• Changes in muscle response as a result of perceived pain

      Eshenaur, Ann Elizabeth; Buxbaum, Jerome D. (1996)
      Chronic musculoskeletal pain is a leading cause of functional limitation, resulting in increased use of the health care system and lost work days. Surface electromyography (EMG) is used as a monitoring test for skeletal muscle activity for individuals with chronic pain. The Baltimore Pain Model is an EMG-based mathematical model developed for use as an objective correlate to levels of perceived pain in skeletal muscle. The purpose of this study was to assess the validity of the EMG model as a physiologic correlate to perceived pain in skeletal muscle. Sixty-one subjects with chronic pain completed the study. Subjects with low back pain (LBP) or facial pain (FP) were assigned to 1 of 3 pain groups, according to their respective EMG recording sites. Pain-free controls were used for comparison. Physical signs and symptoms of pain, and psychological and functional status were assessed. This double-blind study utilized a single subject-subject replication design. All subjects were randomly assigned to 1 of 6 treatment sequences via a Latin square design. Treatment conditions included Lodine, Placebo and Rest (no treatment). EMG from the bilateral masseters was recorded during 4 modes of activity. EMG from the bilateral erector spinae was recorded during 8 modes of activity. All subjects received a pre-treatment EMC, and in addition, subjects with pain recorded their perceived pain levels on a visual analog scale (VAS). The EMG and VAS were repeated 3 times. Subjects were then given 1 of 3 treatments. The EMC and VAS were repeated 3 times at both 30 and 60 minutes following treatment. Subjects returned for 2 more identical study sessions, with the exception of a different treatment intervention. VAS scores were compared with 6 EMG parameters to determine whether there was a relationship between change in pain level and change in EMG activity. Changes in the EMG and pain measures were assessed with both single case and multivariate analyses. Results indicated that changes in the majority of the EMG parameters were reflective of changes in level of pain intensity, regardless of type of treatment intervention. EMG predicted change in pain most consistently when recordings were made over the masseters. During specific movements, CF intercept was the best predictor of change in LBP. Placebo was more effective in reducing LBP and FP than either Lodine or Rest. Results of this study support the use of surface EMG as a physiologic correlate to perceived chronic pain.
    • The perceived meanings of cancer pain: An instrument development

      Chen, Mei-Ling; Belcher, Anne E. (1997)
      The purpose of this study was to develop a reliable and valid instrument that measures the perceived meanings of cancer pain for Taiwanese patients. A 46-item Perceived Meanings of Cancer Pain Inventory (PMCPI) which contains six scales was constructed for field testing. Two hundred cancer patients with pain were recruited from three teaching hospitals in Taiwan. The field testing of the PMCPI included three parts. An item analysis procedure using 100 randomly selected subjects was conducted to select items for the purpose of increasing the internal consistency and decreasing the item number in each scale. The selected items were cross validated with the remaining 100 subjects. A two-facet (item and occasion) generalizability study (G study) was conducted on selected items to estimate the variances associated with each facet and person. Twenty of the 200 subjects constituted the G study sample in which patients responded to study instruments twice. A series of confirmatory factor analyses with weighted least squares (WLS) estimations were performed on selected items to evaluate the construct validity for each scale and each pair combination of the scales. A total of 27 items was selected from the item analysis procedure. Cross validation shows that the fluctuation rate of alpha ranges from -9.24% to 16.25%. The alpha coefficients (n = 200) obtained from the selected items are.763,.783,.709,.556,.620, and.750 for Loss, Threat, Challenge, Blame-Other, Blame-Self and Spiritual-Awareness, respectively. The results of the G study indicate that the variances associated with "occasion" for each scale are near zero. However, the proportions of variances associated with "person-occasion interaction" were found to be 15.78% for the Threat scales. The proportion of variances associated with "item" is small for each scale except Loss (16.02%). The proportion of variances associated with "person-item interaction" ranges from 5.23% to 33.12%. The percentage of variance associated with "individual differences" ranges from 20.81% to 37.09%. The unspecified error variance which cannot be separated from "person-item-occasion interaction" accounts for 26.23 to 65.66% of total variance. The confirmatory factor analyses show that Loss, Challenge and Spiritual-Awareness scales have good model-data fit; the Threat scale also demonstrates reasonable fit after deleting one item. The measurement models of Blame-other and Blame-Self scales do not fit the data well enough. Six two-factor measurement models were formed using the four valid scales; all six models fit the data well. The four scales were tested for parallel items. The results show that the data are consistent with the parallel-item measurement models. Potential demographic and disease/treatment factors that may influence the four scales were identified.