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Article: Pain and sleep


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http://www.medscape.com/viewarticle/480566

Physiologic Correlates of Pain During Sleep

Disclosures

Brenda Bursch, PhD

Although the functions of sleep remain unclear, sleep is generally believed to be a restorative and energy-conservation process. Sleep deprivation can lead to sleepiness, fatigue, negative mood, disorientation, a decrease in growth hormone secretion, and a lower pain threshold. Reports of insomnia are common among those in pain. Most related research has focused on chronic pain patients and healthy participants undergoing experimental pain procedures.

In this symposium,[1] Dr. Isabelle Raymond described a study focused on inpatients with burns.[2] Previous research found that burn inpatients suffer from sleep problems, that poorly controlled pain can worsen sleep quality, and that sleep problems can lead to increased pain during the first week of hospitalization. In their study, they collected data on 16 conscious patients (ages 18-50) admitted within 72 hours of their injuries. Data were collected for a total of 164 nights with the following measures: the Pittsburgh Sleep Quality Index, actigraphy, and visual analog scale pain assessment, in addition to monitoring of medications. They found that patients averaged 8 hours of sleep over 24 hours. Sleep was fragmented, however, with most episodes of sleep lasting only 10-15 minutes. Overall, the patients experienced frequent and long wakenings, with much variability in sleep patterns exhibited in this sample. Pain intensity was related to total wake time and to pain intensity during procedures. Baseline (background) pain was related to more disturbed sleep. Although the causal direction is not known, analgesic medication use was also found to be related to sleep disturbance.

Dr. Carol Landis described a study on electroencephalogram (EEG) biomarkers of sleep quality in fibromyalgia (FM) patients.[3] Previous research revealed that compared with controls, midlife women with FM reported poorer sleep quality and higher psychologic distress. They also had more early-night transitional sleep, more sleep-stage changes, and a higher sleep-fragmentation index. However, they did not differ in alpha-EEG nonrapid eye movement activity. The current research used the same comparison groups; they kept daily symptom diaries and spent 3 nights in a sleep laboratory. EEG measurement was used to evaluate for microstructure abnormalities, including spindle activity. The FM group was found to have decreased spindle activity and longer spindles, but this particular difference was nonsignificant. The pain pressure threshold predicted spindle number and length.

Dr. Diana McMillan[4] reported data from a study of heart-rate variability during sleep. Investigators compared controls with 2 other groups of middle-age women with FM or insomnia. Changes in autonomic activity cause heart-rate fluctuations called heart-rate variability, and this is revealed by irregularities in the distance between R waves in QRS complexes. Factors that affect heart rate and variability include posture, respiration frequency, age, sex, physical or mental stress, pain, numerous disease conditions, and some medications. In the current study, the initial trends suggested that the FM group had a slower but more variable heart rate, with more arousals as compared with the other 2 groups. However, as the number of subjects who were compared increased, the difference in heart-rate variability disappeared. The finding of slower heart rate in the FM group was contrary to expectation.

References

1. Landis CA, Raymond I, McMillan DE. Physiological correlates of pain during sleep. Program and abstracts of the 23rd Annual Meeting of the American Pain Society ; May 6-9, 2004; Vancouver, British Columbia, Canada. Symposium 326.

2. Raymond I, Nielsen TA, Lavigne G, et al. Quality of sleep and its daily relationship to pain intensity in hospitalized adult burn patients. Pain. 2001;92:381-388. Abstract

3. Landis CA, Frey CA, Lentz MJ, et al. Self-reported sleep quality and fatigue correlates with actigraphy in midlife women with fibromyalgia. Nurs Res. 2003;52:140-147. Abstract

4. McMillan DE. Interpreting heart rate variability sleep/wake patterns in cardiac patients. J Cardiovasc Nurs. 2002;17:69-81. Abstract

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