From pain research to pain treatment: role of human pain models

Chronic widespread musculoskeletal pain in patients with obstructive sleep apnea syndrome and the relationship between sleep disorder and pain level, quality of life, and disability

[Purpose] The aim of this study was to ascertain the prevalence of chronic widespread musculoskeletal pain in patients with obstructive sleep apnea syndrome and to assess the relationship between sleep disorder and pain, quality of life, and disability. [Subjects and Methods] Seventy-four patients were included in the study and classified as having mild, moderate, or severe obstructive sleep apnea. Chronic widespread pain, quality of life, and disability were evaluated. [Results] Forty-one patients (55.4%) had chronic widespread pain. Female patients had a higher incidence of chronic pain, and female patients with chronic pain had higher body mass indexes, pain levels, and disability scores than did male patients. Physical component scores of female patients with chronic pain were lower than those of male patients. No correlation was observed between the degree of sleep disorder and severity of pain, pain duration, disability, or quality of life in obstructive sleep apnea patients with pain. [Conclusion] This study showed a 55.4% prevalence of chronic widespread pain in patients with obstructive sleep apnea and a greater risk of chronic pain in female than in male patients. Female patients with obstructive sleep apnea and chronic pain have higher pain and disability levels and a lower quality of life.

New models for visceral pain

PURPOSE OF REVIEW

After the initial use of unspecific stimuli, scientists have recently put a lot of effort into the development of new visceral pain models. These models will help to study physiological and pharmacological questions closely related to clinically treated visceral pain. The aim of this review is to provide an overview of the new models published most recently and encourage further studies in this field.

RECENT FINDINGS

Four rodent and three human models have been introduced. Each of these models addresses specific types of visceral pain, related to the urogenital tract (n=3), to the gastrointestinal tract (n=3), and to visceral organs (n=1). Mechanical distension as a brief stimulus was used mainly, but chemical stimuli resulting in intermediate to prolonged duration of pain were also investigated.

SUMMARY

Developments in the scientific visceral pain field are encouraging. Growing interest in studying aetiology, physiology and pharmacology of visceral pain proves the clinical importance of this pain entity. However, these new models need further evaluation. Future studies will show which of these new models will become a standard scientific tool.

Validation of an automated punctate mechanical stimuli delivery system designed for fMRI studies in rodents

Functional magnetic resonance imaging (fMRI) is increasingly being used for animal studies studying the transmission of nociceptive information. Application of noxious mechanical stimuli is widely used for animal and human assessment of pain processing. Any accessory hardware used in animal imaging studies must, however, be sufficiently small to fit in the magnet bore diameter and be non-magnetic. We have developed a system that can apply mechanical stimuli simultaneously with fMRI. This system consists of a standardized instrument to deliver mechanical stimuli (VonFrey monofilament) and a gas-pressured mechanical transducer. These components were integrated with a computer console that controlled the period of stimuli to match acquisition scans. Preliminary experiments demonstrated that the force-stimulus transducer did not influence MRI signal to noise ratio. Mechanical stimulation of the hindpaw significantly increased blood oxygen level dependent (BOLD) signal intensity in several midbrain regions involved in the processing of nociceptive information in the rat (p<0.001, uncorrected for multiple comparisons). This system can be applied to both animal and human imaging studies and has a wide range of applications for studies of nociceptive processing.

The effect of cryotherapy on nerve conduction velocity, pain threshold and pain tolerance

OBJECTIVES

To determine the impact of the application of cryotherapy on nerve conduction velocity (NCV), pain threshold (PTH) and pain tolerance (PTO).

DESIGN

A within-subject experimental design; treatment ankle (cryotherapy) and control ankle (no cryotherapy).

SETTING

Hospital-based physiotherapy laboratory.

PARTICIPANTS

A convenience sample of adult male sports players (n = 23).

MAIN OUTCOME MEASURES

NCV of the tibial nerve via electromyogram as well as PTH and PTO via pressure algometer. All outcome measures were assessed at two sites served by the tibial nerve: one receiving cryotherapy and one not receiving cryotherapy.

RESULTS

In the control ankle, NCV, PTH and PTO did not alter when reassessed. In the ankle receiving cryotherapy, NCV was significantly and progressively reduced as ankle skin temperature was reduced to 10 degrees C by a cumulative total of 32.8% (p<0.05). Cryotherapy led to an increased PTH and PTO at both assessment sites (p<0.05). The changes in PTH (89% and 71%) and PTO (76% and 56%) were not different between the iced and non-iced sites.

CONCLUSIONS

The data suggest that cryotherapy can increase PTH and PTO at the ankle and this was associated with a significant decrease in NCV. Reduced NCV at the ankle may be a mechanism by which cryotherapy achieves its clinical goals.