with anxiety disorders is chronic stress, which
has also been associated with symptoms of RAP. Stress has been linked to both RAP and
psychopathology, and chronic stress has been linked specifically to symptoms of anxiety
and depression (Grant et al., 2004). In regard to stress and its association with recurrent
abdominal pain, Walker, Garber, Smith, Van Slyke, and Claar (2001) established that
children with RAP report more daily stressors and experience more pain in response to
those stressors. Further, these authors found that the association of stress with
psychological and somatic symptoms was stronger for children with RAP than for
healthy controls. The effect of significant life stressors on the occurrence of RAP has
been established cross-culturally (Meng Boey & Goh, 2001), but the further association
of daily stressors with abdominal pain in children is a key finding in our understanding of
RAP because it pinpoints chronic stress as an important component of research in RAP.
Anxiety disorders in children are often made up of fears of social evaluation.
Psychosocial stress can further exacerbate symptoms of anxiety and have also been
studied in association with RAP.
Greco, Dufton, and Freeman (2007) examined peer victimization as a source of
psychosocial stress in children with RAP. This study showed that children with RAP
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who experienced higher amounts of overt peer victimization visited the school nurse
more often and reported more pain. The amount of pain a child initially experienced did
not affect the number of trips to the school nurse. Instead of pain appearing as the main
cause for a trip to the nurse, the findings suggest that the victimization itself mediated the
occurrence of RAP and withdrawal from school activity (Greco et al., 2007).
This research provides evidence for the theory that RAP may be an outcome of
stress and suggests that the ways in which children respond to daily stress may determine
the outcome of the experience or non-experience of symptoms of RAP.
Physiological Stress Reactivity and Recovery
As noted above, the relation between symptoms of anxiety and somatic symptoms
in both clinical populations is well established. Of broad interest to the current study is
exploring these two types of symptoms more fully, and physiological reactivity to and
recovery from stress among the three groups is a focus of the current study. On measures
of physiological reactivity in response to stress, both children with RAP and anxious
children have shown baseline heart rates that tended to be greater than healthy controls,
but not different from each other (Dorn et al., 2003). Unfortunately, the results of the
physiological data from this study failed to reach statistical significance and thus
prevented conclusions. A recent study by Dufton et al. (2007) found that in a sample of
children with RAP who participated in a laboratory stressor prior to the cold pressor task,
half of the children experienced the expected elevation in heart rate related to a laboratory
stress task and half experienced a decrease in heart rate levels. However, these
differences in heart-rate change were not related to participants’ scores on measures of
pain in response to the cold pressor. The current study uses a protocol similar to that of
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Dufton et al. (2007), but includes comparison groups (anxious and healthy control
children) and a larger sample size and thus hopes to clarify the issue of divergent heartrate changes to stress in a RAP sample.
Feuerstein et al. (1982) found that children with and without RAP experienced an
increase in heart rate in response to the cold pressor task and that the groups did not differ
from each other. Although these findings do not support the hypothesis that children with
RAP will show a physiological stress reactivity pattern different from healthy controls,
the lack of findings can be contributed to both the small sample size (n = 10) and the
extremely cold nature of the cold pressor task (0 to 1 °C). The current study administered
the cold pressor task at approximately 4 °C with a larger sample size and therefore group
differences were expected in physiological reactivity to both stress and pain.
These apparent similarities between children with RAP and children with anxiety
disorders suggest that RAP may not be a phenomenon different from anxiety disorders,
but rather a different manifestation of similar underlying processes. The experimental
manipulation in the current study will provide valuable information for subjects across
time and between groups regarding physiological arousal in response to stress and
physiological patterns of stress recovery. The degree to which these groups differ will
provide more helpful information on how to think about possible interventions for
children with RAP.
Involuntary Engagement Responses to Stress
Involuntary engagement responses to stress are defined as automatic
psychological, emotional, and physiological processes that an individual experiences as a
result of a perceived stressor. Specifically, involuntary engagement stress responses,
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which include physiological and emotional reactivity, intrusive thoughts, rumination, and
impulsive action, are associated with more symptoms of psychopathology (Compas et al.,
2001). The idea that children with RAP are hypervigilant to environmental threat
supports the hypothesis that RAP is a manifestation of anxiety, not a different
phenomenon altogether. A monitoring style, defined as the extent to which an individual
scans for or attends to threatening information and expressed as hypervigilance in the
current study, has been correlated with anxiety disorder symptoms in an undiagnosed
sample of children (Muris et al., 2000).
Pain Intensity and Tolerance
Regarding pain responses in children with RAP, Dufton et al. (2007) showed
lowered pain tolerance in a cold pressor task administered after a stressor than when
tested before the administration of a stressor. The Dufton et al. study demonstrated that
after the administration of a serial subtraction task and a social stress interview, children
with RAP in an experimental condition in which they were exposed to these stress tasks
before the cold pressor task removed their arms significantly earlier (i.e., were less
tolerant of the pain) than children who were administered the cold pressor task before the
stressor tasks. These findings suggest that children with RAP experience lowered pain
tolerance in response to stress relative to a non-stressful environment. In an early study
on the subject, Feuerstein et al. (1982) used a very small sample of children with RAP,
hospital controls, and healthy controls and found that the cold pressor task was painful
and distressing for all three groups but that there were not differences between the
groups. The apparent contradiction of this earlier study to recent findings could be
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explained by both the small sample size (n = 10) and the lack of a stress task
administered before the cold pressor task in the Feuerstein et al. (1982) study.
In light of the findings that pain responses were only affected after the
administration of a stress task, the current study used the cold pressor task following a
laboratory stress task in order to measure pain intensity and tolerance after each child had
experienced stressors. In the current study, all participants were administered the cold
pressor task after two psychological stress tasks in order to investigate how these pain
responses might differ between groups as part of an overall variability in response to
stress. The current theory proposes that RAP involves a physiological stress response
similar to anxiety, so it follows logically that the children with RAP exposed to a pain
task directly after they have experienced stress will display a heightened physiological
response. The current study hopes to clarify how stress might affect physiological
systems similarly but pain responses differently in children with RAP and children with
an anxiety disorder compared to healthy children.
Summary of Current Knowledge
Research has shown that RAP, a prevalent and debilitating problem among
children, is highly comorbid with symptoms of anxiety. Both children with RAP and
anxious children are populations associated with symptoms of somatic complaints and
anxiety, although each group presents with a different primary complaint. Underlying
mechanisms similar to those present in anxiety disorders have been implicated as a cause
of RAP and intervention target.
Previous research has demonstrated a trend for children with RAP to respond
physiologically differently to stressors than other populations, but has failed to reach
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statistical significance. Patterns of hypervigilance and involuntary responses to stress
have been demonstrated in children with anxiety and children with RAP, further
supporting the theory that there are key similarities in these populations. Children with
RAP have been shown to report higher pain intensity and lower pain tolerance after the
administration of a psychological stressor, suggesting that RAP is a result of maladaptive
psychological stress responses.
Hypotheses
The hypotheses are as follows: (1) The two clinical groups (i.e. children with
RAP and children with an anxiety disorder) will differ from healthy controls but not from
each other in mean heart rate measured at four distinct time intervals during the
experiment: Baseline, Psychological Stress Tasks, Physical Stress Task, and Recovery
Period. (2) Children with RAP will report significantly more Involuntary Engagement in
proportion to other types of coping than the rest of the sample. (3) Children with RAP
will report higher pain intensity and lower pain tolerance than children with anxiety and
healthy controls in response to the cold pressor task. (4) We also make predictions about
the relations among variables: (4a) mean HR (beats per minute) for the four intervals
mentioned above will be positively correlated with CBCL and YSR Somatic Complaints
and Anxious/Depressed psychological symptoms. (4b) The Involuntary Engagement
Scale will be positively correlated with mean HR from the four intervals. (4c) Pain
Intensity Rating from the cold pressor task will be positively correlated with the CBCL
and YSR Somatic Complaints scale. (4d) We also hypothesize that we will be able to
predict psychological and somatic symptoms reported on the YSR and CBCL from mean
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heart rate and involuntary engagement responses beyond what differences between the
groups tell us.
Method
Participants
The study included 63 participants (29 male, 34 female) ages 8- to 16-years old
(mean age 11.64 years). Twenty-one children met criteria for recurrent abdominal pain
as defined by Apley (1975), 21 children met DSM-IV diagnostic criteria for an anxiety
disorder, and 21 children did not meet for RAP or an anxiety disorder were designated
healthy controls. There were no significant age differences between the groups. The
presence of an anxiety disorder in the anxious group was determined by the
administration of the anxiety disorder portions of the Kiddie Schedule for Affective
Disorders and Schizophrenia, Present and Lifetime Version (K-SADS-PL), a semistructured interview that gathers reports from the parent and child. Of the 21 children in
the sample who were recruited on the basis of their RAP, 11 (52%) also met criteria for a
DSM-IV anxiety disorder. Of the 21 children recruited for anxiety disorders, 5 (24%)
also met criteria for RAP. The 21 healthy controls did not meet criteria for RAP or an
anxiety disorder.
Children with RAP were recruited from two sources: (1) RAP patients who had
previously participated in Dr. Lynn Walker’s studies of recurrent pain and had agreed to
be contacted again for research purposes and (2) children of Vanderbilt Medical Center
staff who responded to an email recruiting children with frequent stomachaches for a
research study. Criterion for RAP in this study followed Apley’s criteria for RAP (1975):
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at least three episodes of abdominal pain in the past three months severe enough to impair
functioning or interrupt activities.
Participants in the anxiety disorder group were assigned according to their
meeting criteria of one or more of the following DSM-IV anxiety disorders: Separation
Anxiety, GAD, and Social Phobia. Participants in this group were recruited through the
Vanderbilt University Community Mental Health Center (Tom Catron, Ph.D., Director)
and through an email to Vanderbilt Medical Center staff recruiting children with frequent
worries for a research study. Children that qualified for both RAP and an anxiety
disorder were assigned a group label based on their recruitment strategy and “primary
complaint” defined by whether they had consulted a psychologist or physician for their
difficulties.
Healthy control children were recruited from a variety of sources: (1) well
children who had participated in Dr. Lynn Walker’s study previously and had agreed to
be contacted again for research purposes, (2) fliers distributed at an area Women’s First
Convention describing opportunities for participating in a Child Stress and Health Study,
(3) emails to Vanderbilt Medical Center staff describing an opportunity to participate in a
Child Stress and Health Study, (4) and referrals from families who had already
participated in the study.
Exclusionary criteria included a known chronic health condition, physical
handicap, mental retardation, and attention-deficit-hyperactivity disorder (ADHD).
One parent of each child also participated in the study. Recruitment focused on
obtaining a sample representative of Nashville’s population. The sample identified
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themselves as 71% white, 19% African American, 3%Asian, 6% other, and 2% Hispanic.
The groups were matched on gender and age.
Measures
Physiological Measures. Heart Rate was measured using BIOPAK physiological
data equipment. Wavelet Spectrum Analyses of the data were conducted and used in data
analyses. This physiological data was collected continuously throughout the time the
participants were participating in the experimental protocol.
Pain Responses. During the cold pressor task, two pain variables were taken.
Pain intensity was recorded at 20 seconds as the number reported from a 10-point VAS.
Participants who removed their arm before 20 seconds had elapsed rated pain intensity of
the task on the VAS immediately after removing their arm. Pain tolerance was the total
time elapsed from the time at which the arm was submerged to the time at which the
participant removed their arm.
Emotional and Somatic Symptoms. Participants completed the 112-item Youth
Self Report (YSR). The 112-item YSR provides information on the participants’
perceptions of their psychological and somatic symptoms as well as level of functioning
and has a strong test-retest reliability of .79-.95 (Achenbach, Dumenci, & Rescorla,
2002). The parent completed a demographics questionnaire and the Child Behavior
Checklist (CBCL). The CBCL, a 112-item parent-version of the YSR, assesses the
parent’s perception of the child’s internalizing and externalizing problems in the past six
months and has good test-retest reliability ranging from .79 to .95 (Achenbach, Dumenci,
& Rescorla, 2002).
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Stress Reactivity. Participants completed the Responses to Stress Questionnaire
(RSQ; Connor-Smith et al., 2000) concerning social stressors. The 57-item RSQ assess
coping mechanisms in reference to age-appropriate social stressors and has been shown
to have good reliability and validity, including internal consistency with alphas ranging
from .73 to .85 (Connor-Smith et al., 2000). The RSQ measures three styles of coping:
primary control engagement coping (problem solving, emotional expression, emotional
regulation), secondary control engagement coping (positive thinking, cognitive
restructuring, acceptance, distraction), and disengagement coping (avoidance, denial,
wishful thinking); it also measures two types of stress responses: involuntary engagement
(rumination, intrusive thoughts, emotional arousal, physiological arousal, impulsive
action) and involuntary disengagement (cognitive interference, involuntary avoidance,
inaction, emotional numbing).
Procedure
Parents provided informed consent and participants provided assent. All
experimental procedures were carried out in two rooms in the Jesup Building on the
Peabody Campus of Vanderbilt University. Children participated in the experimental
protocol in one room and their parent in another. The rooms were quiet and separated
from foot traffic in the building. After informed consent and assent were obtained,
children placed the physiological sensors on their chest in order to record physiological
data. They wore two sensors on their sternum to measure heart rate. Participants sat
quietly for five minutes while baseline physiological data were recorded.
Participants then completed two psychological stressors. The first was a serial
subtraction task designed to mimic an academic stressor. Starting at 400, they were
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instructed by the experimenter to subtract by 7’s for two minutes. Participants were
stopped and instructed to start over at 400 when they made a mistake.
The second stressor was a social stress interview based on the model of Ewart and
Kolodner (1991) and designed to mimic a socially stressful situation. The interview
began by asking each participant to identify a specific stressor they would like to discuss,
chosen from examples that fall into three categories: school stress, family stress, and
friend stress. They were instructed to pick the most stressful category, and from that
category choose a specific stressful situation that had happened recently. If participants
choose a category or stressor for which they could not remember a specific episode, they
were instructed to choose another kind of stress for which they could. Participants were
asked to describe the details surrounding the stressful event, including time, place, people
present, and chronology of events. They were then asked to describe their emotions,
reactions, and bodily sensations experienced during and after the event as a result of the
stressor. The experimenter structured the interview so that the participant relived the
specific stressful situation in as much detail as possible, in an effort to elicit the same
physiological reactions that were elicited at the time of the actual stressor. This interview
has been shown to be a reliable method of eliciting a physiological stress response (Ewart
& Kolodner, 1991).
Immediately after the social stress interview, participants completed the physical
stressor, a cold pressor task that involved them putting their arm in a cooler full of
freezing cold water. The cooler was prepared before the participant arrived in order to
allow the water time to reach 4°C, and was then maintained at as close to 4°C as possible.
There was a mesh wire barrier in the cooler that separated the ice from the area where the
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participants rested their right arm in a sling. Two small water pumps were placed under
the sling in order to circulate the water and ensure that the participant’s arm did not warm
the water around itself as insulation.
In order to measure pain responses to the physical stressor, participants were
instructed to keep their arms in the water as long as possible, “doing or thinking about
whatever is necessary” in order to keep their arm in the water. Participants rated their
pain on a 10-point Visual Analogue Scale (VAS) at 20 seconds. The VAS has
demonstrated reliability and validity as a measure of pain intensity in children, and has
correlated highly with independent observations of children’s pain behaviors (LeBaron,
Zeltzer, & Fanurik, 1989). Participants were told to extract their arms at 4 minutes if they
had not already done so. Participants sat for up to 5 minutes to dry and warm their arm
and collect a period of physiological recovery data.
Participants were then given the opportunity to complete questionnaires in the lab
in exchange for a $40 gift certificate to Target. All participants chose to stay and
complete the questionnaires. When the child was finished, the parent reentered the room
and the family was given $75 cash compensation and a $40 gift certificate to Target.
Participants were debriefed and given a visual explanation of their physiological data.
The parent removed the participant’s chest sensors.
Data Analytic Strategy
Participants were deleted pair-wise in the analyses; that is, those participants who
were missing data on a certain variable were excluded from those analyses but were
included in the analyses for which they had data. For example, children under the age of
11 did not complete the YSR. On multiple regression equations, however, participants
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were excluded list-wise. That is, participants who were missing data at any of the
predicting steps or were missing the dependent variable were excluded from the
regression equation.
Results
Table 1 displays means and standard deviations for the three groups on the
measures of pain intensity, pain tolerance, mean heart rate for the length of the
experiment and for four key intervals, stress reactivity as measured by the proportion of
involuntary engagement stress responses to total items endorsed on the RSQ, and
anxious/depressed and somatic complaints scales from the YSR and CBCL.
Although differences between the groups on the YSR and CBCL
anxious/depressed and somatic complaints scales were not part of the formal hypotheses,
it is interesting to note the findings. YSR self-reports of anxious/depressed symptoms did
not differ significantly between the groups, although the effect sizes for the differences
between children with RAP and healthy controls and anxious children and healthy
controls were d = 1.1 and d = 1.0, respectively. YSR self-reports of somatic complaints
were significantly higher in the RAP group (T = 62, SD = 5.6) than in the anxious (T =
56, SD = 6.0) and healthy control (T = 55, SD = 5.0) groups, F (2, 34) = 7.30, p = .002.
The effect size of this difference between children with RAP and healthy controls is d =
1.4.
Parent reports of their children’s anxious/depressed symptoms from the CBCL
were significantly higher for children in the anxious group (T = 64, SD = 9.5) than in the
RAP (T = 57, SD = 5.3) and healthy control groups (T = 54, SD = 4.9 ), F (2, 60) = 12.1,
p < .001. Cohen’s d = 1.4 for the difference between anxious children and healthy
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controls on this measure, and d = .99 for the difference between anxious children and
children with RAP. Parent reports of somatic complaints from the CBCL did not differ
between the RAP (T = 63, SD = 8.5) and anxious groups (T = 60, SD = 10.2). Both
clinical groups were significantly higher on the somatic complaints scale than the healthy
control group (T = 53, SD = 4.2), F (2, 60) = 7.5, p = .001. The effect sizes for the
difference between the RAP and healthy control and anxious and healthy control groups
were d = 1.6 and d = .93, respectively.
Hypothesis 1: Mean Heart Rate
A group by time repeated-measures ANOVA was conducted to test the first
hypothesis concerning differences between groups in mean heart rate at the four
individual time intervals (i.e. Baseline, Psychological Stressors, Cold Pressor, Recovery).
There was a significant main effect for time, Wilks’ Lambda F (3, 49) = 12.64, p < .001.
There was also a significant quadratic effect for time, F (1, 51) = 20.65, p < .001. Results
of Least Significant Difference tests in pair-wise comparisons reported a significant
difference in mean heart rate (beats per minute) between Baseline (M = 86.8, SE = 1.48)
and Psychological Stress Intervals (M = 89.2, SE = 1.37), p < .01. There was no
significant change in mean heart rate from the Psychological Stressors interval to the
Cold Pressor interval. The mean heart rates during the Psychological Stressors and Cold
Pressor (M = 88.7, SE = 1.50) intervals were both significantly different from the
Recovery Interval (M = 85.5, SE = 1.41), p’s < .01. The mean heart rates from the
Baseline and Recovery Intervals were not significantly different.
There was no main effect for group, and no interaction of group by time. An
additional series of one-way ANOVAs was conducted, one at each time interval, in order
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to determine if similar changes in heart rate between the groups were not masking a
difference in physiological reactivity. There were no significant differences at any of the
four time points. An additional group by time repeated-measured ANOVA was
conducted using mean heart rate at Baseline as a covariate, and no main effect for group
was found. Figure 1 graphically displays the mean heart rate between groups across the
four time intervals. Although not significant, there is a trend for mean heart rate in the
RAP group to be higher than the other two groups during the intervals of Stress Tasks,
Cold Pressor, and Recovery Period. The effect size reflecting the differences between
children with RAP and anxious children ranged from d = .24 to d = .40 on the three postBaseline intervals. Notably, the effect size for the difference between children with RAP
and anxious children at Baseline was minimal, d = .002. The effect size reflecting the
differences between children with RAP and healthy controls ranged from d = .22 to d =
.43 on all four time intervals. All of these effect sizes, except the non-difference between
RAP and anxious at Baseline, reflect small to medium effect sizes, suggesting that our
sample was underpowered and that further research should aim to include a larger sample
to investigate heart rate differences between groups in response to stress.
Hypothesis 2: Stress Reactivity
With regard to the second hypothesis concerning self-reported stress reactivity as
measured by the involuntary engagement scale on the RSQ (e.g., physiological reactivity,
emotional reactivity), a one-way ANOVA revealed that children with RAP reported
significantly more involuntary engagement responses to stress in proportion to the rest of
their endorsements (M = .26, SD = .04) than both anxious (M = .22, SD = .03) and well
children (M = .23, SD = .04), F (2, 54) = 5.59, p < .01. This confirmed our hypothesis
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that the self reports of children with RAP would demonstrate more stress reactivity in
response to stress than the rest of the sample in proportion to total endorsements on the
RSQ.
Hypothesis 3: Pain Intensity and Pain Tolerance
With regard to the third hypothesis concerning pain responses, a one-way
ANOVA was conducted with group as the factor. Children with RAP had a significantly
higher mean rating of pain intensity of 6.8 (SD = 2.2), whereas anxious children had a
mean rating of 4.6 (SD = 2.2), F (2, 57) = 3.95, p < .05.
This difference yields an effect
size of d = 1.0. On the measure of pain intensity, therefore, our hypothesis was partially
confirmed: children with RAP rated the Cold Pressor significantly more painful than
anxious children on a Visual Analogue Scale ranging from 1 to 10. There was no
difference between the healthy control group and the RAP group or the healthy group and
the anxious group. In another one-way ANOVA with group as the factor, the groups did
not differ on the measure of pain tolerance, thus supporting the null hypothesis with
respect to this variable.
Associations among Physiological and Psychological Symptoms
The fourth hypothesis focused on the associations between physiological and
psychological factors related to stress, anxiety, and pain. This hypothesis was tested in a
series of analyses.
Hypothesis 4a: Correlations between Mean Heart Rate and Psychological
Symptoms. Mean heart rate (beats per minute) was positively and significantly correlated
with YSR Anxious/Depressed symptoms for all four time intervals examined (r’s ranged
from .44 to .54, all p < .01). Mean heart rate was also positively and significantly
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correlated with CBCL Somatic Complaints for the Baseline Interval (r = .38, p < .01),
Psychological Stressors Interval (r = .35, p < .01), and Recovery Interval (r = .40, p <
.01), with a tendency to be correlated with Cold Pressor Interval (r = .26, p = .06). Mean
HR was not, however, correlated with YSR Somatic Complaints or CBCL
Anxious/Depressed symptoms. Thus, our hypothesis concerning the relation between
mean HR and psychological symptoms was partially confirmed.
Hypothesis 4b: Correlations between Mean Heart Rate and Involuntary
Engagement. Mean HR from all four intervals was positively correlated with Involuntary
Engagement proportion scores from the RSQ (r’s ranged from .30 to .47, all p < .05),
confirming our hypothesis concerning such associations.
Hypothesis 4c: Correlation between Pain Intensity and Somatic Symptoms. Our
hypothesis concerning the relation between Pain Intensity Rating on the cold pressor task
and reports of somatic complaints was partially confirmed: Pain Intensity correlated
positively and significantly with YSR Somatic Complaints (r = .44, p < .01), but not with
CBCL Somatic Complaints.
Hypothesis 4d: Predicting Psychological Symptoms in a Multiple Regression. A
series of multiple regressions were performed in order to account for the variance in
scores on the YSR and CBCL Anxious/Depressed and Somatic Complaints scales.
Predicting YSR Anxious/Depressed Symptoms. The first multiple regression
predicted YSR Anxious/Depressed symptoms from group, mean heart rate over the
period from baseline to recovery from the stress and pain procedure, and involuntary
engagement proportion scores from the RSQ. In the first step of the regression equation,
group was not a significant predictor of self-reported symptoms of anxiety/depression.
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At the second step, mean heart rate across the time of the experiment was a significant
predictor of YSR Anxious/Depressed symptoms (β = .51, p = .002). At the third and
final step, involuntary engagement was not a significant predictor of symptoms of anxiety
and depression. At the final step, however, group became a significant predictor (β = .35,
p = .03) and mean heart rate remained significant, although the magnitude of the effect
was smaller (β = .36, p = .04). The three predictors accounted for 41% of the variance in
YSR Anxious/Depressed self-reports. These findings suggest the possibility of a
suppressor effect of involuntary engagement responses on group differences. Once
involuntary engagement is controlled for in the last step of the regression, group
differences appear significant and mean heart rate remains so in predicting self-reported
psychological symptoms.
Predicting YSR Somatic Complaints. The second multiple regression predicted
YSR Somatic Complaints from group, mean heart rate over the period from baseline to
recovery from the stress and pain procedure, and involuntary engagement proportion
scores from the RSQ. In the first two steps of the regression model, group and mean
heart rate were not significant predictors of YSR Somatic Complaints. When added in
the third step, involuntary engagement stress responses did significantly predict selfreported somatic complaints (β = .51, p = .01). Children’s reports of the way that they
respond to stress predicted 12% of the variance in their self-report of somatic complaints.
Predicting CBCL Anxious/Depressed Symptoms. The third regression
predicted CBCL Anxious/Depressed Symptoms from group, mean heart rate over the
period from baseline to recovery from the stress and pain procedure, and involuntary
engagement proportion scores from the RSQ. In the first step of the regression equation,
Jackson 23
group was a significant predictor of parent-reported psychological symptoms (β = .51, p
< .001). At step two, mean heart rate was not a significant predictor and group remained
significant (β = .51, p < .001). At step three, involuntary engagement was not a
significant predictor, but mean heart rate tended towards significance (β = .27, p = .053),
and group remained a significant predictor (β = .47, p = .001). In considering parent
reports of psychological symptoms, these three predictors accounted for 29% of the
variance in CBCL anxious/depressed symptoms.
Predicting CBCL Somatic Complaints. The fourth regression predicted CBCL
Somatic Complaints from group, mean heart rate over the period from baseline to
recovery from the stress and pain procedure, and involuntary engagement proportion
scores from the RSQ. Group was a significant predictor of parent reported somatic
complaints (β = .31, p = .03). At step two, mean heart rate was a significant predictor of
CBCL Somatic Complaints (β = .31, p = .03), and group remained significant (β = .31, p
= .02). At the final step, involuntary engagement stress responses did not predict CBCL
Somatic Complaints, mean heart rate lost some of its effect (β = .29, p = .052), and group
remained significant (β = .32, p = .02). These three predictors account for 11% of the
variance in CBCL somatic complaints scales.
Discussion
This study examined the physiological and emotional factors of stress responses
in children with chronic pain, children with anxiety, and a comparison group of healthy
controls. The study found that the psychological and somatic symptoms of children with
RAP and anxious children were similar. Although physiological data did not differ
significantly between the groups, the current study found that children with RAP reported
Jackson 24
themselves to be significantly more reactive to stress than the rest of the sample and that,
across the sample, psychological and somatic symptoms, as well as self-report of stress
reactivity were all correlated positively with mean heart rate. Children with RAP also
responded differently to a painful physical task, and pain ratings across the sample were
positively correlated with somatic complaints. In explaining the variance in
psychological and somatic symptoms across the sample, the current study found that,
group (RAP, anxious, control), mean heart rate, and involuntary engagement proportion
scores predicted YSR and CBCL anxious/depressed symptoms and somatic complaints
differently depending on the reporter and the type of symptom.
Although children with RAP present with physical pain and discomfort and
anxious children present with psychological symptoms as their primary complaint, both
groups had elevated anxious/depressed and somatic symptoms, although some failed to
reach levels significantly different from healthy controls. In the current sample, 11
(52%) of the 21 children with RAP also met criteria for a DSM-IV anxiety disorder and 5
(24%) of the 21 anxious children also met criteria for RAP. The purpose of this study
was to compare the two clinical groups based on the primary presenting complaint (either
RAP or anxiety) to each other and to healthy controls in their responses to stress through
an experimental protocol and to find associations between physiological reactivity and
other reports of psychological symptoms and stress reactivity.
This study determined a significant effect for time on mean heart rate over the
period from baseline to recovery from the stress and pain procedure. These findings
support the serial subtraction task, social stress interview, and cold pressor task as valid
methods of inducing physiological stress reactivity in children. Although this study did
Jackson 25
not find differences between the groups in mean heart rate at any of the intervals or
across the total time of the experiment, the trends of the data support the idea that
children with RAP respond to and recover from psychological and physical stress
differently than healthy children. Considering the small to medium effect sizes of these
differences, future research should include larger samples in order to determine possible
group differences. The number of children with comorbid symptoms of recurrent
abdominal pain and anxiety in the current study does not undercut the correlation and
regression analyses that used the entire sample. The number of children with comorbid
symptoms in the RAP and anxious groups from our sample may explain our lack of
findings concerning the differences between the groups on physiological reactivity to and
recovery from stress. Future analyses of this sample will be conducted based solely on
the presence or absence of RAP and then solely on the presence or absence of anxiety, as
well as include a fourth comparison group of children with both RAP and anxiety in
order to determine what group differences may exist in that respect. Further analyses
with this current sample will also explore other physiological measures that were
collected, such as vagal tone and galvanic skin response, as they may be better indicators
of group differences in physiological reactivity.
This study also found that the more anxious/depressed a child reported they were,
the higher their mean heart rate was averaged across the time of the experiment, which
confirms previous research concerning self-reported anxiety symptoms and their
association with elevated heart rate (Weems et al., 2005). Because heart rate is a measure
of overall physiological arousal, our findings support other research that shows that
symptoms of anxiety are associated with higher physiological arousal (Rosenberg &
Jackson 26
Kagan, 1989; Weems et al., 2005). This study also demonstrated that parent reports of
children’s somatic complaints are associated with higher physiological arousal. The fact
that mean heart rate on all four of the time intervals was associated with self-reported
psychological symptoms demonstrates that feeling anxious/depressed is associated not
only with higher stress reactivity, but also with higher resting and recovery rates.
The fact that different measures from the child- and parent-report, namely
Anxious/Depressed and Somatic Complaints scales, respectively, both correlate with
heart rate tells us something interesting about what children vs. parents may consider the
primary concern, especially in light of the finding that child reports of somatic complaints
and parent reports of anxious/depressed symptoms are not associated with heart rate.
Possible explanations for these findings include: (1) children voice their feelings of
anxiety and depression as somatic complaints to their parents, and thus parents are more
aware of the somatic symptoms, or (2) parents observe a general pattern of behavior in
their children and assume that they are physically not feeling well. In either case, areas
for future research include an investigation of communication between parents and
children on the nature of their psychological and physical complaints to determine how
children can receive parental support during their experience of negative psychological
symptoms.
Current theory proposes that RAP is part of an overall pattern of physiological upregulation associated with hypervigilance to perceived environmental threat. In the
current study, children with RAP used proportionately more involuntary engagement
stress responses than the rest of the sample. Involuntary engagement includes
rumination, intrusive thoughts, physiological and emotional reactivity, and impulsive
Jackson 27
action. Compas et al. (2001) demonstrated that involuntary engagement stress responses
are associated with more symptoms of psychopathology, and this maladaptive and
automatic examination of the environment appeared in children’s self-reports and was
associated across the sample with higher mean heart rates during the period from baseline
to recovery from the stress and pain procedure. These findings suggest that children with
RAP respond to stress in a maladaptive manner and support the theory that RAP is part of
an overall pattern of psychological and physiological stress reactivity. These findings
also demonstrate that children are reasonable reporters of their own physiological
reactivity and provide validity for the RSQ as a measure of stress responses.
Children with RAP responded differently in their reports of pain intensity during
the cold pressor, supporting the idea that children with RAP do not experience a limited
visceral hypersensitivity, but sensitivity to peripheral pain as well. Future research
should treat children with RAP within the context of their overall pattern of hyperalgesia.
This is also the first study to show that the cold pressor task is a valid measure of pain
responses.
Children’s self-reports of somatic complaints were positively associated with how
painful they rated the cold pressor task, but parent reports were not. This finding
provides validity for the YSR Somatic Complaints scale because when children reported
that they experienced more somatic discomfort, they reported the same thing when
assessed during a physical stressor. Considering this study’s previous finding, which
suggests that parents report their child’s psychological symptoms as somatic symptoms,
the CBCL Somatic Complaints scale may not contain the information purely related to
Somatic Complaints that would be necessary to find an association with Pain Intensity.
Jackson 28
On the measure of pain tolerance, that is, the total length of time a child kept his
or her arm in the cold pressor, there was a large floor effect. Standard deviations for this
variable were as large as or larger than the means, reflecting the fact that many children
only kept their arms in the cold pressor for a few seconds before removing it. Since it is
ethically unacceptable to require children to keep their arms in the water for longer than
they feel they are able, future research should consider using water slightly warmer than
4°C in order to increase the variance of pain tolerance.
The ability of mean heart rate and involuntary engagement proportion scores from
the RSQ to predict psychological and somatic symptoms from the YSR and CBCL above
and beyond what group label could account for varied depending on the reporter and the
type of symptom. The current study found that when involuntary engagement reports
were controlled for, group and mean heart rate over the period from baseline to recovery
from the stress and pain procedure were roughly equivalent significant predictors of selfreported psychological symptoms. The ability to predict self-reported somatic
complaints, however, depended solely on involuntary engagement responses to stress.
This important finding demonstrates that automatic stress responses play a key role in the
experience of somatic symptoms. Thus, future intervention research designed to reduce
somatic symptoms in children should focus on modifying automatic stress responses.
In predicting parent reports, the current study demonstrated that group label
helped predict CBCL psychological and somatic symptoms; that is, the label assigned to
a child based on the presence of recurrent abdominal pain or a clinical diagnosis of
anxiety explained to a large extent how parents responded about their children’s
psychological symptoms. All of the children in the sample who qualified for the anxious
Jackson 29
group had seen a counselor or psychologist concerning their psychological difficulties at
some point in their life, and all children assigned to the RAP group had been to a
physician at least once for their pain and had never received an organic diagnosis. Since
these children’s “primary-complaint” labels of anxiety or RAP depend largely on both
what their parents view as the primary complaint and where parents choose to seek
consultation, it is not surprising that group label predicts parent reports.
The mean heart rate did not help predict parent reports of children’s
anxious/depressed symptoms, until the regression controlled for involuntary engagement
scores. There is something about heart rate apart from its association with involuntary
engagement scores that helps predict parent-reported psychological symptoms. For
parent reports of somatic complaints, these findings differed in that the reason heart rate
helped predict parent reports of somatic complaints was largely because of the
association with involuntary engagement stress responses. Once these stress responses
were accounted for, heart rate explained less of the variance in CBCL somatic
complaints.
This study’s findings suggest that children with RAP and anxious children may be
more similar than different with respect to psychological and somatic symptoms. This
study provided validity for the cold pressor task as a measure of pain intensity, the
psychological and physical stressors as valid methods of inducing physiological stress
reactivity in children, and for the RSQ as a measure of stress reactivity. Associations
between stress reactivity and psychological and somatic symptoms were found, as well as
the ability of different measures of stress reactivity to account for psychological and
somatic symptoms. Considering these findings, future intervention research for both
Jackson 30
children with RAP and anxious children should focus on reducing maladaptive automatic
stress responses, such as physiological and emotional reactivity, rumination, intrusive
thoughts, and impulsive action.
Jackson 31
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Jackson 34
Table 1
Means and Standard Deviations of Key Variables
Pain Intensity (1 to
10)
Pain Tolerance (sec)
RAP
Anxious
Well
Mean (SD)
Mean (SD)
Mean (SD)
6.8a (2.2)
4.6b (2.2)
5.4ab (2.9)
66a (65)
80a (94)
F (2, 59) = .19, p = .83
87.3a (10.6)
86.7a (9.0)
F (2, 52) = .44, p = .65
78a (84)
F scores
F (2,57) = 3.95, p = .025
Whole Experiment:
Mean Heart Rate
(bpm)
89.6a (10.3)
Baseline: Mean
Heart Rate (bpm)
88.1a (10.6)
87.8a (11.5)
85.7a (11.2)
F (2, 52) = .24, p = .78
Psychological
Stressors: Mean
Heart Rate (bpm)
91.3a (10.9)
88.2a (10.5)
88.9a (8.9)
F (2, 52) = .46, p = .63
Cold Pressor: Mean
Heart Rate (bpm)
91.6a (10.1)
87.3a (11.6)
87.0a (11.3)
F (2, 51) = 1.00, p = .37
Recovery: Mean
Heart Rate (bpm)
87.5a (11.8)
84.8a (11.1)
.26a (.04)
.22b (.03)
.23b (.04)
F (2, 54) = 5.59, p = .006
56.8a (6.0)
56.8a (6.4)
52.4a (2.3)
F (2, 34) = 2.21, p = .13
61.8a (5.6)
56.0b (6.0)
54.6b (4.9)
F (2, 34) = 7.30, p = .002
56.5a (5.3)
63.8b (9.5)
53.6a (4.9)
F (2, 60) = 12.10, p < .001
63.3a (8.5)
60.1a (10.2)
53.4b (4.2)
F (2, 60) = 7.54, p = .001
Involuntary
Engagement Stress
Responses
YSR
Anxious/Depressed
(T-Scores)
YSR Somatic
Complaints
(T-Scores)
CBCL
Anxious/Depressed
(T-Scores)
CBCL Somatic
Complaints (TScores)
abc
85.2a (8.2)
F (2, 52) = .37, p = .70
: within a variable, a difference in superscript represents a significant difference between
groups, p < .05
Jackson 35
Figure 1 Caption
Mean heart rate (bpm) across time for groups, displayed at four key intervals of the
experimental protocol. There were no significant differences between groups at any time
point.
Jackson 36
Figure 1
Mean Heart Rate Across Time for Groups
Mean Heart Rate (bpm)
100.00
97.00
94.00
Well
91.00
RAP
ANX
88.00
85.00
82.00
Baseline
Stress Tasks Cold Pressor
Time Intervals
Recovery
Jackson 37
Table 2
Correlations: Mean Heart Rate (bpm) on four intervals to psychological symptoms and pain response
Baseline:
Heart
Rate
1.
.86**
--
.74**
.78*
--
.86**
.91**
.79**
--
4. Pain Intensity -.16
-.11
.03
-.01
--
5. CBCL
Somatic
Complaints
.35**
.26+
.40**
.20
--
.47**
.44*
.54**
.14
.32+
--
.05
.09
.04
.02
.44**
.15
.26
--
.21
.17
.06
.15
-.15
.52**
.32
-.01
--
.30*
.47**
.35*
.30*
.13
.14
.42**
.35*
-.08
1. Psych.
Stressors: Heart
Rate
2. Cold Pressor:
Heart Rate
3. Recovery:
Heart Rate
.38**
6. YSR Anx/Dep .44*
7. YSR Somatic
Complaints
8. CBCL
Anx/Dep
9. Involuntary
Engagement
** p < 0.01 (2-tailed)
* p < 0.05 (2-tailed)
+
.05 < p < .06
2.
3.
4.
5.
6.
7.
8.
9.
--
Jackson 38
Table 3
Regression Equations: Predicting YSR and CBCL Psychological and Somatic Scales.
Equation 1 – YSR Anxious/Depressed
Final R2 = .41
2
Step 1: R change = .08
β
sr
Group: Well, RAP, Anx
.28
.28
Step 2: R2 change = .26**
Group: Well, RAP, Anx
.28
.33
Mean HR across experiment
.51**
.53
Step 3: R2 change = .08
Group: Well, RAP, Anx
.35*
.41
Mean HR across experiment
.36*
.38
Involuntary Engagement
.32
.34
2
Equation 2 – YSR Somatic Complaints
Final R = .21
2
Step 1: R change = .003
β
sr
Group: Well, RAP, Anx
.06
.06
Step 2: R2 change = .009
Group: Well, RAP, Anx
.06
.06
Mean HR across experiment
.08
.08
Step 3: R2 change = .21*
Group: Well, RAP, Anx
.17
.19
Mean HR across experiment
-.16
-.15
Involuntary Engagement
.51*
.45
2
Equation 3 – CBCL Anxious/Depressed
Final R = .32
2
Step 1: R change = .26***
β
sr
Group: Well, RAP, Anx
.51***
.51
Step 2: R2 change = .04
Group: Well, RAP, Anx
.51***
.52
Mean HR across experiment
.19
.22
Step 3: R2 change = .03
Group: Well, RAP, Anx
.47**
.49
+
Mean HR across experiment
.27
.28
Involuntary Engagement
-.19
-.20
Equation 4 – CBCL Somatic Complaints
Final R2 = .19
Step 1: R2 change = .09*
β
sr
Group: Well, RAP, Anx
.31*
.31
2
Step 2: R change = .10*
Group: Well, RAP, Anx
.31*
.33
Mean HR across experiment
.31*
.32
Step 3: R2 change = .002
Group: Well, RAP, Anx
.32*
.33
Mean HR across experiment
.29+
.29
Involuntary Engagement
.05
.05
Note: β = standardized beta. sr = semi-partial correlation.
* p < .05. **p < .01. ***p < .001, +p = .053
F (3, 28) = 6.44, p =.002
F (3, 28) = 2.43, p =.09
F (3, 45) = 7.14, p =.001
F (3, 45) = 3.52, p = .02