November 8, 2002

Study links anger to pain

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Vanderbilt Children's Hospital held a costume contest for faculty and staff last week. The top three prizes for best costume went to Rachel Stacey, left, as The Cat in the Hat, Dr. Arnold Strauss as Dr. Grinch, and Cheri Kline as Raggedy Andy. (photo by Dana Johnson)

Study links anger to pain

If you’re especially prone, when angry, to throw or kick things and generally raise hell, a new study done at Vanderbilt University Medical Center shows that, when it comes to the body’s innate ability to quell physical pain, your central nervous system tends to function differently from that of most other people.

Psychologists who study pain are increasingly turning their attention to various poorly understood associations among anger, certain behavior patterns related to the experience of anger, increased sensitivity to acute pain and increased occurrence of chronic pain. A new study led by psychologist Stephen Bruehl, Ph.D., assistant professor of Anesthesiology, casts light on physiological mechanisms underlying these associations. The study appears in a recent issue of Pain, the journal of the International Association for the Study of Pain.

In previous studies and again in this study, increased sensitivity to acute pain was found, in roughly equal degrees, among test subjects who claim to become easily angered, test subjects who claim that they bottle up their anger, and test subjects who claim that they vent their anger more explosively. Pushing beyond these known associations, Bruehl’s study tests the hypothesis that these anger variables are somehow associated with dysfunction of endogenous opioids, which are pain-quelling, stress-relieving, mood-lifting agents produced in various sites throughout the body. Endogenous opioids that specifically quell pain are produced in the brain and spinal cord.

“Endogenous opioids work on the same receptors as morphine—they are literally the body’s own morphine,” Bruehl said. A total of 88 research subjects, including 43 chronic low back pain sufferers and 45 pain-free normals, were individually ranked against each other in terms of tendency to be easily angered, to vent anger, and to bottle up anger. (Ranking was based entirely on self-reporting on standardized, validated questionnaires.) Each receiving $250, all subjects were dealt brief, measured painful stimuli in two lab sessions held one week apart. In one lab session the subject received a drug to block the pain-quelling action of endogenous opioids, and in the other session the subject received a saline placebo (with neither the subject nor the research monitor knowing which was which). Subjects reported their pain level verbally during each pain task and again in a brief questionnaire immediately following each task. Increased pain intensity after receiving the opioid blockade medication, compared to the placebo, indicated subjects who were producing endogenous opioid analgesia during the pain tasks.

The pain tasks were the same in both lab sessions: the first task was 2000 grams of pressure applied for one minute to the back of the index finger of the subject’s dominant hand, and the second task was constriction of blood circulation to the subject’s non-dominant arm (using a blood pressure cuff) for up to five minutes or until the subject’s pain tolerance was reached.

Bruehl’s statistical analysis took into account several variables present in the study group, including use of antidepressant or narcotic analgesic medications, ethnicity, order of placebo/drug administration in the two lab sessions, and self-reported level of depression (depression is known to be associated both with pain perception and with self-reporting of the three anger variables).

• Among the one-half of the subjects who ranked above the mean in tendency to vent anger, the drug used to block endogenous opioid action had no aggregate effect on acute pain perception. In other words, a tendency to vent anger more explosively was associated with complete dysfunction of the pain-quelling action of endogenous opioids. This association was similar among both healthy subjects and those with chronic low back pain.

• A similar but not quite statistically significant trend was noted among subjects who ranked above the mean in tendency to become easily angered, allowing Bruehl to conclude that, given a larger test group, the study would have shown an association between tendency to frequent anger and endogenous opioid dysfunction. The trend also held equally among chronic-pain and healthy subjects.

• Among subjects who ranked above the mean in tendency to bottle up anger, the drug used to block endogenous opioid action was associated with increased pain perception roughly equal, in the aggregate, to that among subjects who ranked below the mean. So a tendency to bottle up anger, while it is associated with increased sensitivity to acute pain, is nonetheless associated with normal function of the pain-quelling action of endogenous opioids. Again, the association was similar among subjects with and without chronic pain.

“This study is part of a larger project to understand the impact of endogenous opioid dysfunction on chronic pain,” Bruehl said. Because chronic pain patients are on pain medication it’s more difficult to study their endogenous opioid function; however, a previous study by Bruehl had suggested an association between chronic pain and endogenous opioid dysfunction. Chronic pain is also associated with extremes in all three of the self-reported anger variables. By establishing similar association between anger-related factors and endogenous opioid function among both healthy subjects and those with chronic pain, the present study disproves the hypothesis that anger is somehow at the root of an association between chronic pain and endogenous opioid dysfunction.

A curious result of the study, though it’s of less direct bearing on an understanding of chronic pain, is the indication that different mechanisms underlie the association between pain and the venting of anger (now associated with endogenous opioid dysfunction) and pain and the bottling up of anger (now disassociated from endogenous opioid dysfunction).

While people who say they have more of a tendency to vent anger exhibit poor endogenous opioid function in the lab, Bruehl said that may be simply because, in the study methods used, subjects were not angered during the pain stimulus and didn’t get a chance to realize any potential pain-quelling benefit that may come with the actual venting of anger. Bruehl plans next to test the hypothesis that venting anger helps quell pain by promoting endogenous opioid function.

Bruehl’s study partners included, from the department of Anesthesiology, Ok Yung Chung, Pamela Ward and Benjamin Johnson, and, from the The Chicago Medical School Department of Psychology, John W. Burns. n