Pain
-
Comparative Study
An analysis of factors that contribute to the magnitude of placebo analgesia in an experimental paradigm.
Placebo analgesia was produced by conditioning trials wherein heat induced experimental pain was surreptitiously reduced in order to test psychological factors of expectancy and desire for pain reduction as possible mediators of placebo analgesia. The magnitudes of placebo effects were assessed after these conditioning trials and during trials wherein stimulus intensities were reestablished to original baseline levels. In addition, analyses were made of the influence of these psychological factors on concurrently assessed pain and remembered pain intensities. ⋯ The results further demonstrated that placebo effects based on remembered pain were 3 to 4 times greater than those based on concurrently assessed placebo effects, primarily because baseline pain was remembered as being much more intense than it actually was. However, similar to concurrent placebo effects, remembered placebo effects were strongly associated with expected pain levels that occurred just after conditioning. Taken together, these results suggest that magnitudes of placebo effect are dependent on multiple factors, including conditioning, expectancy, and whether analgesia is assessed concurrently or retrospectively.
-
The whiplash syndrome has immense socio-economic impact. Despite extensive studies over the past years, the mechanisms involved in maintaining the pain in chronic whiplash patients are poorly understood. The aim of the present experimental study was to examine the muscular sensibility in areas within and outside the region involved in the whiplash trauma. ⋯ In the present study, muscular hyperalgesia and large referred pain areas were found in patients with chronic whiplash syndrome compared to control subjects both within and outside the traumatised area. The findings suggest a generalised central hyperexcitability in patients suffering from chronic whiplash syndrome. This indicates that the pain might be considered as a neurogenic type of pain, and new pharmacological treatments should be investigated accordingly.
-
The psychophysical responses to noxious cold stimulation of the skin in normal human subjects are not well understood. Continuous pain ratings with the visual analogue scale is an important method to assess these responses. In this study, we addressed several important issues about the parameters with which stimuli are delivered: the type of skin stimulated, the rate with which the stimulus temperature decreases, and the dimension of the pain rated by subjects. ⋯ The McGill Pain Questionnaire (MPQ) was used to assess the quality of cold-evoked pain. Supra-threshold stimuli (34 degrees C base) were delivered at 0.5, 1 or 2 degrees C/s to 2 degrees C, held for 20s and returned to baseline at 9 degrees C/s. These studies revealed: (1) Cold thresholds, measured with MOL, were lower (i.e. occurred at higher absolute temperatures) for the hairy skin of the dorso-lateral hand compared to the glabrous skin of the thenar eminence. (2) A similar pattern was evident for cold induced pain thresholds with MOL at 1.5 degrees C/s and with intensity and affect VAS scales at 0.5 and 1 degrees C/s. (3) Exponents for supra-threshold ratings fit to power functions were larger for the glabrous skin site than the hairy skin site regardless of cooling rate or dimension of pain measured. (4) All pain indices were higher for slower cooling rates. (5) No significant differences were found in the pain indices for pain ratings of intensity and affect. (6) A substantial proportion of subjects chose words representing paradoxical heat with the MPQ. (7) Painful paradoxical heat sensations occurred most often during cooling, while innocuous warm sensations mainly occurred during the rewarming phase.
-
Recent studies suggest that peripheral morphine may represent a valuable treatment in inflammatory painful diseases. This study examined effects of intraplantar morphine against noxious pressure and paw edema in rats with repeated acute inflammation induced by two carrageenin injections 7 days apart. This model mimics at least partly some aspects of recurrent inflammatory pain encountered in the clinical situation. ⋯ The intraplantar injection of morphine (100 and 150 microg) produced a transient increase in the volume of inflamed hindpaw, not reversible by intraplantar naloxone methiodide (40 microg). Pretreatment with intraplantar morphine had no effect on reduction of vocalization thresholds to paw pressure and edema related to a second ipsilateral injection of carrageenin 7 days later. These findings suggest that peripheral morphine may be useful for the clinical management of acute inflammatory pain rather than in recurrent inflammatory painful situations.
-
Patients accepting randomization in a randomized controlled trial (RCT) may not be representative of the clinical population from which they are drawn, calling into question the generalizability of study findings. Comparison of randomized and non-randomized inpatient and outpatient samples at baseline and in treatment outcomes up to one year was made to determine whether the findings of the RCT generalized to non-randomized patients in the same treatment program. One hundred and twenty one patients with intractable pain, randomized between inpatient, outpatient and waiting list control, were compared with 128 who elected for either inpatient or outpatient treatment. ⋯ NNTs estimate the number of patients required in the treatment condition for one of them to achieve the specified outcome who would not have achieved it in the comparison condition. Across a range of measures at one month follow-up, comparison of inpatients with outpatients gave NNTs between 2.3 and 7.5, and comparison of inpatients with waiting list controls gave NNTs between 2.3 and 3.6. At one year inpatients showed greater likelihood than outpatients of maintaining these treatment gains.