Lasers and other thermal stimulators for activation of skin nociceptors in humans.

Pain can be induced by thermal, chemical, and mechanical stimulation in animals and man. Of the thermal stimulation modalities, heat is the most commonly used, as a variety of reliable stimulation techniques are available. Heat is a natural stimulus modality to evoke pain, and it has been used to study animal nociception and human pain perception for (a) examining the mechanisms of tissue injury and sensitisation and (b) quantifying the therapeutic effects of pharmacological, physical, and psychological interventions. This paper summarises the current understanding of the physiology and psychophysical response to painful heat stimulation in humans. By understanding the underlying mechanisms, new methods of heat stimulation may be developed for basic and clinical applications. Traditionally, contact heat, indirect thermal heat by focused light bulb, and laser pulses have been the methods used to induce heat pain in humans for experimental and clinical studies. The following lasers have been used in pain research: argon (488-515 nm), copper vapour (510-577 nm), semiconductor (e.g. 970 nm), neodymium-YAG (1064 nm), thulium-YAG (2000 nm), and CO(2) (10,600 nm).

Surface electromyography in the identification of chronic low back pain patients: the development of the flexion relaxation ratio.

OBJECTIVE: To develop a reliable and repeatable way to monitor changes in the flexion relaxation phenomenon of the lumbar paraspinal muscles during forward flexion by the development of a flexion relaxation ratio and observation of the sEMG activity in standing and during forward flexion in patients with chronic low back pain (CLBP) and healthy controls. DESIGN: Two experiments were conducted, the first to assess the test-retest reliability of the measure in a group of CLBP (n = 11) patients; the second compared the results between a group of normal healthy controls (n = 20) and a group of CLBP patients (n = 70). RESULTS: Repeated measurements over 4 weeks demonstrated between session reliability of between 0.81 and 0.98 for the dynamic activity. The levels of sEMG activity in the fully flexed position was significantly greater in the fully flexed position in the CLBP group than the controls. The flexion relaxation ratio (FRR), a comparison of the maximal sEMG activity during 1 s of forward flexion with activity in full flexion, demonstrated significantly lower values in the CLBP than the control group. The combined discriminant validity for the FRR for all four sites resulted in 93% sensitivity and 75% specificity. CONCLUSION: The FRR clearly discriminated the patients from the healthy controls. These results indicate that dynamic sEMG activity of the paraspinal muscles can be reliably measured and is useful in differentiating CLBP patients from normal controls. RELEVANCE: Analysis of the pattern of different levels of muscle activity during a forward flexion can be used in CLBP where normalization of the sEMG signal to the maximum voluntary contraction may be difficult. The FRR may be used in the assessment of change in the flexion relaxation phenomenon following treatment interventions.

Cognitive modification of pain: information in combination with N2O.

The present study sought to discover whether information clarifying how the analgesic/sedative drug nitrous oxide (N2O) works would result in increased analgesic responses to painful stimuli when various concentrations of N2O were administered. Subjects were provided with high and low levels of information regarding the action and use of N2O as an analgesic and sedative. Absolute sensation threshold (AST), pain threshold (PTh), and pain tolerance (PTo) to tooth pulp shock were measured in microamperes during administration of each of 3 concentrations of N2O (15%, 30%, and 45%, with oxygen). Subjects rated stimulus intensity and stimulus aversiveness in response to a fixed painful stimulus, and completed questionnaires regarding the perceived efficacy of N2O and their subjective mood state throughout the session. The marked differences observed in pain reports between the high information group and the control group confirm that providing information to people receiving a drug for pain relief yields higher sensation thresholds, pain thresholds, and tolerance of pain. In addition, we observed that in the presence of N2O an equivalent fixed painful stimulus will be perceived as less painful after appropriate information is provided. These findings suggest that experimentally influencing thought processes, in combination with an analgesic, can have the effect of increasing analgesia.